CHAPTER 2Loads 2.1 INTRODUCTION 2.1.1 Scope This chapter specifies the minimum design forces including dead load, live load, wind and earthquake loads, miscellaneous loads and their various combinations. These loads shall be applicable for the design of buildings and structures in conformance with the general design requirements provided in Chapter 1. 2.1.2 Limitations Provisions of this chapter shall generally be applied to majority of buildings and other structures subject to normally expected loading conditions. For those buildings and structures having unusual geometrical shapes, response characteristics or site locations, or for those subject to special loading including tornadoes, special dynamic or hydrodynamic loads etc., sitespecific or casespecific data or analysis may be required to determine the design loads on them. In such cases, and all other cases for which loads are not specified in this chapter, loading information may be obtained from reliable references or specialist advice may be sought. However, such loads shall be applied in compliance with the provisions of other sections of this Code. 2.2 DEAD LOADS 2.2.1 General Part 6 61 Structural Design Part 6 Structural Design The minimum design dead load for buildings and portions thereof shall be determined in accordance with the provisions of this section. In addition, design of the overall structure and its primary loadresisting systems shall conform to the general design provisions given in Chapter 1. 2.2.2 Definition Dead Load is the vertical load due to the weight of permanent structural and nonstructural components of a building such as walls, floors, ceilings, permanent partitions and fixed service equipment etc. 2.2.3 Assessment of Dead Load Dead load for a structural member shall be assessed based on the forces due to : i) weight of the member itself, ii) weight of all materials of construction incorporated into the building to be supported permanently by the member, iii) weight of permanent partitions, iv) weight of fixed service equipment, and v) net effect of prestressing. 2.2.4 Weight of Materials and Constructions In estimating dead loads, the actual weights of materials and constructions shall be used, provided that in the absence of definite information, the weights given in Tables 6.2.1 and 6.2.2 shall be assumed for the purposes of design. Table 6.2.1 Unit Weight of Basic Materials Unit Unit Material Weight Material Weight (kN/m3) (kN/m3) Aluminium 27.0 Granite, Basalt 26.4 Asphalt 21.2 Iron cast 70.7 Brass 83.6 wrought 75.4 Bronze 87.7 Lead 111.0 Brick 18.9 Limestone 24.5 Cement 14.7 Marble 26.4 Coal, loose 8.8 Sand, dry 15.7 Concrete stone aggregate (unreinforced) 22.8* Sandstone 22.6 brick aggregate 20.4* Slate 28.3 (unreinforced) 86.4 Steel 77.0 Copper 1.7 Timber 5.911.0 Cork, normal 3.7 Zinc 70.0 Cork, compressed 25.5 Glass, window (sodalime) * for reinforced concrete, add 0.63 kN/m3 for each 1% by volume of main reinforcement 2.2.5 Weight of Permanent Partitions When partition walls are indicated on the plans, their weight shall be considered as dead load acting as concentrated line loads in their actual positions on the floor. The loads due to anticipated partition walls, which are not indicated on the plans, shall be treated as live loads and determined in accordance with Sec 2.3.3.3. 2.2.6 Weight of Fixed Service Equipment Weights of fixed service equipment and other permanent machinery, such as electrical feeders and other machinery, heating, ventilating and airconditioning systems, lifts and escalators, plumbing stacks and risers etc. shall be included as dead load whenever such equipment are supported by structural members. 2.2.7 Additional Loads 62 Chapter 2 Loads In evaluating the final dead loads on a structural member for design purposes, allowances shall be made for additional loads resulting from the (i) difference between the prescribed and the actual weights of the members and construction materials; (ii) inclusion of future installations; (iii) changes in occupancy or use of buildings; and (iv) inclusion of structural and nonstructural members not covered in Sec 2.2.2 and 2.2.3. 2.3 LIVE LOADS 2.3.1 General The live loads used for the structural design of floors, roof and the supporting members shall be the greatest applied loads arising from the intended use or occupancy of the building, or from the stacking of materials and the use of equipment and propping during construction, but shall not be less than the minimum design live loads set out by the provisions of this section. For the design of structural members for forces including live loads, requirements of the relevant sections of Chapter 1 shall also be fulfilled. 2.3.2 Definition Live load is the load superimposed by the use or occupancy of the building not including the environmental loads such as wind load, rain load, earthquake load or dead load. 2.3.3 Minimum Floor Live Loads The minimum floor live loads shall be the greatest actual imposed loads resulting from the intended use or occupancy of the floor, and shall not be less than the uniformly distributed load patterns specified in Sec 2.3.3.1 or the concentrated loads specified in Sec 2.3.3.2 whichever produces the most critical effect. The live loads shall be assumed to act vertically upon the area projected on a horizontal plane. Table 6.2.2 Weight of Construction Materials Weight Weight per Material per Material Unit Area Unit Area (kN/m 2 ) (kN/m 2 ) Bangladesh National Building Code 63 shall not be less than that listed in Table 6. lap and fastenings) Rubber paving.191 Steel. In areas where vehicles are used or stored.033 Ceiling 1. 10 mm thick 0.1470.153 (incl. per 10 mm thickness 0. 13 mm thick 0.2. excl.034 6 mm thick(deep corrugations) 0. lap and fastenings) Hardboard.096 75 mm thick 0.527 4.0 mm thick 0.268 terracotta (French pattern) 0.8 mm thick 0. the concentrated load shall be applied over an area of 300 mm x 300 mm and shall be located so as to produce the maximum stress conditions in the structural members.2 mm thick 0.6 mm thick 0. 100 mm thick 2. flat. lap and fastenings) 250 mm thick 5.230 0.2. applied uniformly over the entire area of the floor.5 m on centres in absence of the uniform live loads.8 mm thick 0. 90% of the listed values may be used. 25 mm thick 0.024 Fibrous plaster.2 mm thick 0. corrugated sheeting 150 mm thick 3.287 Bituminous felt(5 ply) and gravel 0. studding) 4.671 0.134 Fibre insulation board.0 mm thick 0.961 1.0 mm thick 0. 25 mm thick 0. Unless otherwise specified in Table 6. 25 mm thick 0. plaster Roof burnt clay. 2.2 Concentrated Loads : The concentrated load to be applied nonconcurrently with the uniformly distributed load given in Sec 2.024 Plywood.526 Tiles Clay tiling. per 10 mm thickness 0.012 normal (sawdust filler). per mm thickness 0.092 Aluminium.8 mm thick 0.360 clay tiles 0.062 100 mm thick 2.043 Concrete (stone aggregate)* 3 mm thick.60. per 10 mm thickness 0.480 Slates (two faced incl.158 Fibrous plaster board. 25 mm thick 0.388 * for brick aggregate.Part 6 Structural Design Floor Roof (contd.269 (incl.028 Plaster board. per 10 mm thickness 0.120 Terracotta Hollow Block Masonry 0.1.106 Brick masonry work.3. ramps.360 Asbestos cement.3.5 mm thick 0.) Asphalt.540 (incl.980 3 mm thick. 150 mm thick 3. per 100 mm thickness 1..9.151 1.3. per 10 mm thickness 0.3 or in the following paragraph. standard corrugations 0.345 Asbestos cement sheeting heavy duty (mineral filler).60 mm thick 0.061 Aluminium sheet(plain) 1.575 Concrete slab (stone aggregate)* concrete .3.1 Uniformly Distributed Loads : The uniformly distributed load shall not be less than the values listed in Table 6.671 Miscellaneous Steel sheet.092 0.3.2. per 10 mm thickness 0.019 Cement plaster. per 10 mm thickness 0.7 mm thick 0.9 solid. corrugated sheeting PVC sheet.3. flat galvanized Felt (insulating).019 1.067 cement.3.048 Particle or flake board.540 Galvanized steel floor deck (excl. or any portion thereof to produce the most adverse effects in the member concerned.910 Acrylic resin sheet.5 mm thick 0.082 Plaster 0. per 10 mm thickness 0. per 10 mm thickness 0. topping) 0.081 0. deep corrugations 0.00 mm thick 0.80 mm thick 0. corrugated sandlime. provision shall be made for concentrated loads consisting of two or more loads spaced nominally 1. 13 mm thick 0. 2.3. Each load shall be 40 per cent of the gross weight of the maximum size 64 . per 100 mm thickness 1.335 9.995 150 mm thick 1.383 Walls and Partitions Magnesium oxychloride Acrylic resin sheet.053 lime. such as car parking garages.075 0.431 Suspended metal lath and plaster 0.527 solid.077 100 mm thick 0. repair shops etc.431 6.900 6 mm thick (standard corrugations) 0. per 10 mm thickness 0. galvanized std. corrugated sheeting Glass.072 Terrazzo paving 16 mm thick 0. reduced as may be specified in Sec 2. per 10 mm thickness 0.6 mm thick 0. per 10 mm thickness 0.3. Chapter 2 Loads Bangladesh National Building Code 65 . 2. not indicated on the plans.6 0. The distributed load shall be applied over the area of the roof projected upon a horizontal plane and shall not be applied simultaneously with the concentrated load. Note : (1) Greater of this load and rain load as specified in Sec 2.1 Regular Purpose Flat.2. The uniform live loads for these cases are provided in Table 6. 66 .0) 0. Pitched or sloped roof (slope ≥ 1.9 2 Arched roof or dome (rise < 1/8 span) III 1. and agriculture buildings 0.9 2.4. The concentrated load shall be assumed to act upon a 300 mm x 300 mm area and need not be considered for roofs capable of laterally distributing the load.3. subject to a minimum of 1. In the case of light partitions.3. floors shall be investigated in the absence of the uniform live load. a uniformly distributed live load may be applied on the floor in lieu of the concentrated line loads specified above. equipment and materials but shall not be less than those given in Table 6. wherein the total weight per metre run is not greater than 5. and those induced during maintenance by workers.4.Part 6 Structural Design vehicle to be accommodated and applied over an area of 750 mm x 750 mm.2. The condition of concentrated or uniform live load producing the greater stresses shall govern.3.2 kN/m2.3. e. Pitched or sloped roof (1/3 ≤ slope < 1. For the storage of private or pleasuretype vehicles without repair or fuelling.3 shall be the greatest value for any of the occupancies concerned.5 1.5 0.3 Provision for Partition Walls : When partitions.4 Minimum Roof Live Loads Roof live loads shall be assumed to act vertically over the area projected by the roof or any portion of it upon a horizontal plane. except those with cloth same as given in I through IV above covers based on the type and slope.9 VI Canopies and awnings. the value to be used from Table 6.3. reinforced concrete slabs.3. their weight shall be included as an additional live load acting as concentrated line loads in an arrangement producing the most severe effect on the floor.3 shall be taken as the design live load for roof.9 2. kN I Flat roof (slope = 0) 1. Pitched or sloped roof (0 < slope < 1/3) 1.6. Such uniform live load per square metre shall be at least 33% of the weight per metre run of the partitions. 2.5 kN.g. Pitched and Curved Roofs : Live loads on regular purpose roofs shall be the greatest applied loads produced during use by movable objects such as planters and people.3. unless it can be shown that a more favourable arrangement of the partitions shall prevail during the future use of the floor. and shall be determined as specified in the following sections : 2. are anticipated to be placed on the floors. applied over an area of 750 mm x 750 mm.4 More than One Occupancy : Where an area of a floor is intended for two or more occupancies at different times. 2. Arched roof or dome (1/8 ≤ rise < 3/8 span) IV 1.4 Minimum Roof Live Loads(1) Type and Slope of Roof Distributed Concentrated Load. kN/m2 Load.0) 0. Table 6. Arched roof or dome (rise ≥ 3/8 span) V Greenhouse.8 0. for a minimum concentrated wheel load of 9 kN spaced 1.0 0.2.5 m on centres.2.8 II 1. Chapter 2 Loads 2.3.4.2 Special Purpose Roofs : For special purpose roofs, live loads shall be estimated based on the actual weight depending on the type of use, but shall not be less than the following values : a) roofs used for promenade purposes 3.0 kN/m2 b) roofs used for assembly purposes 5.0 kN/m2 c) roofs used for gardens 5.0 kN/m2 d) roofs used for other special purposes to be determined as per Sec 2.3.5 2.3.4.3 Accessible Roof Supporting Members : Roof trusses or any other primary roof supporting member beneath which a full ceiling is not provided, shall be capable of supporting safely, in addition to other roof loads, a concentrated load at the locations as specified below : a) Industrial, Storage and Garage Buildings Any single panel point of the lower chord of a roof truss, or any point of other primary roof supporting member 9.0 kN b) Building with Other Occupancies Any single panel point of the lower chord of a roof truss, or any point of other primary roof supporting member 1.3 kN 2.3.5 Loads Not Specified Live loads, not specified for uses or occupancies in Sec 2.3.3.1 and 2.3.3.2, shall be determined from loads resulting from : a) weight of the probable assembly of persons; b) weight of the probable accumulation of equipment and furniture, and c) weight of the probable storage of materials. 2.3.6 Partial Loading and Other Loading Arrangements The full intensity of the appropriately reduced live load applied only to a portion of the length or area of a structure or member shall be considered, if it produces a more unfavourable effect than the same intensity applied over the full length or area of the structure or member. Where uniformly distributed live loads are used in the design of continuous members and their supports, consideration shall be given to full dead load on all spans in combination with full live loads on adjacent spans and on alternate spans whichever produces a more unfavourable effect. 2.3.7 Other Live Loads Live loads on miscellaneous structures and components, such as handrails and supporting members, parapets and balustrades, ceilings, skylights and supports, and the like, shall be determined from the analysis of the actual loads on them, but shall not be less than those given in Table 6.2.5. Table 6.2.5 Miscellaneous Live Loads Structural Member or Component Live Load(1) (kN/m) Bangladesh National Building Code 67 Part 6 Structural Design 1. Handrails, parapets and supports : a) Light access stairs, gangways etc. i) width ≤ 0.6 m 0.25 ii) width > 0.6 m 0.35 b) Staircases other than in (a) above, ramps, balconies : i) Single dwelling and private 0.35 ii) Staircases in residential buildings 0.35 iii) Balconies or portion thereof, stands etc. having 1.5 fixed seats within 0.55 m of the barrier vi) Public assembly buildings including theatres, 3.0 cinemas, assembly halls, stadiums, mosques, churches, schools etc. vi) Buildings and occupancies other than (i) through (iv) above 0.75 2. Vehicle barriers for car parks and ramps : a) For vehicles having gross mass ≤ 2500 kg 100(2) b) For vehicles having gross mass > 2500 kg 165(2) c) For ramps of car parks etc. see note (3) Note : (1) These loads shall be applied nonconcurrently along horizontal and vertical directions, except as specified in note (2) below. (2) These loads shall be applied only in the horizontal direction, uniformly distributed over any length of 1.5 m of a barrier and shall be considered to act at bumper height. For case 2(a) bumper height may be taken as 375 mm above floor level. (3) Barriers to access ramps of car parks shall be designed for horizontal forces equal to 50% of those given in 2(a) and 2(b) applied at a level of 610 mm above the ramp. Barriers to straight exit ramps exceeding 20 m in length shall be designed for horizontal forces equal to twice the values given in 2(a) and 2(b). 