With the experience of Japan, Indonesia, Pakistan, North and South Region of America recently rescued operational methodology for earthquake, landslide, tsunami, floods and tidal force may be lesson learnt for disaster prone countries like Bangladesh.
In Japan, the magnitude 9.0 Tohoku earthquake that took place on March 11, 2011, resulted from thrust faulting on or near the subduction zone plate boundary between the Pacific and North American plates, which resulted in at least 15700 people killed, 4600 missing, 5300 injured, around 13900 dwellings were displaced and 332,400 buildings, 2100 roads, 56 bridges and 26 railways damaged by the devastating earthquake and tsunami along the entire east coast of the Japan peninsula. In Indonesia by tsunami with a wave height of two meters thousands of helpless people were flashed away in the catastrophe.
Every year we face several natural disasters like cyclones, tornadoes, tidal waves and floods in Bangladesh. But in recent times we have to think of another disaster which could be a very fatal for us. It is earthquake. A review of the earthquake chapter is needed to face any possible disaster in Dhaka and the country.
The extent to which buildings are damaged by an earthquake generally depends on the structural characteristics, severity of ground shaking and collateral hazards. The performance of the engineered building in an earthquake is usually linked to the building code. The engineered buildings typically performed much better than non-engineered ones when exposed to the same earthquake ground shaking hazard, all other factors such as age and quality of construction being equal.
The building code integrates the amplitude, frequency composition and duration of the ground motion input at the site, the building materials and the quality of construction. Because the life safety is the fundamental assertion on which all building codes are based, building construction in accordance with modern building code are expected not to collapse in a major earthquake, to suffer only repairable damage in moderate to large magnitude earthquakes, and to suffer only minor damage in low to moderate magnitude earthquakes.
Observation of the nature and spatial distribution of damage in past earthquakes have provided the best lessons and insights on building performance. Post earthquake studies have shown what to expect about the performance of specific building types, which can be used as a guide for improving risk assessment and risk management. Further such knowledge enabled us to reduce the loss from ground shaking, ground failure, surface fault rupture, regional tectonic deformation, tsunami wave run-up, and aftershocks.
Within minutes of shaking, the earthquake reveals the vulnerabilities of buildings, households and communities of a country. The consequences expose flaws in governance, planning, siting of physical structure, design, construction, and use of the built environment in a country with seismic hazard. The scale of physical damage and social disruption inflicted upon a community or nation by an earthquake event is the measure of how vulnerable the community or the nation is. Vulnerability is a set of prevailing or consequential conditions, which adversely affect an individual, a household or a community. Vulnerability can also be defined as the degree of loss to a given element at risk, or set of such elements, resulting from an earthquake of a given magnitude for intensity, which is usually expressed on a scale from 0 (no damage) to 10 (total loss). A range of factors, including the following, determines vulnerability:
- The population density
- Level and nature of physical assets
- The location of these assets with respects to hazardous areas
- Economic activities located in the earthquake risk zones.
- Human action and hazards continually interact to alter vulnerability, both at the household and macroeconomic level.
- Poor design and construction practice. Seismic design provisions were not mandatory in the building permit process. Lateral seismic load was not considered in the design.
- Presence of soft stories for commercial and parking purposes
- Lack of proper seismic detailing, inadequate spacing and improper bending of transverse reinforcement steel in the columns, inadequate splice and embodiment length for the longitudinal bars in the columns.
- Pounding effect due to the lack of appropriate space between buildings.
- Poor quality of materials and poor quality control.
- Addition of load without any consideration of the design (e.g., huge water tanks and in one case, even a swimming pool was added to the rooftop when the buildings were already in use).
Earthquakes affect the full range of social classes-from royalties to the homeless. Apparently, earthquake treats everyone equally. However, some are more equal than others! Actually, the poor and socially disadvantaged groups of the society are the most vulnerable to, and affected by, earthquakes and other natural hazards, reflecting their social, cultural, economic and political environment. Usually, communities in seismic countries are subject to a multitude of natural hazards and environmental problems. The natural hazards themselves are the source of transient hardship and distress, and a factor contributing to persistent poverty. Disasters exacerbate poverty by inflicting physical damage, loss of income-generating opportunities and resulting indebtedness. Thus at the household level, poverty is the single most important factor determining vulnerability to natural hazards including earthquake. The vulnerability is reflective of:
- The location of housing (poor and marginal lands).
- Poor quality building (non-engineered, using poor quality materials).
- Primary types of occupation, level of access to capital (low).
