9 to 14-storey buildings most vulnerable

The nine to fourteen storeyed buildings standing on the lowland area in the capital are the most vulnerable to earthquake while the one to five storeyed buildings are relatively safe here, a research work revealed yesterday.

A building collapses when the vibration frequencies of the building and the ground become the same during an earthquake and the possibility of the high rise buildings to collapse is high in Dhaka, said Dr Maksud Kamal, teacher of geology department at Dhaka University, while presenting his findings at a seminar.

Dr Maksud presented the findings of his research yesterday at the seminar organised by Shahosro Gabeshona Kendra, an organisation to encourage research works, at the Curzon Hall auditorium of Dhaka University. Dr Muhammad Zafar Iqbal, convenor of the organisation, chaired the programme.

Maksud worked on 305 square kilometres (sq km) area in the capital and examined the vibration frequencies of the buildings and grounds at micro level. From the study he identified 100 sq km as the most risky zone for the nine to fourteen storeyed buildings during an earthquake.

"All types of earthquake are not destructive for all buildings," he said citing the example of the 1985 tremor in Mexico. "During that tremor only 18-22 storeyed buildings collapsed," he said adding, "while the Taiwan tremor in 1999 destroyed the low rise buildings only."

The vibration frequency of the ground depends on the characteristics of the soil and the soil of Dhaka city, which is mostly filled up to six metres, is not suitable for nine to fourteen storeyed buildings, he noted in his paper.

The ground of Dhaka represents 17 different soil types and each soil type exhibits its own characteristics in responding to earthquake ground motion, it said.

Citing the 1958 aerial survey, Dr Maksud said 65 percent land of Dhaka city was lowland and the city has been growing up on that soft soil. Pointing to this fact, he requested the authorities to make a detail mapping of the safe heights for buildings in different parts of the city.

To reduce the earthquake vulnerability he recommended developing an appropriate landuse regulation for urban earthquake risk management and updating and implementing the building code.

Muhammad Zafar Iqbal urged the government to arrange detailed research in this sector to reduce earthquake vulnerability as the capital is situated in an earthquake prone area.

"If an earthquake occurs here, we will be most affected as we do not have minimum preparation," he said.

Prof Hossain Monsur, chairman of geology department of DU, and Dr Shamsul Alam of Chittagong University of Engineering and Technology also spoke at the function. Abu Naser Khan, secretary general of Poribesh Bachao Andolon, conducted the seminar.