The increased frequency of earthquakes around the world has brought home the urgency of a planned program for ensuring safety in design and instruction of new buildings and comprehensive need for retrofitting the existing building against collapse during disasters such as earth quakes, cyclones or flooding.
1. At the time of building construction, there may not have been idcquate concern regarding disasters such as earthquakes and hence the building might have been executed without fulfilling the requirements if safety measures.
2. In the case of old buildings, deterioration of the material with age their changesin the occupancycategory may place the building in a vulnerable category introducing significant structural deficiency.
During an earthquake the ground and the structure shakes violently. This back-and-forth motion can cause a building to fall off its foundation, resulting in major damage to the structure and sometimes even total collapse. Seismic retrofit is not rocket science, and the basic principles are easily understood. One can quickly learn all that is needed to make informed decisions regarding the retrofitting of one’s own home. Retrofitting focuses on strengthening the house-to- foundation connections using specially designed hardware and engineered construction methods. Retrofitting allows a house to withstand much greater earthquake forces with much less structural damage.
Since disasters and the forces generated by them are unpredictable, retrofitting cannot guarantee that a house will receive no damage at all. However, it has been proven that retrofitting greatly reduces the amount of damage a house receives and is highly effective in preventing catastrophic collapse and loss of life. While retrofitting the building is provided with additional strength, stiffness and ductility to ensure acceptable performance during future disasters. Modem building codes have been written so that newer homes usually don’t need to be seismically reinforced if they are properly constructed. However, builders sometimes do not understand provisions of the code that are specific to detailing reinforcement and neglect to follow these aspects of the building code. A proper evaluation will reveal if a building needs retrofit, regardless of whether it is new or old. Walls and columns are the most critical elements duringdisasters. Thousands of structures in metropolitan areas in India need assessment and retrofitting if loss of life is to be minimized during disasters. The concepts of assessment and retrofitting are well known and will enable both life safety and reduction in loss of property damage. The cost of retrofitting will not be prohibitive, because only existing weaknesses in building that are identified during building that are identified during evaluation are rectified during retrofitting.
Architects do not design retro- fits; this is something done by j structural or civil engineers. As in other fields, engineers tend to special ize, so if you choose to work with an engineer, be sure he is one with special training in retrofit design. Contractors, I who have had special training in retrofit engineering principles, can take up installation. Seismic retrofit technology is continually evolving, and a retrofit contractor needs to understand and follow the most current seismic retrofit standards. It is also important that he teams up with a structural engineer. A retrofit generally costs between 5 percent and 10 per cent of a home’s value. For many home owners the one-time cost of a retrofit equals a few years of earthquake insurance. And insurance won’t prevent or reduce damage to your home, but retrofitting will.
for more info:http://www.bangalore5.com