Earthquakes are natural phenomena that occur at several places of the world. Severe earthquakes, when near inhabited districts, have caused extensive loss of life and property. Although some progress in the area of seismic prediction has been made, earthquakes cannot be accurately predicted in time, magnitude or location. Therefore, the main way of decreasing losses is to construct seismic resisting structures. Recent earthquakes illustrate that the older buildings, which are not designed to resist earthquakes, have been damaged rather than the buildings which have been designed according to seismic codes. Many existing buildings in Egypt were designed to resist the gravity loads only (GLD) without seismic provisions. The need is raised to study the vulnerability of these buildings to avoid a serious risk. In this paper, the light is shed on the significant contributions in the field of seismic vulnerability evaluation of buildings in order to suggest a suitable procedure for seismic evaluation of existing R.C. buildings in Egypt. Seismic evaluation was applied on the selected two case studies, one represents the GLD buildings and the other represents the buildings designed according to Egyptian code. Moreover, pushover analysis was conducted to investigate the vulnerability of these buildings.

Introduction

Seismic vulnerability evaluation is defined as an approved process or methodology of evaluating deficiencies in a building that prevents the building from achieving a selected performance objective. The seismic vulnerability evaluation of the existing buildings is required for the following: buildings may not have been designed to resist seismic forces or designed before the publication of the current seismic codes, the condition of buildings is apparently of poor quality or deteriorated with time and change of use of the building and the soil has a high liquefaction potential. Depending on the seismic evaluation, a building can be demolished, retrofitted to increase its capacity, or modified to decrease its seismic demand [1,2]. The earthquake risk at any location depends on the seismic hazard as well as the vulnerability of its structures. The seismic hazard evaluation considers the likelihood of earthquake of a particular magnitude or intensity affecting a site. The ‘‘risk” means expected loss (such as lives, injury, property damage) due to a particular hazard for a given area and reference period. Based on mathematical calculations, risk is the product of hazard and vulnerability [3]. The seismic vulnerability of a structure can be described as its susceptibility to damage by ground shaking, and this includes foundations, columns, beams, and floor slabs [2]. The seismic vulnerability evaluation is a complex process, which has considered design of building as well as deterioration of the material and damage caused to the building [1]. The vulnerability of a building subjected to an earthquake is depended on seismic deficiency of that building. The seismic deficiency is defined as a condition that will prevent a building from meeting the required performance objective. Thus, a building evaluated to provide full occupancy immediately after an event may have significantly more deficiencies than the same building evaluated to life safety. Life Safety performance level means the damage to the structure has occurred (after earthquake) but some margin against either partial or total structural collapse remains, while, immediate occupancy performance means very limited damage to both structural and nonstructural components. The most categories of seismic deficiencies are as follows: 1 – Discontinuity in the load path which transferred the inertial forces from the mass to the foundation; 2 – Low strength for the lateral load system elements such as weak stories; 3 – Low stiffness of lateral loads system elements such as soft story condition; 4 – Low ductility of lateral load system elements; 5 – Lack of Redundancy, Redundancy means providing multiple continuous load paths in the structural system; 6 – Configuration Irregularities: The vertical irregularities that may affect the seismic performance are stiffness Irregularity, weight (Mass) irregularity, vertical geometric irregularity such as setbacks and vertical discontinuity in load path or the lateral force-resisting elements. The horizontal irregularities that may affect the seismic performance are torsional Irregularity, reentrant corner irregularity and diaphragm discontinuity irregularity; 7 – Deterioration of structural materials; 8 – The pounding action which occurs when the gap between buildings is insufficient; and 9 – Foundation deficiencies [4].