Masonry Structures.pdf

18711 Masonry Structures INTRODUCTION Load-bearing construction in the affected area is mostly masonry, with some adobe. Masonry buildings in the area are not designed, but merely constructed based on traditional practices that may include some rules of thumb. Masonry construction constitutes over 95 percent of the building stock in the affected area, which by and large did not perform well. Over 1,200,000 masonry buildings either collapsed or were severely damaged. Masonry construction is present in both rural and urban areas. Masonry construction in each region has special characteristics due to the bias towards locally available material, limitations of construction skills, and constraints to construction activity. Past earthquakes have highlighted the inherent weaknesses of this type of construction, and the lessons from the 2001 Bhuj earthquake offer yet another vivid demonstration to the local populace of the vulnerability of their hand-made, unengineered dwellings. This chapter gives an account of the state of the practice of masonry construction in the Kachchh region and a review of its performance during the 2001 Bhuj earthquake. Relevant Indian Standards and other pertinent literature on masonry construction available in the country are also presented. GROWTH OF CONSTRUCTION IN THE KACHCHH REGION: HISTORICAL PERSPECTIVE The Kachchh region has two distinct eras of development. Early construction took place under royal families that lived in the region over the past five centuries. More recent and more significant construction in the region was driven by the India-Pakistan partition in 1947. On the recommendation of Mahatma Gandhi, the Government of India granted 6,070 hectares (15,000 acres) of land near the Port of Kandla for the purpose of developing a township and commissioned the Sindhu Resettlement Corporation (SRC) Limited in 1948 with the main aim of settling and rehabilitating the persons displaced from the Sindh province of West Pakistan, now known as Pakistan. In 1955, after a careful review, the government revised the land available to SRC to 2,600 acres; the Port of Kandla received an adjoining 4,320 acres. By 1958, SRC completed a major part of the construction in two locations, which are today’s cities of Adipur and Gandhidham. However, the growth of the region during 1950-1960 was less than expected. The slow increase in livelihood was due to marginal growth in commerce, trade, industry, and communications. The Anjar earthquake in 1956, whose epicenter was 55 km from Bhuj, and two wars with Pakistan in 1965 and 1971 also discouraged many settlers, and, in fact, there was a significant exodus during 1960-1970. However, the growth of the Kandla Port Trust, the construction of new highways during the 1970s, and the commissioning of the Broad Gauge Railway line in the 1980s, led to an influx of people into the region. Though relatively little Masonry Structures 188 construction took place during 1960-1995, recent trends show an upsurge in new construction. One interesting feature of this construction is that the use of lime mortar became popular in masonry construction due to the severe shortage of cement experienced countrywide during the early 1980s. Over the past 50 years, the main organizations that have led construction activity in the Kachchh region were the SRC Limited, the Kandla Port Trust, the Indian Railways, the Department of Telecommunications, and the Military Engineering Service. These organizations were responsible for improving infrastructure and introducing new construction technology. The SRC Limited popularized the use of hollow cement block walls, lintel bands, and vertical reinforcements at wall corners in masonry construction, and ties/stirrups with 135-degree hooks in reinforced concrete construction. Such structures performed well during the 2001 Bhuj earthquake. Construction in other parts of Kachchh was only as a consequence of the development in the Gandhidham-Adipur areas. Migrant artisans from Gandhidham area carried the skill and technology to the interiors, and implemented many private projects. Government construction techniques stood as examples for citizen builders to emulate. For instance, lintel bands were common in the construction of the Indian Railways. This may have inspired a few individuals to include these in their own houses. The excessive use of cement-based masonry and the gradual exclusion of lime from masonry was a net outcome of the recent construction. This has resulted in widespread brittle damage in such masonry structures. OVERVIEW OF DAMAGE Collapses of masonry dwellings in the Kachchh region were responsible for the majority of fatalities during the 2001 Bhuj earthquake. The meizoseismal area and adjoining areas that sustained intensities of shaking IX and X include many important towns and villages of the Kachchh region (Figure 11-1), some of which are densely populated. For instance, the town of Bhuj has a population of about 160,000, Anjar of about 55,000 and Bhachau of about 20,000. These towns lie south of the epicenter. There are other villages and towns northwest of the epicenter, such as Manfara and Rapar, which also suffered significant damage. Table 11-1 gives an estimate of the masonry structures and huts damaged during the earthquake. Most of the damage to masonry structures occurred in the Kachchh district, which lies in the most severe seismic zone (V) of the country. Table 11-1. Damage statistics for different types of construction in the Kachchh region. Damage Level* Type of Construction Complete Partial Pukka (well built) houses Kachcha (poorly built) houses Huts Total 187,122 167,205 16,266 370,593 510,419 387,320 34,295 932,034 * From www.quakegujarat.com, official site of Government of Gujarat (September 2001) Masonry Structures 189 �� Figure 11-1. Epicentral region of the 2001 Bhuj earthquake showing villages discussed in this report. Aerial photographs of damage are available for Bhachau, Anjar, Ratnal, and adjoining areas of Gandhidham, all in the epicentral region. Figure 11-2 shows the near total destruction of the village of Bhachau, 8 km from epicenter. The town of Ratnal and villages near Gandhidham, 44 km from the epicenter, sustained similar, near complete, devastation. In Anjar, a town where nearly 300 school children died while marching in the Republic Day parade, building damage was widespread. While devastation was nearly complete in some areas, others escaped with only moderate damage. Initially, significantly different soil conditions were suspected for the contrasting damage pattern, but it was the older construction that collapsed, while the newer construction suffered only moderate damage. Damage patterns showed serious lack of earthquake-resistant construction features in the region (Figures 11-3 and 11-4). Villages reduced to rubble showed a more or less uniform choice of construction material and techniques. The overall analysis of these damages reiterates the ills of masonry construction. Random rubble with mud mortar is the most vulnerable type of construction. Wall failure was the most common cause of structural collapse (Figure 11-5). In a few cases, the roof alone collapsed, causing casualties (Figure 11-6). Failure of reinforced concrete slab roof system was present where slab reinforcements lapped at the same location, creating a weak link for fracture (Figure 11-7). Masonry in mud mortar has inherently very poor shear strength. As a consequence, wall thicknesses are necessarily large, sometimes as thick as 750 mm. These thick walls were often not made into a single wythe with interlocking stones that run through the thickness of the wall. In most instances, these walls sustained separation of wythes, thereby losing even the vertical load carrying capacity (Figures 11-8 and 11-9). �� Damage to masonry construction due to inadequate connections between the walls. Aerial photo of near total devastation of village Bhachau. .Masonry Structures 190 Figure 11-2. Damage to masonry construction due to inadequate connections between the walls. Collapse of this masonry structure was due to wall failure. the roof alone was responsible for structural collapse. Figure 11-3. such as this masonry structure. Figure 11-4. Figure 11-7. Figure 11-6. Figure 11-5. In a few instances. Reinforced concrete roof slab with slab reinforcements lapped at the same location failed. Such hybrid construction sustained severe damage in the weaker lower story. Separation of wythes caused collapsed of wall and roof. walls were made from rammed earth and adobe or uncut stone masonry with mud mortar.1 • Clay brick masonry in mud mortar with tile roof. • Semi-dressed/dressed stone masonry (coursed) in mud/cement mortar with reinforced concrete. These include: • Random rubble stone masonry (uncoursed) in mud/cement mortar with clay tile roof. Dressed-tosize or cut-stones were used in stone masonry for walls in urban areas and in cases where owners could afford higher costs. Sometimes. Lack of through-stones caused separation of wythes. . For instance.Masonry Structures 191 Figure 11-8. TYPES OF CONSTRUCTION Masonry dwellings in the Kachchh region include many types of load-bearing construction. the older first story walls may have been constructed in random rubble stone masonry with mud mortar. • Random rubble stone masonry (uncoursed) in mud/cement mortar with reinforced concrete slab roof. A large number of masonry structures are hybrid in nature (Figures 11-17 through 11-21). and reinforced concrete slabs. Figure 11-9. the building stock in the region has a wide spectrum of masonry construction techniques (Figures 11-10 through 11-16). In older construction. With the passage of time and the numerous changes that took place over the last 50 years. Consequently. present day stone masonry uses cut/dressed stones or burnt clay bricks. the opposite has also been observed. 