A Seismic Structural Configurations Sudhir k Jian c v r Murty and Durgesh C Rai 2012

ASeismic StructuralConfigurations Gregory MacRae Much of the material contained in this lecture handout is used with the permission of Prof. Durgesh Rai from his 2009 Myanmar lectures. This marerial is the property of Professors Sudhir K. Jain, C.V.R.Murty and Durgesh C. Rai of IIT, and is for the sole and exclusive use of the participants of the December 2012 Ahmedabad Course at IITGN Why Do We Care About Seismic Configuration? We want to have the building resist earthquake as simply as possible This results in best seismic performance Consider also travel from one point to another. ANALOGIES Travel Between Different Points Traveller health Direct route Steady gradient No overhanging trees No pirates/crocodiles Solid/nonslip path No extra burdens 4 Building Seismic Performance Proper design/detailing Direct load path No concentration of effort – e.g. Soft storey No dangerous non-structural elements Gaps between adjacent structures Good foundation No attachments that may interfere with performance Configuration Rai. Murty and Jain . Murty and Jain .• Important Factors in Design 6 Rai. Murty and Jain .Seismic Configuration • Seismic Configuration – Geometry. Size and Shape – Location and size of Structural Elements – Location and size of Non-Structural Elements 7 Rai. Murty and Jain . Size and Shape ??? Convex 8 Concave Rai.Seismic Configuration… • Geometry. Murty and Jain .Seismic Configuration… Simple 9 Complex Rai. Seismic Configuration… • Overall size Too long Too tall Too large in plan Buildings with one overall size much larger/smaller than other two. Murty and Jain . do not perform well during EQs 10 Rai. Murty and Jain .OFFSET BUILDINGS • Alphabetic Shapes 11 Rai. OFFSET BUILDINGS… • Re-entrant corners 12 Rai. Murty and Jain . Murty and Jain .Seismic Configuration… • Shape Simple Plan ::good Corners and Curves :: poor 13 Simple plan shape buildings do well during EQs Separation joints make complex plans into simple plans Rai. Murty and Jain .Seismic Configuration… • Indirect load path Slopy Ground Setbacks Hanging or Floating Columns Unusually Tall Storey Weak or Flexible Storey 14 RC Wall Discontinued in Ground Storey Discontinuing Structural Members Sudden deviations in load transfer path along height lead to poor performance Rai. Seismic Configuration… • Simple. Murty and Jain . quantitative guidelines required Rai. direct load transfer path gives better performance • Regular configuration preferred – Even distribution of mass and stiffness in building plan and with building height • In buildings with irregular configuration 15 – Ductility demand gets concentrated in a few storeys or elements – Simple code expression not valid. Murty and Jain . while the latter are raised from the ground. both swing back-and-forth when shaken horizontally. Rai. The former are hung from the top.Symmetric Buildings • Swing Analogy 1-storey building 16 3-storey building Rope swings and buildings. Symmetric Buildings… • Symmetry – Mass – Stiffness Identical Vertical Members 17 Uniform Movement of Floor EQ Ground Movement Identical vertical members placed uniformly in plan of building cause all points on the floor to move by same amount. Murty and Jain . Rai. UNSymmetric Buildings • Swing Analogy:: Mass Unsymmetry Light Side of Building Twist Swing with equal ropes EQ Ground Shaking 18 Heavy Side of Building Even if vertical members are placed uniformly in plan of building. more mass on one side causes the floors to twist. Rai. Murty and Jain . Rai. Murty and Jain .UNSymmetric Buildings… • Swing Analogy:: Stiffness Unsymmetry Vertical Axis about which building twists Swing with unequal ropes 19 Earthquake Ground Movement Building on slope ground Buildings have unequal vertical members. they cause the building to twist about a vertical axis. Murty and Jain .Seismic Configuration… • Location and size of Structural Elements 20 Rai. UNSymmetric Buildings… • Other types of stiffness unsymmetry Wall Wall Columns 21 Wall Columns Buildings with walls on two/one sides (in plan) Rai. Murty and Jain . Murty and Jain .UNSymmetric Buildings… • Combined Unsymmetry Earthquake Ground Shaking One-side open ground storey building twists during EQ shaking 22 Rai. UNSymmetric Buildings… • Consequences Earthquake Ground Movement These columns are more vulnerable Vertical members of buildings that move more horizontally sustain more damage 23 Rai. Murty and Jain . Seismic Design… • Pounding 24 Rai, Murty and Jain Seismic Configuration… • Relative distance Pounding can occur between adjoining buildings due to horizontal vibrations of the two buildings 25 Rai, Murty and Jain Seismic Design… • Connectors between buildings to be designed carefully 26 Rai, Murty and Jain Diaphragms Murty and Jain .Floor Diaphragms • Out-of-plane versus In-plane flexibility – Out of plane is important for gravity loads – In-plane is important for seismic loads 28 Rai. Floor Diaphragms… • Floor rigid in-plane – Moves like a rigid block in its own plane • Translation Uniform Movement of Floor Uniform Movement of Floor Earthquake Ground Movement Earthquake Ground Movement 29 Rai. Murty and Jain . Murty and Jain .Floor Diaphragms… • Rotation Earthquake Ground Movement • Combined Translation and Rotation 30 Earthquake Ground Movement Rai. Murty and Jain .Floor Diaphragms… – Floors apply horizontal force on vertical elements • Vertical elements act as horizontal springs 31 Rai. 4F 0.Floor Diaphragms… • Rigid diaphragm F 0.4F – Forces are proportional to stiffness of walls 32 Rai. Murty and Jain .4k 0.2k 0.2F 0.4k 0. Murty and Jain .4k F/4 F/2 F 0.4k F/4 – Forces are proportional to tributary area – Wall stiffnesses do not come into calculations 33 Rai.Floor Diaphragms… • Flexible diaphragm 0.2k 0. Murty and Jain .Floor Diaphragms… • Act like beams in horizontal plane 34 Rai. Floor Diaphragms… • Many of them… 35 Rai. Murty and Jain . Murty and Jain .Floor Diaphragms… • Cut-outs ?? 