3-D Modeling of the Modified, Disconnected Spread Footing System at Segment 4 of the Golden Ears Bridge

Abstract

The modified disconnected spread footing (MDSF) system is an innovative foundation concept that was used for support of the northern approach structure (Segment 4) at the Golden Ears Bridge crossing of the Fraser River in British Columbia, Canada. This foundation system consists of conventional rectangular spread footings supported by groups of lightly reinforced, 36 m long precast concrete piles. Unlike traditional piled foundations, the piles in the MDSF are separated from the spread footing by a lean concrete layer and a thin gravel layer. The driven piles are used to transfer axial compressive loads. Other structural demands (i.e., shear, moment, and uplift loads) are transferred to the soils through the spread footing and a group of short drilled shafts, which are rigidly connected to the spread footing. This paper describes the modeling techniques used in the three-dimensional (3-D) computer model developed to simulate the unique load-transfer mechanism occurring in the MDSF system under gravity and seismic loading. The 3-D model was developed using the computer program FB-MultiPier, which couples nonlinear finite element analysis for superstructure with nonlinear spring models for soils. Calibration of the 3-D model was conducted through a series of runs in which the contribution of each footing element (i.e., spread footing, piles, and shafts) were separately evaluated. It was demonstrated that the computer model is capable of handling the complex load-transfer mechanism in the MDSF system.