2.3.8 Impact and Dynamic Loads The live loads specified in Sec 2.3.3 shall be assumed to include allowances for impacts arising from normal uses only. However, forces imposed by unusual vibrations and impacts resulting from the operation of installed machinery and equipment shall be determined separately and treated as additional live loads. Live loads due to vibration or impact shall be determined by dynamic analysis of the supporting member or structure including foundations, or from the recommended values supplied by the manufacture of the particular equipment or machinery. In absence of a definite information, values listed in Table 6.2.6 for some common equipment, shall be used for design purposes. Table 6.2.6 Minimum Live Loads on Supports and Connections of Equipment due to Impact (1) Equipment or Machinery Additional load due to impact as percentage of static load including self weight Vertical Horizontal 1. Lifts, hoists and related operating machinery 100% – 2. Light machinery (shaft or motor driven) 20% – 3. Reciprocating machinery, or power driven 50% – units. 4. Hangers supporting floors and balconies 33% – 68 Chapter 2 Loads 5. Cranes : a) Electric overhead cranes 25% of i) Transverse to the rail : maximum 20% of the weight of trolley wheel load and lifted load only, applied onehalf at the top of each rail ii) Along the rail : 10% of maximum wheel load applied at the top of each rail b) Manually operated cranes 50% of the 50% of the values in values in (a) (a) above above c) Caboperated travelling cranes 25% – – Not applicable Note : (1) All these loads shall be increased if so recommended by the manufacturer. For machinery and equipment not listed, impact loads shall be those recommended by the manufacturers, or determined by dynamic analysis. 2.3.9 Reduction of Live Loads Reduction of live load is permitted for primary structural members supporting floor or roof, including beam, girder, truss, flat slab, flat plate, column, pier, footing and the like. Where applicable, the reduced live load on a primary structural member shall be obtained by multiplying the corresponding unreduced uniformly distributed live load with an appropriate live load reduction factor, R as listed in Table 6.2.7 and set forth in Sec 2.3.9.1. 2.3.9.1 Load Groups : All possible live loads applied on floors and roof of a building due to various occupancies and uses, shall be divided into three load groups as described below for determining the appropriate live load reduction factors. a) Load Group 1 : Uniformly distributed live loads arising from the occupancies and uses of (i) assembly occupancies or areas with uniformly distributed live load of 5.0 kN/m2 or less, (ii) machinery and equipment for which specific live load allowances have been made, (iii) special roof live load as described in Sec 2.3.4.2, and (iv) printing plants, vaults, strong rooms and armouries, shall be classified under Load Group 1. Reduction of live load shall not be allowed for members or portions thereof under this load group and a reduction factor, R =1.0 shall be applied for such cases. b) Load Group 2 : Uniformly distributed live loads resulting from occupancies or uses of (i) assembly areas with uniformly distributed live load greater than 5.0 kN/m2, and (ii) storage, mercantile, industrial and retail stores, shall be classified under Load Group 2. Live load reduction factor, 1.0 < R < 0.7 shall be applied to this load group depending on the tributary area of the floors or roof supported by the member as specified in Sec 2.3.9.3. c) Load Group 3 : Uniformly distributed live loads arising due to all other occupancies and uses except those of Load Group 1 and Load Group 2, shall be grouped into Load Group 3. Live load reduction factor, 1.0 ≤ R ≤ 0.5 as specified in the Sec 2.3.9.3, shall be applied to tributary areas under this load group. Bangladesh National Building Code 69 Pier.73 80 0. industrial.2 d) Printing plants. or Factor.53 ≥ 220 0.74 ≥ 800 0. or Reduction Group Occupancy or Use roof.00 live load greater than 5.3.0 kN/m2 or less. Column.92 b) Storage. Footing and the like : Tributary areas of these members shall consist of portions of the areas of all floors.2.81 220 0. strong room and armouries 2 a) Assembly areas with uniformly distributed ≤ 50 1. parking garage.67 100 0.9. 60 0.62 120 0.3) Load Area (floor.50 610 .70 3 a) Uniformly distributed live loads from all < 25 1. Flat plate and Flat slab : Tributary area for such a member shall consist of the portion of the roof or a floor at any single level that contributes loads to the member concerned.00 occupancies and uses except those listed 2530 0.84 280 0. vaults.86 140 0.2 Tributary Area : The tributary area of a structural member supporting floors or roof shall be determined as follows : a) Tributary Area for Wall.57 180 0.59 140 0.4.0 kN/m2 . Girder.90 in load groups 1 and 2 above.0 c) Special roof live loads as specified in Sec 2. 40 0.76 400 0. Table 6. mercantile.88 retail stores 120 0. roof or combination thereof that contribute live loads to the member concerned.84 50 0.7 Live Load Reduction Factors for Various Occupancies and Uses Tributary (1) Live Load (2.97 80 0.78 60 0.Part 6 Structural Design 2. b) Tributary Area for Beam. b) Live loads from machinery and equipment for which specific load allowance has been made all 1.79 300 0.3. combination) R At (m2) 1 a) Assembly areas with uniformly distributed live load of 5. 100 0. reference shall be made to reliable literature pertaining to these loads.1 shall be identified and summed up.4.9. the design wind load shall also include additional loading effects due to wind induced vibrations of the building.25 + 14 A t for Load Group 3 2. 2.1. The design wind load shall include the effects of the sustained wind velocity component and the fluctuating component due to gusts.4 and associated with an annual probability of occurrence of 0. and finally.4. usually of limited extent. b) The reduced live loads or load intensities shall then be obtained for each load group by multiplying the unreduced live loads or load intensities by the corresponding reduction factors.3. caused by the common windstorms including cyclones. or specialist advice shall be sought. Chapter 2 Loads Note : (1) At = sum of all tributary areas with loads from any one load group (i. and c) forces generated due to special types of winds. Bangladesh National Building Code 611 .02.1 Scope : Provisions of this section shall apply to the calculation of design wind loads for the primary framing systems and for the individual structural components and cladding of buildings.9. R is based on the relations: R = 0. However. c) The total reduced live load on a structural member shall be determined by summing up the reduced live loads from each load group. Load Group 1.4.9.4.7 corresponding to each portion of the tributary area. 2. the general design requirements as specified in Chapter 1 shall also be fulfilled. 6 + 8 A t for Load Group 2 and R = 0. (3) Live load reduction factor. and a value of the reduction factor R shall be obtained from Table 6.4 WIND LOADS 2. PORCH COVER) : A rooflike structure. AWNINGS (e. 2.2 Limitations : Provisions of this section shall include forces due to alongwind response of regularshaped buildings. 2. thunderstorms and norwesters. BASIC WIND SPEED.4. For calculation of wind loads arising due to the above special cases and for buildings requiring more accurate loading information.e. the following cases shall remain beyond the scope of these provisions : a) forces due to crosswind response of buildings and structures.1 and on the tributary area of the floor or the roof and combination thereof supported by a primary structural member. For the overall design of structures. BUILDINGS : Structures that enclose a space and are used for various occupancies. projecting from a wall of a building. The reduced live load on a structural member shall be determined using the following steps: a) Portions of the tributary area pertaining to each of the three load groups specified in Sec 2.3.3 Determination of Reduced Live Load : The value of the live load reduction factor.g. the shape and size of the building and the terrain exposure condition of the site as set forth by the provisions of this section. For slender buildings. R shall depend on the load group specified in Sec 2. b) forces.1 General The minimum design wind load on buildings and components thereof.3. such as torsion etc. such as tornadoes.2 Definitions The following definitions shall apply only to the provisions of Sec 2.4. Vb : Fastestmile wind speed in km/h corresponding to the level of 10 metres above the ground of terrain ExposureB defined in Sec 2.1. 2 or 3) (2) Linear interpolation may be made to obtain values of R lying between the listed values. generated due to unusual or unsymmetrical geometry of the building.2. shall be determined based on the velocity of the wind. etc. The system primarily receives wind loading from relatively remote 612 . ESSENTIAL FACILITIES : Buildings and structures which are necessary to remain functional during an emergency or a post disaster period. FREE STANDING ROOF : A roof (of any type) with no enclosing walls underneath. PRIMARY FRAMING SYSTEM : An assemblage of major structural elements assigned to provide support for secondary members and cladding. purlins. which has a constant slope. fences. FASTESTMILE WIND SPEED : The highest sustained average wind speed in km/h based on the time required for a milelong sample of air to pass a fixed point. DESIGN WIND PRESSURES. studs. Examples include curtain walls. ISOTACH : A line on a map joining points of equal wind speed. or p = pressure that is uniform with respect to height as determined by the sustained wind pressure q h h evaluated at mean roof height h. and roof trusses. freestanding carport. HOARDING : Free standing (rectangular) signboards. supported clear of the ground. Doors or other openings in exterior walls shall be considered as openings unless such openings and their frames are specifically detailed and designed to resist the wind loads in accordance with the provisions of this section. GABLED FRAME : A rigid frame having vertical side members and a sloped top with a ridge. e. p : Equivalent static pressure due to wind including gusts to be used in the determination of wind loads for buildings. roof sheeting. GRADIENT HEIGHT: Height from the mean ground level above which the variation of wind speed with height need not be considered. with no roof attached. grits. Net pressures act normal to a surface in the specified direction. PRESSURE : Air pressure in excess of ambient. PITCHED ROOF : A bifold.Part 6 Structural Design CANOPY : A roof adjacent to or attached to a building.g. ENCLOSED BUILDING : Buildings which have full perimeter wall (nominally sealed) from floor to roof level. It forms over warm tropical oceans and decays rapidly over land. The pressure shall be assumed to act in a direction normal to the surface considered and is denoted as: p = pressure that varies with height in accordance with the sustained wind pressure q evaluated z z at height z. biplanar roof with a ridge at its highest point.. FREESTANDING WALLS : Walls which are exposed to the wind on both sides. CYCLONE : An intense lowpressure centre accompanied by heavy rain and galeforce winds. exterior glass windows and panels. e. generally not enclosed by walls.g. OPENINGS: Apertures or holes in the exterior walls of a building or structure. Negative values are less than ambient and positive values exceed ambient. COMPONENTS AND CLADDING : Structural elements that are either directly loaded by the wind or receive wind loads originating at relatively close locations and transfer those loads to the primary framing system. MOONSCAPE ROOF : A planar roof with no ridge. 2. TRIBUTARY AREA : That portion of the surface area receiving wind loads assigned to be supported by the structural element considered. valleys and plains which strongly influence wind flow patterns. SLENDER BUILDINGS AND STRUCTURES : Buildings and structures having a height exceeding five times the least horizontal dimension. CI : A factor that accounts for the degree of hazard to human life and damage to property. q : The theoretically computed incident pressure of a uniform air stream (fastestmile speed) of known density. or a fundamental natural frequency less than 1. and often observable as a funnel cloud attached to the cloud base. Chapter 2 Loads locations.0 Hz. biplanar roof with a valley at its lowest point. for a specific terrain exposure condition and for a known occupancy of a building. roof and floor diaphragms. space trusses. and rodbraced frames. shear walls. TOPOGRAPHY : Major land surface features comprising hills. STRUCTURES : See Sec 1. UNENCLOSED BUILDING OR STOREY : A building or storey which has 85% or more openings on all sides. the least horizontal dimension at midheight shall be used. TROUGH ROOF : A bifold. For those cases in which the horizontal dimensions vary with height. TORNADO : A violently rotating column of air. TERRAIN : The surface roughness condition when considering the size and arrangement of obstructions to wind. STRUCTURE IMPORTANCE COEFFICIENT. evaluated at a given height above ground level. Bangladesh National Building Code 613 . Examples include rigid and braced frames. pendant from the base of a connective cloud.2. SUSTAINED WIND PRESSURE. metres.2.4 (b). metres p = design pressure to be used in determination of wind loads for buildings. a = width of pressure coefficient zone used in Fig 6.2. in kN/m2 z r = risetospan ratio for arched roofs s = surface friction factor given in Table 6. kN F¢ = design wind forces on components and cladding.4 only : A = tributary area. square metres. Cz = combined height and exposure coefficient for a building at height z above ground D = diameter of a circular structure or member. metres. kN/m2 p = design pressure evaluated at height z =h.12 S = structure size factor given in Fig 6.8. metres M = larger dimension of a sign. kN/m2 q = sustained wind pressure evaluated at height z=h.2.2x106 CG = gust coefficient CI = structure importance coefficient Cp = pressure coefficient to be used for determination of wind loads on buildings and structures. Ct = local topographic coefficient given in Sec 2.2.7 and 6. square metres. kN/m2 h p = internal pressure. A = area of other structures or components and cladding thereof projected on a plane normal to wind direction.4. = C p ¢ overall pressure coefficient for buildings and structures to be used for wind loads on primary framing systems using Method 2 in Sec 2. F2 = design wind forces on primary framing system.4.6. kN/m2 i p = design wind pressure evaluated at height z above ground. Hz F1.12.4.6.4 TI = turbulence intensity factor evaluated at twothirds of the mean roof height or parapet height of the structure (see Eq 2. metres B = horizontal dimension of buildings and structures measured normal to wind direction.Part 6 Structural Design 2. metres Do = surface drag coefficient given in Table 6.11) 614 .2. f = fundamental frequency of buildings or structures in a direction parallel to the wind. C pi¢ = internal peak pressure coefficient to be used for wind loads on buildings and components. kN/m2 z q = sustained wind pressure. metres d = diameter of a circular structure or member. metres N = smaller dimension of a sign. metres D¢ = depth of protruding elements (ribs or spoilers).3 Symbols and Notation The following symbols and notation shall apply to the provisions of Sec 2.8. metres. J = pressure profile factor as a function of ratio g L = horizontal dimension of a building or structure measured parallel to wind direction. C pe ¢ = external peak pressure coefficients to be used for wind loads on building components and cladding.4.6. = C pe external pressure coefficients for surfaces of buildings and structures to be used for wind loads on primary framing systems using Method 1 in Sec 2.4. kN/m2 h q = sustained wind pressure evaluated at height z above ground.4 (a). Cc = velocitytopressure conversion coefficient = 47. except that eaves height may be used for roof slope of less than 10 degrees. c = average horizontal dimension of the building or structure in a direction normal to the wind. kN G = gust response factor for primary framing systems of flexible buildings and structures Gh = gust response factor for primary framing systems evaluated at height z = h Gz = gust response factor for components and cladding evaluated at height z above ground h = mean roof height or height to top of parapet whichever is greater of a building or structure. 