36 Rai. Murty and Jain .Floor Diaphragms… • Openings only under compulsion 37 Rai. Open Ground Story . Murty and Jain .Open Ground Storey • Known for decades – Poor seismic configuration 39 Rai. Open Ground Storey… • Garage doors 40 Rai. Murty and Jain . Murty and Jain .Open Ground Storey… • Three Situations… 41 Rai. Murty and Jain .Open Ground Storey… • Understood… well!! 42 Rai. Murty and Jain .Open Ground Storey… • Lessons learnt !! 43 Rai. Murty and Jain .Structural Walls • Steel or RC – Do not interrupt wall in lower levels 44 Rai. Short Column Effect • Mistaken Identity of Infills 45 Rai. Murty and Jain . Irregularities provisions in Codes . Building Configuration • Irregularities in Buildings – Mass – Stiffness – Geometry Indian Standards 47 . Building Configuration… • Building Codes Configuration emphasised in buildings – Comprehensive section on identifying irregularities – Quantitative definitions of irregular buildings • Two types of Irregularities addressed – Plan Irregularities – Vertical Irregularities 48 Rai. Murty and Jain . Building Configuration… • Plan Irregularities – Torsion Irregularity Heavy Mass Irregular Orientation of Lateral Force Resisting System 2 1 49 Floor 1.2 1 2 2 2 Rai. Murty and Jain . 20 Rai.Building Configuration… – Re-entrant Corners A L A A A L 50 A A L 0.15 0. Murty and Jain . Murty and Jain .Building Configuration… – Diaphragm Discontinuity Flexible Opening Opening 51 Plan Rai. Building Configuration… – Out of Plane Offsets Shear Wall Shear Wall Shear Wall 52 Rai. Murty and Jain . Building Configuration… – Non-Parallel System y x 53 Rai. Murty and Jain . Building Configuration… • Vertical Irregularities – Stiffness Irregularity (Soft Storey) ki ki+1 ki ki-1 54 ki 0 . Murty and Jain .7 k i 0.8 1 ki 1 ki 2 ki 3 3 Rai. Building Configuration… – Mass Irregularity Wi+1 Wi Wi-1 55 Wi Wi 2 Wi 2 Wi 1 1 Rai. Murty and Jain . 20 Rai. Murty and Jain .15 0.Building Configuration… – Vertical Geometric Irregularities A A A A A L L A L 56 L 0. Building Configuration… L1 L1 L2 L2 L2 1. Murty and Jain .5L1 57 Rai. Building Configuration… – In-plane Discontinuity in Lateral Load Resisting Elements Upper Floor Plan Lower Floor Plan 58 Rai. Murty and Jain . 8 S i 1 Si+1 Si Si-1 59 Rai.Building Configuration… – Strength Irregularity (Weak Storey) Si 0 . Murty and Jain . Murty and Jain .SEISMIC CODES 60 Rai. Seismic Codes… 61 Rai. Murty and Jain . Murty and Jain .Non-Structural Components Rai. Murty and Jain .Non-structural Elements 63 Rai. Murty and Jain .Facades 64 Rai. Murty and Jain .Non-structural Elements… Bare Finished 65 Rai. Murty and Jain .Non-structural Elements… 66 Rai. Non-structural Elements… • Infringements understood 67 Rai. Murty and Jain . Non-structural Elements… • Problems 68 Rai. Murty and Jain . Non-structural Elements… • Electrical power failures 69 Rai. Murty and Jain . Murty and Jain .Non-structural Elements… • Secondary disasters 70 Rai. Murty and Jain .Non-structural Elements… • Chemical Spill 71 Rai. Non-structural Elements… • Chemical Disasters 72 . Non-structural Elements… • Overhead safety 73 Rai. Murty and Jain . Non-structural Elements… • Indirect losses 74 Rai. Murty and Jain . Non-structural Elements… • Disruption of services 75 Rai. Murty and Jain . Non-structural Elements… • May be acceptable 76 Rai. Murty and Jain . Non-structural Elements… • Not acceptable 77 Rai. Murty and Jain . Solutions 78 Rai. Murty and Jain . Solutions… 79 . Solutions… • Securing masonry chimneys 80 Rai. Murty and Jain . Murty and Jain .Solutions… • Securing masonry parapets 81 Rai. Solutions… 82 Rai. Murty and Jain . Solutions… 83 Rai. Murty and Jain . Solutions… 84 . Murty and Jain .Non-structural Elements… • Half-hearted… not good! 85 Rai. all the engineer can do is to provide a band-aid .” 86 Rai. a noted Earthquake Engineer of USA – aptly summarised the intense importance of seismic structural configuration in his words: “If we have a poor configuration to start with. even a poor engineer cant harm its ultimate performance too much. if we start-off with a good configuration and reasonable framing system. Conversely. Murty and Jain .Importance of Configuration • Henry Degenkolb.improve a basically poor solution as best as he can. Soft storey No dangerous non-structural elements Gaps between adjacent structures Good foundation No attachments that may interfere with performance .ANALOGIES Travel Between Different Points Traveller health Direct route Steady gradient No overhanging trees No pirates/crocodiles Solid/nonslip path No extra burdens 87 Building Seismic Performance Proper design/detailing Direct load path No concentration of effort – e.g. Signature Tower: Jakarta 638m #5 in the world in 2020 The tallest in a seismic region 111 Stories 88 .