Abstract
Under complex seismic forces, the failure characteristics of the plastic hinge region at the bottom of the pier column and the methods improving the ductility have attracted extensive attention. In this study, steel fiber-reinforced concrete with fine aggregate (SFRC-FA) was applied to locally replace the conventional concrete in the potential plastic hinge region at the bottom of the pier column. Five SFRC-FA pier column specimens with different stirrup ratios and different replacement lengths and one conventional reinforced concrete pier column specimen were produced. Using the seismic behavior tests under the combined bending-shear-torsion-axial force, the failure mode, torsional bearing capacity, energy dissipation, and the torsional plastic hinges of the pier columns were investigated. In addition, an equation for calculating the torsional bearing capacity of the new composite pier columns was proposed. The results showed that (1) compared with the reinforced concrete pier column, the plastic hinge was shifted from the bottom of the pier column to the middle of the height of the pier column due to the application of SFRC-FA at the bottom of the pier column, which improved the torsional bearing capacity; (2) the effect of reducing the stirrup ratio of the SFRC-FA replacement region on the torsional bearing capacity, cracking mode, energy dissipation, and ductility was not obvious; (3) the accuracy of the new equation based on the space truss model proposed in this article was verified by comparison with the experiments of this study and other researches.
Highlights
FRC and ECC are efficient cement-based composites that can compensate for the drawbacks of quasibrittleness of conventional concrete and has better structural performance than conventional concrete [23,24,25,26,27,28,29,30,31,32,33,34,35,36]
Zhang and Dias-da-Costa [27] carried out experiments and finite element analysis to investigate the seismic vulnerability of multispan continuous girder (MSCG) bridges with steel fiberreinforced concrete (SFRC) piers. is study found that the seismic vulnerability of MSCG bridges with SFRC located only in the plastic region of the piers showed similar behavior when compared with the design adopting SFRC for the whole pier
Kim et al [29] proposed a modified smeared crack truss model, in which steel fibers were modeled as average direct tensile contribution elements, considering directionality and distribution of fibers. e proposed model estimated the shear behavior of the SFRC members well. e test results by Li et al [31,32,33,34,35] indicated that the use of ECC materials in the connection plastic region as a replacement of conventional concrete and partial replacement of transverse reinforcement can significantly enhance the joint shear resistance, energy absorption capacity, and cracking response. erefore, it has been shown that FRCs materials represent a feasible alternative for use in earthquake-resistant structures [33]
Summary
Five specimens of RC pier columns locally replaced with SFRC-FA and one specimen of ordinary RC pier column were constructed and tested at Zhejiang University to investigate the influence of SFRC-FA replacement length, stirrup ratio, and axial-torsional loading on the seismic behavior of pier columns. As one of the purposes of this study is to clarify the influence of the SFRC-FA replacement length and the stirrup ratio on the seismic behavior of pier columns under combined action of axial force and torsion, all the specimens were designed to fail under torsional loading, in accordance with the 2008 Guidelines for seismic design of highway bridges [37]. A hydraulic jack was used to exert axial load on the top of pier column through the spherical hinge, which connected the top of the column and the bottom of the jack to maintain an unconstrained boundary condition in the ring direction and constrain the horizontal displacement of the columns During the selected loading steps in the tests, the observed damage was recorded with photographs and sketches. e location of cracks, spalling, and any buckled reinforcing bars were documented
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