Why do buildings collapse?

By Nithin Sridhar

Two buildings have collapsed in the last one week in Thane district of Maharashtra. The first incident occurred on the night of 28-July in Thakurli town, when a two-storey building- MatruKrupa- collapsed. At least 6 people were killed and around 20 families were feared to be trapped.

In the second incidence within a week, a three-storey building "Krishna Nivas" collapsed on the early morning of 4-August in Naupada locality, Thane West. At least 12 people including six women and one child have died and seven others were injured.

Both the buildings were in a shabby condition and the Thane Municipal Corporation had declared Krishna Nivas, dangerous. But, these are not the only cases of building collapses in the Thane region.

In April 2013, a seven-storied under construction building, which was being illegally erected in Mumbra, Thane, collapsed killing 74 people including 23 women and 18 children and injuring more than 100 people.

The lower floors of the building were allowed to be occupied, even though the construction of upper floors were incomplete. The eye witness accounts had said that a section of the building collapsed, causing the entire building to come down.

Urbanization and building collapse

According to the document "Disaster Management in India", 2,833 people died due to building collapse in 2008. The number of people who died in 2009 stood at 2,847. The collapse of buildings, especially the multi-storey ones have been continuously increasing in last few years.

Due to real estate boom, new high-rise buildings are coming up everywhere, and there is a huge competition in this sector. In order to stay in this competition, the builders are hard-pressed to complete these buildings as early as possible.

This has resulted in flouting of various building norms by the builders.

Many also employ unskilled workmen and use poor building materials without any proper structural design that ultimately lead to the collapse of the buildings.

For example, in 2013 Thane incident, the seven-story building was finished within 7 months, and the lower floors were allowed to be occupied by construction workers and their families without getting occupancy certificates. Further, it was found that sub-standard construction materials were used by the builder in order to increase the profit margin.

Commenting on the 2013 incident, the "India Disaster Report 2013" released by National Institute of Disaster Management said:

"Unfortunately the events like the Thane building collapse are a regular phenomenon in rapidly urbanizing cities of India. Such accidents often involve buildings in low-income, semi-formal and informal housing sectors. There are indeed gaps in the system that lead to poor construction which need to be addressed at various levels. Most of the illegally constructed buildings are more often than not, likely to be substandard and dangerous. The buildings which are constructed without professional engineering protocols and usually with untrained construction workers are most vulnerable."

Another major reason for building collapse is that the owners of buildings are irresponsible and have no concern for the condition of their buildings.

The old buildings are left in dilapidated conditions and are never repaired. Even when structural cracks begin to appear, no actions are taken, resulting in eventual collapse, as happened in Matru Krupa.

Even before the building collapsed, portions of inner slabs had begun collapsing. But the owners apparently did not make any effort at getting them repaired.

A building is a vertical load carrying RCC member

A building is basically a vertical load bearing reinforced concrete (RCC) member which is designed to take on various loads and pressure applied on it without breaking, bending, overturning, or collapsing.

The buildings and their foundations are usually designed to carry dead loads, live loads and sometimes even resist horizontal forces due to wind or earthquakes.

The dead loads are nothing but the self-weight of the buildings and the weight of the other immovable objects that may be kept inside the building. The live loads are the movable loads that are imposed for a short duration at a particular position. For example, weight of the moving cars on a bridge is the live load applied on a bridge.

Similarly, in buildings, people and various other objects which are not stationary constitute live loads.

A margin of safety called "factor of safety" is taken into consideration during the design of any building so that a building is designed to resist a higher range of loads than what it is going to be exposed to in practice.

Therefore, a properly designed structure which is executed according to those designs should not collapse or show deep structural faults until its design life ends. But, many of the modern day buildings are undergoing failure on both the counts of durability and serviceability.

Stability of a building

The stability of a building is understood with respect to its ability to resist various stresses, displacement, and deflections that may lead to the collapse of the buildings.

The stability depends on various factors like, type and distribution of loads on the building; the shape, size and materials used in the building etc. A building may collapse when a local failure at one structural member leads to failure at adjacent members which will in-turn lead to failure of the whole building.

Sometimes, a shear wall may fail causing a side-sway failure. An overstressing of the sub-soil below the foundation may result in settlement of sub soil which in-turn will lead to overturning failure of the building.

Causes of building collapse

According to "Study of Recent Building Failures in the United States" report:

"The principal causes of building failures are categorized as deficiencies in design,detailing, construction, maintenance, use of materials, and inadequate consideration of external events. Deficiency in design constitutes errors, mistakes, oversight, omission, or conceptual flaw that could have taken place during the design process of the building. Detailing is a ''transition'' process between design and construction periods, in which the details of the structural design are prepared for their implementation through shop drawings. Detailing deficiency includes errors, mistakes,omissions, and discontinuity/loss of design concept. Construction deficiency occurs as problems with workmanship and deviation of results from the specifications."

The India Disaster Report 2013 points out the following causes of building collapse:

1. The structure is not strong enough to support the load and hence it fails when it reaches a critical stress level. The structure may be weak due to its shape, size, or choice of its material.
2. The instability due to geometry, design, or material choice, will cause the structure to fail from fatigue or corrosion.
3. Failure may also occur due to improper selection of materials, incorrect sizing, improper heat treating, or shoddy workmanship.
4. Failure may also occur from use of defective materials. The material may have been improperly manufactured, or may have been damaged from prior use.
5. Vandalism, sabotage, and natural disasters can overstress a structure to the point of failure. Improper training of those who use and maintain the construction can also overstress it, leading to potential failures.

Remedies against building collapse:

First and foremost remedy will be to curb illegal constructions.

The municipal corporations should also carry out a survey of the health of the various buildings to ensure the safety of its residents. Strict action should be implemented against those who subvert the law and build illegal buildings or add extra floors than permissible according to local building codes.

At a technical level, no construction should ever be started without a proper structural design by a structural engineer.

The builders must employ quality materials and good workmanship in the execution of a structure. Soil tests must be compulsorily conducted before the construction of any building. Strict supervision as well as third party assessment must be implemented to assess the quality of work at a construction site.

Prabhakar, in his 1998 paper "Building collapses and remedies" lists various remedies to be adopted. Some of them are:

1. The structural designs prepared by the engineer appointed by a builder must be cross-checked by another structural engineer appointed by the municipal corporation. The municipal corporation may hire external structural consultants for the purpose. This will prevent faulty structural designs that may result in building failure.
2. The site execution of construction work, especially with respect to RCC work must be supervised by an external licensed supervising engineer appointed by Municipal Corporation.
3. Soil investigation report of the site must be made mandatory and must be conducted by a reputed institute or a laboratory. This will reduce the risk of building collapse by foundation failure.
4. The final copies of design and drawings must be given to the owners of the building for safe keeping which will become useful when any structural repairs are to be done in future.
5. Any structural repairs work or addition of new floors must be done only after consulting structural engineers.
6. For buildings which are old and which are showing signs of deterioration, immediate health check must be carried out and proper repairs must be implemented after consulting a structural engineer.

These measures, if properly implemented by both the local authorities and the builders, will prevent incidents of building collapses and will effectively save hundreds of lives.