Use of Soil-Structure Interaction Analyses to Optimize Cement Silos Foundation Design

Nonlinear dynamic soil-structure interaction (SSI) analyses were performed to evaluate a proposed deep-foundation scheme for heavy cement silos at Pier F in the Port of Long Beach, California. A conventional, code-based design with 24-inch octagonal precast concrete piles called for 552 piles to resist shear forces generated by the design earthquake. However, the SSI analyses performed with FLAC demonstrated that the number of piles could be reduced by more than 50%. The piles were modeled with elastic-perfectly plastic beam elements connected to a simplified superstructure whose mass and fundamental period approximated the dynamic characteristics of the silos. Piles interacted with foundation soils through non-linear p-y and t-z springs; and soils were represented by an elastic-plastic Mohr-Coulomb model coupled with an empirical pore-pressure generation scheme.