Reinforced Concrete Moment Frame Building with Infills and Slender Shear Wall Core, India

From World Housing Encyclopedia


1. General Information

Report: 210

Building Type: Reinforced Concrete Moment Frame Building with Infills and Slender Shear Wall Core

Country: India

Author(s): Mayank Sharma, Yogendra Singh, Henry Burton

Last Updated:

Regions Where Found: This building type is very common throughout urban and semi-urban areas in India. Both fully infilled and open ground story variants can be easily found in abundance in any Indian city or town. It may be a single building or a cluster of multiple buildings housing a large community. The number of buildings within a cluster may range between 2 to 50. A significant portion of urban India's population lives in such multi-family apartments. Such buildings are also fairly common in neighboring countries such as Bangladesh, Nepal, Pakistan and Sri Lanka.

Summary: The building type being summarized is a residential reinforced concrete infilled framed tower with a slender shear wall lift and/or staircase core. Usually height of such buildings ranges from 8 to 20 stories with each story being 2.8m to 3.5m high. Although modern buildings in urban areas are expected to be code-compliant, older buildings (>25 years old) in semi-urban areas could be non-engineered or designed only for gravity loads. The frame bays are traditionally infilled with unreinforced burnt clay bricks. During last decade use of alternative infill materials such as AAC (Autoclaved Aerated Concrete) blocs and fly-ash bricks has also gained popularity. However, use of such alternative materials is limited to bigger cities only, and the burnt clay bricks, due to their easy availability, are still the material of choice in smaller semi-urban towns. Ground story of the building is usually not infilled and used for parking or commercial purposes. Lateral load is resisted by moment frames along with lift/staircase shear wall core. Presence of open ground story represents a severe soft story deficiency and greatly increases the seismic vulnerability of such buildings (Burton and Sharma, 2017). The damage and energy dissipation is largely limited to the ground story and the probability of story mechanism formation is very high. Several such buildings sustained partial or complete collapse during the Bhuj Earthquake, 2001. Placement of a single shear wall core near the center of the building may result in a torsionally flexible system whereas presence of asymmetric lift/staircase core might result in severe torsional irregularity.

Length of time practiced: Less than 25 years

Still Practiced: Yes

In practice as of:

Building Occupancy: Residential, 50+ units

Typical number of stories: 8-20

Terrain-Flat: Typically

Terrain-Sloped: Occasionally

Comments: Strength and stiffness of infills is often neglected during the structural analysis and design process of such buildings. One of the reasons for this practice is the misconception amongst structural engineers that presence of infills always adds to the strength of the building and improves its seismic performance. The other reason is non availability of design code provisions for such buildings. The recent revision of the code, IS 1893 (2016) has included some guidelines to include the effect of stiffness of infills in the analysis, however, the code is still silent about how to take into account the strength of infills and the resulting weak ground storey effect. Provisions are also not available to consider the safety of infills in out-of-plane action, which results in use of very slender infill walls, susceptible to out-of-plane failure during earthquake shaking.


2. Features

Plan Shape: Other

Additional comments on plan shape: There is a huge variation in observed floor plan shapes. All possible plans including square, rectangular, L-shape, Y-shape, T-shape and other irregular shapes are often encountered. Therefore, torsional irregularity is a big issue for such buildings, which increases the seismic vulnerability further. Each floor could have anywhere between 1 to 12 units housing anywhere between 5 to 50 residents. Typical unit size ranges from 700 sq ft. to 2500 sq ft. Each unit could have a balcony cantilevering 1.2m to 2m outside the building. Depending on the size of floor plate, there could be one or more lift/staircase cores in the building. Asymmetrical placement of such core leads to increased torsional irregularity.

Typical plan length (meters): 30

Typical plan width (meters): 30

Typical story height (meters): 3

Type of Structural System: Other

Additional comments on structural system: In many cases, shear wall core is located near the center of the building. In such a case the building may have a torsionally flexible system having a dominant torsional mode. In some cases, the lift core is only connected to the rest of the structure through a corridor slab. In such cases, the lateral load carrying capacity of core is greatly diminished due to unavailability of a direct load transfer path. Torsional irregularity is often observed in these buildings. This irregularity could be due to multiple reasons including asymmetrically placed shear wall cores, asymmetric placement of infills, irregular floor plan etc. The plan irregularity combined with soft and weak open ground story makes these buildings highly vulnerable to earthquakes. The extreme vulnerability of these buildings was abundantly exposed in the 2001 Bhuj earthquake, when a large number of buildings at more than 300 km from the epicenter of earthquake, suffered severe damage and collapse.

