水泥基复合材料加固小偏心受压钢筋混凝土柱承载力

通过对工程水泥基复合材料(ECC)加固钢筋混凝土(RC)柱和未加固RC柱进行小偏心受压试验,研究ECC加固RC柱小偏心受压性能。试验结果表明,ECC加固层能有效约束核心混凝土;与未加固柱相比,加固柱的裂缝细而密,达到峰值荷载时受压区ECC尚未被压碎,破坏过程比较平缓,有较好的完整性,并表现出一定的延性特征;相对偏心距相同时,加固柱的开裂荷载、峰值荷载及延性相比未加固柱分别提高了107%～236%、45%～159%、37.4%～41.3%。依据试验结果,绘制出各加固柱跨中荷载-挠度曲线,可分为4个阶段：弹性阶段、裂缝稳定扩展阶段、最大荷载阶段及下降段。随着加固层厚度的增大,相同荷载下ECC竖向应变及钢筋应变越小;随着相对偏心距的增大,相同荷载下ECC竖向应变及钢筋应变越大。基于混凝土结构理论及力学原理,分析ECC加固层对核心混凝土柱的约束机制,提出ECC约束混凝土抗压强度和峰值应变的表达式,推导出加固柱受压承载力计算公式,承载力计算值与试验值相对误差在10%以内,二者吻合良好,为ECC加固混凝土柱在实际工程中的应用提供理论参考。

Bearing capacity of reinforced concrete columns strengthened by engineered cementitious composite under small eccentric compression load

Small eccentric compression tests on engineered cementitious composite (ECC)-strengthened reinforced concrete (RC) columns and the unstrengthened column as reference were carried out to investigate the influence of the thickness of the ECC reinforcement layer on the compressive performance of strengthened RC columns. The test results show that the ECC reinforcement layer effectively restrains the core concrete, and strengthened columns exhibit obvious ductile failure pattern. Compared with the unstrengthened RC column, the cracks of the reinforced column are thin and dense. When the peak load is reached, the compression zone is not crushed, and the failure process is relatively gentle, with better integrity, exhibiting certain ductility characteristics; The cracking load, peak load and ductility are increased by 107%-236%, 45%-159% and 37.4%-41.3%. The mid-span load-deflection curves are drawn based on the test results, which could be divided into four stages: The elastic stage, the stable crack propagation stage, the maximum load stage and the descending stage. With the increase of reinforcement layer thickness, the strains of ECC and reinforcing bars are smaller under the same load; With the increase of relative eccentricity, the strains of ECC and reinforcing bars are larger under the same load. Based on the theory of concrete structure and mechanical principle, the action mechanism of ECC reinforced layer on the core column was analyzed and the expressions of compressive strength and peak strain of the ECC-strengthened RC columns were proposed. The calculation formula of the bearing capacity of the strengthened column was established and the relative error between the theoretical results and the experimental values is less than 10%, which is in good agreement with the test results. Hence, the established calculation method could provide theoretical support for the application of ECC strengthened concrete column in practical engineering.