دانلود کتاب حرکات زمینی خاص سایت برای طراحی لرزه ای ساختمان ها و سایر سازه ها

During an earthquake, the ground shakes in all directions. Inertia of structures prevents them from moving in unison with the ground. Structures deform and develop stresses. Design engineers need ground motions that could occur during the life of structures. ASCE 7 (2017a) prescribes seismic design ground motions for all structures in the United States except nuclear power plants, large dams, pipelines, bridges, and liquefied natural gas (LNG) tanks. Early predictions of ground motions were “deterministic.” Geologists predicted the size (magnitude) and location of earthquakes that could occur during the life of a structure. Seismologists predicted the “worst case” ground motions produced by these earthquakes. Ground motions predicted by deterministic analysis were given vague names such as maximum credible, maximum probable, or maximum foreseeable. In due course, geologists realized that the time, location, and magnitude of future earthquakes are highly uncertain, and they cannot be reliably determined. Seismologists realized that the ground motions produced by specific earthquakes are also highly uncertain and that the “worst case” ground motions cannot be reliably determined. Therefore, the ground motions predicted by deterministic analysis were not “maximum”; they could be exceeded during the life of a structure, but the probability of exceedance was unknown. Deterministic terms such as maximum credible, maximum probable, or maximum foreseeable did not have any meaning. A probabilistic analysis (Esteva 1970, Cornell 1971, Reiter 1991, McGuire 2004) was needed to assign meaning to the predicted ground motions.