Estimating number of simultaneously yielding stories in a shear building subjected to earthquake excitation

A procedure for estimating the number of simultaneously yielding stories (NSYS) in a shear type building subjected to seismic ground excitation is proposed. Proper estimation of NSYS values will lead to more accurate estimation of axial force demand in columns which will result in economical design of columns. In this procedure, the main pulse of the velocity record responsible for causing the maximum number of stories to yield simultaneously was identified and isolated to idealize it by a full-sine velocity pulse, as an extension of the procedure for estimating the NSYS for a full-sine pulse velocity base excitation developed previously by the authors. A set of eighteen earthquake records sorted into three categories of earthquakes were considered, namely: earthquake excitations having (i) a single dominant pulse (ii) multiple distinct pulses, and; (iii) no distinct pulses in their velocity record. Since most of these earthquakes have relatively long duration main pulses, another set of eighteen earthquake records was obtained by condensing their acceleration time scale and was used to study the proposed procedure for earthquakes that have shorter duration main pulses. The estimated maximum value of NSYS obtained from the proposed procedure was found to be adequately close to the actual value observed from OpenSees analysis for the structures and earthquakes considered.