Characterization and evaluation of the seismic performance of pile-supported bridge structures.

摘要

Bridge and viaduct structures are often supported on cast-in-drilled-hole (CIDH) extended reinforced concrete piles. These systems have significant cost savings when compared to smaller driven piles that may be eventually integrated with a pile-cap to facilitate group action. Typical applications include the multi-column and single-column bent where each supporting pile shaft is extended above ground into a column having approximately the same diameter and reinforcement. However, the flexural strength of the extended pile shaft is fairly uniform along its length, resulting in the possible yielding of the pile shaft below ground level. Unfortunately, direct inspections of the below-ground portions of pile foundations in previous earthquakes have been sparse and as such our knowledge of the local distribution of damage (if any) is fairly limited.; For the extended pile shaft supported system, the lateral displacement of the superstructure during an earthquake may be significantly larger than that of an equivalent fixed-base column depending on the height of the bridge structure, the supporting soil conditions, and the ground motion characteristics. This is due to the possible occurrence of large displacements and rotations at the ground level upon yielding of the pile shaft. Although the implications of large lateral displacements on the overall response of the structure are well recognized, a quantitative assessment of such effects on the 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 been thoroughly carried out.; This dissertation summarizes a study of the inelastic seismic response of bridge and viaduct structures supported on extended pile shafts. Specifically, the work presented herein includes: (1) results of a full-scale experimental program assessing the global and local inelastic response of reinforced concrete pile shafts, (2) subsequent modeling of the experimental results and a parametric study where a range of soil types and strengths are considered, (3) an assessment of the performance of extended pile shaft supported bridge structures under strong, long-duration and/or long-period ground motions, (4) an evaluation of the influence static and dynamic P-Δ effects have on this class of structures, (5) a comparison of dynamic analysis results with current nonlinear static analysis procedures and (6) presentation of an alternative approach for estimating inelastic displacements.