Seismic performance of stainless and conventional steel energy dissipation bars in precast segmental bridge columns
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The use of stainless steel reinforcing bars in seismic applications has recently attracted much attention in the civil engineering community due to its superior material properties, including high corrosion resistance and high specific strength. However, as with all new materials, a number of shortcomings are unavoidable, such as high initial costs, unknown low-cycle fatigue behavior, uncertain ductility properties and unidentified bond-slip behavior between the embedded bar and grouted duct in precast concrete element for use in segmental bridge members. The performance of precast segmental post-tensioned concrete bridge columns in seismic regions has been investigated by many other researchers. Mild steel energy dissipation bars (ED bars) that were continuous across the column segment joints were added into the columns to increase the hysteretic energy dissipation capacity. In phase I experimental study, mechanical properties and low-cycle fatigue behavior of Talley S24100, Talley 316LN, Talley 2205 and Arminox UNS S32304 stainless reinforcing steel, A706 carbon black reinforcing steel, and MMFX II high strength, corrosion resistant reinforcing steel were investigated. Talley S24100 was found to obtain the highest ductility and the best low-cycle fatigue performance among the steels investigated. Therefore, compared to A706, Talley S24100 was considered to be the superior substitute material for ED bars. Succeeding phase II and phase III study on the bond-slip response of stainless steel reinforcing bars in grouted ducts of precast concrete element was then carried out with a focus on the influence of various duct/bar diameter ratios and different embedment lengths. A series of monotonic pull-out and tension cyclic tests were conducted to investigate the constitutive bond-slip relationship between the bar and duct confined grout and their further applications under seismic loadings. Results showed that for A706 and Talley S24100 steels, both the duct/bar diameter ratio and embedment length influenced the bond-slip behavior in the monotonic pull-out tests. A one-dimensional nonlinear bond spring model exhibited a good performance in simulating the test results. In addition to the conventional bond-slip model, an "end-slip model" is also proposed in this study to describe the loaded end slip behavior of a bar anchored in grouted duct with a relatively deep embedment (12, 16 and 24 d b ). Each bond-slip and end-slip model has a five segment structure (each segment is linear). Recommended design equations were developed for development lengths for A706 and Talley S24100 reinforcing steels, respectively. The local ED bar strains at different column top drift levels were investigated.