CFRP中等约束钢筋混凝土方柱反复受压本构模型

为填补FRP约束混凝土滞回本构模型的空白,对边长305mm,高915mm及边长204mm,高612mm两种尺寸的CFRP约束钢筋混凝土方柱,采用500t四棱柱压力试验机进行了单调及反复轴压试验.试验结果表明,大尺寸CFRP约束钢筋混凝土方柱的应力-应变关系曲线存在软化段,CFRP的约束作用为中等约束,且尺寸效应对CFRP的有效约束作用有明显影响;箍筋对单调受压应力-应变曲线形状、极限压应变、反复受压卸载曲线和残余应变影响均较大.基于试验结果提出了考虑钢筋、尺寸效应及CFRP包裹层数等影响参数的CFRP中等约束混凝土方柱的反复受压本构模型.模型由描述包络线的单调受压本构模型、曲线形式的卸载曲线及直线形式的再加载曲线3部分组成,模型预测结果与试验结果吻合较好.

Cyclic Stress-strain Model for CFRP Moderately-confined Reinforced Concrete Square Columns

To address the knowledge gaps of the cyclic stress-strain model of FRP-confined concrete, this paper presented the experimental results of CFRP-confined plain and RC square columns under monotonic and cyclic axial compression. The specimens were divided into two groups on the basis of size. The width of the cross section and the height of the total column were 305 mm, 915 mm and 204 mm, 612 mm for the two groups, respectively. Test results showed that the stress-strain curves of the CFRP-confined larger columns exhibited a localized strain-softening behavior, in which the confinement of CFRP wrap was moderately-confined and significantly influenced by size effect. Moreover, the ultimate compression strain, unloading curves and plastic strain were remarkably influenced by hoops. Based on the test data, a cyclic axial stress-strain model for FRP-confined square concrete columns was proposed. The proposed cyclic axial stress-strain model consists of three main components, namely (i) a monotonic stress-strain model to describe the envelope curve, (ii) a polynomial expression for the unloading curve, and (iii) a straight line for the reloading path. The influences of internal steel reinforcements, size effect and as well as the number of layers of CFRP wrap were considered. The good agreement between the predictions of the proposed model and the test results demonstrates the capability and accuracy of the proposed model.