CFRP中等约束钢筋混凝土方柱单轴受压应力-应变模型

为考察纵筋、箍筋、碳纤维（CFRP）包裹层数、尺寸效应及预设损伤对CFRP约束钢筋混凝土方柱单轴受压应力-应变关系的影响，对边长305mm、高915mm及边长204mm、高612mm共22个CFRP约束钢筋混凝土方柱模型试件进行了单轴受压试验。结果表明：纵筋对应力-应变曲线上的峰值点应力有一定影响，而箍筋对应力-应变曲线形状和应力-应变曲线上的极限点应变均有很大影响，其对应力-应变模型的影响不可忽略；CFRP约束后明显改善了方柱延性，但对峰值点应力提高幅度不大，试验曲线大多存在软化段，为中等约束情况；尺寸效应对CFRP的约束作用有明显影响，已有基于约束比的强弱约束划分对本文试验结果不再适用；预设损伤对应力-应变曲线影响不大，损伤水平较大时峰值点应力和极限点应变稍有降低。提出了可考虑箍筋、CFRP及尺寸效应影响的修正约束比，建议了CFRP约束钢筋混凝土方柱强、中等及弱约束的界定标准，在此基础上建立了CFRP中等约束钢筋混凝土方柱的单轴受压应力-应变模型，模型预测结果与试验结果吻合较好。

Stress-strain model for CFRP moderately-confined reinforced concrete square columns

In order to investigate the influence of longitudinal and hoop reinforcement, layers of carbon fiber-reinforced polymer (CFRP) jackets, size effect and predamage on the stress-strain relationship of CFRP-confined RC columns, 22 square RC columns confined with CFRP were tested under uniaxial compression. The specimens included two dimensions, 305mm×305mm in cross section and 915mm in height, 204mm×204mm in cross section and 612mm in height. Test results show that the longitudinal reinforcement mainly influences the peak stress and the hoop reinforcement strongly influences both the shape of stress-strain curve and the ultimate strain. The influence of inside reinforcement should not be ignored in the stress-strain model of square columns. RC square columns confined with external CFRP experienced significant increase in ductility, but slightly enhancement in strength. Most tested stress-strain curves are moderately-confined, in which a localized strain-softening behavior occurred. Size effect strongly influences the effective confinement of CFRP. The definition of lightly-confined or heavily-confined using proposed confinement ratio method is inapplicable. The predamage has small effect on the whole stress-strain curves, the peak stress and ultimate strain slightly decrease under large damage level in this test. Based on the test data, a confinement ratio model which considered the influence of hoop reinforcement, CFRP and the section effect was proposed. Then the definitions of lightly-confined, moderately-confined and heavily-confined were suggested using the proposed confinement ratio. The stress-strain model for CFRP moderately-confined square reinforced concrete columns was proposed based on the test results. The predicted results of the proposed model agreed well with test data.