| dc.description.abstract | The seismic response of a structure situated on soil with relatively low stiffness is influenced by the material properties of the soil and the type of foundation employed, such as shallow or deep foundations. This thesis aims to assess the response of soil type designated as S1 as per Eurocode 8-1 to various recorded time histories, scaled to recommended ground acceleration, and evaluate the soil-structure interaction at the same ground condition. The shear force induced at the shallow and pile foundation is determined using the finite element program PLAXIS 2D and Eurocode and compared. This study aims to perform a site response analysis of the site and perform soil-structure interaction on the same site considering shallow and deep foundations.
A representative soil model is constructed with appropriate boundary conditions. For dynamic analysis in PLAXIS 2D, a soil column has been adopted for site response, while a full-scale model of size 150m x 25 is used for seismic analysis on foundations. The choice of boundary condition was based on an extensive literature review, previous experiments, and tests performed during the thesis where input motion and motion registered at the model's base were tallied. The site response analysis was performed on three input motions; Imperial Valley, Friuli, and Nahanni, which were scaled as per recommendations. The results from PLAXIS were compared to a one-dimensional response analysis from DEEPSOIL, and an agreeable observation was noted.
The soil model is then used for free vibration analysis of the buildings considered in the study. The results from PLAXIS and theoretical solutions were tallied and later confirmed with Eurocode, all in tandem with each other. Results from dynamic analyzes show that in all cases of the input motion, the choice of foundation type significantly influences the base shear registered in PLAXIS 2D. The base shear and shear forces on piles are more than when a pile foundation is used, highlighting the need for better design guidelines, as piles could lead to fatal design scenarios. However, it should also be noted that since Eurocode estimations of base shear were extremely high or rather conservative, risk could be somewhat averted. Yet again, in the case of shallow foundations, the results proved that Eurocode overestimated the base shear by three times, leading to extremely uneconomical designs. Likewise, parametric studies performed on the soil strata proved that the ground response was not dependent on the thickness of soil clay or stiffness of stiff clay beneath the soft clay. | |