2.4.4.4.8.3 z = height above ground level. This category includes air fields.2.4.2. having isotachs representing the fastest mile wind speeds at 10 metres above the ground with terrain Exposure B for a 50year recurrence interval.4. industrial areas. the value marked for that wind region shall be used.4.2.12. shall be obtained as follows: i) When the location is listed in Table 6.1 Basic Wind Speed Map : The Basic Wind Speed Map as shown in Fig 6.5 km or more in width.4.4. open park lands.1 Exposure Category : The terrain exposure in which a building or structure is to be sited shall be assessed as being one of the following categories: a) Exposure A : Urban and suburban areas.8.1. whichever is greater. 2. whichever is greater.4. metres a = powerlaw coefficient given in Table 6.12 e = ratio of solid area to gross area for open sign face of a trussed tower.4. or lattice structure q = angle of the plane of roof from horizontal.4. degrees. vegetation and manmade constructions. Basic wind speeds for selected locations are also provided in Table 6. 2.5.2. ii) If the location lies within any wind region (shown shaded in the map of Fig 6.4. over 1. Exposure C extends inland from the shoreline 400 m or 10 times the height of structure. km/h X = distance to centre of pressure from windward edge.1.4. except that Exposure B shall be assumed for buildings or structures having h ≤ 20 m and sited in a terrain with Exposure A. sparsely builtup outskirts of towns.5.4 Terrain Exposure A terrain exposure category that adequately reflects the surface roughness characteristics of the ground shall be determined for the building site. 2. metres zg = gradient height given in Table 6. flat open country and grasslands. Chapter 2 Loads V = basic wind speed.3 Selection of Exposure Category for Components and Cladding : Design wind load on the components and cladding of all buildings and structures shall be determined on the basis of the exposure category defined in Sec 2.2. wooded areas. hilly or other terrain covering at least 20 per cent of the area with obstructions of 6 metres or more in height and extending from the site at least 500 metres or 10 times the height of the structure.1). 2. Bangladesh National Building Code 615 . coastal areas and riversides facing large bodies of water.12 b = structural damping coefficient (fraction of critical damping) g = ratio obtained from Table 6.2 Selection of Exposure Category for Primary Framing System : Design wind load for primary framing systems for all buildings and structures shall be determined based on the terrain exposure categories defined in Sec 2. value of the basic wind speed shall be taken from that table. metres Y = response factor as a function of the ratio g and the ratio c/h given in Fig 6. c) Exposure C : Flat and unobstructed open terrain.4. b) Exposure B : Open terrain with scattered obstructions having heights generally less than 10m extending 800 m or more from the site in any full quadrant.1 is the map showing the basic wind speeds in km/h for any location in Bangladesh. 2. The minimum value of the basic wind speed set in the map is 130 km/h.2. degrees u = heighttowidth ratio for sign or hoarding f = angle between wind direction and chord of tower guy.5 Basic Wind Speed 2.2 Selection of Basic Wind Speed : Value of the basic wind speed required for any specific location where a building or structure is sited. taking into account the variations in ground roughness arising from existing natural topography.2. 2. along the height above the ground. linear interpolation shall be made between the adjacent isotachs to obtain the basic wind speed.Part 6 Structural Design iii) For a location lying on any isotach in the map.8. i. and hence the pressure. the fastestmile wind speed.2.1 and Table 6. For areas where local records or terrain conditions indicate higher values of basic wind speeds (substantiated by sitespecific analysis) than those reflected in Fig 6. c) terrain exposure of the building site.2. structures and components thereof shall be calculated.6.4.4.4.e.1 taking into account the following effects which shall be determined in accordance with the provisions of this section : a) equivalent static pressure or suction on building surfaces arising due to the sustained or mean wind velocity. 616 . 2. within the scope and limitations given in Sec 2.1 Basis of Wind Load Calculation : The minimum design wind load on buildings. iv) For a location lying outside the positions (i) through (iii) above. the value of that isotach shall be taken. the sitespecific values shall be adopted as the minimum basic wind speeds.6 Determination of Design Wind Loads 2. b) variation of the mean wind velocity. Chapter 2 Loads Bangladesh National Building Code 617 . e. i.2. and 618 . Martin’s Island 260 Khulna 238 Sunamganj 195 Kutubdia 260 Sylhet 195 Kishoreganj 207 Sandwip 260 Kurigram 210 Tangail 160 Kushtia 215 Teknaf 260 Lakshmipur 162 Thakurgaon 130 d) configuration and dynamic response characteristics of the building or structure.Part 6 Structural Design Table 6. f) magnification of the mean wind pressure due to the effect of the fluctuating component of wind speed. e) occupancy importance of the building.8 Basic Wind Speeds for Selected Locations in Bangladesh Basic Wind Basic Wind Location Speed (km/h) Location Speed (km/h) Angarpota 150 Lalmonirhat 204 Bagerhat 252 Madaripur 220 Bandarban 200 Magura 208 Barguna 260 Manikganj 185 Barisal 256 Meherpur 185 Bhola 225 Maheshkhali 260 Bogra 198 Moulvibazar 168 Brahmanbaria 180 Munshiganj 184 Chandpur 160 Mymensingh 217 Chapai Nawabganj 130 Naogaon 175 Chittagong 260 Narail 222 Chuadanga 198 Narayanganj 195 Comilla 196 Narsinghdi 190 Cox’s Bazar 260 Natore 198 Dahagram 150 Netrokona 210 Dhaka 210 Nilphamari 140 Dinajpur 130 Noakhali 184 Faridpur 202 Pabna 202 Feni 205 Panchagarh 130 Gaibandha 210 Patuakhali 260 Gazipur 215 Pirojpur 260 Gopalganj 242 Rajbari 188 Habiganj 172 Rajshahi 155 Hatiya 260 Rangamati 180 Ishurdi 225 Rangpur 209 Joypurhat 180 Satkhira 183 Jamalpur 180 Shariatpur 198 Jessore 205 Sherpur 200 Jhalakati 260 Sirajganj 160 Jhenaidah 208 Srimangal 160 Khagrachhari 180 St. gusts. 4.2.5 If a structure is located within a local topographic zone.6. CI I Essential facilities 1.25 III Special occupancy structures 1.2 Sustained Wind Pressure : The sustained wind pressure. Cz Height above Coefficient.9 Cc = velocitytopressure conversion coefficient = 47.4.2. Table 6.6.2x106 Cz = combined height and exposure coefficient as given in Table 6.10 Combined Height and Exposure Coefficient. z Exposure A Exposure B Exposure C (metres) Bangladesh National Building Code 619 .00 V Lowrisk structures 0.4.4. qz shall be modified in accordance with Sec 2.2.1. qz = sustained wind pressure at height z.2.00 IV Standard occupancy structures 1.9 Structure Importance Coefficients. qz on a building surface at any height z above ground shall be calculated from the following relation : qz = Cc CI Cz V b 2 (2.1) where.10 Vb = basic wind speed in km/h obtained from Sec 2. kN/m2 CI = structure importance coefficient as given in Table 6. CI for Wind Loads Structure Importance Category Structure Importance (see Table 6.1 for Occupancy) Coefficient. Cz (1) ground level.25 II Hazardous facilities 1. 2. Chapter 2 Loads g) additional load amplification resulting from the dynamic windstructure interaction effects due to gusts on slender buildings and structures.8.80 Table 6. 404 160.1).084 2.814 2.383 1.451 15.4. or `G as set forth in Sec 2.0 1.065 1.Part 6 Structural Design 04.362 2.0 1.684 280.746 2.0 0.835 2.488 1.4.2) where.0 0.810 1.171 100.0 2.787 2.6.624 1.573 21.928 2.450 1.217 2.513 1.0 2.521 200.212 2.0 0.846 45.0 1.065 80.129 2.769 1.055 1.483 2.058 2.171 2.436 170.120 90.0 0.0 1.371 1.0 0.4.299 130.497 0.337 140.596 240. kN/m2 CG = gust coefficient which shall be Gz .415 0.368 0.4.494 190.849 1.260 120.0 1.0 1.797 40.965 1.465 180.6. pz for a structure or an element of a structure at any height.237 1.909 1.6 Cp = pressure coefficient for structures or components as set forth Sec 2.3 Design Wind Pressure : The design wind pressure.4.934 2.647 2. pz = design wind pressure at height z .876 2.623 24.433 1.422 2. 2.357 2.987 2. 2.286 1.0 0.0 1.667 27.0 0.037 2.002 70.185 1.0 1.565 1.724 300.541 2.313 1.370 12.0 1.6.217 110.0 2.539 1.371 150.671 2.725 1.323 2.586 1.4.139 2.706 30.250 2.866 1.972 1.0 1.263 9.125 1.595 2.5 0.4 Design Wind Load for Buildings and Structures : Design wind load on the main wind force resisting systems of buildings and structures shall be determined by using one of the following two methods: 620 .196 6.7 qz = sustained wind pressure obtain from Eq (2.736 2.0 1.930 60.0 0.572 2.762 Note : (1) Linear interpolation is acceptable for intermediate values of z.287 2.0 0.0 1.677 1.517 18.0 2.0 0.0 1.801 1.155 1.547 220.890 50.743 35.629 2. Gh.6.0 1.883 2.0 0.684 2.0 2.0 1.910 2.330 1. z above mean ground level shall be determined from the relation : pz = CG Cp qz (2.0 1.017 1.0 1.238 1.973 2.641 260. 21 A z = Projected frontal area normal to wind tributary to the framing system at height z. for use with the overall pressure coefficient Cp for the crosssectional shapes provided in Tables 6.2) h Az = area of the building surface or roof tributary to the framing system at height z upon which the design pressure p operates. the total wind force on the primary framing system of a building or a structure shall be calculated using the formula : F2 = å p z A z (2. In the projected area method. shall be calculated as follows : i) For all framing systems: F1 = å pA z (2. kN pz = design wind pressure. or a part thereof. In order to determine the most critical loads.8) and that given by the relation : F1 = å (p .5) where.2.4. b) Method 2 (Projected Area Method) : This method may be used for any building or structure as a whole except those specified in a(ii) above. kN/m2 = pz for windward surfaces as used in Eq (2. in kN/m2.2. Table 6.15 to 6.4) where.21 for various crosssectional shapes. the overall pressure coefficients Cp provided in Tables 6. In the projected area method. According to Method 2.4. gabled frames and other singlestorey rigid frames shall be investigated for both the force F1 obtained from Eq (2. In this method the design wind pressures shall be assumed to act simultaneously normal to all exterior surfaces including roof of buildings or structures.4. the horizontal pressure shall be assumed to act upon the full vertical projected area of the structure and the vertical pressure shall be assumed to act simultaneously upon the full horizontal projected area. F1 = wind force on primary framing systems acting normal to a surface.2) = p for nonwindward surfaces as used in Eq (2. e. The forces F1 .4. given by Eq (2. F2 = total wind force on the framed system of the building in a specified direction.7. in square metres.2.3) where. shall be used for the total height of the building or the structure having a particular crosssectional shape. except where the pressure coefficients are given for the surface area. Bangladesh National Building Code 621 . the total wind force F2 shall be calculated for each wind direction for which the overall pressure coefficient C p is provided. forces along all critical directions shall be investigated.4.2. ii) For gabled frames and singlestorey rigid frames: In order to obtain the most critical loading condition.15 to 6.g. For the maximum force on the building. h The resultant force of the complete framing system of the building shall be taken to be the summation of forces F1 due to the effects of the pressures on all surfaces of the building.17.2.4. acting normal to the building surfaces or the roof. in square metres. or roof. Chapter 2 Loads a) Method 1 (Surface Area Method) : The surface area method shall be used for gabled rigid frames and single storey rigid frames and may be used of other framing systems.4.1). p = design wind pressure on building surfaces.6.4. p = internal pressure = C pi¢ q i h C pi¢ = internal peak pressure coefficient as given in Sec 2. and q = sustained wind pressure evaluated at mean roof height.p i )A z (2. 2. and individual cladding units and their immediate supporting members and fixings etc.2. Gh for Nonslender Buildings and Structures : For the main wind force resisting systems of nonslender buildings and structures.14 q = sustained wind pressure acting on external surfaces of a building q = wind pressure developed at the interior of the building.4. Height h shall be defined as the mean roof level or the top of the parapet. in square metres.6.7 and 6. Gust coefficient. 622 .0 Hz. 2. F¢ = total wind force on a building component perpendicular to the surface.2.2. and q for ( + ve) values of C pe z q = q for (– ve) values of C pe ¢ . walls. b) Gust Response Factor. see Fig 6.6.7 and 6.25 å p z A z (2. z at which the component or cladding under consideration is located on the structure.7) where.11 evaluated at height h above mean ground level of the building or structure. Gh. i The pressures q and q shall be determined as follows : i For h £ 18 m: q = q and q = q h i h For h > 18 m: q = ¢ . h q = q for all values of Cpe. For slender buildings and structures.2. i z If the peak pressure coefficients C pe ¢ and C pi¢ are not provided in Fig 6. whichever is greater.8 and in Table 6.8 for rectangular building C pi¢ = internal peak pressure coefficient as given in Table 6. kN/m2 A z = Projected area of the component normal to wind at level. Gz for Building Components : For components and cladding of all buildings and structures. kN C pe ¢ = external peak pressure coefficient for components.2) shall account for such additional gust loading effects on nonslender and slender buildings and shall be set equal to the Gust Response Factors. pz = design wind pressure for components as given in Eq (2.14. CG as included in Eq (2. of enclosed buildings and structures shall be determined in accordance with the following relation: F¢ = å æè C ¢pe q .4.4. A slender or windsensitive building shall be one having (i) a height exceeding five times the least horizontal dimension. the value of the gust response factor Gz shall be determined from Table 6.. the value of the gust response factor.2).2. z above ground.6) where.4.C ¢pi q i öø A z (2.2.4.Part 6 Structural Design 2.6 Wind Gust Effects : Wind gusts cause additional loading effects due to turbulence over the sustained wind speed.4.2. this additional loading gets further amplified due to dynamic wind structure interaction effects.5 Design Wind Loads for Components and Cladding : Design wind load on individual structural components such as roofs. Gh shall be determined from Table 6.11 evaluated at the height above the ground. or (ii) a fundamental natural frequency less than 1. the following equation may be used for determining the wind forces on structural components : F¢ = ±1. Gz or ` G as set forth below : a) Gust Response Factor. 