- Degree (low) of concentration of assets.
The type of housing construction is a major risk factor for injuries due to earthquakes. Statistics for 1950-1990 show that the greatest proportion of victims die in the collapse of masonry buildings (e.g., adobe, rubble, stone, rammed earth, or un-reinforced fire-brick and concrete block masonry buildings). Such buildings are known to have collapsed even at low intensities of ground shaking. Generally these buildings have heavy roofs and walls. During collapse, they kill many of the people inside. The wood frame houses and concrete-frame houses, if constructed with adequate engineering, are generally safer i.e. they are less likely to collapse. Non-engineered concrete-frame buildings are vulnerable and, when they collapse, they are considerably more lethal and kill higher percentage of people than masonry structures.
While the building code is mandatory in China and Japan, and they have developed the required institutional capacity and the municipal levels in many countries, the seismic building code is not yet a recommended practice in Bangladesh, and the municipal organisations do not have the institutional capacity for the strict implementation of the seismic code for building construction.
A nation or its government in a seismic country is vulnerable to earthquake and disaster risks unless it actively realises the inevitability of earthquakes and the threat they represent to the nation. Nations declare policies to protect people, property, and community resources and provide the legal mandate for implementing mitigation, preparedness, emergency response, and recovery and reconstruction and regulation. Countries without such policies in line with their developmental policies are vulnerable to disasters, including earthquake disaster.
Earthquakes affect everyone and everything in a community. It is not only that buildings are damaged or destroyed and infrastructure is rendered non-operational. Like every other natural hazard, earthquakes can destroy centres of economic, cultural and social activities. In such case, a devastating earthquake disturbs the economic, cultural and social aspects of communities.
The susceptibility of any community or nation to be affected by an earthquake in terms of the disruption to political, economic and cultural relationships or interdependency among the different social constituencies, and the inability to restore these interdependencies to the pre –earthquake levels can be termed the social vulnerability to earthquakes. We usually hear that the development process of a country has stopped due to the impact of one or more disasters. This is due to the vulnerability of the country to natural hazards. Years after the earthquake events, countries like Nicaragua, Turkey, and India are grappling to undo the effects of earthquake on development.
In Bangladesh, Mymensingh, Sylhet and Rangpur are located in the earthquake prone zone. Seven major earthquakes in this region were reported in the last 150 years. The epicentres of two of these were within the territory of the country. More than 90 per cent of structures in the country are non-engineered buildings which are most vulnerable to earthquakes. So, some of these vulnerable buildings need to be demolished to avert major causalities in case of an earthquake. In the old part of the city, rescuers with heavy equipment will not have access to many areas. We will be able to carry only some light equipment and conduct rescue operations if any disaster occurs.
Fire service stations, hospitals and educational institutions should immediately be made resistant to earthquakes to facilitate rescue work directly after disaster. The authorities should also ensure the implementation of the National Building Code 1993, which now awaits a parliamentary nod. A moderate tremor could severely damage many important installations, including most fire service stations and hospitals, therefore, these structures should be rejuvenated so that earthquake disaster management is not hampered. A massive public awareness campaign about post earthquake scenarios should also be launched, because most people are in the dark about how they will manage the post earthquake scenario.
In case of an earthquake, half of the causalities would occur due to building collapse and the rest because of fire and smoke. To minimize the causalities, all multistoried buildings must have prominently defined exit ways. Buildings having parking facilities on the first floors with exposed pillars are most vulnerable to earthquake. We should take measures to strengthen those pillars by constructing concrete walls taking into consideration the use of the area as a car park. RAJUK must step up monitoring and supervision of constructions.
Earthquake loads are similar to that of wind load but are much shorter and sharper. A wooden or R.C.C structure designed to stand in its inciter of relative rest under a wind load of 15-20 Ib/sq.ft is thought to have the capability of withstanding most earthquakes. But masonry does not have such resilience and under sudden shape loading entire masonry may collapse during severe shocks.
Once constructed, the buildings are to withstand great many different and sometimes many hostile stresses during their lifetime. Some of them are imposed by the nature such as the load of wind, rainfall, tidal waves, earthquakes etc. Geo-physical data are much more useful and informative from an architect’s point of view. One must also be aware of the extremes of weather in the region. Further, these extremes are useful only if they occur at regular and frequent intervals. Therefore, a logical approach to the design and construction of structures should take into account these hostile forces for creating a safe and lasting architecture.
Bangladesh National Building Code (BNBC) must be followed to avoid much destruction, damage and loss.