SEISMIC RESPONSE OF VERTICALLY IRREGULAR HSC MOMENT-RESISTING BUILDING FRAMES

The nonlinear seismic behavior of vertically irregular reinforced concrete moment-resisting building frames constructed from Normal-Strength Concrete NSC and High-Strength Concrete HSC has been studied. Seismic analysis of 82 ductile moment-resisting regular and vertically irregular multistory building has been carried out. The reliability of the criteria provided by different codes, in order to distinguish the regular from irregular building frames has been verified. The applicability of the Static Equivalent Lateral Force SELF method has been examined when applied to vertically irregular moment-resisting building frames. The results showed that the limits in UBC-97 and ECL-08 aimed to identify the lateral stiffhess are satisfactory and can be relaxed by about 10%. The limit of storey mass irregularity recommended by UBC-97 leads to severe non conservative results; and therefore, it needs to be modified. The limit identifying setback irregularity of frames at the lower 15% of the total height of the frame gives poor results and it is proposed to change this limit to become 30% of the total height of the frame. The SELF method of UBC-97 is not satisfactory when applied to either NSC and HSC frames with mass or setback irregularities. The SELF method of EC-8, ECL-08 and ESEE-88 are conservative when applied to NSC and HSC building frames having lateral stiffhess, mass and setback irregularities.