1 Clay tiles are used as covering material and supported on a wooden truss-purlin system or on a framework of wooden joists.1 • Semi-dressed/dressed stone masonry (coursed) in mud/cement mortar with clay tile roof. • Solid/hollow cement block masonry in cement mortar with clay tile1/reinforced concrete slab roof. The roof is generally wooden trusses and clay tile. • Burnt clay brick masonry in mud/cement mortar with clay tile1/reinforced concrete slab roof. but the newer extension of the upper story may be in brick masonry laid in cement mortar with reinforced concrete slabs for floors and roof. random rubble stone masonry construction predominates in the Kachchh region. where weak thin walls and poor cement mortar in the upper stories led to collapse. cement mortar. However. in a typical two-story construction. Random rubble stone masonry in cement mortar with RC slab roof. Clay brick masonry in cement mortar with RC slab roof. Figure 11-14. . Clay brick masonry in mud mortar with tile roof.Masonry Structures 192 Figure 11-10. Random rubble stone masonry in mud mortar with tile roof. Figure 11-13. Figure 11-12. Stone masonry in cement mortar with tile roof. Coursed stone masonry in cement mortar with RC slab roof. Figure 11-11. Figure 11-15. while its adjoining 5-story reinforced concrete frame buildings sustained serious damages and collapses. Figure 11-20. Figure 11-21. . experienced minimal damage.Masonry Structures 193 Figure 11-16. This structure performed well. collapsed completely. The second story. This 3-story load-bearing construction (Gandhidham) had exterior walls of stone masonry and interior walls of hollow cement blocks. Cement block masonry in cement mortar with RC slab roof. Figure 11-17. Lintel and plinth bands were provided. The first story of this masonry structure in Anjar. Improper connection between walls (Samakhyali village). of brick masonry with cement mortar. Poor shear strength of stone masonry in the lower story of structure with lintel bands (Bhuj). constructed of random rubble stone masonry in lime mortar. Figure 11-18. Figure 11-19. Loosely formed roof with Mangalore tiles (Bhuj) led to serious damage/ collapse of structures. and as the trauma of a big earthquake in 1956 was forgotten. In some cases. reinforced concrete with cement/lime mortar (Figure 11-22). and most masonry structures were built with no lintel bands. Owners of houses used reinforced concrete loft slabs inside the rooms at lintel levels for providing storage space in the house. Reinforced concrete band at lintel level. some of these good practices were slowly lost. they have been used in the Kachchh region for over 50 years. if the house is small. these relatively thin reinforced concrete slab strips act as lintel bands (Figure 11-23).Masonry Structures 194 LINTEL BANDS Early construction practice in earthquake-prone areas of India did include lintel bands. but the exterior façade is plastered to imitate a lintel band. the loft is provided throughout the house. an interesting lintel feature was introduced in some masonry construction of the region. Indian Railways and Kandla Port Trust. In many cases. The lintel bands were made of wood. or even specially shaped hollow cement blocks for placing horizontal reinforcement. Over time. However. In such instances. Early construction spearheaded by governmental agencies like the MES. Figure 11-22. no lintel band is provided. . Figure 11-23. Improvisation of loft slabs as lintel band. Indeed. with time. and subsequently joined by the SRC Limited in the early 1950s included the practice of providing lintel bands in their masonry construction. reinforced concrete slabs achieve good diaphragm action. and hence the final structural configuration is not always known at the start of the construction. No damp-proof course band is provided in this type of construction. shallow trenches are dug and strip foundations are used. The band is made in 1:2:4 nominal mix concrete with cement and 20 mm coarse aggregates. Subsequent additions were driven by functional needs. A 100-150 mm thick damp-proof course-cum-plinth band is placed on top of the plinth masonry. which may be either hard or soft. and the structural consequences of these additions were not understood. Consequently.2 m-1. After the trench is dug. Since the surface of the . and they performed poorly as they failed to resist the increased torsional shear stresses.9 m-1.25 mm graded aggregates are used. and used as aggregates in this cement concrete. smaller rubble stones and cement mortar are placed in the voids. In buildings with reinforced concrete slabs and configuration irregularities. In the slab concrete. After the trench is dug and the 150 mm thick lean concrete is placed (Figure 11-25). On the other hand. tile roofs do not provide good diaphragm action for proper distribution of lateral loads to walls. In the rural setting. Underlying this layer is murrum soil (weathered rock). a 1. When it is treated only as a damp-proof course.5 m deep 0. Large granite boulders are hand-broken to a size of 40 mm and less. A 600 mm wide trench is cut in the ground up to a depth equal to the thickness of the black topsoil. Only rarely is the 150 mm thick 1:5:10 lean cement concrete layer discussed earlier placed. no reinforcements are required by the government specifications. The largest stones do not always cross the full width of the foundation and usually a distinct vertical layer of small rubble and cement mortar is present in the vertical mid-thickness of the wall. the largest granite stones are picked and their planar faces are made vertical and flush with outside/inside of the wall (Figure 11-26). Black granite stone blocks of random shape and of largest dimension up to 450 mm are used in the random rubble plinth masonry. the above procedure of foundation construction is severely simplified (Figure 11-24b). The preparation of the plinth masonry has a few special features. the first lift is 600 mm wide and the second 450 mm. like the Mangalore (a south Indian city on the south-west coast of India). and shape are often disproportionate and vary abruptly. FOUNDATIONS Foundations in masonry construction have been constructed fairly consistently throughout the Kachchh region. The trench is filled with uncoursed trap stones. Usually. 20 mm. size. and has 4 bars of 12 mm diameter high yield strength deformed bars (fy=415MPa) as longitudinal steel with 6 mm diameter mild steel bars (fy=250MPa) at 150 mm centers as ties.2 m wide trench is dug (Figure 11-24a). Then.Masonry Structures 195 IRREGULARITIES Masonry construction in the region was often built incrementally. leading to vertical and horizontal offsets. Uncoursed. a 150 mm thick 1:5:10 cement concrete made of 40 mm size hand-broken coarse aggregate is placed on the murrum soil. 12 mm and/or 6.7 m height. Even when it is. almost all masonry construction in the affected area is highly irregular in structural configuration. Dry. Then. The trench is stopped at the first sign of the weathered rock or the soft/hard murrum soil. torsional response was generated. randomly cut black basalt/trap stones are used in the masonry with 1:6 cement mortar. the base material at the founding level is only random rubble broken stone in mud/lime mortar. hand-mixed 1:6 cement mortar is placed over these random stones and watered to send the mortar into the voids between the stones. The plinth masonry is stopped 150 mm above the ground level. In usual masonry buildings in cities and major towns. Loosely formed roofs. The geometry. Next. the plinth masonry is constructed over this cement concrete in two lifts each of 0. The topsoil consists of 300-400 mm thick black cotton soil/black silty soil/soft creek soil. a lean cement concrete is laid over the soil. Figure 11-27. Figure 11-26. Basic version adopted in poor quality construction. Masonry in large-block sandstone under construction. Inside foundation surface pointed.Masonry Structures 196 a b Figure 11-24. Large uncoursed granite blocks placed from both sides. Figure 11-25. and b. outside surface left unfinished. Typical foundation specifications for masonry construction in the Kachchh region: a. Figure 11-28. Shallow trenching. . a central weak plane is formed. Formal version adopted in better construction. A plinth band is provided. Random-rubble stone masonry with mud/lime/cement mortar Walls are made with undressed granite stone of different degrees of weathering and up to a maximum dimension of 400 mm in low rise 1-2 story buildings. In addition. This problem of lack of integrity within the wythes of walls is less severe when wall thickness is about 400 mm or less. The construction materials of the region have characteristics that have led to special construction strategies. In most cases. In government construction. vary. Four different types of masonry units are employed for making walls in the Kachchh region. semi-dressed (i. it is lighter than granite. Due to this large size of units. These thick walls are constructed with one mason working on each side of the wall and placing stones to create even surfaces on the exterior faces. jeopardizing the safety and stability of . For example. a pink variety of sandstone is locally available. coupled with the vertical mid-layer of the wall mentioned above. without smooth polishing of the outer surface) stones are used. However. With maximum wall thickness of 600 mm and the largest dimension of stones as 400 mm. the thickness of the mortar usually required between the stones is as large as 80 mm. (where trucks are weighed along the highway). A practice has evolved in the region wherein the plinth masonry is made in the heavy granite and the superstructure wall masonry in the light sandstone. Unlike in the plinth masonry. only one of them is pointed. and up to 600 mm in taller ones. no stone covers the full width of the wall and the much-needed interlocking between the two vertical layers is absent. some private buildings. only a few of these large-block stones are required compared to smallblock masonry. but is heavy. This. locally available weathered lateritic rock is used. as in the case of the