Gravity load-bearing & lateral load-resisting systems: Lateral load resisting system is made up of a combination of moment frame and lift/staircase core shear walls. Shear walls, if connected to the rest of the building properly, are expected to bear most of the lateral load. Moment frame columns are expected to take the gravity loads. The thickness of walls varies from 150mm to 300mm. The structure is founded on a raft or a piled raft depending on the soil conditions. It is well known that infills also participate in the lateral load resistance and interact with the surrounding frames and make those susceptible to shear failure of columns. In addition, the infills increase the strength and stiffness of the upper stories several times, making the ground story (which is usually kept open for parking or other purposes) a weak and soft story. The strength and stiffness of infills is usually ignored, leaving in the soft and weak ground story unaccounted for in the design process.

Typical wall densities in direction 1: 0.1%

Typical wall densities in direction 2: 0.1%

Additional comments on typical wall densities: Typical concrete shear wall density is less than 1% in each direction. Typical infills density is between 4%-10% in each direction.

Wall Openings: The shear walls are typically provided in C/U shaped lift cores. In these cores walls on three sides are solid without any opening, whereas the front side has a series of door openings, on each floor, to access the lifts. There are multiple door and window openings in the infills. A door opening is approximately 1.5m by 2m. Nevertheless, there is large variation in the size of window/ventilator openings. Openings make up more than 20% of total infill area on each floor.

Is it typical for buildings of this type to have common walls with adjacent buildings?: No

Modifications of buildings: Typical modifications include removal and replacement of infill (partition) walls. Other modifications include enclosing balconies to increase room size or to be used as additional space, construction of internal stairways if the buyer of same apartments on consecutive floors is the same. These modification are often done without any approval or consultation of structural engineer.

Type of Foundation: Shallow Foundation: Mat foundation, Deep Foundation: Reinforced concrete skin friction piles

Additional comments on foundation: Generally a concrete raft is used as a foundation system for such buildings. In case of poor soil quality, a piled raft is also used.

Type of Floor System: Other floor system

Additional comments on floor system: A cast-in-place concrete slab monolithic with the concrete beams is used. The floor/roof slabs also act as flanges to the rectangular webs of beams. However, the flange action of the slabs and their adverse effect on the beam column strength ratio, is usually ignored in analysis. However, the diaphragm (in-plane) action of slabs is usually considered in design.

Type of Roof System: Cast-in-place beam-supported reinforced concrete roof

Additional comments on roof system: The monolithic roof slab has a typical thickness of 100-150 mm, which acts as a rigid diaphragm during earthquake.

Additional comments section 2: The main feature of such buildings is the interaction between infilled frame and shear walls. Behavior of the infilled frame is in-turn is governed by the interaction that takes place between the infills and the frames. The extent of this interaction varies depending on the type of material used for infills. Burnt clay brick masonry in cement mortar is the most popular material used for infills. However, due to varying geological conditions and soil characteristics, the strength of bricks and hence that of the infill masonry, varies significantly in different parts of India. The brick strength is much higher in the northern India than in the southern parts. However, use of stronger masonry may not be good for seismic safety of buildings. The stronger masonry infills cause larger shear forces in columns due to their diagonal strut action and may cause their failure in brittle shear mode.


3. Building Process

Description of Building Materials

Structural Element Building Material (s) Comment (s)
Wall/Frame Reinforced Concrete Concrete Compressive Strength (fc) based on cube sample strength = 20-40 MPa Rebar steel yield strength = 415 - 500 MPa
Foundations Reinforced Concrete Concrete Compressive Strength (fc) based on cube sample strength = 15-35 MPa Rebar steel yield strength = 415 - 500 MPa
Floors Reinforced Concrete Concrete Compressive Strength (fc) based on cube sample strength = 15-30 MPa Rebar steel yield strength = 415 - 500 MPa
Roof Reinforced Concrete Concrete Compressive Strength (fc) based on cube sample strength = 15-30 MPa Rebar steel yield strength = 415 - 500 MPa
Other Infills Burnt clay bricks (230 mm X 110 mm X 70 mm) with prism compressive strength = 3.5 - 7 MPa. Infills can be either one brick (110mm) thick or double brick (230 mm) thick. 1:4 or 1:6 cement sand mortar is commonly used in infill masonry.