233 1.040 1.114 1.082 1.045 1.058 1. use building or structure height h for z.000 Note : (1) For main windforce resisting systems.457 1.003 170.0 1.154 6.0 1.0 1.0 1.133 1.252 1.0 1.0 1.057 1.082 24.0 1.0 1.000 240.001 180.321 1.073 1.592 1.005 160.0 1.11 Gust Response Factors.0 1.0 1. c) Gust Response Factor.0 1.140 9.180 1.0 1.0 1.0 1.238 1.043 1.067 35.104 1.0 1.020 110.022 1.000 280.342 1.201 1.049 1.055 45.388 1.039 70.016 120.051 1.0 1.089 21.309 1.170 1.0 1.026 1.087 1.166 1.118 1.072 30.134 1.000 220.189 1.0 1.065 1.087 1.028 90.046 1. Chapter 2 Loads Table 6.121 12.0 1. Bangladesh National Building Code 623 .154 1.103 1.0 1.111 1.654 1.030 1.095 1. Gh and Gz(1) Height above Gh (2) and Gz ground level Exposure A Exposure B Exposure C (metres) 04.178 1.0 1.0 1. (2) Linear interpolation is acceptable for intermediate values of z.0 1.126 1.075 1.294 1.114 1.162 1.141 1. G for the primary framing systems of slender buildings and structures shall be calculated by a rational analysis incorporating the dynamic properties of the primary framing system as given by the following relations.151 1.0 1.0 1.000 190.065 1.046 60.511 1.126 1.2.024 100.000 260.287 1.215 1.018 1.0 1.010 140.0 1.013 130.0 1.000 300.008 150.092 1.033 80.324 1.5 1.000 200.051 50.0 1.035 1.0 1.258 1.081 1.196 1.097 18.418 1.107 15.0 1.363 1.215 1.061 40.053 1.070 1.061 1.098 1.077 27.268 1.0 1. G for Slender Buildings and Structures : Gust response factor. specialist advice shall be sought for further analysis.2. The gust response factor `G as determined by this provision shall account for the load magnification effect caused by the wind gusts in resonance with alongwind oscillations of the structure. s and g shall be those given in Table 6. P = `f J U (2.0T 2 I S ö÷ G = 0. Cases where crosswind or torsional loading is possible. flutter and ovalling nor for any torsional loading effect resulting from such response.11) are defined in Sec 2. 624 .2.4.4.3.8) è b 1+ kc ø where.3 S = structure size factor provided in Fig 6.5 shall be made for determining such effects.2 U = resonance factor given in Fig 6. Do .11) (h 13.72 ) f = fundamental natural frequency of the building or structure.4.4 Other parameters of Eq (2. Hz b = structural damping coefficient (fraction of critical damping) h = mean roof height or height to parapet. galloping. 65 + ç + (2.2.2. but shall not provide allowances for any crosswind response such as that due to vortex shedding. metre Vb = basic wind speed.4.10) sV b 2. or wind tunnel tests specified in Sec 1.9) 55 . km/h k = 0. Values of the parameters a.35 D o TI = a and (2.4.12.2. metre c = average horizontal dimension of the building or structure normal to wind.00656 for building or structure = 0. 44fh `f = (2.4.00328 for open framework (lattice) structure J = pressure profile factor given in Fig 6.4.8) through (2.5.Part 6 Structural Design æ P 11. Chapter 2 Loads Bangladesh National Building Code 625 . 6.33 1.Part 6 Structural Design Table 6.07/h C 0.143 0.005 1.2) for the determination of design wind pressure shall be equal to the values described below: 626 .0061/h 2.010 1.100 0. Structures and Components : The pressure coefficients Cp to be used in Eq (2.4.2.0/h B 0.12 Building Exposure Parameters Building Exposure a Do s g A 0.00 0.85 0.003 0.4.7 Pressure Coefficients for Buildings.222 0. 4.6 and in Table 6.6. These coefficients shall be used along with the coefficients C¢pe for design wind load on components.2. This coefficient shall be used with Method 1 given in Sec 2. or with Cpe for design wind load on buildings as per provisions of Sec 2.5 and Fig 6.2.6.4. Chapter 2 Loads a) Cpe : external pressure coefficient as given in Fig 6.4a(i).4a (ii) Bangladesh National Building Code 627 .2.13 for external surfaces of buildings or structures.14 for internal surfaces of buildings. b) C pi¢ : internal peak pressure coefficients as given in Table 6.2. (a).13 for arched roofs.7 0.Part 6 Structural Design Notation : B : Horizontal dimension of building. use Table 6.01 q values of 1.2 0. in kN/m2 evaluated at respective heights z : Height above ground in metres q : Roof slope from horizontal.4(b) External Pressure Coefficients.2* 0.75 0.65 – 0. Alternatively.9* for all 0. Sec 2.01 q h/L ≥ 1.4.5 0.6 1.15 and Method 2.5 0.9 0.4.6.3 0.35 0. degrees External Pressure Coefficient Cpe for Walls * Surface L/B Cpe For use with Windward wall all values 0.8 pz = CG Cpe qz ≤ 0.9 0.2 0.5 pz = CG Cpe qh 2.5 0.9 0.7 pz = CG Cpeqz * These coefficients may be used when h/B ≤ 5.4.00 – 0.7 to ridge 0.6. Cpe for Roof † Windward Side Wind q (degrees) Leeward Direction h/L 0 1015 20 30 40 50 > 60 Side Normal ≤ 0. in metres except that eave height may be used for q ≤ 10 degrees L : Horizontal dimension of building.2.3 0.8 † Coefficients are to be used with p h = CG Cpe qh .7 0. in metres measured normal to wind direction CG : Gust response coefficient h : Mean roof height.7 h/B or h/L > 2.2 0. qz : Sustained wind pressure.3 0.4.5 Leeward wall 0.5 0.0 0.0.2 0.7 0.6(a) * Both values of Cpe shall be used for load calculations.8 0. (2) Refer to Table 6.00 – 0.2 Side wall all values 0.75 0. in metres measured parallel to wind direction ph : Design wind pressure qh.3 ≥ 4. see Sec 2.7 0.6. 628 .2.7 0.9 0.4 0.01 q and q Parallel h/B or h/L to ridge ≤ 2.5 0.5 0.10 – 0.9 0. Note : (1) These coefficients shall be used with Method 1.01 q 0. Sec 2.3 0.5 0.00 – 0. 6 (c). Chapter 2 Loads (3) For flexible buildings and structures. h/L. Fig 6.5 External Pressure Coefficients. respectively. (4) Plus and minus signs signify pressures acting toward and away from the surfaces. (5) Linear interpolation may be made for values of q. C pe for Primary Framing Systems of Rectangular Buildings Bangladesh National Building Code 629 .2. and L/B ratios other than listed.6.4. use appropriate G as determined by Sec 2. Part 6 Structural Design 630 . h For remaining roof area.7 – r – 0.15 through 6. (3) For components and cladding : a) At roof perimeter.6 1. d) `Cp : overall pressure coefficient as given in Tables 6.3 alternate coefficients given by (6r – 2.3 – 0.3* 1.5 structures 0.13 External Pressure Coefficients. Cpe for Arched Roofs Cpe Condition Risetospan Windward Centre Leeward Ratio.9 – 0.4. reliable references shall be followed or specialist advice shall be sought.8 to be applied on external surfaces of buildings to obtain design wind load on individual components and cladding in accordance with Sec 2.75 r – 0. Table 6. structures or If pressure coefficients Cpe .6 2. use the external pressure coefficients in Fig 6.2.1) shall also be used for the windward quarter.2.2 and b) q based on Exposure B.5.2. Notes: (1) Values listed are for the determination of average loads on primary framing system. C pe components.4(b) is used. C pi¢ .25 wall exceeds that of all other walls by 10% or more and openings in all other walls do not exceed 20% of respective wall area.2 – 0. All other cases ± 0. r Quarter half Quarter Roofs on elevated 0 < r < 0.4 r – 0.7 with q based on spring line slope and q based on Exposure B.14 Internal Peak Pressure Coefficients for Buildings.2.6.75 and 0. ¢ or `Cp are not provided herein for certain buildings.7 – r – 0.7 – 0.4.7 and 6.5 r – 0.7 – r – 0. use external pressure coefficients of this table multiplied by 1.2.2. (2) Plus and minus signs signify pressures acting toward and away from the surfaces.5 0.2 < r < 0.7 – r – 0.21 for various cross sectional shapes to be used with the projected area of buildings or structures when Method 2 in Sec 2. C¢ pi Condition C¢ pi Percentage of total wall area occupied by openings in one + 0.6.25 Bangladesh National Building Code 631 .2.5 Roofs springing from 0 < r < 0. h Table 6. respectively.2 < r < 0.3 < r < 0.5 ground level * When the risetospan ratio is 0. Chapter 2 Loads c) C pe ¢ : external peak pressure coefficient as given in Fig 6. 6. (3) Appropriate positive and negative values of C¢pi shall be considered when determining the controlling load requirement.4.4.5. z h (2) Plus and minus signs signify pressures acting toward and away from the surfaces. 632 .Part 6 Structural Design Notes: (1) Values are to be used with q or q as specified in Sec 2.4 a(ii) and 2.6. (4) Percentage of openings is based on gross area of wall. respectively. respectively. (6) Roof overhangs shall have C pe ¢ given in Fig (b) to be applied at the top surface plus a C pe ¢ = + 0. h of 18 metres or Less Bangladesh National Building Code 633 . C¢ Fig 6. (5) Each component shall be designed for maximum positive and negative pressures.8 applied at the bottom surface.2. (3) External pressure coefficients for walls may be reduced by 10% when q ≤ 10 degrees. (4) Plus and minus signs signify pressures acting toward and away from the surfaces. (2) The horizontal scale denotes tributary area in square metres.7 External Peak Pressure Coefficients pe for Loads on Building Components and Cladding for Buildings with Mean Roof Height. Chapter 2 Loads Note : (1) Vertical scale denotes C pe ¢ to be used with qh based on Exposure B . use C pe ¢ from Fig 6. C¢ Fig 6.5h. zones (3) and (4) may be treated as zone (2) (6) For roofs with a slope of more than 10 degrees.2.7 and qh based on Exposure B (7) Plus and minus signs signify pressures acting toward and away from the surfaces.8 applied at the bottom surface.3 Notation: a : 5% of minimum width or 0. respectively. (9) For parapet use C pe ¢ = ± 1.Part 6 Structural Design Note : (1) Vertical scale denotes C pe ¢ to be used with appropriate qz or qh (2) Horizontal scale denotes tributary area A in square metres (3) Use q with negative values of C pe ¢ h (4) Each component shall be designed for maximum positive and negative pressures (5) If a parapet is provided around the roof perimeter.8 External Peak Pressure Coefficients pe for Loads on Building Components and Cladding for Buildings with Mean Roof Height. h Greater Than 18 metres 634 .2. (8) Roof overhangs shall have C pe ¢ given in Fig (b) to be applied at the top surface plus a C pe¢ = + 0. whichever is smaller h : Mean roof height in metres z : Height above ground in metres. 35 0.0 0.2.0 <0.5 0.55 0.4 0.20 1.4.2 Round (D q z ≤ 0.17 Overall Pressure Coefficients`Cp for Monoslope Roofs Over Unenclosed Buildings and Structures q L/B (degrees) 5 3 2 1 1/2 1/3 1/5 10 0.0 1.16 Overall Pressure Coefficient.35 0.55 1.85 0.35 0.80 2.05 0.2.3 0.3 0.6 0. D¢: depth of protruding elements such as ribs and spoilers.`Cp(2) for Rectangular Buildings with Flat Roofs h/B L/B 0.15 1.6 0.65 1.45 0.20 ≥40.7 0.5 1.2 1.5 0.5 Hexagonal or octagonal: (D q z > 0.0 1.35 0.0 1.7 0.8 1. (2) Linear interpolation may be made for intermediate values of``h/B and L/B.25 0.9 1.45 1.3 25 0.4 Round (D q z > 0. Use `Cp = + 0.0 1.15 (1) Overall Pressure Coefficients. X/L.95 2.08) 0.15 20.1 1.6a(ii).2 Notes: 1) The design wind force shall be calculated based on the area of the structure projected on a plane normal to the wind direction.60 1.167): All 0. etc.9 1.6.167): Moderately smooth 0.50 2.7 0.0 > 3.40 1.4 2.7 0.0 Location of centre of pressure.`Cp for Buildings and Structures such as Chimneys.8 0.85 20 0.1 1.75 15 0. Table 6.0 2.1 0.9 25 0.4 30 0. metres. metres.40 1.45 Bangladesh National Building Code 635 . The force shall be assumed to act parallel to the wind direction.35 0.2 0.95 0.8 1. h: height of structure.167 ) All 1.9 0.25 2.40 1.15 1.1 1.95 30 0.70 1. Table 6.02) 0.55 1.0 1.45 0.3 1.85 2.7 for roof in all cases.25 Note:(1) These coefficients are to be used with Method2 given in Sec 2.00 1. Chapter 2 Loads Table 6.80 2.95 1. metres.9 Very rough(D¢/D ≈ 0.00 1.2.8 0.7 0. for L/B values of : 2 to 5 1 1/5 to 1/2 10 to 20 0.55 2.3 1.10 10.5 0.0 Square (wind along diagonal) All 1.2 1.30 1. 3) Notation : D: diameter or least horizontal dimension.5 0.75 0.0 1.0 1. Shape Type of surface `Cp for h/D values of 1 7 25 Square (wind normal to a face) All 1. 2) Linear interpolation may be used for h/D values other than those shown.2 1. Tanks.7 Rough (D¢/D ≈ 0. metres X: distance to centre of pressure from windward edge of roof. 3) Notation : B: dimension of roof measured normal to wind direction. degrees. 2) Wind shall be assumed to deviate by ± 10 degrees from horizontal. 636 . metres L: dimension of roof measured parallel to wind direction. metres Q: angle of plane of roof from horizontal.Part 6 Structural Design Note: 1) Wind forces act normal to the surface and shall be directed inward or outward. `Cp for Solid Signs At Ground Level Above Ground Level u `Cp M/N `Cp ≤3 1.4 10 1.3 8 1. two cases shall be considered : a) Resultant force acts normal to sign at geometric centre.5 20 1.2 ≤6 1.3 to 0.5 1. in metres. metres N Smaller dimension of sign.2. 4) Notation: u Ratio of height to width M: Larger dimension of sign. Forces shall be assumed to act parallel to the wind direction.9 0.18 Overall Pressure Coefficients.1 2.4 16 1.1 to 0. and b) Resultant force acts normal to sign at level of geometric centre and at a distance from windward edge of 0.85 60 1.8 1.167 < 0.8 0.2. Table 6.167 D q z > 0.6 1.75 40 1. 2) The calculation of the design wind forces shall be based on the area of all exposed members and elements projected on a plane normal to the wind direction.25 times the vertical dimension shall be considered to be at ground level.2 5 1.29 1.1 Notes: 1) Signs with openings comprising 30% or more of the gross area are classified as open signs. 3) To allow for both normal and oblique wind directions.3 times the horizontal dimension.5 20 1.0 1. Bangladesh National Building Code 637 . 3) Notation : e : Ratio of solid area to gross area D : Diameter of a typical round member.85 ≥40 2.3 0.00 Note :1) Signs with openings comprising less than 30% of the gross area shall be considered as solid signs. 2) Signs for which the distance from the ground to the bottom edge is less than 0. metres. Chapter 2 Loads Table 6.75 30 1.00 ≥80 2.19 Overall Pressure Coefficients `Cp for Open Signs and Lattice Frameworks `Cp e Flatsided Round Members Members D q z ≤ 0.2 0.3 10 1.7 1. 29: factor = 0.69 1.025 4. which occurs when the wind is oblique to the faces. and the like. the design wind forces shall be assumed to act normal to a tower face.79: factor = 0. 6) For guyed towers.05 0.00 Notes: 1) The force coefficients shall be used in conjunction with exposed area of the tower guy in square metre. Table 6.L for Tower Guys f `Cp. such as ladders.3 < e < 0.67 For 0.20 90 1.0 1. 7) A reduction of 25% of the design force in any span between guys shall be made for determination of controlling moments and shears.60 0.47 For 0.45 70 1. 2) Notation: 638 .7 – 4.L (degrees) 10 0.45 60 0.35 0. the wind load acting normal to a tower face shall be multiplied by the factor 1.8 < e < 1.0 + 0. in metres. D : Typical member diameter.6 0. 2) For towers with rounded members.2.75 e for e< 0. `Cp for Trussed Towers `Cp e Square Towers Triangular Towers < 0. To allow for the maximum horizontal wind load.15 30 0.5e 0. the cantilever portion of the tower shall be designed for 125% of the design force. 5) Wind forces on tower appurtenances.0 3) For triangular section towers.20 0.20 0.21 Overall Pressure Coefficients.80 0.45 to 0.30 40 0.5 and shall be assumed to act along a diagonal.20 Overall Pressure Coefficients.2e 3.`Cp.35 80 1.05 0.10 0.05 20 0.15 0.0 + e Note : 1) Force coefficients are given for towers with structural angles or similar flat sided members. lights. 4) For square section towers. the design wind forces shall be assumed to act normal to a tower face.1 – 5.Part 6 Structural Design Table 6.7 to 1. the design wind force shall be determined using the values in the above table multiplied by the following factors: For e < 0.D `Cp. conduits. elevators. 8) Notation: e : Ratio of solid area to gross area of tower face.7e 1.7 0.3 + 0.8 1.35 50 0.44 4.2. calculated as chord length multiplied by guy diameter.0: factor = 1. shall be calculated using appropriate force coefficients for these elements.025 to 0.D and`Cp.67 e + 0.0 3. 1 1.4.85 ≥ 0. in degrees. `Cp.9. Ct at Crest Upwind slope Coefficient.9. such as regions around hills and ridges as shown in Fig 6.37 Legend: H tanf = the upwind slope.2.2 shall be modified by multiplying by a local topographic coefficient. Chapter 2 Loads `Cp. Ct (tan f) 0. 2.8 Effect of Local Topography : If a structure or any portion thereof is located within a local topographic zone.2.6.6.2 1.05 1.19 0. 2L u Bangladesh National Building Code 639 . Ct shall be obtained from Fig 6. Ct . f : Angle between wind direction and chord of the guy.D : Force coefficient for the component of force acting in direction of the wind.4. the sustained wind pressure obtained from Sec 2.39 0. Local Topographic Coefficient. Value of the coefficient.3 2.L : Force coefficient for the component of force acting normal to direction of the wind and in the plane containing the angle f. The interpolation shall be linear with horizontal distance from the crest. ECCENTRIC BRACED FRAME (EBF) : A steel braced frame designed in conformance with Sec 1.5 : BASE : The level at which the earthquake motions are considered to be imparted to the structures or the level at which the structure as a dynamic vibrator is supported. For any point within the local topographic zone. Ct shall be obtained by interpolation from the value at crest given in the table and the value of Ct=1 at the boundary of the zone.2 Definitions The following definitions of terms shall be applicable only to the provisions of Sec 2. The term "diaphragm" includes horizontal bracing systems.3.2. 