Comprehensive Assessment of Damage Indices of RC Frames in Conventional and Novel Seismic Design Approaches

Experience of the past earthquakes reveals that conventional force based design (FBD) approach, only provide minimum requirement for life safety performance level of structures. While these methods do not capable to control structural seismic damages. In recent years, displacement based design approaches have been proposed as the main tools of performance based design. Direct displacement based design (DDBD) is recognized as one of the most efficient methods. In this method, an inelastic multi degree of freedom structure is substituted with an equivalent elastic single degree of freedom. The substitute structure is designed for a target displacement and an equivalent viscous damping using elastic displacement response spectrum. The effectiveness of this method has been examined in controlling the overall seismic demands of many structural systems, while the least attention has been paid to the effects of local damages. In this study, seismic performance of a set of RC frames designed with DDBD and FBD approach (based on Iranian seismic code) has been investigated and compared with a focus on local damages. DDBD and FBD method was applied to four reinforced concrete regular frames of 3, 5, 7 and 11 story and performance of the methods was compared using inelastic time history analysis (ITHA). In the seismic assessment process, in addition to general structural responses, the distribution of local damages has also been investigated. The Park–Ang damage index was selected as the seismic damage index and probability of exceedance of the damage limit state was compared using fragility curves developed for five damage levels. Results show that very good control of displacement and inter-story drift of RC frames designed with DDBD approach. Evaluation of the plastic hinge rotation shows, DDBD unlike FBD approach has been satisfied expected performance level. Furthermore DDBD approach provided more control on selected seismic damage index and distribution of damage index at height of structures is more uniform than FBD approach. The cost analysis shows that consumable rebar is increased 6.6%-52.11% and consumable concrete is up to 3.4% in DDBD approach compared with FBD approach, which is more exponential in frames with higher elevations.