Design Process

Who is involved with the design process? Engineer, Architect, Owner

Roles of those involved in the design process: Architect is the first point of contact for the owner/builder. Structural Engineer is usually hired by the architect who sub leases the structural design to him. There is very limited interaction between the structural engineer and the owner.

Expertise of those involved in the design process: Architects and Builders usually lack basic knowledge of structural design and codes. Most of the times, the chief concern of the owner/builder is getting the construction approved from the authority rather than the safety of the structure. Saleability and Usability are usually the primary factors in deciding the building plan shape and column locations. There is no professional certification or minimum qualification requirements amongst structural engineers.


Construction Process

Who typically builds this construction type? Owner, Builder, Contractor

Roles of those involved in the building process: Sometimes owner/builder has a dedicated construction team responsible for site construction. In other cases, the owner hires a contractor for construction.

Expertise of those involved in building process: There is a large variation in the competence level of the construction team. The construction quality at site is, therefore, highly variable.

Construction process and phasing: The first phase is planning and design. Wherein, the floor plans and framing plans of the building are finalized. Thereafter, the design and planning is to be approved by city/municipality officials before starting construction on site. In some cities the structural design has to be approved by an expert in structural engineering such as Professor in a government college. The speed of construction is highly dependent on sale of units and market demands. Before, handing over the unit to buyers/occupants, a completion certificate is needed from the city/municipality authority. Architect is usually responsible for co-ordinating with city/municipality authorities based on the documents signed by both the structural engineer and himself. However, this design and construction process varies from one city/municipality to another.

Construction issues: The quality of materials procured at the site is poor. Often, the measured values of concrete strength are much lower than the specified values. Cost is generally the primary criteria while selecting the materials and their suppliers. Supervision and curing of concrete is usually inadequate and ignored. Jain et al. (2010) have reported that during 2001 Bhuj earthquake it was found that taller buildings performed better than the shorter buildings. This was attributed to possible involvement of better companies resulting in better design and quality control in case of taller buildings.


Building Codes and Standards

Is this construction type address by codes/standards? Yes

Applicable codes or standards: The applicable structural codes are :

IS 456 : 2000 Plain and Reinforced Concrete - Code of Practice IS 1893 : 2002, revised in 2016 (part 1) : Criteria for Earthquake Resistant Design of Structures IS 13920 : 1993, revised in 2016 : Ductile detailing of Reinforced Concrete Structures Subjected to Seismic Forces - Code of Practice

Process for building code enforcement: The structural design and code compliance is to be reviewed and verified by a structural expert such as Professor in a government college, in the large urban areas and metro cities. Structural engineer has to issue a structure stability certificate to be submitted in the authority. However, the responsibility of the structural engineer is limited to the design and doesn't extend to construction and quality control. Corruption and incompetence are the main impediments in the enforcement of building codes. Further, the Indian codes do not provide clear guidelines about adequacy of load path for transferring the seismic forces to shear walls/core from rest of the structure. This results in confusion and unsound structural systems.


Building Permits and Development Control Rules

Are building permits required? Yes

Is this typically informal construction? No

Is this construction typically authorized as per development control rules? Yes

Additional comments on building permits and development control rules: The building permits are usually concerned to the architectural plans. The municipal officers involved in granting the permits are not competent in examining the structural designs and their seismic safety.


Building Maintenance and Condition

Typical problems associated with this type of construction: Quality of construction is generally low. Plan geometry can be highly irregular. Placing of reinforcement at the site may be faulty such as open shear loops, insufficient overlap zones, presence of cold joints in hinging region and insufficient embedded length in longitudinal bars. Other issues include water ingress during monsoon season, lack of after sales maintenance of the building etc. Due to inadequate cover to reinforcement is concrete, poor (porus) quality of concrete, inadequate compaction and curing, results is very early onset of corrosion in this type of construction. This results in damage to RC members and further increases the seismic vulnerability of the buildings.

Who typically maintains buildings of this type? Other

Additional comments on maintenance and building condition: After completion the units are handed over by the Builder to Buyers of individual units. The association of buyers/renters i.e. RWA's (Residents Welfare Associations) are responsible for building maintenance. RWA's often suffer from lack of co-ordination amongst residents and lack of working capital. Poor maintenance is found to be highly correlated with damage sustained during an earthquake (Jain et al., 2010).


