Nonlinear Modeling, Dynamic Analysis, and Experimental Testing of Hybrid Sliding-Rocking Bridges

Abstract

Hybrid sliding-rocking (HSR) bridge columns were recently developed in the context of Accelerated Bridge Construction (ABC) for seismic regions. These columns incorporate end rocking joints, intermediate sliding joints, and unbonded posttensioning to introduce self-centering and energy dissipation into the substructure. This dissertation intends to further the overall understanding of the dynamic behavior of HSR columns, improve their seismic design, and examine their construction feasibility.

First, a modeling strategy is proposed to enable the nonlinear dynamic analysis of HSR columns. For this purpose, four finite element formulations are developed, namely: (1) a gradient inelastic force-based (FB) element formulation; (2) an HSR FB element formulation; (3) a continuous multi-node truss element formulation; and (4) a zero-length constraint element formulation. These element formulations are then implemented in an structural analysis software to validate the capability of the developed strategy in capturing the data from the past tests on HSR columns.

Once validated, the developed modeling strategy is used to evaluate the effects of several design variables on the seismic performance of HSR columns through multiple nonlinear static and time history analyses. The examined design variables directly/indirectly represent: (i) sliding joint distribution, (ii) coefficient of friction at sliding joints, (iii) duct and duct adaptor dimensions, and (iv) posttensioning system properties. Subsequently, a number of recommendations are made about the effective design of HSR columns. The effects of vertical excitation and near-fault ground motions on the response of HSR columns are also examined, showing their minimal impacts.

The above computational investigations are followed by an extensive experimental program to validate the performance of HSR columns with improved design and to examine their actual response under various loading conditions. This program includes testing of four half-scale HSR columns under uniaxial lateral loading, combined uniaxial lateral and torsional loading, and biaxial lateral loading. The columns under uniaxial lateral loading are tested in both cantilever and fixed-fixed conditions. The test results show the low damageability of the HSR columns under displacements representing 950- and 2475-year earthquakes. Selected tests under uniaxial lateral loading are also simulated using the proposed modeling strategy and improvements are suggested accordingly.