Seismic analysis and design of precast concrete segmental bridges
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In this dissertation, the concept of hybrid sliding-rocking (HSR) precast concrete post-tensioned segmental members for seismic applications in bridges is introduced and investigated experimentally and numerically. The HSR members lie into the framework of accelerated bridge construction techniques (ABC) and are primarily intended for applications in moderate and high seismicity areas. The HSR members combine two fundamental components, namely the HSR segmental joints, and the internal unbonded post-tensioning. The HSR joints utilize relative segment-to-segment sliding (joint sliding) and gap opening (joint rocking) to mitigate the applied seismic loading. Joint sliding offers high energy dissipation with minor structural damage as well as moderate self-centering. On the other hand, joint rocking offers low energy dissipation and high self-centering capabilities that deteriorate at larger rocking rotations due to the resulting concrete crushing. The response of HSR joints is affected by the geometry of the post-tensioning (PT) system along the member length. Hence, linear or nonlinear PT geometry may be used to control joint and member response properties. Two distinct types of HSR members were further studied: (i) HSR members with slip-dominant joints and linear PT geometry (abbreviated as HSR-SD members), and (ii) HSR members with rocking- dominant joints and nonlinear PT geometry (abbreviated as HSR-RD members). The concept of HSR bridges was evaluated through a two-stage experimental study. The first stage included shake table testing of a large-scale (∼ 1:2.39) single-span bridge specimen incorporating a HSR-RD superstructure and two HSR-SD single-column piers. Nearly 150 seismic tests were conducted including far-field and near-fault input motions scaled to different seismic hazard levels. The second stage included quasi-static testing of the HSR-SD piers with a sequence of displacement-controlled loading cycles of increasing amplitude that eventually reached a drift ratio of approximately 15%. The experimental findings from the large-scale seismic and quasi-static testing programs were complemented by two additional experimental studies; one focusing on the identification of the frictional properties of the HSR joint interface, and another investigating the response of the strand-anchor systems (i.e., unbonded monostrands with their anchorage setups at their ends). Numerical predictions for the quasi-static testing were provided by a model of the HSR-SD pier generated with the ABAQUS general-purpose finite element software, while numerical predictions for the seismic testing were provided by a model of the HSR bridge specimen generated in SAP2000. Comparisons between numerical and experimental results are presented. This dissertation is concluded with an investigation of the response properties of flexibility-based (or force-based) beam-column elements in the presence of softening section constitutive relations. This study identified and explained critical numerical instability problems observed during the development of force-based elements for HSR members.