Construction Economics

Unit construction cost: Construction cost usually varies from INR 10,000 (USD 150) per m2 to INR 20,000 (USD 300) per m2.

Labor requirements: The speed of construction is highly variable and dependent of market demand of individual units and working capital available with the builder. The average speed of construction may vary from 2 weeks to several months per floor. The number of man-days required will depend on the size of building plan.

Additional comments section 3: The builder floats the plan of the building in the market and collects money from the prospective buyers. Usually, the builder invests no or little money in the project. The progress of construction depends on the money collected from the buyers in the market. This process usually results in delays in completion of project and frustration among the initial buyers, who have invested in the project at early stage, but do not get their house in promised/reasonable time. The delays in project also result in cost escalations and the buyers end up paying more than originally planned. This funding model results in the Builder being primarily concerned with delivering legally approved apartments at the lowest cost possible. Design and construction quality usually takes the backseat.


4. Socio-Economic Issues

Patterns of occupancy: Each floor could have anywhere between one to twelve saleable units and could be housing anywhere between 5 to 50 residents. Building itself could be housing anywhere between 50 to 700 residents. The occupancy is dependent on the floor plan, floor size, unit size and number of stories.

Number of inhabitants in a typical building of this construction type during the day: >20

Number of inhabitants in a typical building of this construction type during the evening/night: >20

Additional comments on number of inhabitants: Day time : 20 to 300 residents Night time : 50 to 700 residents

Economic level of inhabitants: Middle-income class, Hight-income class (rich)

Additional comments on economic level of inhabitants:

Typical Source of Financing: Owner financed, Informal network: friends or relatives, Commercial banks/mortgages, Investment pools, Combination, Government-owned housing

Additional comments on financing: The major source of finance for these buildings is from the prospective buyers. In addition to their savings, these buyers usually take loans from banks. Some initial funds are also managed by the builder/owner and could be sourced from other businesses, bank loans, and formal or informal network of investors. The government encourages bank loans to the prospective buyers, by providing some discounts/income tax incentives on the interest on the housing loans.

Type of Ownership: Own outright, Own with debt (mortgage or other), Units owned individually (condominium)

Additional comments on ownership: In most of these buildings, the individual units are owned by different buyers. These buyers either occupy the unit for their own use or rent it to other people.

Is earthquake insurance for this construction type typically available?: No

What does earthquake insurance typically cover/cost: No earthquake insurance exists for such buildings in India.

Are premium discounts or higher coverages available for seismically strengthened buildings or new buildings built to incorporate seismically resistant features?: No

Additional comments on premium discounts:

Additional comments section 4: There is no insurance on the buildings in India. The builder who has already sold the units to individual occupants/buyers is not responsible for its maintenance. RWA's lack the capital to sponsor repairs and restoration in case of damage due to seismic event. The individual owners would have to fund the loss themselves, in case of any hazardous event or damage.


5. Earthquakes

Past Earthquakes in the country which affected buildings of this type

Year Earthquake Epicenter Richter Magnitude Maximum Intensity
1997 Jabalpur 5.8 VIII
2001 Bhuj 7.7 X
2015 Gorkha 7.8 IX

Past Earthquakes

Damage patterns observed in past earthquakes for this construction type: Primary damage in such buildings is sustained by the open ground story (if present). Damage and Energy Dissipation are localized due to low stiffness and high deformation demands in the ground story. Damage observed include hinging of walls, shear cracks and/or axial failures in columns, story mechanisms leading to complete or partial collapse. Whereas the damage in upper stories is limited to in plane or out of plane cracking or failure of infills.

Additional comments on earthquake damage patterns: The plan (torsional) and vertical (soft and weak open ground storey) irregularities, if present, often combine to cause severe damage in these buildings. These irregularities are further compounded with improper detailing of beam-column joints, lack of capacity design, improper and substandard construction and corrosion induced damage.


