The Effect of Gravity Loads on Seismic Lateral Displacements of R.C. Frames

This paper includes an analytical study for an investigation of the gravity load effect on the seismic lateral displacements of a R.C. building located in Khartoum city (which lies in zone 2, of zone factor, z = 0.1), Sudan. The R.C. building used in this study is a 6-storey residential building with 3-bays in each direction. Two selected frames of the building were analyzed using STAAD-III software, linear static and dynamic analysis software, one in N-S direction and the other in E-W direction. The analysis was performed for two types of restraints: fixed and pinned, for both frames under the same loading. Four cases of damping ratios (0%, 5%, 10% and 20%) were used in the analysis. These ratios were taken as percentages of the critical damping. The software used the Dynamic Response Spectrum method (DRS) to solve the dynamic equilibrium equations of motion. The recorded ground motions of the 1940 El Centro earthquake were selected to be used as input data to calculate the seismic lateral displacements. Regardless of values of damping ratios and types of restraints used, it was found that the gravity load contributed in reducing the lateral displacements by an average amount of 25%. In other words, the lateral displacements caused by the combination of (gravity +seismic) loads are less than those caused by the seismic load only.