foundation of a weighbridge. When the inside surface is required for access and not the outside.Masonry Structures 197 granite stone is nonporous and smooth. or in solid cement blocks. the inside surface is pointed and the outside face is left unfinished (Figure 11-27). in some instances. invites the masonry to split into two vertical wythes. and therefore their bond with the mortar. Under strong seismic shaking. and in construction by qualified engineers. if a plinth masonry is for a residential unit. construction practice in the Kachchh region offers a special construction style. these walls are pointed on both faces. Semi-dressed stones of size about 600 mm × 400 mm × 250 mm are employed in stone masonry (Figure 11-29). This results in walls that have two predominant vertical layers or wythes. Some of the older construction with mud mortar has wall thickness of about 600 mm even in 1. the surface characteristics. The normal practice across India is to use stones with the largest dimension of about 400 mm. In such construction.and 2-story buildings. the cement mortar does not bond effectively with the stone. a damp-proof course is often provided at plinth level (Figure 11-28). Depending on the level of weathering. the plinth masonry is done in either granite stone. Rarely is a plinth band also provided. Small/large block semi-dressed/dressed stones in mud/lime/cement mortar Quarried sandstone or. the vertical surfaces of the plinth masonry are not pointed. In monumental structures. but is weaker in compressive strength. CONSTRUCTION OF MASONRY WALLS The procedure described above for the foundation masonry is also adopted for walls with random rubble masonry in mud or cement mortar. For instance. black granite stone is commonly available in the Kachchh region. the out-of-plane dislodging of one stone due to either out-of-plumb wall or out-of-plane seismic shaking of the wall can lead to the collapse of a significant portion of the large-block masonry above. as described below. only the outside surface is pointed.e. and many government buildings. Often. In masonry construction using cement blocks.. Lifting large granite blocks for masonry construction at higher elevations is difficult. Consequently. Where provided. Standard wall thickness of 230 mm is very common in most buildings. Around . even within the same batch. the entire building. even in reinforced concrete frame buildings. For this reason. For this reason. Over 5. another variety of yellow sandstone is brought from Junagadh in the Saurashtra region. Composition and quality control of the manufacture of cement blocks have varied significantly over the years. This is a matter of serious structural concern. Small-block stones of about 400 mm × 230 mm × 150 mm are also used. particularly in the severe Seismic Zone V. This stone. Burnt clay bricks in mud/cement mortar In recent times. this type of construction has become increasingly common in the Kachchh region. countryside kilns have grown and are producing burnt clay bricks of standard size 230 mm × 115 mm × 75 mm even though the soil is not suitable for making good quality burnt clay bricks. Solid/hollow cement blocks in cement mortar Both solid (Figure 11-30) and hollow cement blocks with up to three cells (Figure 11-31) of varied sizes and shapes have been in use since 1950.000 buildings of varied sizes and functional utility with lintel bands incorporated into the construction were built with hollow cement blocks by the SRC Limited. when a Besser Plant was commissioned at Adipur. The yellow stone is also preferred for the aesthetics of its bright color. though lighter than the granite/trap stone. is still heavy for use in wall masonry construction. However. use of one-and-half brick walls is also observed. particularly in urban areas. There are also instances of the use of 115 mm (half-brick length thick) walls in single-story buildings. Sandstone available in the Kachchh region is of the pink variety. in two and three story buildings. depending on the economic considerations of the user. The quality of these bricks is poor and highly variable. and are used with either mud mortar or cement mortar. This stone is much lighter and can be cut nearly to brick sizes for ease of handling.Masonry Structures 198 Figure 11-29. Stone block units used in masonry construction in the Kachchh region. These burnt clay bricks have a frog on one surface. bricks are often brought from Ahmedabad and other distant locations. The tape is held out to 30 cm. pilasters in the long and slender compound walls seemed to have contributed significant out-of-plane stability. Figure 11-31 Figure 11-32 Figure 11-33 Figures 11-31. the same time. and 11-33. These buildings. Currently. Hollow cement blocks were made of different compositions to give them different finishes. Solid cement blocks. major government agencies like Indian Railways. while the locally improvised machines for cement block construction depend on nominal table vibration and hand compaction. has led to the growth . The older Besser machine used table vibrations and pressure for compaction. such as fly ash. Three types of hollow cement blocks. In urban areas. built in the 1950s with hollow cement blocks. and the Military Engineering Service also extensively used plinth and/or lintel bands. However. Some of the block-making machines recently manufactured in India are small and portable and provide reasonable compaction using table vibration and pressure. performed very well during the 1956 Anjar and 2001 Bhuj earthquakes. In some instances. the Kandla Port Trust. local engineers now recognize that the vertical reinforcement should be anchored into the slab to provide a positive connection for transfer of forces and ensure against sliding of the reinforced concrete slab.Masonry Structures 199 Figure 11-30. 11-32. the hollow blocks construction is waning due to lack of quality in manufacturing. the availability of industrial by-products. The compressive strength of these blocks largely depends on the level of compaction achieved after placing the concrete mix in the steel molds. The hollow blocks permitted vertical reinforcement to be carried through the wall. these vertical reinforcements were not anchored into the reinforced concrete slab in order to allow for thermal expansion/contraction of the slab. also lightweight. Special blocks are also available for introducing the anchors and fasteners for the window and door frames (Figure 11-39). the rafters are done away with. These rafters rest on a horizontal member at the ridge level and directly on the masonry walls at the level of the eaves. of cement-based masonry units (Figure 11-34). The plinth masonry is prepared and the damp-proof course is laid (Figure 11-28). rafters (of about 100-150 mm diameter) are used. Some manufacturers make 230 mm × 100 mm × 75 mm blocks whose lengths match the transverse dimension of the 230 mm columns commonly adopted. and has wooden truss roofs with purlins supporting the clay tiles (Figure 11-40). These cement block units have good thermal characteristics. The hollow bricks also offer the possibility of passing vertical reinforcement through the hollows. Masonry walls of hollow block construction follow a relatively simple sequence. Two types of roofs are usually used in the Kachchh region. Both solid and hollow units are manufactured at a price competitive to that of the traditional burnt clay bricks. One or two intermediate purlins are provided along each of the slopes. Light wood purlins and battens (of size 25 mm × 15 mm) form a grid to place the tiles (Figure 11-40a). In cases where a plinth band is also intended. Table 11-2 presents an overall comparison of the various masonry units in use in the Kachchh region. In the first. which is the thickness of traditional burnt clay brick walls. The standard units are 200 mm × 100 mm × 75 mm. The fly ash brick masonry blocks are handcast by applying a little pressure with a hand tool. and purlins of significant size (up to 75-100 mm in diameter) are placed directly on the gable wall (Figure 11-40b). ROOFING MATERIAL AND ROOF CONSTRUCTION Older roof construction is mostly sloped or pitched. Fly ash bricks have begun to gain popularity as a building material. as required in severe seismic zones. Vertical reinforcements at wall corners are also introduced in the plinth band and passed through the hollow blocks in wall corners (Figure 11-38). often as main members without any shaping. the trusses are not complete with bottom tie members. and in the case of hollow blocks. and one horizontal member (of about 100-150 mm diameter) runs across the length of a room at the ridge level. In most instances. In the second type of roof construction. The reinforcement cage is placed and concrete poured in-situ.Masonry Structures 200 Figure 11-34. Locally available wood logs of rounded cross-section are used. The rafter and battens are smaller . special channel unit blocks are placed (Figures 11-35 and 11-36) to act as the formwork for the reinforcement of the plinth band (Figure 11-37). becoming expensive. 2. Low bonding due to lesser surface area of blocks in contact with mortar and lesser porosity of blocks.Masonry Structures 201 Table 11-2. 380×280×120 at Anjar. II<22%. More joints and hence more homogeneous than large blocks. ecofriendly. only 5% of bricks are recoverable. used commonly in foundations and in masonry up to plinth level only. 95% of the blocks are recoverable due to poor bond and higher strength of blocks.25 1.I<15%.8-3. not soaked before placing.0 1. Block is heavy: small movements for adjusting the position breaks the initial set of the mortar around the blocks in the lower layers due to weak mortars currently in use.50 Quality is poor (no compaction due to lack of vibration).5 1. in brick walls. poor quality. The cost index noted above includes only the cost of manufacture and supply of the masonry unit.60 Notes: Compressive strength is computed over unit plan area of wall. large sulfur content (since made from lignite-based ash) implies chemical corrosion. III<32%). cannot be handled in wet condition thus. Comparison of various masonry units used for roof construction in the Kachchh region Building Unit Sandstone From Junagadh (yellow variety. Small size (230×100×75) Burnt clay bricks Basalt/trap stone 3. and not of the masonry.5 6.5 1. high water absorption. 