Structural and Architectural Features for Seismic Resistance

Structural/Architectural Feature Statement Seismic Resistance
Lateral load path The structure contains a complete load path for seismic force effects from any horizontal direction that serves to transfer inertial forces from the building to the foundation. TRUE
Building Configuration-Vertical The building is regular with regards to the elevation. (Specify in 5.4.1) FALSE
Building Configuration-Horizontal The building is regular with regards to the plan. (Specify in 5.4.2) FALSE
Roof Construction The roof diaphragm is considered to be rigid and it is expected that the roof structure will maintain its integrity, i.e. shape and form, during an earthquake of intensity expected in this area. TRUE
Floor Construction The floor diaphragm(s) are considered to be rigid and it is expected that the floor structure(s) will maintain its integrity during an earthquake of intensity expected in this area. TRUE
Foundation Performance There is no evidence of excessive foundation movement (e.g. settlement) that would affect the integrity or performance of the structure in an earthquake. TRUE
Wall and Frame Structures-Redundancy The number of lines of walls or frames in each principal direction is greater than or equal to 2. TRUE
Wall Proportions Height-to-thickness ratio of the shear walls at each floor level is: Less than 25 (concrete walls); Less than 30 (reinforced masonry walls); Less than 13 (unreinforced masonry walls); FALSE
Foundation-Wall Connection Vertical load-bearing elements (columns, walls) are attached to the foundations; concrete columns and walls are doweled into the foundation. TRUE
Wall-Roof Connections Exterior walls are anchored for out-of-plane seismic effects at each diaphragm level with metal anchors or straps. FALSE
Wall Openings N/A
Quality of Building Materials Quality of building materials is considered to be adequate per the requirements of national codes and standards (an estimate). FALSE
Quality of Workmanship Quality of workmanship (based on visual inspection of a few typical buildings) is considered to be good (per local construction standards). FALSE
Maintenance Buildings of this type are generally well maintained and there are no visible signs of deterioration of building elements (concrete, steel, timber). FALSE

Additional comments on structural and architectural features for seismic resistance:

Vertical irregularities typically found in this construction type: Torsion eccentricity

Horizontal irregularities typically found in this construction type: Soft/weak story

Seismic deficiency in walls: Shear walls might have improper detailing, inadequate shear reinforcement, improper binding of shear reinforcement etc. Whereas, infill panels suffer from inadequate connectivity with the concrete frame, leading to out of plane failures.

Earthquake-resilient features in walls: Some of the buildings have proper design and detailing of RC members and beam-column joints. The open ground stories are sometimes also designed for 2.5 times the design base shear for normal buildings to account for the soft/weak story effect. These buildings are expected to behave reasonably well during earthquake. The clause to design the open ground story for 2.5 times the design base shear was present in IS 1893 (2002). However, it was dropped in the current version of the code, IS 1893 (2016). Rai and Jain (2019) recommend that this clause be reinstated in the revised code.

Seismic deficiency in frames:No strong column weak beam provisions, Inadequate embedment of beam reinforcement bars into columns, improper detailing in the joint region, insufficient shear reinforcement in the joint region are few of the deficiencies. The strut action of infills results in additional shear force in columns, which is ignored in the design.

Earthquake-resilient features in frame: One of the few positive feature of such a building is the redundancy of vertical member. Usually, more smaller size columns are used at shorter spans resulting in increased redundancy that might save the building from complete collapse in some cases.

Seismic deficiency in roof and floors: Large cutouts, post-construction modifications disturb the lateral load path. Such cut-out are usually introduced for MEP(Mechanical Electrical Plumbing) shafts, to provide double height living spaces or for intra-apartment staircases.

Earthquake resilient features in roof and floors: The monolithic floor/roof slabs of adequate thickness act as rigid diaphragms and distribute the lateral load among different lateral load resisting elements.

Seismic deficiency in foundation: In many cases, poor quality of concrete is used in raft. It has frequently been that the compaction of soil before pouring of concrete is inadequate.

Earthquake-resilient features in foundation: The rigid raft/raft on piles foundation avoids differential settlement of column bases. It also provides good integration with the shear wall core. The base-moment from the shear wall core is adequately counterbalanced by closely spaced nearby columns.

Seismic deficiency in other: These buildings house a large number of families and have large requirement of water. In some cases presence of large water tanks on the roofs, architectural features, hoarding on the roof might increase the vulnerability.

Earthquake-resilient features in other: Some of the buildings, store the water in large underground tanks, rather than in large tanks on the top of the buildings. These buildings are expected to have better performance and lessor secondary damage.


