الفهرس 
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Abstract
Structures are subjected to additional loads due to earthquakes may yeild failure in soil and superstructure. The dynamic response of a structure to an earthquake can significantly affected by the geotechnical properties of the bearing soil layers. So, in this thesis the dynamic analysis of structures resting on three types of reinforced and non-reinforced clay sandy soil were studied. Numerical study using PLAXIS 2D (Dynamic module) was carried out. Parametric study was conducted to investigate the effect of reinforcement layers such as number and length of layers as well as, the depth of the first reinforcement layer below foundation. The result of this parametric study was evaluated to show the effect of each parameter on the dynamic response and straining actions of the structure due to earthquake. The present thesis indicates that, it is important to take the effect of soil properties into consideration during the dynamic analysis of the superstructure. Also, the existence of geotextile in the sand is found to be an effective tool to increase the bearing capacity and improve the foundation subgrade response during seismic loading. It can be concluded that the lateral displacement at the foundation level decreased by 63% for all cases; while the vertical displacement decreased by 70%. The structure response also improved with using geotextile layers. The lateral deformation and acceleration reduced by 73%, and 65%respectively. In addition, the induced bending moment and shear force reduced by 71% and 80% respectively.