400×230×200 at Adipur) Locally available in Bhuj (light pink /brown variety) Hollow cement blocks Solid cement blocks Large size (390×200×190) MPa) 3. very high water absorption (20-32%). higher manufacturing cost. as compared to that of bricks. Lighter than bricks and blocks.0 At least 50.50 1.0 Cost 1 Comments Good quarries are used up.7-7.0-100. (Permissible Absorption Brick Class .75 Bond better with mortar than to solid cement blocks. Fly ash bricks 6.5-7. no homogeneity. Higher strength than bricks. When such walls collapse. . very heavy.5-4. Fine texture on surface. low mortar strength and very poor bond is achieved. better insulating property. lately only soft variety is available. and hence low bond leading to failure of walls in two wythes. more cracks in walls after seismic shaking. Figure 11-39. Plinth band reinforcement. Figure 11-38. Corner reinforcement. Cement channel bricks. Special concrete blocks are used to anchor door and window jambs.Masonry Structures 202 Figure 11-35. Special channel bricks facilitate placement of reinforcement bar. . Figure 11-37. Figure 11-36. such as corrugated sheets made of galvanized iron/asbestos/tin and fastened to wood or steel trusses. are common in better quality construction.Masonry Structures 203 in size (25 mm × 15 mm) and are simply nailed or tied with coir rope to the main rafters. Slit-tube tile roofs are also used in the region (Figure 11-44). The overlap along the length at the two ends is about 30 mm. other than through bearing of the rafters or purlins along the gable and other walls. Such roofs also impose a dead load of about 1kN/m2. Each tile overlaps with the adjacent ones by 30 mm along the width and about 60 mm along the length. Today. Reinforcement is nominal. Each piece weighs about 0. masonry dwellings also have reinforced concrete slab roofs. about 25 mm thick.) Roof with heavy rafters and b.) Roof with heavy intermediate purlins. including the weight of battens. they are easily displaced (Figure 11-43). The cross-sections of wooden rafters are much smaller than those of the purlins. These are even more loosely formed. . a grid of rafters and battens are used and the tiles rest on them. is about 1kN/m2. and weighs about 5 kg (Figure 11-41). Relative performance of these two roofing systems indicates the former to be more efficient. this layer causes the sliding of the tiles easily. A heavy purlin runs across the length of the room at the ridge level. In semi-rural or urban areas. there is no positive anchorage of the roof to the walls. Since they are loosely formed. Roof tiles are usually of two types: • Mangalore Tiles.3-0.4 kg. purlins and rafters. 75 mm in diameter and 6-10 mm thick. Mangalore tile is 400 mm × 230 mm in plan. and also require an impervious layer of soil/sheeting to prevent rainwater from seeping in. Roof tiles are supported by battens and purlins of small cross-sections laid over these main rafters or purlins. Mangalore tile roofs can be very heavy and draw large inertial forces. There are two basic forms of the roofs adopted. The purlins and rafters merely rest on the top surface of the walls of the room. Unfortunately. Thus. Both Mangalore and slit-tube roofing systems require specially shaped coping element to cover the ridgeline of the pitched roofs. and the battens are even smaller. • Slit Tube Tiles. The loading from such roofs. Pitched roofs with Mangalore tiles are the most common roofing systems employed in the rural areas of Kachchh. Pitched roofs constructed in the Kachchh region are made of wooden trusses that are often not completed – there is no bottom chord in these trusses. Other roofing materials. a. no positive anchorages are used (Figure 11-42). corrugated galvanized iron/asbestos/tin sheet roofs are also used. Slit-tube clay tile is 150 mm long. No trusses are used in the roof. The slab thickness varies from 75 mm to 125 mm. usually 6 mm diameter mild steel (smooth) bars or 10 mm/12 a b Figure 11-40. Lighter and stiff-in-plane roofs performed well. Because of poor formwork. mm diameter high-strength deformed steel bars at 150 to 250 mm centers along each principal direction. Figure 11-44.. Mangalore tiles slid off this roof. selection of materials and special features of design and construction of earthquakeresistant masonry buildings are given in another Indian Standard (IS:4326-1976). However. the reinforcement bars are seen on the soffit of the slab.3-0. . Figure 11-42. Roof rests on top of walls. Each tile weighs 0. GUIDELINES AND INDIAN STANDARDS The structural design of unreinforced load bearing/non-load bearing masonry walls made of various masonry types is governed by the masonry code (IS:1905-1987). maximum permissible stresses. and usually of grade M15 (i. and methods of design. In many instances. The performance of these roofing systems under seismic shaking has been well established. The Indian Standard masonry code specifies materials to be used. while the heavy and loosely formed ones fared poorly. Mangalore roof tile. the required cover to reinforcement may not be present uniformly throughout the slab. The concrete is hand mixed based on volume batching. Figure 11-43.Masonry Structures 204 Figure 11-41.e. Slit-tube tile roof. 28-day characteristic 150 mm cube compressive strength of 15 MPa).4 kg. which covered both brick and stone masonry construction. they represent documents of authenticated information. medium (M1. Based on their nominal mix proportions. and strengthening of reinforced concrete structures. Provisions for estimating effective thickness. stones. M2) and low (L1. IV. the Bureau of Indian Standards published the bilingual (English and Hindi) version of these two standards (IS:13827-1999. These mortars are required to satisfy the minimum compressive strength requirements for use in masonry work. earthen. The code limits the slenderness ratio (h/t or l/t). as English is not the native language in India. and V (IS:4326). Also. However. In 1999. This publication reviews the structural performance during strong earthquake shaking of masonry. H2). even this document did not receive wide audience. INDIAN STANDARD FOR UNREINFORCED MASONRY (IS:1905-1987) The masonry code gives recommendations for the design of unreinforced load-bearing masonry walls constructed using solid/perforated burnt clay bricks. the masonry code classifies mortars made from cement. one for Earthen Buildings (IS:13827-1993) and another for Low-Strength Masonry Buildings (IS:13828-1993). The Bureau of Indian Standards (New Delhi) has incorporated some contents of the IAEE manual in Indian Standard Guidelines. the ratio is limited to 27. the code requires masonry units to adhere to the strength requirements given in relevant Indian Standards for brick units (burnt clay or sand lime). length and height of walls are available for various end conditions designed in practice. sand-lime bricks. The standard requires that buildings of typical story heights of 3. and the IAEE guidelines did not have the formal recognition of enforcing agencies. 1989). where h and l are the effective height and effective length of the wall. special features are applicable for construction of earthquake-resistant masonry buildings in Seismic Zones III. These specifications were not followed in structures in the affected area. and those in lime mortar are at least 160 mm (in buildings up to 2 stories) or 250 mm (in buildings with more than 2 stories). a region in Seismic Zone V. stone and wooden buildings. lime. For walls in cement mortar. Even though Indian Standards are generally not mandatory in India. These thicknesses are independent of that of plaster. These publications gave formal recognition to the practice of building earthquake resistance into a greater variety of dwellings. restoration. . These provisions seem to be valid for the single story structures built in the Kachchh district. and priced nominally (ISET. lime based blocks. The practice of earthquake-resistant construction would be enhanced if these Indian Standards also become available in regional languages. L2). As per this code. and for structures taller than 2 stories. IS:13828-1999) to increase their usage.Masonry Structures 205 The International Association for Earthquake Engineering (IAEE) published a manual in English for nonengineered construction (IAEE. and burnt clay hollow blocks. This compilation of the basic rules of thumb has been reprinted in India by the Indian Society of Earthquake Technology (ISET). and for walls in lime mortar up to 2 stories to 20. The code specifies a number of stability-related requirements to be incorporated in the planning of the geometry of the structure and choosing the wall thickness. The use of a wide range of quality of mortars and masonry units noted in the postearthquake reconnaissance surveys indicate that material tests are usually not performed and the above specifications on the mortar and masonry units are not enforced. the ratio is limited to 13. and concrete blocks (solid and hollow).2 m. Further. walls in cement mortar are at least 120 mm thick. However. it gives guidelines for repair. concrete blocks. and nonengineered reinforced concrete construction. 