Abstract:
The majority of structural designs were done under the assumption of which the structural elements were fixed at base. But in reality, the soil beneath structure deforms due to seismic load according to its flexibility. This flexibility of soil reduces the overall stiffness of structure and can affect other dynamic responses of structure due SSI effect.
This study work investigates the effect of SSI on dynamic responses of RC buildings; varies with number of story as story-6, story-8 and story-10 regular building, varies with geometric shape as regular, L-shape and C-shape building and varies depth of soil which was found on soft soil, soil-D and subjected to seismic load of Ethiopia seismic zone-4 as ES EN 1998-2015.
Analysis and design of buildings before modeling for SSI effect study were performed by response spectrum analysis with the help of ETABS software. After that the buildings were modeled for SSI analysis as fixed and flexible base. Flexible base was modeled as spring and elastic continuum models with the help of structural analysis software SAP2000ver21. Matched El Centro 1940 earthquake ground motion was used for analysis SSI by using the linear time history analysis method. The effect of SSI was studied on dynamic responses parameters such as fundamental period, base shear, story displacements; inter story drifts and P-Δ effect of columns.
The results obtained from analysis indicate that the effect of SSI on fundamental period was largest for story-6 building and decreased as height increased. But the effects on base shear, story displacement, inter story drift and P-Δ effect of column didn’t depend on the height of buildings. The effect of SSI on fundamental period didn’t affected by geometric shape of buildings. The base shear was more affected for regular and C-shape buildings, whereas the torsional moment was high for L-shape building. The difference between spring and elastic continuum model was depended on depth of soil mass provided. The variation on dynamic response of fundamental period, base shear, story displacement and inter story drift in terms of spring and elastic continuum model was largest at shallow depth and smallest at deep depth.
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