Bridge and viaduct structures are often supported on cast-in-drilled-hole (CIDH) extended reinforced concrete piles. In bridge structures supported on these foundation elements, the inelastic response of the superstructure during an earthquake is strongly related to the supporting soil conditions through their influence on substructure stiffness and ground motion characteristics. Although the implications of soil-structure interaction on the overall response of the structure are well recognized, a quantitative assessment of such effects on the inelastic performance of the structure, which requires analytical models capable of capturing the nonlinearity of the soil and pile under dynamic reversed cyclic loading conditions, has not previously been thoroughly carried out.
This report summarizes a study of the inelastic seismic response of bridge and viaduct structures supported on extended pile shafts. Specifically, the work presented includes three main sections. First, the transverse response of reinforced concrete pile shafts is studied by (1) finite element (FE) modeling of a series of full-scale soil-pile lateral loading tests using a beam-on- nonlinear-Winkler (BNWF) approach, (2) comparis on of the FE and field test data against a simple kinematic model for relating global and local ductility demands, and (3) a parametric study using the kinematic model over a range of soil types and strengths to evaluate current design practice for allowable ductility levels in these types of structures. Second, dynamic FE analyses are used to assess the performance of extended pile shaft supported bridge structures under strong, long-duration and/or long-period ground motions. Third, the dynamic FE analysis results are compared with current nonlinear static analysis procedures (e.g., R- μ∆-T relations), and an alternative “mean spectral displacement” approach for estimating inelastic displacements from the elastic response spectrum of the surface motion is evaluated.
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