1986). no special provisions are necessary for buildings constructed in Seismic Zones I and II. stones. Pozzolana and sand into six grades. namely high (H1. Two separate publications emerged. It outlines general concepts in earthquake-resistant design of such structures. αh can be interpreted as design seismic base shear per unit seismic weight of the structure. I is the importance factor (1. Here. 15n) Min (25. and rammed earth construction. C.12 as specified in IS:4326-1993. B. given by the product βlα0. depending on soil-type and foundation-type). and the details of earthquake-resistant features like bands. For example. IS:13827-1993 provides additional recommendations. including masonry construction using rectangular masonry units. Each method is presented in detail below. and αh is the basic horizontal seismic coefficient (0. INDIAN STANDARD FOR EARTHEN CONSTRUCTION (IS:13827-1993) This Indian Standard covers three types of earthen construction: hand-formed layered construction. the code specifies the following: mortar mix. a quantitative procedure is available for design of masonry buildings. For seismic areas. INDIAN STANDARD FOR EARTHQUAKE DESIGN AND CONSTRUCTION OF BUILDINGS (IS:4326-1993) Indian Standard IS:4326-1993 deals with selection of materials. and ductility. D and E.0-1. Type of Construction Minimum Separation (mm) Box system or frames with shear walls Moment resisting reinforced concrete frame Moment resisting steel frame Note: n is the number of stories in the building. Provisions for estimating the capacity of individual components are given in the code. for any classes of structures. The code requires that the components of the structure be made capable of resisting the most adverse combination of loads expected. Unfortunately. the size and position of openings. 20n) 30n .0 for all others). Min (25. β is the soil-foundation system factor (1.5 for important structures and 1. integral construction including suspended and projecting parts. timber construction and buildings with prefabricated flooring/roofing elements. the least severe with 0.12 and category A.08 for Seismic Zones III.04. special features of design and construction for earthquake-resistant buildings. Category E is the most severe with αh ≤ 0.Masonry Structures 206 In design. For buildings in each category.05 and 0.05. the code specifies minimum values of separation gaps required between adjoining buildings as given in Table 11-3.5. vertical reinforcements. The allowable stress method of design is adopted. simple geometric shapes. when joints are unavoidable in buildings. Attention is drawn to special features of building design and construction. and plan bracings at roof level. General principles are provided to encourage the construction of buildings with low mass. Permissible stresses are specified and procedures for calculation of those in compression and shear are specified. block/adobe construction. quantitative design of masonry buildings is not performed. 0. Minimum separation gap to be provided between adjoining buildings with design horizontal seismic coefficient αh of 0. the building is required to be analyzed as a whole as per accepted principles of mechanics. Thus. IV and V. IS:4326-1993 classifies buildings into five categories A. The Table 11-3.04 ≤ αh ≤ 0. depending on the value of the design seismic coefficient αh. in general. respectively). and E – as in IS:4326. one at the lintel level and another at the roof level. for buildings in other categories. Buildings in category E and important buildings (with ) are prohibited from using low-strength masonry. However. IV and V. this type of construction is to be avoided in high water table sites. The plinth is required to be at least 300 mm above ground.Masonry Structures 207 Standard prohibits earthen construction in Seismic Zones IV and V. The Standard also suggests that a thick plastic sheet be used to prevent water from seeping upwards through the walls. The foundation of such construction is usually strip foundations running along the length of the walls. IV. Heavy roofs consisting of wood joists plus earth toppings are prohibited in Seismic Zones IV and V. It clarifies that buildings constructed in accordance with these guidelines are not totally free from collapse under seismic shaking intensities of VIII and IX. walls have to be reinforced along the vertical direction with cane or bamboo sticks. If walls must be longer than the above limits. INDIAN STANDARD FOR LOW-STRENGTH CONSTRUCTION (IS:13828-1993) The provisions of this Standard are applicable for brick and random rubble stone masonry construction in Seismic Zones III. with lean cement concrete of 1:5:10 or lime concrete of 1:4:8. the bands have to pass over them also. Also. these provisions are not considered necessary. The unsupported length of walls between cross walls is required to be less than the smaller of 10t or 64t2/h. where t is the thickness of the wall and h is its height. For instance. If these cannot be avoided. inclusion of the special design and construction features of the Standard reduces the likelihood of structural collapse. this standard also classifies buildings in Seismic Zones III. However. the walls are required to be strengthened with the following features: • In dwellings situated in Seismic Zones III. The upper limit on the size of the openings in walls is specified in absolute dimension as 1. the walls are to be tied together with at least two bands. Foundation materials are required to be stronger than those used in the walls. Roof beams or rafters are to be avoided over openings. and to have a width of twice the wall thickness. For those in Seismic Zones I and II. These strips are required to be founded at least 400 mm below ground. The bands may be made of wood. the limitation on the building height is specified as . B. When pilasters or buttresses are provided. and V into five categories – A. and V. For example. lintels over such openings shall be reinforced with additional lumber. Trussed roofs are preferred over sloping roofs with just rafters or A-type frames. IV. at least 1. and restricts the height of such construction to one story in Seismic Zone III. foundation masonry fired bricks or stones. the Standard makes specific recommendations on the structural configuration and special earthquake-resistant features to be built into them. Further.2 m away from the corners. C. Roofs are required to be light. These vertical elements have to be tied together with horizontal pieces of bamboo/cane and also anchored in the two bands at the lintel and roof levels. D. Tiled/slate roofs are also considered to be vulnerable and are to be avoided in Seismic Zones IV and V. The amount of openings is restricted to be 33 percent of the wall length in Seismic Zone V and 40 percent in Seismic Zones III and IV. is suggested by the Standard. This Standard refers to low-strength masonry. in addition to requiring a water drain to be built around the outside of the wall to keep the water away from the dwelling. they are required to be strengthened by buttresses in between. The Standard suggests that the rafters used in the roof be rested on longitudinal wooden elements along the walls to enable a uniform distribution of forces from the roof to the walls. Again. the height of the wall is required to be less than 8 times its thickness. It is also recommended that the wall above the foundation up to the plinth be made in the same stronger material recommended for the foundation. particularly in Seismic Zones IV and V. • In Seismic Zone V.2 m. well connected within. Further. and adequately tied to the walls. or D) and number of stories. Brick masonry construction shall be made with bricks of compressive strength not less than 3. Indian Standards suggest special seismic strengthening to increase the earthquake resistance of low-strength masonry buildings. OTHER PUBLICATIONS AND BOOKLETS APPLICABLE TO STRUCTURES IN THE BHUJ AREA The publication Vernacular Housing in Seismic Zones of India reviews the seismic vulnerability of masonry construction in India in 1984 (I-UNM 1984). as specified in IS:13828-1993. Vertical reinforcing steel at corners and junctions of walls. A. Limitations on the number of stories to be constructed in low-strength masonry. The report is based on a field survey and was published in 1984. 4.5MPa. IS:13828-1993 provides empirical details of each of the above seismic strengthening arrangements for direct implementation in the field during construction. Through-stones or bond elements in thick walls. 6. Plinth band. Limitations on size and location of openings in walls. including: 1.. 7. The maximum size and preferred location of openings is identified. such as Table 11-4. Wall thickness is required to be restricted to within 450 mm. resting over the full width of the wall. 5. C. The above seismic strengthening arrangements are required to be built into buildings depending on their category (i. 3. Strength of bricks and wall thickness are to be chosen depending on the height of the building. It lists the status of various aspects of masonry structures. Lintel band over all internal and external walls except partition walls.e.Masonry Structures 208 indicated in Table 11-4. 