Although seismic design codes are often subjected to improvements after each earthquake disaster, old constructions are left unprotected by new technology. The purpose of this paper is to promote public welfare and safety by reducing the risk of death or injury that may result from the effects of earthquakes on existing reinforced concrete (R/C) building stock in Egypt. It aims to evaluate seismic vulnerability of the most commonly used type of multi-story RC buildings. Special attention is placed upon examining R/C buildings with vertical irregularity. The seismic vulnerability assessment for existing R/C buildings is assessed through examining two types of damage indicators: damage index and inter-story drift limit state. A sample building set is selected to reflect existing construction practice including regular buildings and those with vertical irregularities. The effects of vertical irregularity at different floor levels are examined by developing fragility curves of medium-rise gravity load designed R/C buildings. Fragility curves of the investigated building set are determined by nonlinear time history analysis to evaluate the damage state. These curves are used to represent the probabilities that the structural damages, under various levels of seismic excitation, exceed specified damage states by means of earthquake intensity damage relations. The analytical damage evaluation in this study shows that the seismic effects of earthquakes experienced in Egypt may be significant. Moreover, it shows that some of the earthquakes may impose excessive displacement demands on the investigated buildings. The results also show that the irregular buildings are more vulnerable than the regular ones.

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Over the past decade, several studies investigated behavior aspects of irregular structures and limitations of seismic code provisions for such class of buildings. This paper investigates the dynamic and seismic behavior of buildings employing thick transfer slab between two different structural systems, representing podium and upper tower. The shape of these structures is commonly dictated by either aesthetic or functional considerations that often preclude simplicity or regularity. The purpose of this paper is to assess the seismic damage potential of such structures compared to regular buildings. The seismic behavior is examined under the effects of 6 natural ground motions. The structural damage assessment is conducted through examining drift ratios and damage indices of the overall structure as well as of the significant structural components of RC building. Other significant seismic design parameters such as base and story shear are also assessed for the varying ground motion characteristics. The evaluation and the comparison of the seismic behavior of these buildings, has great impact in attenuating the seismic structural response under various earthquake ground motions. Nonlinear dynamic analyses are performed on a 2-dimensional model of R.C. building.

The results of a case study of the internal forces caused by earthquake in two examples of cable-stayed bridges are presented. A comparison is made between the behaviour of a model in which the structure is idealized without the foundation system and a model in which both the structure and the supporting foundation are idealized. The effects of varying the soil conditions on the seismic response are assessed. Also, the effects of out-of-phase support movements, caused by the lapse of time required for the seismic waves to travel from one support to the other, are considered. It is concluded that the effects of these parameters are significant and should not be ignored in the seismic analysis of cable-stayed bridges.Resume : Les rCsultats d'une Ctude de cas des forces internes causCes par un tremblement de terre dans deux exemples de ponts a haubans sont prtsentCs. Une comparaison est effectuCe entre le comportement d'un modkle dans lequel la structure est idtalisCe sans fondations et le comportement d'un modkle dans lequel elle est idCalisCe avec les fondations. Les effets de la variation des conditions de sol sur la rCponse sismique sont Cvalues. En outre, les effets des mouvements dCphasCs causCs par la pCriode de temps requise pour que les ondes sismiques se propagent d'un appui i l'autre sont examinks. Les auteurs concluent que les effets de ces paramktres sont importants et qu'ils ne devraient pas Ctre ignorCs dans l'analyse sismique des ponts i haubans.