INFLUENCE OF KINEMATIC SOIL-STRUCTURE

INTERACTION ON STRUCTURAL RESPONSE

Tuğçe Tetik

(Thesis Supervisors: Prof. Dr. Eser Çaktı and Prof. Dr. Erdal Şafak )

ABSTRACT

The Soil-Structure Interaction (SSI) is a phenomenon that can significantly alter the free field ground motion and, therefore, needs to be considered in the design of structures, especially those founded on soft/weak soils. SSI can be incorporated into the dynamic analysis of structures by implementing foundation impedance functions (FIFs), which provide displacements and/or rotations of the soil-foundation system in terms of unit forces and/or moments applied at the foundation level. As the impedance functions are frequency dependent, the available commercial finite element software, based on the time domain framework, encounters difficulties implementing them. This thesis presents the design of discrete-time domain filters for the frequency-dependent FIFs associated with two selected types of foundation systems considering their geometry, embedment depth, and surrounding soil. The transformation has been obtained using the least squares approximation technique. The correlation between the obtained time domain filters and the actual frequency domain filters has been checked by using R-squared values. The proposed procedure, in which the FIFs act as filters capable of transforming the free field ground motions into the motion of the soil-foundation system, provides an easy way to incorporate SSI into the time-domain dynamic analysis of structures. The examples given also highlight the effect of different frequency content of the ground motion (GM) on the SSI. The results are presented to show the effects of SSI on both the response spectra and the structural response. Foundation input motions (FIMs) are applied to a 5-story building model, and the performance of the building under analysis is compared using free field motion (FFM) and FIM in terms of story displacements, inter-story drifts, top displacement, and base shear using the SAP2000 structural analysis and design program.