640 . BEARING WALL SYSTEM : A structural system without a complete vertical load carrying space frame.1. BUILDING FRAME SYSTEM : An essentially complete space frame which provides support for gravity loads.3. DIAPHRAGM : A horizontal or nearly horizontal system of structures acting to transmit lateral forces to the vertical resisting elements. H = the height of the hill or ridge in meters Lu = the horizontal distance upwind from the crest to a level half the height below the crest in meters.5. This may be determined by comparing the computed midpoint in plane deflection of the diaphragm under lateral load with the storey drift of adjoining vertical resisting elements under equivalent tributary lateral load.Part 6 Structural Design tanfd = the average downwind slope. 2.5. Notes: (1) For intermediate values of upwind slope.2. (2) Ct = 1. see Sec 1.5. For primary framing systems of buildings or structures.0 for a point at or out side the boundary of the local topographic zones as shown in the figure . and with height above the local ground level.3. for purposes of this provision. DUAL SYSTEM : A combination of a Special or Intermediate Moment Resisting Frame and Shear Walls or Braced Frames designed in accordance with the criteria of Sec 1.5. FLEXIBLE DIAPHRAGM : A floor or roof diaphragm shall be considered flexible.1 General Minimum design earthquake forces for buildings.2.5 EARTHQUAKE LOADS 2. linear interpolation is permitted. 2. see Sec 1. BRACED FRAME : An essentially vertical truss system of the concentric or eccentric type which is provided to resist lateral forces. Fig 6.9 Local Topographic Coefficient. BASE SHEAR : Total design lateral force or shear at the base of a structure. the design seismic lateral forces shall be calculated either by the Equivalent Static Force Method or by the Dynamic Response Method based on the criteria set forth in Sec 2.8. when the maximum lateral deformation of the diaphragm is more than two times the average storey drift of the associated storey. Ct for Hills and Ridges. Overall design of buildings and structures to resist seismic ground motion and other forces shall comply with the applicable design requirements given in Chapter 1.2. value of the coefficient. ESSENTIAL FACILITIES : Buildings and structures which are necessary to remain functional during an emergency or a post disaster period. measured from the crest of a hill or ridge or to the ground level at a distance of 5H. structures or components thereof shall be determined in accordance with the provisions of this section. greater than 0. MOMENT RESISTING FRAME : A frame in which members and joints are capable of resisting forces primarily by flexure. STRUCTURE : An assemblage of framing members designed to support gravity loads and resist lateral forces.5. Storeyx is the storey below levelx. VERTICAL LOADCARRYING FRAME : A space frame designed to carry all vertical gravity loads. FLEXIBLY SUPPORTED EQUIPMENT : Nonrigid or flexibly supported equipment is a system having a fundamental period.06 second.5. Vx : The summation of design lateral forces above the storey under consideration.2. ORDINARY MOMENT RESISTING FRAME (OMRF) : A moment resisting frame not meeting special detailing requirements for ductile behaviour. HORIZONTAL BRACING SYSTEM : A horizontal truss system that serves the same function as a floor or roof diaphragm.2. STOREY SHEAR.24. STOREY : The space between floor levels. SHEAR WALL : A wall designed to resist lateral forces parallel to the plane of the wall (sometimes referred to as a vertical diaphragm or a structural wall).3 Symbols and Notation The following symbols and notation shall apply to the provisions of this section : Bangladesh National Building Code 641 . slim vertical structure. RIGIDLY SUPPORTED EQUIPMENT : A rigid or rigidly supported equipment is a system having a fundamental period less than or equal to 0.2. including the equipment. INTERMEDIATE MOMENT RESISTING FRAME (IMRF) : A concrete or steel frame designed in accordance with Sec 8.17 respectively. STRENGTH : The usable capacity of an element or a member to resist the load as prescribed in these provisions.06 second. SPECIAL MOMENT RESISTING FRAME (SMRF) : A moment resisting frame specially detailed to provide ductile behaviour complying with the seismic requirements provided in Chapters 8 and 10 for concrete and steel frames respectively. SOFT STOREY : Storey in which the lateral stiffness is less than 70 per cent of the stiffness of the storey above. PRIMARY FRAMING SYSTEM : That part of the structural system assigned to resist lateral forces. WEAK STOREY : Storey in which the lateral strength is less than 80 per cent of that of the storey above. SPECIAL STRUCTURAL SYSTEM : A structural system not listed in Table 6. 2. TOWER : A tall. Chapter 2 Loads FLEXIBLE ELEMENT OR SYSTEM : An element or system whose deformation under lateral load is significantly larger than adjoining parts of the system.3 or 10. Structures may be categorized as building and nonbuilding structures as defined in Sec 1. SPACE FRAME : A threedimensional structural system without bearing walls composed of members interconnected so as to function as a complete self contained unit with or without the aid of horizontal diaphragms or floor bracing systems. Z corresponding to the seismic zone of the site as set forth in Table 6.2. Zone 1. hx = height in metres above the base to level i. in seconds.5.Part 6 Structural Design Ac = the combined effective area. T = fundamental period of vibration. e.2 w i . considered concentrated at the top of the structure in addition to Fn.22. F¢ = lateral forces on an element or component or on equipment supports. Ae = the effective horizontal crosssectional area. 2.2. ft = lateral force at level i for use in Eq (2. C = numerical coefficient specified in Sec 2. Bangladesh has been divided into three seismic zones.2.26. i. Ft = that portion of the base shear V.2. or x respectively.10 with Zone 3 being the most severe. R = response modification coefficient for structural systems given in Table 6.22. n or x respectively.5..5).8 for structural and nonstructural components and equipment. V = the total design lateral force or shear at the base Vx = the design storey shear in storey x W = the total seismic dead load defined in Sec 2.4.5.1.5). Based on the severity of the probable intensity of seismic ground motion and damages. in square metres of the shear walls in the first storey of the structure.g..2.4.6. hn.5. wx = that portion of W which is located at or assigned to level i or x respectively w x¢ = the weight of the diaphragm and the elements tributary thereto at levelx.2. Fi.5.5.2. for use in Eq (2. Leveln = the uppermost level in the main portion of the structure. x = 1 designates the first level above the base. n.6. hi. De = the length in metres of a shear wall element in the first storey in the direction parallel to the applied forces.5 Design Earthquake Forces for Primary Framing Systems The design earthquake lateral forces on the primary framing systems of every building or structure shall be calculated based on the provisions set forth in this section. Ct = numerical coefficient given in Sec 2.5.Fn.2. W¢ = the weight of an element or component Z = seismic zone coefficient given in Table 6.2. of the structure in the direction under consideration. g = acceleration due to gravity.23.10. I = structure importance coefficient given in Table 6. i = 1 designates the first level above the base.Fx = lateral force applied to leveli. Leveli = level of the structure referred to by the subscript i.10. in metre.5.4 Seismic Zoning 2. including applicable portions of other loads defined in Sec 2. Zone 2 and Zone 3 as shown in Fig 6.5.24.5.5.1 Seismic Zoning Map : The seismic zoning map of Bangladesh is provided in Fig 6. Ax = the torsion amplification factor at levelx. F ¢x = force on floor or roofdiaphragm. 2.25. C‘ = numerical coefficient specified in Sec 2.e. di = horizontal displacement at leveli relative to the base due to applied lateral forces.g. S = site coefficient for soil characteristics given in Table 6.5.2.2. Levelx = the level under consideration e. 2. I¢ = structure importance coefficient specified in Sec 2. Each building or structure shall be assigned a Seismic Zone Coefficient.5. The design seismic forces shall be assumed 642 .8 and given in Table 6.5. in square metres of a shear wall in the first storey of the structure.2 Selection of Seismic Zone and Zone Coefficient : Seismic zone for a building site shall be determined based on the location of the site on the Seismic Zoning Map provided in Fig 6. regular or irregular.1.1 Selection of Lateral Force Method : Seismic lateral forces on primary framing systems shall be determined by using either the Equivalent Static Force Method provided in Sec 2.7 second. c) Total weight of permanent equipment shall be included. iii) Irregular structures not more than 20 metres in height. or structures having irregular features not described in either Table 6. iv) A tower like building or structure having a flexible upper portion supported on a rigid lower portion where: 1) both portions of the structure considered separately can be classified as regular structures. W. Bangladesh National Building Code 643 .3. located on Soil Profile Type S4 as given in Table 6. iii) Structures over 20 metres in height in Seismic Zone 3 not having the same structural system throughout their height except as permitted by Sec 1.5. but shall be used for structures of the following types.6 may be used for the following structures : i) All structures. except otherwise required by the provisions of Sec 1.1 (c).5.24.5. II.5.5. which have a period greater than 0.7. except case b(iv) below. all such loads but not less than 0.2.1 times the period of the upper portion considered as a separate structure fixed at the base.6.5. b) Where an allowance for partition load is included in the floor design in accordance with Sec 2. ii) Regular structures under 75 metres in height with lateral force resistance provided by structural systems listed in Table 6. except case b(iv) below. 2) the average storey stiffness of the lower portion is at least ten times the average storey stiffness of the upper portion.25. or III as defined in Table 6. including permanent partitions. weight or geometric vertical irregularity of Type I.5. regular or irregular. iv) Structures.3. is the total dead load of a building or a structure. ii) Structures having a stiffness. and 3) the period of the entire structure is not greater than 1.5. a minimum of 25 per cent of the floor live load shall be applicable. 2.7.1.3.4.5. and applicable portions of other loads listed below : a) In storage and warehouse occupancies. in Seismic Zone 1 and in Structure Importance Category IV in Seismic Zone 2. or the Dynamic Response Method given in Sec 2. 2.2. The analysis shall include the effects of the soils at the site and shall conform to Sec 2.2 Seismic Dead Load : Seismic dead load. b) The Dynamic Response Method as given in Sec 2.6 kN/m2 shall be applicable.3 or 6.5.6.3.7 may be used for all classes of structure.4 and 1.1. Chapter 2 Loads to act nonconcurrently in the direction of each principal axis of the building or the structure.4. i) Structures 75 metres or more in height except as permitted by case a(i) above.7 complying with the restrictions given below : a) The Equivalent Static Force Method of Sec 2. Part 6 Structural Design 644 . of the structure for the direction under consideration as determined by the provisions of Sec 2. Ct = 0.5.22 Table 6.5. Alternatively.2 Structure Period : The value of the fundamental period.25 S C = (2.5.5.075.083 for steel moment resisting frames = 0. Table 6.2 + (D e h n ) 2 ] (2.1.375R.50 2 0.00 1.00 2.5.5.2. the minimum value of the ratio C/R shall be 0.5. 031 A c .00 1.6.75 and this value may be used for any structure without regard to soil type or structure period.5.2. and eccentric braced steel frames = 0.5. Chapter 2 Loads 2.24 W = The total seismic dead load defined in Sec 2.15 III Special occupancy structures 1.075 II Hazardous facilities 1.2.22 I = Structure importance coefficient given in Table 6.25 1.23 R = Response modification coefficient for structural systems given in Table 6.5.2.2.5.25 1. I¢ Seismic Zone Zone Structure Importance Category Structure (see Fig 6.00 1.2.3) where. Except for those requirements where Code prescribed forces are scaled up by 0.4) Bangladesh National Building Code 645 .00 V Lowrisk Structures 1.10) Coefficient (see Table 6.6 Equivalent Static Force Method This method may be used for calculation of seismic lateral forces for all structures specified in Sec 2.049 for all other structural systems hn = Height in metres above the base to level n.5. The value of Ac shall be obtained from the relation : [ Ac = å A e 0.25 IV Standard occupancy structures 1.25 T = Fundamental period of vibration in seconds.2 C = Numerical coefficient given by the relation : 1. The value of C need not exceed 2.23 Seismic Zone Coefficients. T of the structure shall be determined from one of the following methods : a) Method A : For all buildings the value of T may be approximated by the following formula : T = Ct (hn) 3/4 (2.2) T 2 / 3 S = Site coefficient for soil characteristics as provided in Table 6.073 for reinforced concrete moment resisting frames.1(a) 2.2.1) R where.2. Z Structure Importance Coefficients I.1 for occupancy) Importance Coefficient I I¢ I Essential facilities 1.6.00 3 0.1 Design Base Shear : The total design base shear in a given direction shall be determined from the following relation : ZIC V = W (2.50 1 0.6. Z = Seismic zone coefficient given in Table 6. the value of Ct for buildings with concrete or masonry shear walls may be taken as 0. 646 .9. in square metres of a shear wall in the first storey of the structure. Ae = The effective horizontal crosssectional area. The value of De /hn for use in Eq ( 2.Part 6 Structural Design where. in metre of a shear wall element in the first storey in the direction parallel to the applied forces. De = The length.5. of the shear walls in the first storey of the structure.4) shall not exceed 0. Ac = The combined effective area. in square metres. 3.9. Chapter 1. Shear walls i) Concrete 8 ii) Masonry 8 4. Light steel framed bearing walls with tension only bracing 4 4.6.5. See Sec 2. Special moment resisting frames (SMRF) Frame System i) Steel 12 ii) Concrete 12 2. Ordinary moment resisting frames (OMRF) i) Steel 6 (5) 5 ii) Concrete d. Steel EBF i) With steel SMRF 12 ii) With steel OMRF 6 3. Intermediate moment resisting frames (IMRF). Sec 1. (4) (5) Bangladesh National Building Code 647 . Chapter 2 Loads Table 6. Shear walls i) Concrete with steel or concrete SMRF 12 ii) Concrete with steel OMRF 6 iii) Concrete with concrete IMRF (4) 9 iv) Masonry with steel or concrete SMRF 8 v) Masonry with steel OMRF 6 vi) Masonry with concrete IMRF (3) 7 2.3. Bearing Wall 1. Steel eccentric braced frame (EBF) 10 System 2. Concentric braced frames (CBF) i) Steel 8 ii) Concrete (3) 8 iii) Heavy timber 8 c.24 Response Modification Coefficient for Structural Systems. 3 storeys or less 8 ii) All other light framed walls 6 2. Light framed walls with shear panels i) Plywood walls for structures 3storeys or less 9 ii) All other light framed walls 7 3.6. Special Structural See Sec 1. Light framed walls with shear panels System i) Plywood walls for structures.3.3.3. 