Journal of American Science, 2011;7(12) http://www.americanscience.org http://www.americanscience.org editor@americanscience.org 909 Effect of Pushover Load Pattern on Seismic Responses of RC Frame Buildings Mohammed H. Serror 1 , Nayer A. El-Esnawy 2 , and Rania F. Abo-Dagher 3 1 Assistant Professor, Dept. of Structural Engineering, Faculty of Engineering, Cairo University, Egypt 2 Professor, Dept. of Structural Engineering, Faculty of Engineering, Cairo University, Egypt 3 M.Sc. Graduate, Dept. of Structural Engineering, Faculty of Engineering, Cairo University, Egypt mhassanien@cosmos-eng.com Abstract: Recently, attention has been paid to the performance-based seismic design that requires designing the building for several expected performance levels. This is achievable through a design procedure based on the inelastic responses. In order to estimate the inelastic seismic responses of a building, the pushover analysis is used, for its simplicity compared with the nonlinear time-history analysis. In pushover analysis, however, the first step is to select a particular lateral load pattern, which affects the resulting capacity curve that may over- or under-estimate building seismic capacity. Therefore, the selection of a reasonable lateral load pattern is particularly important in pushover analysis. The aim of this study is to analyze the effect of lateral load patterns on the seismic performance of low-to-mid-rise Reinforced Concrete (RC) frame buildings. The RC frame buildings, which consist of 6, 9, and 12 stories, are designed according to Egyptian codes ECP-201 and ECP-203. The lateral load patterns for pushover analysis are selected as uniform, inverted triangle, first mode, IBC (k=2), and weighted-load vector patterns. Pushover analysis has been performed according to FEMA-356 guidelines. The effect of the selected lateral load patterns on the seismic responses of the RC frame buildings is illustrated. In particular, the top drift of the building, the base shear, and the peak inter-story drift are analyzed. [Mohammed H. Serror, Nayer A. El-Esnawy, and Rania F. Abo-Dagher Effect of Pushover Load Pattern on Seismic Responses of RC Frame Buildings] Journal of American Science 2011; 7(12):909-919]. (ISSN: 1545-1003). http://www.americanscience.org . Keywords: pushover analysis; lateral load pattern; inelastic seismic responses; performance-based design 1. Introduction The current codes for seismic design have the objectives to assure life safety (strength and ductility) and damage control (serviceability limits). The design criteria, accordingly, are formulated based on limits on stresses and member forces calculated from prescribed levels of applied lateral force. The performance-based design, however, is a more general design philosophy in which the design criteria are expressed in terms of achieving stated performance objectives when the structure is subjected to stated levels of seismic hazard (Ghobarah, 2001). SEAOC Vision 2000 (1995) has developed a framework that is able to accommodate multiple performance objectives; meanwhile, it addresses the performance levels for structural and non-structural systems. The Applied Technology Council (ATC 40, 1996) has developed a procedure that involves determining the capacity and demand spectra. At the performance point, the seismic capacity is assumed equal to the demand, which provides an estimate of acceleration (strength) and displacement (demand). The Federal Emergency Management Agency (FEMA 273, 1997) has defined performance levels for structural systems, and proposed drift limits for various lateral-load resisting systems at different performance levels. Moreover, it addresses concepts, philosophy, design methodologies and various applications of performance-based design. It is worth noting that demand evaluation at the low performance levels requires the consideration of the inelastic behavior of the building. Although seismic demands can be determined by inelastic dynamic analysis using the acceleration time-history of a given earthquake, the engineers prefer simple and less expensive procedures for every day design. Accordingly, the pushover analysis has been proposed by recent seismic design codes. Pushover methods have been a practical tool for building evaluation considering the performance-based engineering in several international seismic codes such as the FEMA 273 (1997), Euro-code 8 (EC-8), and International Building Code (IBC-2003). In these seismic regulations, pushover methods such as N2- method, Capacity Spectrum method, and Displacement coefficient method are recommended for determining the inelastic responses of the building during earthquake events. In the pushover analysis, the first step is to select a particular lateral load pattern, which affects the resulting capacity curve that may over- or under-estimate building seismic capacity. Akbas et al. (2003) reported the change in failure mode under