کلیدواژهها
موضوعات
عنوان مقاله English
نویسندگان English
It is well known that structures designed by current codes experience large inelastic deformations during major earthquakes. However, current seismic design practice in almost all seismic design provisions such Iranian Seismic Code is based on elastic structural behavior and accounts for inelastic behavior only in an indirect manner through certain modification factors such as strength reduction factor. Under moderate to severe earthquakes, inelastic activity, including severe yielding and buckling of structural members can be unevenly distributed in the structure, which may result in global collapse or costly repair work. Recently, a new design method has been developed and referred to as Performance-Based Plastic Design (PBPD). This method directly accounts for inelastic behavior by using pre-selected target drift and yield mechanism as key performance limit states. In this paper, for the first time, the effect of soil-structure interaction (SSI) on drift demands distribution along the height of the steel moment frame (SMF) structures designed with performance-based-plastic design (PBPB) approach under strong ground motions are parametrically investigated. The soil beneath the structure is considered as a homogeneous elastic half space and is modelled using the concept of Cone Models. For the the steel moment frame structures, the design base shears are calculated by using the modified energy balance equation and new lateral force distribution based on inelastic analyses. The new distribution of the lateral forces for performance-based plastic design was used from shear proportioning factors that were derived from the relative distribution of maximum story shears obtained from nonlinear dynamic analyses. Then, plastic design method is employed to design the beams and columns with the calculated design base shear and to satisfy the requirements for strong column-weak beam mechanism, which results in the pre-selected yield mechanism. The plastic design procedure proposed herein can be one of the simplified approaches without requiring sophisticated computer nonlinear analyses, by using the preselected yield mechanisms and target drifts. The energy dissipation capacity of the structure designed by these procedures can be less than that required to prevent collapse under severe ground motions. The purpose of this design procedure is to avoid collapse mechanisms characterized by poor energy dissipation capacity, such as soft-story mechanisms. To this end, the plastic hinges should be developed only in beams and at the column bases of the structure during severe earthquakes. The system is then subjected to 20 different earthquake ground motions and the analyses are performed directly in time domain using direct step-by-step integration method. Effect of various parameters including fundamental period, inelastic behavior, SSI key parameters on strength reduction factor and structural damage distribution are examined. The adequacy of different lateral loading patterns is also parametrically investigated. Results indicate that only mid-rise SMFs designed based on current PBPB approach could have the best performance in SSI systems. It is also demonstrated that under slight and moderate SSI effects, SMFs designed according to various load patterns tend to more uniform distribution as compared to the fixed-base counterparts. However, all of them lose their efficiency when the SSI effects and inelastic response are pronounced. Moreover, the influence of SSI key parameters, fundamental period and ductility ratio on dispersion of the drift results are evaluated and discussed.
کلیدواژهها English
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