1. Dual System 1.6 for combination of structural systems.2. Building Frame 1. (3) Prohibited in Seismic Zones 2 and 3.5 for system limitations.5 Systems Notes : (1) Basic Structural Systems are defined in Sec 1. Concentric braced frame (CBF) i) Steel with steel SMRF 10 ii) Steel with steel OMRF 6 9 iii) Concrete with concrete SMRF (3) 6 iv) Concrete with concrete IMRF (3) e.2.5.2. concrete (4) 8 3.3.3.2. R Basic Structural Description of Lateral Force Resisting System (2) R System (1) a. Moment Resisting 1. Shear walls i) Concrete 6 ii) Masonry 6 3. 1. Braced frames where bracing carries gravity loads i) Steel 6 ii) Concrete (3) 4 iii) Heavy timber 4 b.7. (2) Prohibited in Seismic Zone 3. and Sec 1. Prohibited in Seismic Zone 3 except as permitted in Sec 2. 5.7) and (2.5. or in the event that soil profile S4 is established by geotechnical data.5) i =1 i=1 The values of fi represent any lateral force distributed approximately in accordance with the principles of Eq (2. or b) Stiff or dense soil condition where the soil depth is less than 61 metres S2 A soil profile with dense or stiff soil conditions. shall be distributed along the height of the structure in accordance with Eq (2. The concentrated force. In locations where the soil properties are not known in sufficient detail to determine the soil profile type.7) and (2.Part 6 Structural Design Table 6. (2. S Type Description S1 A soil profile with either : a) A rocklike material characterized by a shearwave velocity greater than 1.5. fi.6). Soil profile S4 need not be assumed unless the building official determines that soil profile S4 may be present at the site.8): n V = F t + å F i i= 1 (2.5) shall not exceed that calculated using Eq (2.7b) 648 .0 762 m/s or by other suitable means of classification.5.5. 2.25 V when T > 0.5.2 61 metres S3 A soil profile 21 metres or more in depth and containing more than 6 metres 1. S for Seismic Lateral Forces (1) Site Soil Characteristics Coefficient. This requirement may be satisfied by using the following formula : n n T = 2 p å w id i 2 g å f i d i (2.5.0 when T ≤ 0.2.3) by more than 40%. The value of T determined from Eq (2.5. b) Method B : The fundamental period T may be calculated using the structural properties and deformational characteristics of the resisting elements in a properly substantiated analysis. di shall be calculated using the applied lateral forces.7 second (2. which is the base shear V.5.5. (2. Ft acting at the top of the building shall be determined as follows: Ft = 0. the total lateral force.07 TV ≤ 0.6) where. Fi = Lateral force applied at storey level i and Ft = Concentrated lateral force considered at the top of the building in addition to the force Fn.25 Site Coefficient.8) or any other rational distribution.6. soil profile S3 shall be used.5. where the soil depth exceeds 1.6).5.0 shear wave velocity less than 152 m/s Note : (1) The site coefficient shall be established from properly substantiated geotechnical data.7a) Ft = 0.5 of soft to medium stiff clay but not more than 12 metres of soft clay S4 A soil profile containing more than 12 metres of soft clay characterized by a 2.5.3 Vertical Distribution of Lateral Forces : In the absence of a more rigorous procedure.7 second (2. The elastic deflections. Vx shall be distributed to the various elements of the vertical lateral force resisting system in proportion to their rigidities.6 Combination of Structural Systems : When structural systems defined in Sec 1. davg = The average of the displacements at extreme positions of the building at levelx. Structures may be designed using the procedures of Sec 2.5. Bangladesh National Building Code 649 .4 Horizontal Distribution of Shear : The design storey shear Vx. The accidental torsional moment in any storey shall be determined assuming the storey mass to be displaced from the calculated centre of mass in each direction a distance equal to 5% of the building dimension at that level perpendicular to the direction of the force under consideration.5 Horizontal Torsional Moments : Provision shall be made for the increased shears resulting from horizontal torsion where floor diaphragms are not flexible. including leveln. shall be distributed over the height of the building. 0 (2.1. Allowance shall also be made for the increased shear arising due to any horizontal torsional moments as specified in Sec 2.2 are combined to be incorporated into the same structure. shall be designed as a separate structure.5.5.1a(iv).5. the following requirements shall be satisfied: a) Vertical Combinations: The value of the response modification coefficient. this requirement need not apply to a storey where the dead load above that storey is less than 10 per cent of the total dead weight of the structure. the force Fx shall be applied over the area of the building in proportion to the mass distribution at that level. The flexible upper portion. according to the relation : (V - F t )w x h x Fx = n å w i h i i= 1 (2.4) the effects shall be accounted for by increasing the accidental torsion at each level by an amplification factor.9) where. The more severe loading for each element shall be considered for design.6. Where torsional irregularity exists (Plan Irregularity Type I as defined in Table 6. 2. 2. supported laterally by the rigid lower portions using the appropriate value of R.8) At each storey levelx.2 d avg )] £ 3. or ii) The following procedure is used for structures conforming to Sec 2. dmax = The maximum displacement at levelx.5.5.5. 1. in any storey x is the sum of the forces Fx and Ft above that storey.6.5.6. However.5. The torsional design moment at a given storey shall be the moment resulting from eccentricities between applied design lateral forces at levels above that storey and the vertical resisting elements in that storey plus an accidental torsional moment. 2. Ax determined from the formula: 2 [ A x = d max (1.6. considering the rigidity of the floor or roof diaphragm.6 under the following conditions: i) The entire structure is designed using the lowest value of R for the lateral force resisting systems used. R used in the design of any storey for a given direction shall not be greater than that used for the storey above.3.5. Chapter 2 Loads The remaining portion of the base shear (VFt). 3.3. ii) Any combination of Building Frame Systems.2 may be used to resist design seismic forces in structures less than 50 m in height. the value of R used for the orthogonal direction shall not be greater than that used for the Bearing Wall System defined in Sec 1. or Moment Resisting Frame Systems defined in Sec 1. Only combinations of Dual Systems and Special Moment Resisting Frames (SMRF) can be used to resist the design seismic forces in structures exceeding 50 m in height in Seismic Zone 3. The reactions from the upper portion shall be increased by the ratio of the R values of the two portions. These factored reactions shall be applied at the top of the rigid lower portion in addition to the forces determined for the lower portion itself.2. The rigid lower portion shall be designed as a separate structure using the appropriate value of R . where a structure has a Bearing Wall System in only one direction. b) Combinations Along Different Axes: i) In Seismic Zone 3.Part 6 Structural Design 2. 650 . Dual Systems. seismologic.6.5.5.5. shall conform to the criteria established in this section. tectonic. the normalized response spectra given in Fig 6.2.5.5. Chapter 2 Loads 2.2. The mass and mass moments of inertia of various components of a structure. ii) Normalized Response Spectra : In absence of a sitespecific response spectrum. b) Time History : Ground motion time history developed for the specific site shall be representative of actual earthquake motions for the directions under consideration. be one having 20% probability of being exceeded in 50 years and may be one of the following: a) Response Spectrum : The response spectrum to be used in the dynamic analysis shall be any one of the following: i) Site Specific Design Spectra : A site specific response spectra shall be developed based on the geologic. where used.7 Dynamic Response Method The Dynamic Response Method.2 and 2. shall be calculated based on the seismic dead load specified in Sec 2.2. using a mathematical model specified in Sec 1.7.5.7. 2. The spectra shall be developed for a damping ratio of 0.1 Ground Motion : The ground motion representation as set out in this section shall.11 shall be used in the dynamic analysis procedure given in Sec 2.7. shall approximate the sitespecific design spectra conforming to paragraph a (i) above.1(a) and one of the dynamic analysis procedures given in Sec 2. Bangladesh National Building Code 651 .5. as a minimum.3.7. and soil characteristics associated with the specific site. Response spectra from time history. The analysis of the structure shall be based on an established principle of mechanics.05 unless a different value is found to be consistent with the expected structural behaviour at the intensity of vibration established for the site.2. required for the dynamic analysis. either individually or in combination. an elastic dynamic analysis of a structure shall be performed based on the criteria set forth in this section with a mathematical model conforming to Sec 1.2. displacements. 2.5.6.5.7.5. Alternative factors may be used when substantiated by sitespecific data.6. including deflections. determined by this procedure. at least 90 per cent of the participating mass of the structure is included in the calculation of response for each principal horizontal direction.1 for regular structures except that the base shear shall not be less than 80 per cent of that determined using T from Sec 2.5. The value of the base shear as obtained from Sec 2.5.6.2 Response Spectrum Analysis : Where this procedure is used. ii) When the base shear is greater than that determined from Sec 2. the value need not exceed that required by c(i) above.3 Time History Analysis : When this procedure is followed.5.7.7.5.7. the following values shall be taken : 1.5. The analysis shall include the peak dynamic response of all modes having a significant contribution to total structural response. storey forces. V.1.2(a). for irregular structures. or by the equivalent static procedure provided in Sec 2. member forces and moments.5.6. and base reactions for each mode shall be combined using established procedures in order to estimate resultant maximum values of these response parameters. including accidental torsional effects as prescribed in Sec 2. 2. ii) Possible amplification of building response due to soilstructure interaction and lengthening of building period caused by inelastic behaviour shall be considered.6. a) Number of Modes : The requirement that all significant modes be included may be satisfied by demonstrating that.2c(i).5.5.1. d) Torsion : The analysis shall account for torsional effects. for the modes considered.1 b (iv): i) The ground motion representation shall be developed in accordance with paragraphs a (i) and b above. effects of accidental torsion shall be accounted for by appropriate adjustments in the model such as adjustment of mass locations.6.5. storey shears.6.6. Peak modal response shall be calculated using the ordinates of the appropriate response spectrum curve which correspond to the modal periods. d) Vertical Component: The vertical component of ground motion may be defined by scaling the corresponding horizontal ground accelerations by a factor of twothirds. it shall be adjusted as follows : i) When the base shear is less than that determined from Sec 2.6.1(a ). Maximum modal contributions shall be combined in a statistical manner to obtain an approximate total structural response. by dividing by a factor not greater than the appropriate R value for the structure but shall not be less than that required by Sec 2.5. c) Scaling of Results : Where the base shear for a given direction. is different from the base shear obtained by using the procedure of Sec 2. except for structures required to conform to Sec 2.1(c) All corresponding response parameters. 2.5. When three dimensional models are used for analysis. Where threedimensional models are used for analysis.5.7.Part 6 Structural Design c) Structures on Soil Profile Type S4 : The following provisions shall apply when required by Sec 2. iii) The base shear determined by these procedures may be reduced to a design base shear.5.1(a) and using a response spectrum as specified in Sec 2. modal interaction effects shall be considered when combining modal maximum.1. 90 per cent of the value from Sec 2. an elastic or inelastic dynamic analysis of a structure shall be made using a mathematical model of the structure specified in 652 .5. shall be adjusted in proportion to the adjusted base shear. b) Combination of Modes : The peak member forces.1. 2.75 ZI w x¢ but it shall not be less than 0. These forces shall be applied in the horizontal direction to cause the most critical loading for design.26. b) When the diaphragm is required to transfer lateral forces from the vertical resisting elements above the diaphragm to other vertical resisting elements below the diaphragm due to offset in the Bangladesh National Building Code 653 .8 kN and for furniture need not be determined for design purposes.5. C‘ shall be taken as those given in Table 6.8. ducting and conduit systems which are constructed of ductile materials and connections.11) need not exceed 0. a ground motion time history as specified in Sec 2.2.2. nonstructural components.1(b).5.23 C¢ = Horizontal force Coefficient as specified in Sec 2.10) shall be distributed in proportion to the mass distribution of the element.2.1 Lateral Forces on Structural and Nonstructural Components. the seismic lateral force shall be determined considering the dynamic properties of both the equipment and those of the structure which supports it.8 Seismic Lateral Forces on Components and Equipment Supported by Structures 2.9. c) The value of C¢ for elements.11) å w i i =x a) The force F x¢ determined from Eq (2. component or piece of equipment.5.2.5.5.26 but it need not exceed 2. the values of C¢ may be taken as those given in Table 6.5.8.6.0.5.22 I¢ = Structure Importance Coefficient for components as given in Table 6. and for rigid or rigidly supported equipment supported by structures above grade. b) For nonrigid or flexibly supported equipment. Friction resulting from gravity forces shall not be considered to provide resistance to seismic forces.35 ZI. Seismic lateral forces on attachments for floor or roofmounted equipment weighing less than 1.1(a) and applying at its base or any other appropriate level. 2. or components and equipment laterally selfsupported and located at or below ground level may be twothirds of the value set forth in Table 6.5.2. W¢ = Weight of an element. the value of C¢ shall be taken as twice the value listed in Table 6. In the absence of an analysis or empirical data.5. but the value of C¢ shall not be less than that listed in Table 6.7.5. F¢ obtained from Eq (2.10) for these elements shall not be less than that as would be obtained using the provision of Sec 2. However. supported by a structure and located above grade on a structure.26. component or piece of equipment.8.2 Horizontal Force Coefficient C¢ : The value of the coefficient C¢ shall be determined as follows : a) For elements of structure and nonstructural components.5. The total lateral seismic force. the design lateral forces obtained from Eq (2.2. 2. The timedependent dynamic response of the structure shall be obtained through numerical integration of its equations of motion. For piping.8.10) where. 2. and Equipment : The minimum design seismic lateral forces on elements of structures.3 Seismic Lateral Forces on Floor or Roof Diaphragms : Seismic lateral forces on floor and roof diaphragms and collector elements shall be determined in accordance with the following formula : n ( F t + å F i ¢ ) i = x F ¢x = n w ¢x (2.26.26.2.2. Chapter 2 Loads Sec 1. F¢ = Total lateral seismic force Z = Seismic zone coefficient as given in Table 6. equipment and their attachments including anchorage and bracing to the main structural system shall be determined in accordance with the formula : F ¢ = Z I ¢C ¢ W ¢ (2.5. 