Beyond demolition of vulnerable buildings

The deployment of eight teams by the Rajdhani Unnayan Kartipakkha (RAJUK) following the Friday's powerful quake and three more tremors the next day to assess the vulnerabilities of buildings in Dhaka is a welcome move. It has identified 300 buildings out of 3,252 already assessed at quake risks. The number will be staggering when the city's 2.145 million buildings are assessed. In 2019 also, a survey conducted by the RAJUK under a World Bank-supported project found that over 40 per cent of buildings in the capital and Gazipur were vulnerable to earthquake. At that time 42 buildings were found to be highly risky and were marked for immediate demolition but no action followed the suggestion. In the face of lurking danger, the authorities become highly active but with time, they tend to be oblivious of the follow-up action. Will the current tempo sustain?

After the Friday's biggest jolt in decades, not only quake experts but even ordinary mortals, panicky as they are, feel that a monumental tragedy to be enacted in this chaotically built city is not far away. Reports have it that some people have started shifting to areas in surrounding areas with no high-rise buildings but having large spaces. Anyway, not many people have such options and this cannot be a solution to the problem facing the city of concrete jungle. That the old and vulnerable buildings have to be demolished is indisputable. The authorities must act decisively to save lives before the calamity strikes.

The next option is highly costly. In case of new structures, though, modern technologies can help avoid damage to and destruction of multi-storey buildings on account of powerful quakes. So, the RAJUK must make it mandatory to accommodate one of the proven technologies so far used successfully in Japan or other countries. But for traditional buildings, the use of such technologies is highly costly. Seismic isolation, a technology used in Japan, uses from the base rubber bearings or ball bearings to isolate buildings from the ground. The ground can move independently allowing buildings to remain protected from shocks. Another device is damper or shock absorbers. Large shock absorbers are installed within a building's structure, which absorb seismic energy to convert it into heat. Hydraulic fluid-filled cylinders with pistons and large pendulums at the top of a building counteract its sway at the time of a quake. Then there are the buckling restrained braces (BRBs) which are engineered to yield and deform without buckling and absorb energy, preventing damage to the main structure.

There are other technologies to prevent buildings from collapsing. But these are the most advanced and successful ones. A few multi-storey buildings in Dhaka have used such technologies but retro-fitting of such technologies is highly challenging and costly. Yet there are some people here who can afford the expenses of adding the seismic isolation or BRB technology to their buildings in order to make those resilient to quakes. Yet this city will remain highly vulnerable to powerful quakes measuring 7.0 or higher on the Richter Scale. The Friday's earthquake has laid bare the insufficiency in preparedness for calamities of outsize order. The fire service and civil defence's capability should be enhanced many times more so that it can respond effectively in case of a disastrous quake.