Probabilistic advantage of vibrational redundancy in earthquake-resistant steel frames

Steel frames are, in general, indeterminate and thus they do not necessarily fail when some elements constituting the system are subjected to fracture or buckling during a severe earthquake. The purpose of this paper is to assess the advantage of such redundancy inherent in indeterminate structural systems in a probabilistic sense. Two structural models are introduced to clarify the benefits of vibrational redundancy. One is a dual system composed of two parallel subsystems which have different natural periods. The other is a single system composed of a single subsystem. The former is exemplified by a moment-resisting frame associated with bracing, while the latter by a bracing system. It is demonstrated numerically that the dual system can survive with a higher degree of safety than the single system under the uncertainty condition that earthquake ground motions which hit the systems have random spectral properties. (C) 1999 Elsevier Science Ltd. All rights reserved.