How can home owners ensure earthquake-resistant homes?

[ecis2016.org] We examine the seismic zones in India and building construction rules that home owners can use, to assess whether their homes are earthquake-resistant

In the recent past, earthquakes have been felt in parts of Rajkot, Gujarat and even in the Delhi National Capital Region (NCR) but not limited to these. Earthquakes of a higher magnitude, can cause massive destruction of property and life, which is why the structural safety of buildings and the need for the best seismographs, becomes crucial. In 2016, according to a report titled ‘Earthquake Hazard Zoning Maps’, by the Building Materials Technology Promotion Council (BMTPC), as many as 95% households in the country are vulnerable to earthquakes. The BMPTC is a government-sponsored body, for promoting appropriate building technology.

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India’s seismic zones

About 59% of land area in India is prone to damage due to earthquakes. This land is classified into four zones.

Zone V

Parts of the Himalayan boundary in the north and north-east India, the Kutch region in west India, parts of Jammu and Kashmir, Himachal Pradesh, north Bihar, Andaman and Nicobar Islands and Uttaranchal, are in Zone V, which is the most active region, seismically. This zone is prone to heavy destruction due to earthquakes.

Zone IV

Parts of Jammu and Kashmir, Himachal Pradesh, National Capital Territory of Delhi, Sikkim, northern parts of Uttar Pradesh, West Bengal, Bihar, some parts of Maharashtra (near the west coast), Gujarat and Rajasthan, fall in Zone IV. Zone IV is less active than Zone V but the toll of destruction can still be high.

Zone III

Comparatively safer than Zone IV and V, Zone III comprises the remaining parts of Uttar Pradesh, West Bengal, Rajasthan, Bihar, Jharkhand, Chhattisgarh and Maharashtra that are not in the above two zones. This also includes Madhya Pradesh, Odisha, Andhra Pradesh, Tamil Nadu, Kerala, Goa, Lakshadweep and Karnataka.

Zone II

This is the safest or technically the least active region and covers parts of India that do not lie in any of the aforementioned zones.

Source: National Institute of Disaster Management (NIDM)

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How to ensure that you have an earthquake-resistant home?

The Bureau of Indian Standards and building codes have guidelines to construct structurally safe buildings and earthquake-resistant homes. The following figure encapsulates the internal elements, required for an earthquake-resistant structure.

Source: NIDM 

How to self-assess the safety of residential brick buildings in Delhi?

The NCT of Delhi is in Zone IV, making it one of the earthquake-prone and damage-prone areas. In areas such as this, a maximum earthquake intensity of VIII on the MSK Intensity Scale is likely. This may result in damage to kutcha structures and masonry buildings. Buildings that are constructed with good quality cement mortar may develop cracks, while buildings constructed in sandy soil on a high water table, face the risk of greater damage, says the National Institute of Disaster Management.

Here is how you can self-assess the risk of damage for your residential building:

Number of storeys

A one or two-storeyed building, using one brick (nine inches) thick walls, will be relatively safer than a three-storeyed building. The fourth storey, if added, will be very unsafe and will make living in the lower storeys riskier.

Thickness of the load carrying walls in each storey

If the property uses half-bricks, of 4½-inch-thick load bearing walls, this can make the structure unsafe and if it is used in higher storeys, it could even turn catastrophic. Too many openings in a wall for windows also result in weakening the walls. The use of small piers in between openings that is less than 45 cms, will also increase the risk of destruction. The ideal combined width of the openings should be as follows:

Mortar used for construction

The stronger the mortar, the safer the building will be. The use of mortar specified for safety is 1:6 cement-sand mortar, that is, one part cement with six parts of sand. Lime-surkhi or lime-cinder mortar is much weaker, says the NIDM.

Horizontal seismic bands

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Source: NIDM

Seismic safety elements are important and include the horizontal bands that are provided at the plinth level and lintel level of doors, windows and external and internal walls. These strengthen the walls against earthquake destruction and provide an earthquake-resistant home.

Vertical reinforcing bars

At every corner and T-junction of the room, vertical reinforcing bars should be provided, right from the foundation to all the storeys and to the top roof slab.

FAQs on structural safety of buildings

What is retrofitting?

Retrofitting refers to the strengthening of the building, to avoid damage due to earthquakes. Retrofitting may be required in some buildings, because the old building bye laws may be outdated. One should hire a licensed structural engineer to study the property, before retrofitting.

What is a structural safety certificate?

This certificate confirms that the structure’s construction plan satisfies the safety requirements, vis-à-vis an earthquake or a cyclone. Usually, the civic administration issues the structural safety certificate, after a thorough inspection. The certificate is proof of the fact that the structure is fit for use and the same has been determined, after adequate verification and soil testing. In 2011, the Delhi government made the structural safety certificate mandatory for property registration.

What is on-site EWS?

On-site early earthquake warning and security system (On-site EWS) senses the primary waves of an earthquake and triggers an alarm. It can even be programmed to halt certain ongoing activity, such as elevator parking, shutting power, water and gas lines or even entry and exit gates. This can be useful for residential and commercial projects.

What to do during an earthquake?

It is always good to have an emergency plan and you should discuss this with all responsible members of your family/ building. The National Disaster Management Division has given the following plan to be followed during an earthquake:

• Turn off utilities, such as gas and the electricity fuse box.
• If you are near an exit, hold your arms to cover your head and rush out.
• If you are stuck in a staircase or a high-rise building, just ‘Drop-cover-hold’ or sit and lie down under a sturdy piece of furniture and cover as much of your upper body as possible.
• Do not use the elevators.
• If you are on the road, occupy a free space, away from structures, bridges, metro stations and power lines.
• If you are driving, you should stop and move away to a safe zone.
• Stay calm but prepare yourself in advance, in case of aftershocks.

List of Indian cities in various seismic zones

FAQs

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