whar are the specifications of an earthquaqe-proof building ?
Answers
overlooked because there is no allocated design fee through a lack of coordination between the
structural and building services engineers. There is therefore no formal responsibility taken for the
design of the restraints and the building services contractor is often left to install “what looks
right”, if anything at all. Audits on five buildings showed that there had usually been an effort
made to provide restraint for building services, but there were often overlooked components in the
load path whose failure could still cause the whole system to fail. Laboratory shake table
investigations on a selection of building services confirmed that input accelerations from the main
structure would be amplified at the building services component and that it would not be sufficient
to assume that the restraints could always be designed for a maximum acceleration of 1g. An
introduction is given to a design guide produced by BRANZ, which provides input accelerations,
determined from the complicated provisions of NZS 4203:1992, that may be used by engineers
wishing to design a seismic restraint system from first principles. For building services
contractors, not wishing to master the provisions of the design standard but still needing to provide
an acceptable solution to the New Zealand Building Code, there is a selection of acceptable design
solutions for various building services items.
The seismic forces generated by earthquakes increase with the mass and the height of the building. Therefore, it is desirable to adopt light-weight materials and low-rise structures in highly earthquake-prone regions, unless they are properly designed, detailed and constructed, based on the prevailing standards.
Most of the construction in India are ‘non-engineered’ and built in masonry. Often, the connections between the roof and the walls, and between cross-walls, are weak, rendering such buildings vulnerable to collapse.
There are recommendations available in our national codes on providing seismic-resistant features in such buildings — such as providing small reinforced concrete bands in the walls at the plinth, lintel (above the windows and doors) and roof levels, and various other measures to ‘tie’ the components of the building together. These measures ensure that integrity is preserved during ground shaking. The concrete bands should be horizontally continuous throughout the walls to help in tying the components of the building together. It is also important to ensure that the materials used (such as brick and mortar) as well as construction practices, should be of good quality.
Retrofitting old buildings that do not have such concrete bands is also possible. Ferrocement bands and embedded metal strips that run across the walls (horizontally and vertically) can preserve the integrity of the buildings to a large extent.
In the case of modern buildings, which are ‘framed’ (comprising a skeleton of columns and beams, typically made of reinforced concrete) or having shear walls, it is possible to ensure safety against collapse through proper structural design and detailing, to achieve the desired strength and ductility. There should be adequate number of frames in the two perpendicular directions in plan. The frames should be more-or-less symmetrically distributed to minimise twisting of the building.
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