Earthquake design criteria for structures

Abstract

The earthquake resistant design of structures plays an important role in seismic regions both from the point of view of public safety and from the point of view of economical construction. Since construction is at a rate of approximately $15 billion per year in the seismic regions of the United States, unnecessary expenditures on earthquake protection could be very costly but, on the other hand, very costly damage could result if a city has inadequate earthquake protection and is shaken by a strong earthquake. The loss of life in an inadequately protected city could be very large, as evidenced by the reported 700,000 casualties inflicted by the Tang-Shan, China earthquake of 28 July 1976. The engineering profession has the technical responsibility for the safe and economical protection against earthquakes. The prime consideration in achieving this protection is the formulation of proper earthquake design criteria. Because the time and place of occurrence of future earthquakes cannot be foretold, the earthquake forces to which a structure will be subjected during its lifetime can not be specified at the time it is being designed and, therefore, consideration mast be given to the desired performance of the structure if it should be subjected to weak earthquakes which have a relatively high probability of occurrence, or to very strong earthquakes which have relatively low probability of occurrence. The earthquake design criteria must then be formulated so that the building is, indeed, capable of the desired performance, and this formulation should be the responsibility of the project engineer.