重复荷载作用下T形截面柱箍筋约束混凝土加卸载准则

为研究T形截面柱箍筋约束混凝土在重复荷载作用下的加卸载模型，在已有5根箍筋约束混凝土T形截面柱轴心重复受压性能试验研究基础上，采用ANSYS有限元软件对其受力过程进行分析，研究了T形截面柱箍筋对核心混凝土的有效约束作用。综合有限元分析结果及试验结果，建立了T形截面柱约束混凝土的抗压强度和峰值应变计算式，计算值与试验值吻合良好。通过分析重复荷载作用下箍筋约束混凝土的应力-应变包络线、共同点轨迹线的特征，发现共同点轨迹线与包络线形状相似，给出了应力-应变包络线方程，计算结果与试验结果吻合良好。据此建立了重复荷载作用下T形截面柱箍筋约束混凝土的卸载曲线、再加载曲线方程，计算曲线与试验曲线吻合较好，说明建议的加卸载准则能较好地反映轴压重复荷载作用下箍筋约束混凝土的应力-应变曲线的变化规律。

Loading and unloading criteria of T-shaped concrete columns confined by stirrups under repeated axial load

To study the loading and unloading model for the confined concrete in T-shaped columns, based on the experimental study on the compression properties of five T-shaped columns confined by stirrups under repeated axial load, the loading process was analyzed by the finite element (FE) software. The confinement mechanism of T-shaped columns confined by stirrups under repeated axial load was studied. Based on the test results and FE analysis, the calculation formula for the compressive strength and peak strain of the confined concrete were proposed for T-shaped concrete columns. It is shown that the test results are in good agreement with the FE results. The stress-strain envelope and common point curve of the confined concrete in T-shape columns were studied. The results show that the shape of the stress-strain envelope is similar to the common point curve. An equation was proposed for the stress-strain envelope and was shown to predict well the test results. An equation for the loading and unloading curve of confined concrete was also proposed. The predictions of the equation are in good agreement with the test results, which indicate that the proposed model is able to describe the stress-strain relationship of concrete confined by stirrups when the T-shaped columns were tested under repeated axial load.