带小直径纵筋并外包CFRP的RC圆墩抗震性能研究

Research on Seismic Behaviors of RC Circular Pier with Longitudinal Rebar of Reduced Diameter and CFRP Wrap

桥梁震害调查显示,钢筋混凝土(RC)桥墩易受损,影响震后救援和灾后重建。采用小直径纵筋替换受损纵筋并外包碳纤维布(CFRP)的技术修复受损桥墩可缩短震后修复周期,节省重建费用。以某不规则连续梁桥的RC圆墩为工程背景,选择小直径纵筋的长度和直径、外包CFRP层数为参数,开展7根缩尺比例为1∶6的RC圆墩试件的拟静力试验;选用OpenSees建立有限元模型,采用试验结果验证其准确性,并开展参数分析。研究结果表明:设置小直径纵筋的桥墩的塑性变形集中在小直径纵筋高度范围内,桥墩破坏被限制在塑性铰区域内;与未设置小直径纵筋的桥墩相比,小直径纵筋使桥墩承载力降低20%~27%,但桥墩位移延性提高42%~85%,曲率延性提高47%~242%,耗能性能提高32%~56%;在满足桥墩承载力设计要求的情况下,使用小直径纵筋可有效提高桥墩抗震性能;设置小直径纵筋的桥墩在小直径纵筋区域内的实测CFRP最大应变明显大于未设置的试件,说明对设置小直径纵筋的桥墩外包CFRP,可防止桥墩过早破坏,提高延性;随着小直径纵筋长度增大或直径减小,桥墩耗能性能先增大后减小;建议以钢筋疲劳寿命需求为下限,塑性铰长度为上限选择小直径纵筋长度;选择满足保证塑性铰以外的纵筋受力始终在弹性范围内的条件下的最大直径为小直径纵筋直径;增大修复区域的混凝土强度可弥补设置小直径纵筋造成的桥墩承载力降低。

Investigations on the seismic damage of bridges after earthquakes indicate that reinforced concrete(RC) piers are easily damaged, which influences the rescue and reconstruction after earthquakes. Repairing damaged piers with the technology, which substitutes the damaged original longitudinal rebar using a longitudinal rebar with a reduced diameter(turned rebar) and envelops the RC piers with the carbon fiber reinforced polymer(CFRP), can shorten the repair period after earthquakes and reduce the reconstruction costs. The RC circular pier in a continuous girder bridge with irregular piers was selected as the case study. Quasi-static tests on seven RC circular pier specimens with a reduced scale factor of 1∶6, considering the length and diameter of the turned rebar, and the layer of CFRP wrap as parameters were adopted. The finite element models were implemented using the OpenSees finite element software, and the accuracy was verified by the test results. Parametric analysis was performed using the finite element model. The results indicate that the plastic deformation of piers with the turned rebar was concentrated within its length, and the failure of piers was limited within the plastic hinge zone. Comparing the piers without the turned rebar, the load bearing capacity of piers with the turned rebar could decrease by 20%-27%;however, the displacement ductility, curvature ductility, and energy dissipation capacity increased by 42%-85%, 47%-242%, and 32%-56%, respectively. It was established that the turned rebar could effectively improve the seismic performance of piers when the load bearing capacity of piers satisfies the design requirements. The measured maximum strains of the CFRP wraps within the length of the turned rebar in the piers with the turned rebar, were significantly larger than those in the piers without the turned rebar. It can be concluded that the CFRP wraps could be chosen for piers with the turned rebar to prevent the premature failure of piers and improve the ductility. With an increase in the length of the turned rebar or a decrease in the diameter of the turned rebar, the energy dissipation capacity of the pier first increases and then decreases. Selecting the length of the turned rebar is proposed, considering the fatigue life of rebar as the lower limit and the length of the plastic hinge zone as the upper limit. The maximum diameter obtained, under the condition of ensuring that the stress of the longitudinal rebar outside the plastic hinge zone is always within the elastic range, can be considered as the diameter of the turned rebar. Using concrete with higher strength in the repair zone of the pier can increase the load bearing capacity of the pier with the turned rebar.