2.0 is used in load calculations. these forces shall be added to those determined from Eq (2.75 applied at centre of gravity (4) 4.9. the fundamental period T.5.5. Walls including the following: a. bins and piping. Components and Equipment Elements of Structures and Nonstructural Components and Equipment(1) Value of C¢ I Elements of Structures 1. Supported on or projecting as an unbraced cantilever above the roof more 2. W shall include all loads defined for buildings in Sec 2.5. vessels.75 All interior bearing and nonbearing walls and partitions(3) d. shall be determined in accordance with Sec 2. In addition. (i) the structure is less than 15 m in height. if.5.2 Fundamental Period : For structures with primary framing systems similar to buildings.8 m high 2.5. Determination of seismic lateral forces for such structures shall be based on the following provisions: 2.2 and 2.5. Table 6. –– Diaphragms(3. trussed towers and tanks on legs: a.8 with following modifications : a) Intermediate moment resisting frames (IMRF) may be used in structures within Seismic Zone 3 and in structure importance categories III through V.2.11).5.00 than onehalf their total height b.Part 6 Structural Design placement of the elements or to changes in stiffness in the vertical elements. Chimneys.9.5.5.2. C¢ for Elements.6.9. Unbraced (cantilevered) parapets 2.1 Seismic Dead Load : For nonbuilding structures. Connections for prefabricated structural elements other than walls. and (ii) R = 4.6.26 Horizontal Force Coefficient. Other exterior walls above the ground floor(2. Nonstructural Components 1. including those supported below the roof with unbraced 0.9.5.5) II.2 respectively.5. 0.24) shall be determined in accordance with the provisions of Sec 2.75 Masonry or concrete fences over 1.5.2.3 Structures Similar to Buildings : The seismic lateral forces on structures with primary framing systems similar to buildings (i. W ¢ shall include all normal operating contents for structures such as tanks. Exterior and interior ornamentation and appendages 2.5.9 Seismic Lateral Forces on NonBuilding Structures Nonbuilding structures shall include all selfsupporting structures other than buildings that carry gravity loads and resist the effects of earthquake and other lateral forces. T shall be obtained by using a rational method such as Method B of Sec 2.00 b. stacks.5 through 2. Penthouse (except when framed by an extension of the structural frame) 0.75 3.5.75 c. For other structures. with force 0.e. All others. b) Seismic dead load and structure period shall be calculated in accordance with Sec 2.2. structural systems listed in Table 6. or braced or guyed to the structural frame at or above their centres of mass 654 .00 2.2.75 projection above the roof less than onehalf their height. 2. 0.3) 0. 2. the seismic dead load. 3.2 kN/m2 shall be used.2 (3) Where flexible diaphragms provide lateral support for walls and partitions. boilers.5.7. heat exchangers. (8) Equipment includes. Anchorage for permanent floorsupported cabinets and book stacks more than 0.5 kN/m2 partition load allowance. (2) See Sec 1. together with support systems and 0.8.5. but is not limited to .75 anchorage 2. (6) Ceiling weight shall include all light fixtures and other equipment or partitions which are laterally supported by the ceiling. For the purpose of determining the seismic force.5.5 m in height (including contents) 6. Ceilings constructed of lath and plaster or gypsum board. It also includes major conduit. mechanical and plumbing equipment and associated conduit. ducting and piping serving such equipment and fire sprinkler systems. 7) III.2 for items supported at or below grade. Storage racks (including contents) 0. Anchorage for suspended ceilings and light fixtures(4.75 ductwork and piping.75 Access floor systems(4.7. transformers and lifesafety equipment. the value of C¢ for anchorage shall be increased 50 per cent for the centre onehalf of the diaphragm span.8.75 7.5. and machinery (8) Notes: (1) See Sec 2.2. Tanks and vessels (including contents).00 4. 0. See Sec 2. (7) W‘ for access floor systems shall be the dead load of the access floor systems plus 25 per cent of the floor live load plus a 0. Signs and billboards 2.8.3 and 2.2 for additional requirements for determining C¢ for nonrigid or flexibly mounted equipment. cooling towers. Electrical. switchgear. (5) See Sec 1. Chapter 2 Loads 3.9 and 2. a ceiling weight of not less than 0.2.8. Bangladesh National Building Code 655 . 6) 0.75 5. control panels. motors. screw or nail attached to suspended members that support a ceiling at one level extending from wall to wall need not be analysed provided the walls are not over 15 m apart. chillers. Equipment 1. airhanding units.75 1. (4) Applies to Seismic Zones 2 and 3 only. pumps. 0. V shall be determined using the provisions of Sec 2.6.7.10 and Sec 1.5. Inverted pendulumtype structures 3 6. 2. R for NonBuilding Structures Structure Type Coefficient R 1.06 second) including their anchorage. All other selfsupporting structures not otherwise covered 4 b) The vertical distribution of the total lateral seismic force. Tanks.5. guyed stacks and chimneys 4 5.5 Z I W (2.4 considering the entire weight of the tank and its contents.3. Table 6.5.2.5. V.27. which are not covered by Sec 2. Exception: For irregular structures assigned to Structure Importance Categories I and II. 2.9.5. Castinplace concrete silos and chimneys having walls continuous to the 5 foundation 3. the total lateral force.5.5.3 respectively. Alternatively.9.27 Coefficient. V shall be determined in accordance with the relation : V = 0. However.9.9.9. chimneys.7 shall be used. the ratio C/R shall not be less than 0.5 Flatbottom Tanks at or Below Grade : Seismic forces for flatbottom tanks or other tanks with supported bottoms. may be determined by one of the following procedures: 1.5. Cooling towers 5 7. Bins and hoppers on braced or unbraced legs 4 8. founded at or below grade. the procedures of Sec 2. Using procedures of Sec 2. those with period. which includes consideration of the actual ground motion anticipated at the site and the inertial effects of the contained fluid. Signs and billboards 5 10.2. Storage racks 5 9. Using provisions of Sec 2.5.6 Other Structures : For structures (other than buildings).2.5. which cannot be modeled as a single mass. Trussed towers (free standing or guyed). Distributed mass cantilever structures such as stacks.5.Part 6 Structural Design 2.2. the minimum seismic lateral forces shall be determined in accordance with the following provisions : a) The total lateral seismic force. b) A substantiated analysis prescribed for the particular type of tank provided that the seismic Zones and Structure Importance Categories are in conformance with Fig 6. shall be calculated using the procedure of Sec 2.3 through 2.e. vessels or pressurized spheres on braced or unbraced legs 3 2.4 Rigid Structures : For rigid structures (i.12) 2. 656 .9. a) A response spectrum analysis.6 with the coefficient R taken from Table 6. silos and skirt 4 supported vertical vessels 4. T £ 0. Amusement structures and monuments 3 11.5. such forces may be determined using one of the following methods.5. 3 respectively. 2. consideration shall be given to both hydrostatic and hydrodynamic effects.6.2 Controlled Drainage : Roofs equipped with controlled drainage provisions shall be designed to sustain all rainwater loads on them to the elevation of the secondary drainage system plus 0. 2.3 Rain Loads Rain loads shall be determined in accordance with the following provisions. shall be based on 50year return period. Chapter 2 Loads c) When any other established standard or method is used as a basis for obtaining the seismic lateral forces for a particular type of nonbuilding structure covered by this section.4. In this case. For structures other than essential and hazardous facilities. SITESPECIFIC DATA : Data obtained either from measurements taken at a site or from substantiated field information required specifically for the structure concerned. ii) The values for total lateral force and total base overturning moment used in design shall not be less than 80% of the values which would be obtained using these provisions. arising due to approaching windgenerated waves shall also be determined in addition to the hydrostatic load on them. values of maximum flood elevation. Ponding instability shall be considered in this situation. these values. shall be taken corresponding to 100year return period.1. may be determined based on information from reliable references or specialist advice may be sought.6. hydrodynamic forces..2 Definitions The following definitions and notation shall apply to the provisions of this section only.6.4 and 1. For essential facilities like cyclone and flood shelters and for hazardous facilities specified in Table 6. the amplitude of such wind induced water waves shall be obtained from sitespecific data. 2.6. ESSENTIAL FACILITIES : Buildings and structures which are necessary to remain functional during an emergency or a post disaster period. required for the determination of flood and surge load. loads due to flood shall be determined considering hydrostatic effects which shall be calculated based on the flood elevation of 50year return period. RATIONAL ANALYSIS : An analysis based on established methods or theories using mathematical formulae and actual or appropriately assumed data. wind velocities etc.3.25 kN/m2. 2. 2.6.1 Blocked Drains : Each portion of a roof shall be designed to sustain the load from all rainwater that could be accumulated on it if the primary drainage system for that portion is undersized or blocked.1 General The procedures and limitations for the determination of selected miscellaneous loads are provided in this section.6. For riverside structures such as that under Exposure C specified in Sec 2. Ponding instability shall be considered in this situation. such a standard may be used subject to the following limitations: i) The Seismic Zones and Structure Importance Categories shall be in conformance with the requirements of Sec 2. Required loading shall be determined in accordance with the established principles of mechanics based on site specific criteria and in compliance with the following provisions of this section. Loads that are not specified in this section or elsewhere in this chapter. surge height.1 Flood Loads on Structures at Inland Areas : For structures sited at inland areas subject to flood.4.6.4.2 Flood and Surge Loads on Structures at Coastal Areas : For structures sited at coastal areas.2. 2.1.4 Loads Due to Flood and Surge For the determination of flood and surge loads on a structural member.6. 2.3.4. 2.6 MISCELLANEOUS LOADS 2.5.1. the hydrostatic and hydrodynamic loads shall be determined as follows : Bangladesh National Building Code 657 . such nonstructural elements shall be designed to sustain a maximum uniformly distributed load of 1.3) where. 2. Such forces shall be calculated based on 50year or 100year return period of flood or surge. shall be the air temperature in the shade.3 Breakaway Walls : When nonstructural walls. yT : The elevation of the extreme surface water level. shall be considered in the design of structures or components thereof in accordance with the provision of this section. hf ) (2.4. associated with cyclones. in km; x = 1.5 Temperature Effects Temperature effects. given in Table 6. The corresponding wind velocities shall be 260 km/h or 289 km/h respectively.2) hs = Maximum surge height as specified in a(i) below. the following provisions shall be considered : a) The temperatures indicated. which may not be associated with a cyclonic storm surge.6. partitions or other nonstructural elements located below the maximum flood or surge elevation. in metres. hs. i) Maximum Surge Height. to be used in the rational analysis. shall be that corresponding to a 50year or a 100year return period as may be applicable.6. 658 .0 kN/m2 but not less than 0. b) Hydrodynamic Loads : The hydrodynamic load applied on a structural element due to wind induced local waves of water. if x<1. Values of yT are given in Table 6. are required to break away under high tides or wave action.5 kN/m2 applied on a vertical projection of the area. where. The range of the variation in temperature for a building site shall be taken into consideration. hs : The maximum surge height. metres. if significant. Hm produced by floods or surges as given by the relation : Hm = max (hs. shall be determined by a rational analysis using an established method and based on site specific data.6. 2.1) where.28. hf = yT – yg and (2.2(a). metres yg = Elevation of ground level at site. the following relation may be used : hs = hT – (x – 1) k (2. hT = design surge height corresponding to a return period of Tyears at sea coast. based on site specific analysis. yT = Elevation of the extreme surface water level corresponding to a Tyear return period specified in (ii) below. x = distance of the structure site measured from the spring tide highwater limit on the sea coast. k = rate of decrease in surge height in m/km; the value of k may be taken as 1/2 for ChittagongCox's BazarTeknaf coast and as 1/3 for other coastal areas. shall be taken as hw = hs/4 ≥1m. shall be that obtained from a site specific analysis corresponding to a 50year or a 100year return period.6. hs is given in Sec 2.6.6. In the absence of a sitespecific data the amplitude of the local wave. b) Effects of the variation of temperature within the material of a structural element shall be accounted for by one of the following methods. In the absence of a more rigorous site specific analysis.4. ii) Extreme Surface Water Level .2.29 for selected coastal locations which may be used in the absence of any site specific data. yT for a site.Part 6 Structural Design a) Hydrostatic Loads : The hydrostatic loads on structural elements and foundations shall be determined based on the maximum static height of water. In determining the temperature effects on a structure.2. 5 5.1 8. ii) design the structural element to sustain additional stresses due to temperature effects.1. Chapter 2 Loads i) relieve the stresses by providing adequate numbers of expansion or contraction joints.2.2 7.6 Sandwip.1. and MaheshkhaliKutubdia 7.7 Sarankhola to Shyamnagar 5.28 Design Surge Heights at the Sea Coast.6 Bhola to Barguna 6.1.9 9.9 9.3 6. Note : (1) These values may be used in the absence of site specific data for structures other than essential facilities listed in Table 6.6 Islands Chittagong to Noakhali 7.1. (2) These values may be used in the absence of site specific data for essential facilities listed in Table 6.8 Chakaria to Anwara. Bangladesh National Building Code 659 . Table 6. hT* Coastal Region Surge Height at the Sea Coast. Hatiya and all islands in this region 7. MCSP. hT (m) T = 50year(1) T = 100year(2) Teknaf to Cox's Bazar 4.4 * Values prepared from information obtained from AnnexD3. 75 Chardouni Patharghata 4.32 3. the temperature effect can be considered insignificant and need not be considered in design.19 Banigram Patiya 5.72 4. d) When it can be demonstrated by established principle of mechanics or by any other means that neglecting some or all of the effects of temperature.65 3. exposure condition of the element and the rate at which the material absorb or radiate heat.60 3.94 4.02 7.Part 6 Structural Design Table 6.23 3.62 4.05 5.87 Lemsikhali Kutubdia 4. does not affect the safety and serviceability of the structure.66 Mongla Monglaport 3.36 Kobodak Shyamnagar 3.76 Daulatkhan Daulatkhan 4. MCSP Note : (1) These values may be used in the absence of site specific data for structures in Structure Importance Categories III. IV and V listed in Table 6. ii) the warping or any other distortion caused due to temperature changes and temperature gradient in the structural element.53 7.16 Sonapur Sonagazi 7.72 Dashmina Dashmina 3.95 5. 