The effects of ground motion characteristics on the seismic fragility curves of RC buildings

Over the past two decades, Egypt was hit by few earthquakes that resulted in significant loss of life and property. Several Reinforced Concrete (RC) buildings were damaged or collapsed. In the present research work, the seismic vulnerability of the most common used RC building system, in Egypt, is assessed. The investigated samples include 3-, 5-, 7-and 12-story buildings. The seismic vulnerability of these sample buildings is inspected through examining the fragility curves. These curves are used to represent the probabilities that the structural damage, under various level of seismic excitation, to exceed specified damage states by means of earthquake intensity damage relations. Four damage states are defined: slight, minor, moderate, and severe, in order to express the condition of damage. Fragility curves are represented by lognormal distribution functions with two parameters and developed as a function of Peak Ground Acceleration (PGA). Different characteristics of ground motion excitation are employed in the analysis. Ground motions with different frequency contents are utilized; Low, Medium and High frequency content earthquakes. The study assesses the effects of ground motion characteristics on fragility analysis. A two dimensional finite element computer program for seismic inelastic structural analysis is employed. The computer program takes into account cracking, reinforcement of RC members and both geometric and material nonlinearity. This study represents an attempt to evaluate the seismic vulnerability of the building stock in Egypt. The results show also that the effects of input ground motion characteristics may have a significant effects on fragility curves. Therefore, diligent consideration is required when ground motions are selected for the derivation of fragility curves.