Seismic codes have been drawn up covering all risks in design but findings suggest that the constructions have not kept pace with standards. A look by R RAMABHADRAN PILLAI
Earthquakes strike without warning. All scientific advances are naught when it comes to predicting earthquakes.
This unpredictability bestows a lot of responsibility on governments, planners, and builders to ensure that human settlements comply with safety codes and guidelines to prevent or at least minimise damage .
Post-quake studies confirm that damage arises mostly from collapse of buildings. Various countries have developed seismic codes to provide guidelines for construction in earthquake-prone areas. The codes are formulated on the basis of factors such as seismic risk, geographical peculiarities, and construction material and methods.
The Bureau of Indian Standards has brought out a few seismic codes, such as the Indian Standard Criteria for Earthquake Resistant Design of Structures, the Indian Standard Code of Practice for Earthquake Resistant Design and Construction of Buildings, the Indian Standard Guidelines for Improving Earthquake Resistance of Earthen Buildings, the Indian Standard Guidelines for Improving Earthquake Resistance of Low-Strength Masonry Buildings, and the Indian Standard Code of Practice for Ductile Detailing of Reinforced Concrete Structures.
The codes have been developed from the findings made in regions hit by earthquakes. Quakes that have inflicted damage to life and property, including those in the Himalayan region, the Andaman and Nicobar islands, Koyna, Latur, Bhuj, Jabalpur, Chamoli, and Muzaffarabad, have been analysed for preparing guidelines to build safer habitats.
B.R. Ajit, architect and head of the Indian Green Building Council Kochi chapter, says many modern buildings are being constructed with reinforcements to strengthen the structure. “The corners of buildings should not be left bare and vulnerable spaces should be strengthened. Multi-storey buildings, supported on pillars, with open car parking on the ground floor, are more vulnerable to hazards arising out of quakes in comparison to those having closed spaces,” he says.
In Japan, where earthquakes are frequent, disconnected foundations, a system which makes use of material resembling bearings, are effectively being used to counter the impact of quakes. In India, such systems are yet to be introduced, he says.
In a paper brought out on seismic activity, the Building Materials and Technology Promotion Council, New Delhi, a government-sponsored body for promoting appropriate technology for building and development, points out that existence of non-engineered buildings has been one of the major causes of collapse of buildings in most of the affected regions. The study observes that poor quality of construction materials was an important cause of failure of reinforced concrete structures in Ahmedabad, which is about 300 km from the source of the Bhuj earthquake.
The Indian Standard Codes for Earthquake Resistant Design and Construction advocates the use of proper quality of building materials in the stipulated way. The codes should be followed in the construction of buildings so as to ward off the effects of tremors. Strong constructions can withstand the possibility of collapse, though some damage may occur. To achieve this objective, the structure, particularly their main elements, should be built with ductility. Four virtues
An earthquake-resistant building has four virtues in it — good structural configuration, lateral strength, adequate stiffness, and good ductility, says a study conducted by the Indian Institute of Technology, Kanpur.
Good structural configuration implies that the building's size, shape and structural system carrying loads are such that they ensure a direct and smooth flow of inertia forces to the ground. Good lateral strength will ensure that the maximum horizontal force that it can resist is sufficient to withstand a collapse. Adequate stiffness indicates the state of the lateral load resisting system which ensures that the quake-induced deformations in it do not damage the contents under low-to-moderate shaking. Good ductility indicates its capacity to undergo large deformations under severe earthquake , which can be improved by favourable design and detailing strategies.
Seismic codes cover all these aspects. The Department of Earthquake Engineering, Indian Institute of Technology, Roorkee, in a field survey conducted earlier in the National Capital Region on earthquake-resistant design and construction practices prevailing in India, presented a picture of deficiencies in respect of seismic performance. A majority of the buildings were incapable of withstanding the ground shaking hazard expected in the area as per the Indian seismic design code, indicating a very poor enforcement of the code.
An investigation of the construction practices prevailing in the area also revealed that ductile detailing practices as per the Indian code of practice are not being followed.
The Bureau of Indian Standards has grouped the country into four seismic zones — zones II, III, IV and V. Of these, Zone V is the most seismically active region, while zone II is the least.
The Modified Mercalli (MM) intensity scale measures the impact of the earthquakes on the surface of the earth. Accordingly, Zone II is a low-intensity zone, while Zone III is moderate-intensity zone and Zone IV is severe-intensity zone. Zone V is very severe intensity zone.
Broadly, Zone V comprises entire north-eastern India, parts of Jammu and Kashmir, Himachal Pradesh, Uttaranchal, Rann of Kutch in Gujarat, part of North Bihar, and Andaman and Nicobar Islands. Zone IV covers the remaining parts of Jammu and Kashmir and Himachal Pradesh, Delhi, Sikkim, northern parts of Uttar Pradesh, Bihar, and West Bengal, parts of Gujarat and small portions of Maharashtra near the west coast, and Rajasthan.
Zone III comprises Kerala, Goa, the Lakshadweep islands, remaining parts of Uttar Pradesh, Gujarat and West Bengal, parts of Punjab, Rajasthan, Madhya Pradesh, Bihar, Jharkhand, Chhattisgarh, Maharashtra, Orissa, Andhra Pradesh, Tamil Nadu, and Karnataka. Zone II covers the remaining parts of the country.