摘要：
In order to determine the appropriate tension control stress and the height of steel wire to the bottom of RC beam and provide reasonable parameters for external prestress strengthening,seven test beams of contraction scale were designed.The mechanical property,failure mode and ultimate bearing capacity of RC beams strengthened by external prestress respectively under different tension control stress and the height of steel wire to the bottom of RC beam were investigated.The main content of the test included load,deflection,strain,the appearance and development of cracks.The results show that the failure modes of the reinforced beams are similar with those without strengthening,and all the test beams show significant plastic failure characteristics.There are obvious cracks occurrence and development process before the failure for test beams,but the duration is much longer for reinforced beam than that of the beams without strengthening.At the same time,the theoretical bearing capacity of each test beam is calculated according to the bearing capacity theory.The ANSYS software is employed to compare the experimental value and the calculated value.The increasing height of steel wire to the bottom of RC beam is beneficial to the improvement of the bearing capacity.However,when the height increases to a certain degree,the secondary effect is remarkable on account of the increase of the deflection,so the improvement effect of the bearing capacity is significantly weakened.The bigger the tension control stress is,the bigger the cracking load and ultimate load of reinforced beam will be,and the smaller the steel wire stress increment will be.Large tension control stress gives full play to the external prestress strengthening effect.Whereas,when the tension control stress decreases to a certain degree,there is almost no effect on the bearing capacity with any the tension control stress.Compared with the change of tension control stress,the influence of the height of steel wire to the bottom of RC beam on the mechanical property is more significant.Moreover,the external prestress strengthening can significantly improve the bearing capacity of the original beam as well as its ductility,and the plasticity development is more complete in the destruction stage.%为了确定合适的张拉控制应力和束高,为体外预应力加固提供合理的参数,制作了7根缩尺试验梁,分别开展了不同张拉控制应力和束高下的体外预应力加固RC梁受力性能、破坏模态和极限承载力的试验研究,测试了荷载、挠度、应变、裂缝的发生以及发展状况等.同时,依据承载力理论计算得到各试验梁的理论承载力,利用ANSYS软件将试验值与计算值进行对比分析.研究结果表明:被加固梁破坏模态与未加固梁类似,均呈现显著的塑性破坏特征,二者破坏前有明显的裂缝发生、发展过程,但持续时间较未加固梁大大增加;增大束高有利于提高梁的承载能力,但束高增大到一定程度后,由于挠度增加导致钢束对梁体二次效应显著,梁体承载能力的增大效应显著削弱;张拉控制应力越大,被加固梁开裂荷载与极限荷载越大,钢绞线应力增量越小,较大的张拉控制应力有利于充分发挥体外预应力加固效应,但当张拉控制应力小到一定程度时,改变张拉控制应力大小对被加固梁承载力几乎无影响;相比于变化张拉控制应力,束高的改变对梁体受力性能的影响更加显著;体外预应力加固在提高原梁承载能力的同时,显著改善了其延性,破坏时梁体塑性发展更加充分.