2. with story heights not exceeding 3 m and spans of walls between crosswalls limited to 5 m. where strip footings are made of masonry (other than reinforced concrete or reinforced masonry) and soil is soft or of uneven properties. In-plan bracing of flexible roof system. Roof band (except when the roof is made of reinforced concrete) when roof is flat and gable bands when roof is pitched. B. Building Category Building Type A B C D Brick Masonry Construction Flat roof Pitched roof (including attic) Stone Masonry Construction Flat roof • Lime-sand or mud mortar • Cement mortar (1:6) Pitched roof (including attic) • Lime-sand or mud mortar • Cement mortar (1:6) 3 2 3 2 3 2 2 1 2 3 1 2 2 3 1 2 1 2 1 2 1 2 1 2 . another agency. Similarly. The wood used in the roofing is not formally cut and shaped. . Traces of traditional wisdom were seen in some structures that survived the shaking with little damage. Some academic organizations and nongovernmental organizations in India have also published useful information on earthquake-resistant masonry construction. which is a good beginning towards taking the subject of earthquake-resistant structures directly to the common man. There are no connections between the walls. Dehra Dun. This booklet is one in a series of booklets prepared for use by ordinary homeowners. quality of workmanship. and size and location of openings. they were structurally unsuitable to resist lateral seismic loads because of the building materials used. also published a booklet in Hindi on earthquake-resistant house construction (LVS 1995). Earthquake-resistant features are not built into this system. The detailed review of stone masonry houses in the Bhuj region identified the following general characteristics: • Poor roof design: heavy. or between the walls and roof.Masonry Structures 209 structural integrity and configuration. Lok Vigyan Santhan. three months after the earthquake destroyed the original structure. In this type of construction. it was being rebuilt using the same rubble in reconstruction. no lintel band is being provided. even after this earthquake (Figure 11-45). The booklet was published in two languages—in Hindi (RGF 1994a) and English (RGF 1994b). little attention is paid to the details that make the roof and walls act together as a single entity. While these low-strength masonry units were high on fulfilling functional needs. Housing of this type. loosely formed and not properly anchored to the walls • Weak walls: thick random rubble stone walls in mud mortar with weak strength and connections between the adjoining walls • Reasonable foundation design: overall geometry and balance of the structure. found primarily in economically weaker sections of the society. The Rajiv Gandhi Foundation published another booklet on earthquake-resistant house construction (RGF 1994c). readily available. Owing to the coarse shapes of the stones. Heavy purlins carrying the weight of the roof cause stress concentration on the walls at the support points. who may not always get an engineer to help them decide how to construct their house. performed abysmally during the 2001 Bhuj earthquake. illustrating that knowledge of earthquake-resistant construction is not being implemented consistently. published a booklet on “Do’s and Don’ts for Protection” against the earthquake problem. and hence very popular in the Kachchh region. in association with the University of Roorkee. Again. The Rajiv Gandhi Foundation in New Delhi. Such large masonry blocks with unusually large mortar thickness of a basically weak mortar material (mud) resulted in very poor performance of a large number of such structures in Bhuj. TYPICAL STRUCTURAL DAMAGE The most elementary of masonry construction is random rubble stone (granite) masonry in mud mortar. The unusually large size (up to 600 mm) pink sandstone masonry units and mud mortar (up to 75 mm thickness) used in making two-story residential buildings resulted in brittle performance (Figure 11-46). Pink sandstone is lighter than granite. The above are but a few of the examples of efforts to generate awareness and provide information about earthquake-resistant construction to the broadest possible audience. The stone-mud walls sustained severe cracking at these locations (Figure 11-48). Roorkee. For instance. the thickness of the mud mortar required for leveling is sometimes as large as 8 cm (Figure 11-47). It identifies deficiencies in masonry structures and suggests measures to overcome those deficiencies. Walls built with large stones and no through-stones separated into wythes impairing the vertical load-carrying capacity. The 2001 Bhuj earthquake provides opportunity to capitalize on and push the mass education of the people of India living in seismically active areas towards building safer and less vulnerable houses. thereby providing some lateral resistance to the inherently weak stone (granite) masonry in mud mortar. Figure 11-48. Walls built with large stones and no through-stones separated into wythes impairing the vertical load-carrying capacity. In such cases. Semi-dressed/dressed stone masonry in cement mortar in general sustained lesser damage than random rubble in mud mortar construction. such as fine shear cracks in stiff walls. Figure 11-46.Masonry Structures 210 where lintel and post system provided lateral resistance (Figure 11-49). Pink sandstones cut to 450 mm largest dimension were used in the construction of some residential units (Figure 11-50). Pink sandstone of up to 600 mm in size was used in construction of these twostory housing units. Mud mortar is sometimes as thick as 8 cm. Random rubble from the original (collapsed) structure is being used to rebuild this unreinforced masonry house. The tape is held out by 30 cm. the shear cracks in walls ran through masonry blocks. Structures with tall gable walls faced out-of-plane stability problems. . In the majority of cases. Figure 11-45. The plinth in such construction is usually in random rubble granite stone masonry in cement mortar. lintel bands are not provided in the Kachchh region. These structures sustained only minor damage. Figure 11-47. The strength of these sandstone masonry units can be comparable to that of cement mortar sometimes. Older construction used a large amount of wood in the post and lintel system. Single story construction with semi-dressed sandstone is common. This practice may have come from the construction of monumental/heritage construction in the area that used wood frame in a significant way to counter seismic forces. Unconfined masonry piers sustained damage. A good percentage of the recent construction in the Kachchh region is burnt clay brick masonry in cement mortar. academic. Pointing is done on the outside and plastering on the inside. The single-story structures performed very well. thereby providing some lateral resistance to the inherently weak stone (granite) masonry in mud mortar. These structures showed a full range of performances. though they did sustain shear cracks and sliding along masonry courses. The single-story and two-story random rubble masonry residential units in cement mortar with reinforced concrete slab roofs at the Indian Railways residential colony in Gandhidham have plinth and lintel bands. and today cement block construction is common throughout the Kachchh region. or with discontinuous lintel bands. Construction with lintel bands performed well. Cement blocks offer lower lateral resistance than does burnt clay masonry. The wall-roof interface had nominal sliding and separation. Collapse of hollow block masonry structures was not observed. and residential buildings in the Kachchh region are built of cement block construction (Figures 11-52 and 11-53). performed very poorly. and the short walls between the plinth and lintel bands sustained shear cracks (Figure 11-51). The main features of these buildings include lintel and plinth bands. Only minor cracks were seen in those structures. collapse of parapets. The first hollow cement block manufacturing plant was established in the 1950s. and severe damage to stair towers. the two story residential units suffered damage such as sliding of service water tanks. underway in Bhuj at the time of the earthquake. the Indian Railways and the Kandla Port Trust have built good engineering practices into their construction. This construction. The reinforced concrete slab roof is simply rested on the walls. Special hollow cement blocks for construction of columns encouraged construction of multistory buildings (Figures 11-55 through 11-57). and vertical reinforcement at wall corners. Dressed sandstone masonry in cement mortar with plinth and lintel bands was used in single-story row housing at the Kandla Port Trust campus. Over the years. . provides a plinth band. suggests that excessive weathering of outer layer may have led to the falling off of the outer wythe of the hollow block wall. A major problem with the hollow cement blocks is their durability. but not a lintel band. Older construction used a large amount of wood in the post and lintel system. However. Structures without lintel bands. depending on the level of earthquake-resistant features built into them. Vertical shearing off of the hollow cement block wall into two wythes and the partial collapse of the wall (Figure 11-58). Offices. Hollow cement block construction without plinth and lintel bands performed poorly (Figure 11-54). Figure 11-50.Masonry Structures 211 Figure 11-49. Where the service water tanks are located over the slab of the stair towers. structures with solid cement block structures did not fare too well. Traditional racking in hollow cement block shear walls and failure of Mangalore tile roof was observed at the Commerce College Building in Adipur. irrespective of whether the masonry is in sandstone. This construction incorporates plinth and lintel bands. and at the plinth beam level. The walls are pointed on the outside with cement mortar. or bhongas. Collapse of the roof of a two-story building under construction (Figure 11-59). The walls are made of sun-dried (adobe) bricks and are about 500 mm thick. TRADITIONAL CONSTRUCTION IN KACHCHH REGION BHONGAS Traditional houses. The out-of-plane collapse of the compound wall at the school building in Gandhidham is owing to the large unsupported block masonry panel (Figure 11-61). solid cement blocks were introduced over the past two decades.Masonry Structures 212 Due to falling quality control in the manufacture of hollow block units. In two-story masonry structures. like compound walls and parapets. the problem was even more aggravated. and of a warehouse building (Figure 11-60) is attributed to the lack of bands to hold the walls together in addition to the tall wall heights. and the increasing popularity of fly ash-based cement blocks. There is no lintel band and no plinth band. unlike their hollow counterparts. the diameter varying from 3 m to 6 m (Figure 11-63). Their use in tall walls therefore makes them particularly vulnerable in the out-of-plane direction. in the Kachchh region consist of a single room circular in plan. A Figure 11-51. their low compressive strength. When the blocks are made as wide as the wall (usually 230 mm). clay brick or cement blocks and in mud/cement mortar. The roof is pitched and made of bamboo sticks and