Abstract:
Bangladesh is one of the earthquake prone countries. Major cities like Dhaka, Chittagong, Sylhet, Mymenshing and Rangpur are at the top of vulnerability list. As capital city Dhaka is the pivotal point to draw due attention. Many of the key point installations and critical structures are vulnerable to earthquake. Building structures are the major element of vulnerability due to an earthquake shake. Buildings already constructed but not considered earthquake force in the design and/or not maintaining quality construction are vulnerable. After seismic assessment, buildings may be categorized as high, moderate and low vulnerable. Also it may be classified as key point installation, critical and important structure. To take care of the vulnerable buildings retrofitting and reconstruction are the means and ways. The issue of demolition and reconstruction comes only if the retrofitting of the building is not cost effective.
Seismic retrofitting in building sector is a new concept in Bangladesh. A lot of works have to be done in retrofitting areas. Building retrofitting is quite different from normal construction work. It is quite different in design and execution because an existing building is concern here. In this area of construction Bangladesh is yet to develop capacity. An existing building has to be seismically assessed first, then retrofit design has to be done and finally actual retrofit has to be completed while the building is functioning its normal purpose. The technical personnel in these entire three fields are lacking. In recent time after implementation of BNBC 1993, PWD has realized the necessity of the capacity development of the area.
But this sector is in badly needed of retrofitting. Most of the KPIs, schools, hospitals, fire stations are not safe from earthquake and they require retrofitting. Most vulnerable buildings are those with load bearing walls, age old lime surki mortar masonry, and foundation on soft and filled up soil.
Initiative so far has been taken for retrofitting as follows:
- MoFDM initiative is to assess and design of retrofitting of Dhaka Medical College hospital and two secretariat building with an amount of Tk. 1,40,00,000/- supported by CDMP still in the inception level.
- Following seismic assessment and design it needs to implement the retrofitting task.
- Considering 15% retrofitting cost, the total amount will be more or less Tk. 30 crore (300 million) which will have to borne by the GoB or by outsourcing.
- Preparation and submission of the project is possible only after initial task of assessment and design followed by estimate.
Government initiatives:
- Incorporation of earthquake issue into revised SOD
- Formation of Earthquake Preparedness and Awareness Committee headed by the Honorable Minister in charge of ‘Ministry of Food and Disaster Management’ and duly approved by the Prime Minister.
- Incorporation of national earthquake expert in the National Disaster Management Advisory Committee
- Inventory of all the building structures and also vulnerability atlas showing all vulnerable buildings including life lines.
- Retrofitting Assessment and Design project for Dhaka Medical College Hospital and two administrative building of Bangladesh Secretariat
- Signing of MoU for capacity building and technology transfer project between PWD and JICA (Annex-B)
Definition:
Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. With better understanding of seismic demand on structures and with our recent experiences with large earthquakes, the need of seismic retrofitting is well acknowledged. Prior to the introduction of modern seismic codes (BNBC) in the early 1990s for Bangladesh, most of the structures were designed without adequate detailing and reinforcement for seismic protection. Moreover, state-of-the-art technical guidelines for seismic assessment, retrofit and rehabilitation have been published around the world.
The retrofit techniques are also applicable for other natural hazards such as tropical cyclones and tornadoes. It is important to note here that to reduce the hazards and losses management of non-structural elements is equally important. It is also important to keep in mind that there is no such thing as an earthquake-proof structure.
Different level of retrofitting: Level and extent of retrofitting will be different for different structures depending on the importance factor and retrofitting cost will be different. Example may be cited here that level of hospital, school and residential building will not be the same.
Types of buildings: Retrofitting cost and time will be largely dependent upon the types such as reinforced concrete structure, load bearing masonry structures etc. Types of Dhaka city buildings are as follows:
Non-engineered building
a)unreinforced masonry building with –
- i) cement sand mortar
- ii) lime surki mortar
iii) mud mortar
- b) reinforced cement concrete building not considering seismic force into its design and construction
Engineered buildings
Reinforced cement concrete building considering seismic force into design of foundation, structure and construction.
Causes of vulnerability:
Not designed considering the earthquake induced force and/or because of not ensuring quality of construction and materials.
If a building is designed and constructed for vertical load only but not for earthquake load the cost for retrofitting will be as minimum as 3% – 5% of the finished building cost. But if the building is not properly design and under-reinforced or un-reinforced then that building may cost as high as 30%. Again retrofitting cost may be upto 50% – 60% if the building is of lime or mud mortar. Usually buildings need retrofitting cost more than 60% or 70% is not feasible for retrofitting rather demolishing the same.
Cost analysis/cost effectiveness:
Retrofitting is one of the important element of earthquake risk reduction matrix (Annex-A) which will be an integral part of the Earthquake Risk Reduction Plan. Since Bangladesh do not have any such plan no well defined organization is responsible or mandated for retrofitting of the govt. buildings and no regulatory authority is there to ensure the retrofitting of the private buildings. Rajuk at present not even capable of ensuring the set-back space and of building height.
UKAid (DFID) bldg:
Only building in Bangladesh so far we know where seismic retrofitting has been done. But to maintain very high degree of safety and for not incorporating locally available construction techniques and materials, cost of retrofitting were as high as 100%.
Tauquir’s house:
Retrofitting has been done for one five storied residential building at Mohakhali DOHS using local technology of reinforced concrete walls and column jacketing to make the building free from torsion due to earthquake load. I believe that with an earthquake shake of intensity VII, no live loss will occur. The cost was only 2.5% of the present building cost.
Rajuk or City Corporation has no plan for retrofitting program but inventory of risky building in Dhaka city.
PWD is implementing a technology transfer project with the assistance of JICA and as a field demonstration, real retrofitting of few critical public building structures at Dhaka, Chittagong and Sylhet would be done.
US Embassy bldg.:
US embassy here in Bangladesh has a plan to go for retrofitting of more or less 80 building in baridhara and gulshan area where the embassy people are residing.
Bangladesh has its experience of mentionable high-quality building repair work. Though these repaired buildings are not fully earthquake resistance but undoubtedly these buildings got some more resistance capacity to earthquake force and we can utilize the experience and technologies used, for our future retrofitting program. These are Rokeya Hall of Dhaka University, British council office building and Directorate of Food bldg.
Priority should be fixed for retrofitting of the building:
PM house and office/cabinet/kpi/cr/school/hospitals
Conclusion:
Seismic retrofitting of building structure including foundation is a new concept in Bangladesh. It will take time to achieve mentionable success in this field. Though MoFDM and PWD took initiative in this regard, it is not more than a drop of water in the sea. A well-organized initiative is a must for mentionable achievement. National Earthquake Risk Reduction Plan can play a pivotal role in this respect and that plan should include a risk reduction matrix (Annex-A) showing every details of activity, output, outcome and implementing agency with time period for implementing the activities. It is to be mentioned here that earthquake issues have been incorporated in the revised SOD and Disaster Management Bureau is the mandated organization to prepare and implement National Earthquake Risk Reduction Plan as overall coordination of earthquake as well as other disaster management issues.
