Base Shear Redistribution Between the R/C Dual System Structural Components

Abstract eng:
The experience provided by the recent earthquakes showed that buildings with structural walls have had satisfactory performance for collapse prevention. Conversely, some of the dual system buildings (wall frame) were rated as severely damaged therefore implying an urgent need for strength assignments redefinition between the structural components. The elastic response of dual buildings is mainly governed by the wall response and the frame contribution could be neglected (bellow 15% of the base shear what makes them a secondary member). In the inelastic range the situation could drastically change and frame contribution increases (even up to the 50%) but these elements are then under-designed and not capable to carry the increased load. A set of dual building structures were selected, designed and analyzed. The model buildings were 4, 7 and 10 stories high with two frames and one wall-frame in longitudinal and four frames in the transverse direction. Column dimension varied thus causing stiffness and strength redistribution among the wall and frame, in elastic and inelastic range. Seismic analysis including elastic, nonlinear static (push-over) and nonlinear dynamic analysis have been done. Observed were base shear distribution, displacement and ductility demands of the wall and frames through system degradation. The results have shown that wall contribution diminishes as deformations are increasing and its share could go up to almost 50% what required high ductility of the frame elements. That they do not have if they were originally designed as “secondary” seismic elements according to the material Eurocodes.

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