thatch. the concept of header and stretcher is not adopted in masonry construction. Figure 11-52. but a dampproof course is provided at the plinth level. These singlestory houses performed very well. these units are heavy and cannot be handled comfortably. stair towers performed very poorly (Figure 11-62). Consequently. did not performed well during this earthquake. Long unsupported spans made of such blocks. Solid cement blocks tend to have flat surface without the key that is present in standard burnt clay bricks. . They have smooth surface characteristics that create a poor bond with the cement mortar. Granite stones up to 350-400 mm are used by the Indian Railways in the construction of single and twin residential units in Gandhidham. Nominal cracking was seen at the interface between the roof and the walls. However. Beams and slabs were of in-situ concrete. Figure 11-56. Figure 11-54. Special elements were also made for sill and lintel bands so that reinforcement could pass through them. Innovation in concrete block technology led to the manufacture of special blocks for making columns and encouraged builders to construct multi-story frame structures using concrete blocks. Hollow cement block construction without plinth and lintel bands performed poorly and sustained severe cracked walls. Single-story row housing in the Kandla Port Trust residential colony performed well.Masonry Structures 213 Figure 11-53. Figure 11-57. . Figure 11-55. Figure 11-59. Out-of-plane collapse of cement block wall. Figure 11-62. . Figure 11-61. and not on the stair tower. The building was under construction at the time of the earthquake.Masonry Structures 214 Figure 11-58. Roof collapse of two-story building of solid cement blocks. The cantilever projection of masonry work that defines the staircase sustained severe distress. the tank was resting on the slab (not in the picture). Hollow cement block wall separated into two wythes. Warehouse of solid cement blocks had no lintel band. Figure 11-60. In this case. Large local stresses are generated in the circular walls at locations where the horizontal post of the roof system rests. Plinth and collar bands are also included in some instances. In recent times. The brittle mud walls gave way under these large local stresses. and the wall 2. The major departure from the traditional construction in new construction is that the traditional thatch roof is replaced with a heavy Mangalore tile roof (Figure 11-65).Masonry Structures 215 central post (100-150 mm diameter) is propped by a wooden log (200-250 mm diameter) running diametrically across the room and resting on the walls. few openings. Most of the older ones and those made in mud mortar suffered collapse. The bhongas had many earthquake-resistant features such as light roof. . the plinth is raised about 300 mm above ground. bhongas made with bricks and cement mortar performed better. Traditional construction of rural houses consisted of circular mud walls and thatch roofing. some bhongas were also made in burnt clay bricks and cement mortar. walls with small slenderness. The bhongas suffered varying levels of damage. resulting in the collapse of the entire structure. However.0 m below ground. Figure 11-64. No separate foundation is made for this structure. Figure 11-63. Large local stresses are generated in the circular walls at locations where the horizontal post of the roof system rests. There are no openings built under the point where the wooden log is supported on the wall. The adobe wall is started about 1. Figure 11-65. low lateral strength and the heavy log of wood supporting the roof are negative factors. supports the roof (Figure 11-64). and low height. Heavy Mangalore roof tile has recently begun replacing light thatch roof.1 m above that. these historic structures showed no collapse. Many of these historic houses performed well during this earthquake. It has highly decorative woodwork surrounding the openings and vertical posts (Figures 11-68 and 11-69). The Kachchh region is known to be subjected to moderate to severe seismic shaking. Intermediate horizontal bands reduce the panel size of the masonry (Figure 11-66). Details of a typical Pol construction. In general. a Figure 11-66. and some of these structures tilted out-ofplumb after the earthquake. The large number of wood frames used in the transverse direction (shown in black) are highlighted in b. b . These pols are examples of the earthquakeresistant construction prevalent in the region. In some of these buildings. This three-story house has a long plan. A pol consists of a highly redundant wooden frame infilled with clay brick masonry in lime mortar (Figure 11-67). A wood frame with thin clay brick infill masonry in lime mortar formed the basic structural system. deterioration due to aging and indiscriminate additions was significant.Masonry Structures 216 POLS Pols are three-story houses built in Historic times. Spalling of plaster and frame infill separation were observed (Figure 11-69). and earthquake resistance was consciously built into historic housing constructed for centuries. This lintel and post method of construction has a flooring system of wooden floor planks finished with heavy stone slabs laid on broken clay brick pieces in mud mortar. Spalled plaster and frame infill separation in this Pol. Figure 11-69.Masonry Structures 217 Figure 11-67. Pols. historic structures in the region. have highly redundant wood frame infilled with clay brick masonry with lime mortar. . Decorative bracing on historic Pol. Figure 11-68. Comprehensive repair and strengthening was not undertaken after the 1956 earthquake. DAMAGE IN ANJAR The town of Anjar was shaken not long ago during the 1956 Anjar earthquake (Mw 6. was different in the following aspects: Structures were made of cement mortar instead of lime/mud mortar. 9. as was common in the old Anjar area. No earthquakeresistant features like bands were provided. Anjar is divided into 12 wards. The old town lies in the middle of Anjar and consists of wards 3. Around this central area lies the new Anjar. 5. and at the time of the January 26. 4. The development of new Anjar took place mostly in the last decade. the most central of which sustained the most damage. 4. Structures in wards 3. This new masonry construction.Masonry Structures 218 Figure 11-70.000 during the 1956 earthquake.5-3 km2. and 10 (circled by a dashed line). however. Lintel bands had become a more common feature in residential construction. 4. Ward 10 is apparently reclaimed from a 300-400 year old pond. Damage was primarily restricted to the five wards of the old Anjar town.0). and 10 were rebuilt after they collapsed during the last earthquake from the rubble using the construction methods prevalent at that time.000. Wards 5 and 9 sustained lower levels of damages in both this earthquake and the 1956 event. The town of Anjar is divided into wards (Figure 11-70). Older structures that were either undamaged or reconstructed after the 1956 earthquake were spread over a central area of 2. Construction in new Anjar had similar configurations to those in the old Anjar area. Residents of Anjar recall the 1956 event to be of a shorter duration. Use of mud mortar is rare in this type of construction. These wards were also damaged during the 1956 Anjar earthquake. with relatively lighter shaking intensity than the 2001 event. Construction in the old Anjar area is random rubble sandstone masonry in lime mortar with walls up to 750 mm thickness. . Wards 3. 2001 event it was around 55. The population of Anjar was around 30. and 10 in old Anjar sustained near total collapse of all buildings. The town of Anjar has an area of about 12 km2. . Re-use of the rubble from the 1956 earthquake. Lessons from Anjar highlight the vulnerability of re-used construction material and of structures without earthquake-resistant features. the extensive use of weak lime mortar. coupled with the construction of walls in two wythes makes these structures vulnerable under strong seismic shaking (Figure 1173). However. It is important that these features be incorporated into construction. Structures with stone masonry walls in lime mortar may have weathered over the last four decades. or inclined members providing bracing) would have allowed buildings to perform much better under seismic shaking (Figures 11-75 and 11-76). Post-1956 Anjar earthquake construction in old Anjar was no better than practices in effect before the earthquake. Also. • Inadequate roof-to-wall connection. coupled with the lack of basic earthquakeresistant features.e. particularly when massive reconstruction work in the area is about to begin. Wood runners were placed room-wise (i. and highly irregular dwelling units. nor any formal guidelines to make masonry construction earthquakeresistant. just for the length of the room and not over the full length of the house spanning over the walls) due to lack of adequate lengths (Figure 11-77). Even though there was total devastation in old Anjar. These structures again performed poorly during the 2001 Bhuj earthquake (Figures 11-71 and 11-72). This resulted in the floor system of each room behaving independently and pulling apart from the others during strong shaking (Figures 11-78 and 11-79). contributed to this total collapse in the older section of Anjar. The large thickness of up to 750 mm. . an occasional structure stood upright in this area and showed that construction with lateral force resisting elements (wooden post and lintel systems. the country had neither adequate awareness of earthquake-resistant construction at that time. Figure 11-72. Figure 11-71. The re-used sandstone masonry blocks from the rubble of the 1956 event may have poor bond characteristics. Total or near total collapses of structures in this region suggest the following deficiencies: • Inadequate walls. The area most affected in Anjar was the area of town that sustained collapses during the 1956 Anjar earthquake and was then rebuilt with the rubble.Masonry Structures 219 It was expected that construction practice in this old town would take a turn for the better after the 1956 earthquake. leading to further deterioration of their strength. the failure of the walls into two wythes has contributed to the collapse of the roof systems and the consequent large number of fatalities. Unsupported masonry panels in tall masonry walls performed poorly (Figure 11-74). In old Anjar. this building with lintel and post system survived. Figure 11-75. Figure 11-74. where almost all structures collapsed.Masonry Structures 220 Figure 11-73. . Reducing height of unsupported masonry panels in the tall gable walls may be an important contribution in the reconstruction effort. The thick walls with small size rubble and no through-stones led to splitting of walls into two wythes and in many cases impaired the gravity load carrying capacity. if any.Masonry Structures 221 Figure 11-76. Figure 11-78. Floors pulled apart in strong ground shaking. This implies that the inverted V-shaped roof system has a greater tendency to open up and flatten out—either because the nailing between the two rafters at the crown is only nominal. Flooring system is three layers of closely-spaced cross runners. Inadequate floor-to-wall connection. The inclined reinforced concrete slabs of stairs may have provided some lateral strength to the weak masonry system. Owing to the difficulties in investigating below the ground. 