Constructionshows
Geologists put Bangladesh in moderate earthquake prone zone. Each year this country experiences thousands of mild to moderate earthquake. Thanks to heaven that the latest severe earthquake happened about a century ago. The great Bengali-Assam earthquake, struck in 1897, almost vanquished the entire Bengal and Assam region. Scientists have alerted people of probability of new earthquake within a few years.
Bangladesh has her own building codes which is in combined regarded as ‘Bangladesh National Building Codes (BNCC)’. It was first published in 1993. The building code has been periodically updated since then. Before that engineers and architects used to follow British Standard and American codes with some arbitrary local design factors.
Chapter 6 of BNBC discusses about the loadings on the structures. The guideline for calculating earthquake loading has been included in this chapter. According to the BNBC, entire Bangladesh is divided into three zones (zone 1, 2, 3) where northeast part is most vulnerable and southwest part is the least. Middle portion of the country is considered at medium risk. The zonal coefficients of these zones are respectively 0.075, 0.15 and 0.25. The capital of the country, Dhaka, is located in the middle portion.
Figure: Seismic zonal map of Bangladesh (BNBC 2006)
There are two methods specified in BNBC to calculate seismic loadings. Engineers are free to choose any of these methods. Buildings are classified from (I) to (V) based on the structural importance category. Foundation soil types and structural frame response have also been classified to calculate the seismic. The earthquake load is placed in load combinations with different factors. There are 12 load combinations for reinforced concrete buildings. Among them, 5 load combinations include Seismic load. For steel structures it’s 2 out of 5.
Many old Bangladeshi buildings are not constructed as per BNBC standard. But things are changing rapidly. New buildings are designed by following the BNBC rules strictly. This practice put Bangladeshi buildings in the positive side of safety.
