Abstract:The collapses of building structures during recent earthquakes have raised many questions regarding the adequacy of current seismic provisions to prevent a partial or total collapse. They have also brought up questions as to how to determine the collapse safety margin of structures, what is the inherent collapse safety margin in code-designed structures, and how to strengthen structures to effectively augment such margin. The purpose of this paper is to present a comprehensive review of the analytical methods that are currently available to assess the capacity of building structures to resist an earthquake collapse, point out the limitations of these methods, describe past experimental work in which specimens are tested to collapse, and identify what is required for an accurate evaluation of the seismic collapse capacity of a structure and the safety margin against such a collapse. It is contended that further research is needed before the collapse capacities of structures and their safety margin against collapse may be evaluated with confidence.

SUMMARYIt is shown that two of the damping ratios of certain systems composed of a building and a small attachment in resonance are given by the average of the damping ratios of the two independent components. Based on this fact and the fact that the seismic response of a building can always be reduced by increasing its damping, it is demonstrated that the attachment of a small heavily-damped system in resonance can increase the damping of a building and reduce thus its response to earthquake excitations. Numerical solutions are presented to confirm the demonstration, and recommendations are given to calculate the parameters of such systems.

No abstract