660 .41 4.1.37 Patharghata Patharghata 3.92 Patuakhali Patuakhali 2.55 5.2.88 Shaflapur Moheshkhali 4.1. yT* Coastal Area yT (m) Location Thana T=50 years(1) T=100 years(2) Teknaf Teknaf 2.87 3.87 (river estuary) Kaikhali Shyamnagar 3.29 Extreme Surface Water Levels During Monsoon at Selected Locations of the Coastal Area above PWD Datum.08 4.09 6.1.51 3.1.93 3.79 3.84 Raenda Sarankhola 3.94 Hatiya Hatiya 5.2 Companyganj Companyganj 7.03 Khepupara Kalapara 2.66 3.12 * Values prepared from information obtained from Annex D3.02 Bamna Bamna 3.24 Chittagong Bandar 4.11 Sandwip Sandwip 6.67 4. the structural analysis shall take into account the following : i) the variation in temperature within the material of the structural element.88 Patenga Bandar 4.73 Galachipa Galachipa 3.84 3. c) when the method b(ii) above is considered to be applicable.44 Cox's Bazar Cox's Bazar 3.33 2. (2) These values may be used in the absence of site specific data for structures in Structure Importance Categories I and II listed in Table 6. lying below ground level. loads due to soil and hydrostatic pressure shall be determined in accordance with the provisions of this section and applied in addition to all other applicable loads.6. plus full hydrostatic pressure.1 Pressure on Basement Wall : In the design of basement walls and similar vertical or nearly vertical structures below grade. When a portion or the whole of the adjacent soil is below the surrounding water table. Allowance shall be made for possible surcharge due to fixed or moving loads. Chapter 2 Loads 2. Bangladesh National Building Code 661 .6. 2.6 Soil and Hydrostatic Pressure For structures or portions thereof.6. provision shall be made for the lateral pressure of adjacent soil. computations shall be based on the submerged unit weight of soil. Only windows or other similarly weak and light weight structural elements may be taken as ventilation areas even though certain limited structural parts break at pressures less than qo. Ao is the total window area in m2 and v is the volume in m3 of the room considered. ii) The internal pressure shall be assumed to act simultaneously upon all walls and floors in one closed room. 662 . shall be assessed in accordance with the provisions of this section.12(a) may be taken as static action. and iii) The action qo obtained from Fig 6. where t1 is the time from the start of combustion until maximum pressure is reached and t2 is the time from maximum pressure to the end of combustion.2. The pressure may be applied solely in one room or in more than one room at the same time.. the values shall be chosen within the intervals as given in Fig 6. internal dust explosion etc. In the latter case.12(a) shall be assumed to depend on a factor Ao/v.6. all rooms are incorporated in the volume v. However. evaporation of volatile liquids.2.1 Explosion Effects in Closed Rooms : a) Determination of Loads and Response : Internal overpressure developed from an internal explosion such as that due to leaks in gas pipes. The hydrostatic head shall be measured from the underside of the construction. if any. in rooms of sizes comparable to residential rooms and with ventilation areas consisting of window glass breaking at a pressure of 4 kN/m2 (34 mm machine made glass) may be calculated from the following method : i) The overpressure.12(b) shall be used in a dynamic analysis.6. 2. where. qo provided in Fig 6.12(b). shall be taken as the full hydrostatic pressure applied over the entire area.6. the upward pressure of water. For t1 and t2 the most unfavourable values shall be chosen in relation to the dynamic properties of the structures.7 Loads Due to Explosions Loads on buildings or portions thereof.2.6.7. 2.2 Uplift on Floors : In the design of basement floors and similar horizontal or nearly horizontal construction below grade.Part 6 Structural Design 2.2. When a time dependent response is required. an impulsive force function similar to that shown in Fig 6. 2.2. such as a basement.7. L2 or L3 as given below producing the most unfavourable effect : i) L1 = W1 (2. floors and roofs and their supporting members separating a use from an explosion exposure. 2. in the basement below ground level. 2. but for a minimum internal pressure or suction of 5 kN/m2. In the case of buildings having floors that are acted upon by a live load larger than 5.6. 2. in addition to all other loads specified in this chapter. Chapter 2 Loads b) Limitations : Procedure for determining explosion loads given in (a) above shall have the following limitations: i) Values of qo given in Fig 6. shall be considered to have the characteristic values provided in Table 6.6.2.7. 2. of Storeys (1) Vertical Load Above the Air Raid Shelter kN/m2 < 2 28 34 34 > 4 41 Buildings of particularly stable construction 28 (2) irrespective of the number of storeys Note : (1) Storeys shall mean every usable storey above the shelter floor (2) Buildings of particularly stable construction shall mean buildings having bearing structural elements made from reinforced insitu concrete.30. the characteristic vertical load shall be determined in accordance with provisions of Sec 2.30 Characteristic Vertical Loads for an Air Raid Shelter in a Building No. for specific cases.0 kN/m2.6.4c) Bangladesh National Building Code 663 .7. ii) Fig 6. such as those from external gas cloud explosions.6.6. external explosions due to high explosives (TNT) etc.8. Table 6. the minimum live load on helicopter landing or touch down areas shall be one of the loads L1.8 Vertical Forces on Air Raid Shelters For the design of air raid shelters located in a building e.1 Characteristic Vertical Loads : Buildings in which the individual floors are acted upon by a total distributed live load of up to 5.2.0 kN/m2.0 kN/m2.8.2 Minimum Design Pressure : Walls. vertical forces on air raid shelters generally located below ground level.0 kN/m2. such vents shall be designed to relieve at a maximum internal pressure of 1. shall be determined. 2. including the dead load. by rational analyses based on information from reliable references or specialist advice shall be sought.4 Loads Due to Other Explosions : Loads arising from other types of explosions.12(a) are based on tests with gas explosions in room corresponding to ordinary residential flats.6.4b) iii) L3 = w (2. and probability of occurrence of an explosion shall be checked in each case using appropriate values. above values shall be increased by the difference between the average live loads on all storeys above the one used as the shelter and 5.6.12 shall be taken as a guide only. and may be applied to considerably different conditions with caution after appropriate adjustment of the values based on more accurate information.1 below.4a) ii) L2 = kW2 (2.3 Design Pressure on Relief Vents : When pressurerelief vents are used. shall be designed to sustain the anticipated maximum load effects resulting from such use including any dynamic effects.6.6.9 Loads on Helicopter Landing Areas In addition to all other applicable loads provided in this chapter.6.2.g. Loads such as F.0 kN/m2.2 Definitions ALLOWABLE STRESS DESIGN METHOD (ASD) : A method for proportioning structural members such that the maximum stresses due to service loads obtained from an elastic analysis does not exceed a specified allowable value.5 whichever is applicable.7.7 COMBINATIONS OF LOADS 2.7.2 through 2. 2. DESIGN STRENGTH : The product of the nominal strength and a resistance factor. All other loads are variable loads. Floor live loads shall not be considered where their inclusion result in lower stresses in the member under consideration. FACTORED LOAD : The product of the nominal load and a load factor. LIMIT STATE : A condition in which a structure or component becomes unfit for service and is judged either to be no longer useful for its intended function (serviceability limit state) or to be unsafe (strength limit state).6 of this chapter.4 or 2. environmental effects.7.6. Permanent loads are those loads in which variations in time are rare or of small magnitude. This is also called Working Stress Design Method (WSD).7.5 is selected for a particular construction material. H or S shall be considered in design when their effects are significant. W1 = Actual weight of the helicopter in kN.10 Erection and Construction Loads All loads required to be sustained by a structure or any portion thereof due to placing or storage of construction materials and erection equipment including those due to operation of such equipment shall be considered as erection loads. 664 . specified in Sec 2. L2 shall be a single concentrated load including impact applied over a 300 mm x 300 mm area.7. The loads L1 and L2 may be applied anywhere within the landing area to produce the most unfavourable effects of load. moments. and restrained dimensional changes. or act in the reverse direction. and = 1.5 any other specific load combination provided elsewhere in this Code shall also be investigated to determine the most unfavourable effect. The most unfavourable effects from both wind and earthquake loads shall be considered where appropriate.Part 6 Structural Design where. Provisions shall be made in design to account for all stresses due to such loads. differential settlement. it must be used exclusively for proportioning elements of that material throughout the structure.7. L1 shall be applied over the actual areas of contact of landing. w = A distributed load of 5.1 General Buildings.7. deformations and other effects produced in structural members and components by the applied loads. The load. but they need not be assumed to act simultaneously. wind. foundations and structural members shall be investigated for adequate strength to resist the most unfavourable effect resulting from the various combinations of loads provided in this section. The most unfavourable effect of loads may also occur when one or more of the contributing loads are absent. The combination of loads may be selected using the provisions of either Sec 2.7. 2. LOAD EFFECTS : Forces. W2 = Fully loaded weight of the helicopter in kN. occupants and their possessions. LOAD FACTOR : A factor that accounts for unavoidable deviations of the actual load from the nominal value and for uncertainties in the analysis that transforms the load into a load effect. k = 0.4 and 2. In addition to the load combinations given in Sec 2. once Sec 2. The live load.4 or 2.5 for helicopters with rigid or skidtype landing gear. 2.75 for helicopters equipped with hydraulic type shock absorbers. earthquake etc. However. NOMINAL LOADS : The magnitudes of the loads such as dead. live. LOADS : Forces or other actions that arise on structural systems from the weight of all permanent constructions. E = earthquake load E ¢ = amplified earthquake load equal to (0. 1. W = wind load 2.7. H = loads due to weight and lateral pressure of soil and water in soil L = Lf + (Lr or P) Lf = live loads due to intended use and occupancy. D + (H or F) 7. D + S + (W or E) 10. D + S + L + (H or F) + (W or E) Bangladesh National Building Code 665 . D + L + (H or F) + (W or E) 12. movement due to differential settlement. moisture changes.1 Combination of Loads : Provisions of this section shall apply to all construction materials permitting their use in proportioning structural members by allowable stress design method. including builtin partitions.7. shrinkage. Lr = roof live loads P = loads due to initial rainwater ponding R = seismic coefficient defined in Sec 2.7. D+L 3.3 S = selfstraining forces and effects arising from contraction or expansion resulting from temperature changes. D+S+L 9. WORKING STRESS DESIGN METHOD (WSD) : See ALLOWABLE STRESS DESIGN METHOD. 0. RESISTANCE FACTOR : A factor that accounts for unavoidable deviations of the actual strength from the nominal value and the manner and consequences of failure. 2. such effects shall be included with the live loads Lf . including loads due to water pressure during flood and surge.4 Combinations of Loads and Stress Increase for Allowable Stress Design Method 2.9D + (W or E) 6. Chapter 2 Loads NOMINAL STRENGTH : The capacity of a structure or component to resist the effects of loads.3 Symbols and Notation D = dead load consisting of : a) weight of the member itself. including loads due to movable objects and movable partitions and loads temporarily supported by the structure during maintenance. This is also known as Load Factor Design Method (LFD) or Ultimate Strength Design Method (USD). or combinations thereof. D + L + (W or E) 11. D 2.5. If resistance to impact loads is taken into account in design. Lf includes any permissible reduction.375R)E F = loads due to fluids with welldefined pressures and maximum heights. c) weight of permanent equipment. D + L + (H or F) 8. all loads listed herein shall be considered to act in the following combinations. D+S 4. This is also known as strength reduction factor. b) weight of all materials of construction incorporated into the building to be permanently supported by the member. creep in component materials. STRENGTH DESIGN METHOD : A method of proportioning structural members using load factors and resistance factors satisfying both the applicable limit state conditions. D + (W or E) 5. allowing for modelling effects and differences between laboratory and field conditions. When this method is used in designing structural members. as determined by computations using specified material strengths and dimensions and formulas derived from accepted principles of structural mechanics or by field tests or laboratory tests of scaled models. The combination that produces the most unfavourable effect shall be used in design.4. 1 E) 5.5.4S + 1.5. areas occupied as places of public assembly.4. 1. 1.2D + 1.4D + 1. 1.5E) Exception : The load factor on Lf in combinations (3).0 for garages.75 [ 1.2.5Lf) 6.9D + E ¢ 2. 0.1E) ] 11.5 (Lr or P) 3. 0.75 [ 1. the maximum permissible increase in the allowable stresses of all materials and soil bearing capacities specified in this Code for working (or allowable) stress design method.(b) and elsewhere in this Code.0 kN/m2.4D 2. 0. shall be 33%.2D + 0. the following additional load combinations shall be considered : 7.7 (W or 1. 1.2D + 1.4D + 1. 0.4.4D + 1.7. or S are significant. Related Appendix Appendix A Conversion of Expressions from SI to FPS Units 666 .7L ] 8. any other code or standard having load combinations applicable for that construction material may be used provided that other requirements of Sec 2.7L + 1.1E) ] 9.7W ] 10.5L + E ¢ 8.5.4D + 1.5.5.75 [ 1.7 are satisfied.2 Load Combinations for Steel Structures 1.9D + (1.3W or 1. 1. and all areas where the live load exceeds 5.2S and included with the above combinations to obtain the most unfavourable effect.7.7 (H or F) 7.9D + 1.7L + 1.5 Combinations of Loads for Strength Design Method When strength design method is used.4S + 1. 1.4 S 4.5Lf + 0. 0.7 (H or F) + 1.3 (W or 1.1 and 2.7. structural members and foundations shall be designed to have strength not less than that required to resist the most unfavorable effect of the combinations of factored loads listed in the following sections : 2. 1.7 ( H or F) + 1.7.4D + 1.7.3F.4D + 1.7L+ 1.6Lf + 0.7 (W or 1.5.7L + 1.2D + 1. 1.75 [ 1. 2. 1. (4) and (5) shall be equal to 1. when load combinations (7) through (11) in Sec 2.7.4D + 1.4S+1.75 [ 1.7L 3.2 Stress Increase : Except as specified in Sec 1.4 D + 1. H.7 (W or 1. and 1.Part 6 Structural Design 2. 0.4D 2.5. When the structural effects of F.1E) ] 12.3W + 0.7.3 Load Combinations for Design using Other Materials : When structural members are designed using the strength design method and using a construction material not covered in Sec 2.7.6 (Lr or P) + (0. their factored values shall be considered as 1. 0. 0.6H.0.9D + 1.5E + (0. Also for buildings in Seismic Zone 3 and in Seismic Zone 2 having an Structural Importance Coefficient.5Lf or 0.2D + 1.5 (Lr or P) 5. 0.8W) 4. I greater than 1. 1. 1.1 Load Combinations for Reinforced Concrete and Masonry Structures 1.1 above is used.7 ( H or F) 6.4 (D+L+E) 2. 1. Chapter 2 Loads This page is intentionally left blank. Bangladesh National Building Code 667 .