Ren Zhigang, Li Qi, Liu Chuang
School of Civil Engineering and Architecture, Wuhan University of Technology, Wuhan 430070, China.
Yichang Urban Construction Investment Holding Group Co., Ltd., Yichang 443000, China.
Materials (Basel). 2022 Feb 1;15(3):1137. doi: 10.3390/ma15031137.
Round-ended rectangular concrete-filled steel tube (RRCFST) columns are prone to local buckling that are close to straight steel plates when used as piers of a bridge and affect its long-term use. In order to solve this problem, tie bars were used in this research to stiffen RRCFST columns. Eleven specimens with tie bars and three specimens without tie bars were tested to analyze influences of cross-sectional aspect ratio, longitudinal spacing, limb numbers and diameter of the tie bar on failure model, confined effect, bearing capacity and ductility of RRCFST stub columns. Finite element models (FEM) with different concrete constitutive models for rectangular and circle parts were established and validated to reveal the mechanism of the constrained effect of tie bars. Experimental and FEM results show that the local buckling scope was decreased and gradually moved to middle height with decreased longitudinal spacings tie bars. The addition of tie bars in RRCFST columns with large aspect ratios slightly enhanced the ultimate bearing capacity, the diameter of tie bars changing from 8 mm to 12 mm greatly enhanced displacement and energy ductility by 58.4% and 85.1%, respectively. However, more tie bars (e.g., two or three limbs) utilization could not further improve the bearing capacity and failure mode. While, the tie bars had very limited contribution to bearing capacity and ductility for RRCFST columns with small aspect ratios, because the outer steel tubes already individually provided for enough confinement on inner concrete. By considering different concrete confined models for rectangular and round-ended parts, an analytical model was proposed and validated to predict the ultimate bearing load for RRCFST stub columns with tie bars.
圆端矩形钢管混凝土（RRCFST）柱用作桥梁桥墩时，靠近平直钢板的部位容易发生局部屈曲，影响其长期使用。为解决这一问题，本研究采用拉结筋对RRCFST柱进行加劲。对11个有拉结筋的试件和3个无拉结筋的试件进行了试验，以分析截面高宽比、纵向间距、拉结筋肢数和直径对RRCFST短柱破坏模式、约束效应、承载力和延性的影响。建立并验证了采用不同混凝土本构模型的矩形和圆形部分的有限元模型（FEM），以揭示拉结筋的约束作用机理。试验和有限元结果表明，随着拉结筋纵向间距的减小，局部屈曲范围减小并逐渐向柱中高度移动。在高宽比大的RRCFST柱中增加拉结筋对极限承载力有轻微提高，拉结筋直径从8mm变为12mm时，位移延性和能量延性分别大幅提高了58.4%和85.1%。然而，更多拉结筋（如两肢或三肢）的使用并不能进一步提高承载力和破坏模式。同时，对于高宽比小的RRCFST柱，拉结筋对承载力和延性的贡献非常有限，因为外钢管已经单独为内部混凝土提供了足够的约束。通过考虑矩形和圆端部分不同的混凝土约束模型，提出并验证了一个分析模型，以预测带拉结筋的RRCFST短柱的极限承载力。