2. the deficiencies in the foundations. Figure 11-77. which are themselves tall. Discontinuous runners over interior walls contributed to damage and/or structural failure. . Heavy roofs with large diameter wooden logs in the roof truss. LESSONS LEARNED The widespread damages experienced by masonry structures can be attributed to inadequacies of the roof and walls. Figure 11-79. slender and vulnerable to outof-plane collapse. Performance of the masonry construction in the quake-affected area suggests that the roofing systems employed in the Kachchh region had the following deficiencies: 1. were usually not exposed. or because the purlins are just resting on gable walls. Roof truss is usually an A-frame with no bottom tie member. and the oversized openings located at undesirable locations are often the cause of wall collapses. Failure of the large block masonry. namely 1993 Killari earthquake and 1999 Chamoli earthquake. The former primarily demonstrated extensive collapse of random rubble masonry walls due to lack of integrity within them. It is hoped that the studies on seismic damages sustained by the masonry construction of the Kachchh area will also lead to positive changes in the construction practices of the region. particularly at the gable walls. which is supposedly to act as a single unit. For these reasons. 3. and implies an unstable roof system that can collapse. Observations made in the aftermath of these two past earthquakes in India have had positive influence on subsequent construction in those areas.7 earthquake is no surprise. and seismic forces from such roofs are not safely transferred to the walls.Masonry Structures 222 3. 6. walls are properly connected through the deployment of proper bonding courses in alternate layers. and often fall apart into two distinct wythes. and the latter primarily showed lack of integrity in the heavy pitched roofs composed of tiles supported on wooden rafters and purlins. These damages stand as graphic examples for the people of the region on the vulnerability of their own construction. namely: 1. Walls are not adequately connected to each other. Roofing elements. Rafters rest directly on the masonry walls with no connection between the roof and the walls. CONCLUSIONS Masonry construction in the Kachchh region is built by rules of thumb and traditions of construction technology that are handed down from one generation to the next. Such a construction sequence takes away the basic essence of making an earthquake-resistant house. The walls of buildings built with hollow cement blocks are usually left unplastered and hence suffered extensive weathering. one cannot guarantee that no collapse will occur in these constructions. and thereby of the buildings. In limited cases. 4. The presence of a clean vertical construction joint at the corners. Thus. the large number of fatalities from building/dwelling collapses during this Mw 7. where the integrity of the wall system is most desired. and consequently the diaphragm action in the roof is absent. Wall systems employed in the Kachchh region also showed numerous deficiencies. Similar lessons were learned in the aftermath of two Indian earthquakes of the past decade. This matter may require detailed investigation. Walls are very thick (up to 400-600 mm). are themselves not integrally connected. Walls are not connected to the roof with positive mechanisms. . Gable roofs do not have tie bracing in the horizontal plane. there is ample room for this type of construction to deviate from desired construction practice. long unsupported walls. nor do experienced engineers always supervise such construction. is a major deficiency in this construction. No engineering calculations are performed to assess their seismic adequacy. 2. Instances of weathering of the hollow blocks were noted in some places where the outer layer of the hollow blocks has fallen off. tall slender walls. 4. Damage to masonry construction in the Kachchh region were due to known ills of masonry and the use of heavy and loosely formed roofs. This suggests that large inertial forces are not always transferred to the walls. Owing to the above structural and constructional features. Construction practice is such that one wall is built at a time. namely the tiles. 5. 5. which clearly violate the requirements of buildings in Seismic Zones IV and V as per the Indian Standard guidelines. A Manual of Earthquake Resistant Masonry Construction. Bureau of Indian Standards. RGF. Rajiv Gandhi Foundation. Further. Lok Vigyan Sansthan. Dehra Dun. Rajiv Gandhi Foundation. 1994a. and earthen construction published in 1993 (IS:138271993 and IS:13828-1993) are. New Delhi. Guidelines for Earthquake Resistant Masonry Construction. Indian Standard Improving Earthquake Resistance of Earthen Buildings—Guidelines. International Association of Earthquake Engineering. Tokyo. Indian Standard Structural Use of Unreinforced Masonry—Code of Practice. Foreign Disaster Assistance. Washington.C. IS:13828-1993. New Delhi. Adipur. I-UNM 1984. New Delhi. New Delhi. even for gravity loads. Bureau of Indian Standards. very few masonry structures are formally designed. Indian Standard Improving Earthquake Resistance of Low Strength Masonry Buildings— Guidelines. July 1995. ACKNOWLEDGMENTS The authors are grateful to the large number of engineers in both government and private sectors of the state of Gujarat. New Delhi. not implemented owing to lack of knowledge of their existence. in India. Interestingly. Indian Standard Improving Earthquake Resistance of Low Strength Masonry Buildings— Guidelines. IS:1905-1987. Earthquake Problem: Do’s and Don’ts for Protection. 1989. New Delhi. (in Hindi). The authors from IIT Kanpur gratefully acknowledge financial support from the Department of Science and Technology. RGF. Hindi Edition.S.S. despite the existence of a design code for this purpose (IS:1905-1987. LVS. 1995. low-strength masonry. there are small efforts in the aftermath of an earthquake. Earthquake Resistant House. (in Hindi). REFERENCES IAEE. and that to a limited audience. D. Indian Standard Improving Earthquake Resistance of Earthen Buildings—Guidelines. Bureau of Indian Standards. ISET. Vernacular Housing in Seismic Zones of India. who provided information and showed the damaged structures in detail. Unfortunately. Program to Improve Low-Strength Masonry Housing. Earthquake Resistant House Construction—Instruction Booklet. 1994c. Bureau of Indian Standards. Rajiv Gandhi Foundation. Bureau of Indian Standards. Earthquake Problem: Do’s and Don’ts for Protection. IS:13827-1999. 1994b. Government of India for partial support towards the studies on the Bhuj earthquake. . the only other way of educating local people and artisans en-mass regarding the quality of their own construction is through the test of another real earthquake. A report prepared under Joint Indo-U.Masonry Structures 223 Information dissemination on lessons learned from seismic performance of masonry construction during past earthquakes in India is generally absent. RGF. New Delhi. IS:13828-1999. Indian Society of Earthquake Technology University of Roorkee. Bilingual Edition. IS: 4326-1993) for over three decades. IS:13827-1993. INTERTECT and University of New Mexico for U. Comprehensive long-term planning is urgently required. Roorkee. 1986. in general. Bilingual Edition. even the Indian Standards dealing with earthquakeresistant masonry. Agency for International Development. Japan. Third Edition. and in particular to all the enthusiastic team of engineers of the SRC Limited. English Edition. New Delhi. Murty.Return to Table of Contents Next Chapter Masonry Structures 224 CHAPTER CONTRIBUTORS Principal Author C. Australia Figure 11-64 by Kishore Jaiswal. India Debashish Nayak. Ahmedabad. India Figure 11-66 by Debashish Nayak. Indian Institute of Technology Kanpur. Kanpur. Kanpur. India . M. M. M. Mumbai. B. India Figure Credits C. Arlekar.V. Kanpur. California. University of Woloongong.EERI.R.R. Adipur. Ahmedabad Municipal Corporation. India Durgesh C. Sindhu Resettlement Corporation Limited. USA Figure 11-21 by Durgesh Rai Figures 11-63 and 11-65 by Robin Choudhurry. Udasi. India Contributing Authors Jaswant N. Indian Institute of Technology Bombay. University of Southern California.EERI. Indian Institute of Technology Kanpur. India H. Murty and Jaswant N. Ahmedabad. Ahmedabad Municipal Corporation. except as noted below. Rai. Indian Institute of Technology Kanpur. M.V. Figure 11-2 by J.EERI. Los Angeles. Bardet. Arelkar took all the photos in this chapter.EERI.P.

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