Implementation of Direc Displacement Based Design for Pile and Drilled Shaft Bents

Abstract

The work in this thesis attempts to implement the Direct Displacement Based Design (DDBD) method to the seismic design of long reinforced concrete pile and drilled shaft bents embedded in soft soils. DDBD has been successfully used to design bridge columns that are fixed at ground level and without soil interaction. The implementation of DDBD for column bents, however, requires the consideration of soil-structure interaction effects--namely added flexibility and damping. The main objective of this research is to develop an equivalent model to predict yield displacement and ductility and to assess the equivalent viscous damping as a function of ductility demand and soil type.

The proposed equivalent cantilever model replaces a nonlinear soil-column system. In the equivalent model, the column is considered fixed at some depth below ground at the point of maximum moment and possible formation of an underground plastic hinge. The yield displacement of the column is matched with the yield displacement of the soil-column model by introducing a coefficient and the energy dissipation characteristics are matched by the introduction of equivalent viscous damping as function of ductility and soil type. Charts and equations are provided to compute all the parameters involved in the equivalent formulation. These aids resulted from parametric studies that involved nonlinear static and nonlinear time history analyses of soil-column systems.