Navigation

Vashi2Panvel.com: Navi Mumbai: October 15: “Earthquakes don’t kill. Collapsed buildings do. Non-essential buildings rule, ill-informed home-makers, callous builders and poorly trained construction workers worsen an earthquake’s impact,” said Pushpendra Singh, ED-Disaster Management Institute, Bhopal in an editorial in Hindustan Times post the recent earthquakes that flattened Pakistan and parts of Kashmir. But one would promptly ask, ‘what are these buildings norm?’ and ‘why builders do not adhere to it?’

“Earthquake Engineering Sectional Committee, CED 39 has standardized the design and construction of earthquake resistant structures. Not only that it is also concerned with its measurements and tests. But nobody follows these measures hence the susceptibility of damage during earthquake here is quite high,” says PB Menon, Chairman-Society of Ecological and Environmental Protection.

“This Bureau of Indian Standard (BIS) deals with assessment of seismic loads on various structures and earthquake resistant design of buildings. Its basic provisions are applicable to buildings, elevated structures, industrial and stack like structures, bridges, concrete masonry and earth dams, embankments and retaining walls and other structures.”

“It also contains provisions that are general in nature and applicable to all structures. Besides, it contains provisions that are specific to buildings only. It covers general principles and design criteria, load combinations, design spectrum, main attributes of buildings, dynamic analysis, apart from seismic zoning map and seismic coefficients of important towns, map showing epicenters, map showing tectonic features and lithological map of India,” he adds further.

One of the most modern standards, BIS, also provides guidance in selection of materials, special features of design and construction for earthquake resistant buildings including masonry construction, timber construction, prefabricated construction etc. But builders hardly adhere to it. The Disaster Management Bill has been postponed thrice in the parliament sessions and unless it gets through successfully, the guidelines would not be made mandatory.

So, what are the essentials that a builder must observe while construction?
The standard clearly states the pre-requisites as lightness, continuity of Construction, avoiding/reinforcing projecting and suspended parts, building configuration, strength in various directions, stable foundations, ductility of structure, connection to non-structural parts and fire safety of structures. Special construction features like separation of adjoining structures, crumple section, Foundation design, roofs and floors and staircases have been elaborated in the standard. It also covers the details pertaining to the type of construction, masonry construction with rectangular masonry units, masonry bearing walls, openings in bearing walls, seismic strengthening arrangements, framing of thin load bearing walls, reinforcing details for hollow block masonry, flooring/roofing with precast components and timber construction.

The standard states that earthen buildings should preferably be avoided in flood prone, high rainfall areas and seismic zones IV and V. It recommends light and single-storeyed buildings. Cement-sand mortar should not be leaner than 1:6 in masonry. If this requirement is fulfilled, no separate provisions for Zone I and II are required.

Important aspects of the standard

a) The revised seismic zone map has only four zones, instead of five.
b) According to the revision, first the builders must calculate the actual force that may be experienced by the structure during the probable maximum earthquake. Then the concept of response reduction due to ductile deformation or frictional energy dissipation in the cracks is brought into the code explicitly by introducing the `response reduction factor' in place of the earlier performance factor.
c) The values of seismic zone factors have been changed; these now
reflect more realistic values of effective peak ground acceleration considering Maximum Considered Earthquake (MCE) and service life of structure in each seismic zone.
d) A clause has been introduced to restrict the use of foundations
vulnerable to differential settlements in severe seismic zones.

FACT FILE:
· The syllabi of relevant engineering courses have been revised to include structural design and engineering. A national level exercise is underway to retro-train civil engineers.
· Traditional structures in many regions of our country are strongly earth-quake resistant. The bungas of Bhuj and the bamboo tarza of Assam are apt examples.
· A magnitude of 6.5 richter scale earthquake in Bam, Iran, in December 2003 killed over 30,000 while a magnitude of 7.1 earthquake in Hokkaido, Japan caused only 12 injuries. The main reason being their seismically engineered buildings.


Swati Pandey