New method to assess seismic vulnerabilities of buildings

Researchers at the Indian Institute of Technology Mandi have developed a method to assess the ability of buildings in the Himalayan region to withstand earthquakes.

The method is simple and allows decision-makers to prioritize strengthening and repair work that must be undertaken for enhancing building’s resistance to earthquakes.

Rapid Visual Screening (RVS) of buildings is often performed to assess building vulnerabilities at a large scale. RVS uses visual information to decide if a building is safe to occupy or requires immediate engineering work to enhance earthquake safety.

Through extensive field surveys, researchers have collected a large amount of data on the types of buildings present in the Mandi region of the Himalayas and the typical attributes of these buildings connected to their earthquake vulnerability.

A numerical study was also carried out to establish guidelines for counting the number of stories in hilly buildings for their RVS. Further, based on the vulnerable characteristics present in buildings, an improved RVS method was proposed.

The methodology developed for screening buildings is a simple single-page RVS form that does not require much expertise to fill. It considers the various vulnerability attributes unique to the buildings in the case study region.

Calculations made using these observations produce a seismic vulnerability score for buildings differentiating vulnerable buildings from the more robust ones, and allowing better decision-making for maintenance and repair. The computation process is designed to minimizes the possibility of human bias or subjectivity of the assessor in scoring a building.

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This study, led by Dr. Sandip Kumar Saha, Assistant Professor, School of Civil and Environmental Engineering, IIT Mandi and co-authored by his Ph.D. student Yati Aggarwal; has been published in the Bulletin of Earthquake Engineering journal.

Existing RVS methods are based on data from different countries. They are not particularly applicable to the Indian Himalayan region because of some unique characteristics of the buildings in this region. For example, the Himalayan region (as with much of India) has many non-engineered structures.

There is also chaotic distribution and growth of infrastructure due to a lack of awareness among the local construction workers and poor planning by the stakeholders. It is, therefore, essential to use a region-specific RVS guideline that considers factors like local construction practices, typology, etc.

Explaining the research, Dr. Sandip Kumar Saha, said, “We have devised an effective method to screen reinforced concrete (RC) buildings in the Indian Himalayan region so that repair work may be prioritized according to the condition of the buildings and the risk from impending earthquakes can be minimized.”

“We have shown that the proposed method is useful for segregating reinforced concrete buildings in hilly regions according to the damage that they are expected to experience in the event of an earthquake,” said Yati Aggarwal, PhD Scholar, IIT Mandi.

The Himalayas are among the world’s most earthquake-prone regions because of an ongoing collision between the Indian and the Eurasian plates. There have been periodic and devastating earthquakes in these regions leading to the loss of life and property. The Great Kashmir Earthquake of 2005 killed over 1,350 on the Indian side of Kashmir, injured at least 1,00,000 people, ruined tens of thousands of houses and buildings, and rendered millions of people homeless.

The assessment of buildings in the Himalayan region is an urgent need because of region’s earthquake vulnerability. The “seismic gap” of the past two centuries makes a big earthquake quite likely. A seismic gap (the absence of a large earthquake) is believed to represent the time taken to accumulate stress, which is then released in a large earthquake.

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“It is time that human habitats in these areas are bolstered so that they can withstand any mild or severe earthquakes that may occur in the future,” researchers cautioned.