Seismic Vulnerability Rating

For information about how seismic vulnerability ratings were selected see the Seismic Vulnerability Guidelines

High vulnerabilty Medium vulnerability Low vulnerability
A B C D E F
Seismic vulnerability class |-o-|

Additional comments section 5: The expected vulnerability of these buildings varies a lot depending on the design and construction. The non-engineered (or gravity only designed) buildings are expected to vulnerability class B to C, Whereas the properly designed and constructed buildings may have vulnerability class D or E.


6. Retrofit Information

Description of Seismic Strengthening Provisions

Structural Deficiency Seismic Strengthening
Soft/Weak story Soft story effects can be mitigated by adding infills in the ground story and avoiding its use as parking. Addition of shear walls could be another solution. The latter being slightly more complex construction wise and might lead to disruption of building use for some period. Jacketing of ground story columns using reinforced concrete has also been tried in some buildings.
Torsional Irregularity Torsion irregularity might be reduced through introduction of shear walls along perimeter/flexible side of the building. However, such an exercise is highly complex and may require the assistance of very skilled engineers.
Improper Detailing Wrapping of RC members and joints using FRP is used to compensate for inadequate confinement and shear reinforcement.

Additional comments on seismic strengthening provisions:

Has seismic strengthening described in the above table been performed? Very rarely seismic strengthening is done to reduce the building vulnerability. Few buildings were strengthened by jacketing of columns after the Bhuj (2001) earthquake. Such rare projects are usually initiated by RWA's. There is no such initiative from city/municipal authorities to do so.

Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages? In the city of Ahmadabad, repair of ground storey columns damaged due to 2001 Bhuj earthquake, was undertaken. These columns were jacketed either using RC or steel.

Was the construction inspected in the same manner as new construction? No. The construction of retrofit was very informal. The detailing of reinforcement in RC jackets was clearly inadequate.

Who performed the construction: a contractor or owner/user? Was an architect or engineer involved? The retrofit was done by the building owners informally. No architect or engineer was involved. Even if an engineer was involved in some cases, the engineer was not trained for retrofit work.

What has been the performance of retrofitted buildings of this type in subsequent earthquakes? No such experience is available.

Additional comments section 6:


7. References

  • IS 456 : 2000 Indian Standard Code of Practice for Plain and Reinforced Concrete (Fourth revision), Bureau of Indian Standard, New Delhi.
  • IS 13920 : 1993 Indian Standard Code of Practice for Ductility Detailing of Reinforced Concrete

Structures Subjected to Seismic Forces, Bureau of Indian Standard, New Delhi.

  • IS 13920 : 2016 Indian Standard Code of Practice for Ductile design and Detailing of Reinforced Concrete Structures Subjected to Seismic Forces, Bureau of Indian Standard, New Delhi
  • IS 1893 : 2002 (part 1) Indian Standard Criteria for Earthquake Resistant Design of Structures , Bureau of Indian Standard, New Delhi.
  • IS 1893 : 2016 (part 1) Indian Standard Criteria for Earthquake Resistant Design of Structures , Bureau of Indian Standard, New Delhi.
  • Burton, H., and Sharma, M., (2017) Quantifying the Reduction in Collapse Safety of Main Shock–Damaged Reinforced Concrete Frames with Infills. Earthquake Spectra: February 2017, Vol. 33, No. 1, pp. 25-44
  • Jain, S.K., Mitra, K., Kumar, M., Shah, M., (2010) A Proposed Rapid Visual Screening Procedure for Seismic Evaluation of RC-Frame Buildings in India. Earthquake Spectra: August 2010, Vol. 26, No. 3, pp. 709-729
  • Rai, D.C., Jain, S.K., (2019) Proposed Modifications for Code on Criteria for Earthquake Resistant Design of Structures IS 1893: 2016 (part 1). November 2019

Authors

Name Title Affiliation Location Email
Mayank Sharma Student Researcher IIT Roorkee Department of Earthquake Engineering, India Institute of Technology, Roorkee, India msharma@eq.iitr.ac.in
Yogendra Singh Professor, Railway Bridge Chair IIT Roorkee Department of Earthquake Engineering, India Institute of Technology, Roorkee, India yogendra.singh@eq.iitr.ac.in
Henry Burton Associate Professor and Englekirk Presidential Endowed Chair in Structural Engineering UCLA Department of Civil and Environmental Engineering, University of California, Los Angeles, California , USA hvburton@ucla.edu
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