مهندسی عمران شریف (May 2016)
EVALUATION OF DETERMINISTIC AND PROBABILISTIC EFFECTS OF REDUNDANCY ON THE RESPONSE MODIFICATION FACTOR FOR RC MOMENT RESISTING FRAMES WITH EQUAL
Abstract
The general opinion regarding the overstrength capacity of a structure is explained by the process of first local yielding to total failure being due to structural redundancy. Furthermore, results of some research indicate that this part of the overstrength capacity can be introduced as a redundancy reduction factor. On the other hand, some other research showed that an analytical parameter, according to the lines of vertical seismic framing and the theory of structural reliability, can be formulated as the redundancy reduction factor independent of the overstrength reduction factor in the analytical definition of the response modification factor. A general conceptual question is why structural redundancy has been regarded as a desirable property. Is it because making more overstrength capacity or just increasing the number of seismic resistant frames will make the structural behavior more desirable, as well as increasing the reliability of the systems? To answer these questions, six and nine floor three-dimensional reinforced concrete framed structures with the same story area and the same equal lateral resistance were designed. In this research, the essential parameters of the response modification factor for the studied structures were estimated numerically. Furthermore, by considering the strength factor as a random variable, both the deterministic and probabilistic effects of redundancy on the response modification factor were also evaluated. The results of this research illustrated that imposition of an increase in redundancy, where no more overstrength capacity will be made, might not improve the behavior of the framed structure.It is assumed that the same ultimate lateral resistance of structures that causes an increase, to a certain level, in redundancy, can also enhance both the ductility capacity and the inelastic capacity of structures. However, any further increase in the redundancy of that certain level might have a negative effect on the ductility capacity.
