配置高强竖向预应力筋混凝土梁抗剪性能试验研究

Experimental study on shear behavior of reinforced concrete girders with high-strength vertical prestressed tendon

目前国内外有代表性的混凝土结构设计规范对配置三向预应力混凝土箱梁的抗剪设计均未考虑竖向预应力对梁抗剪承载能力的影响,并对梁内抗剪钢筋的抗拉设计强度取值进行了限制,是否合适值得重新审视。对4片配置高强竖向预应力筋混凝土工字梁的抗剪性能进行了试验研究,主要研究纵向和竖向预应力的施加对配置高强竖向预应力筋混凝土梁抗剪性能的影响以及试验梁剪切破坏时高强竖向预应力筋的强度发挥水平。结果表明:就所研究的情形而言,施加3.2MPa竖向预压应力可使梁斜截面开裂荷载提高约22%、临界斜裂缝倾角增加约17°、抗剪承载能力提高约30%。剪切破坏时,竖向预应力筋是否张拉对加载过程中抗剪钢筋的应变增量影响很小,未张拉的竖向抗剪钢筋内最大应力为713MPa,预张拉后,抗剪钢筋最大应力增量为709MPa,但叠加其初始张拉应力后其内最大应力可达1440MPa。对竖向抗剪钢筋进行张拉能使高强抗剪钢筋的强度得到较好发挥,但同时导致临界斜裂缝的倾角增大、水平投影长度减小。因此,与配置普通箍筋的混凝土梁抗剪设计相比,配置竖向高强预应力筋混凝土梁竖向抗剪钢筋的最小间距、最小配筋率及初始张拉应力均应特别考虑。

So far,representative domestic and overseas design codes on concrete structures did not consider the influence of vertical prestress on shear bearing capacity of three-way prestressed concrete box girder. Additionally,a maximum tensile strength was imposed on the vertical shear reinforcement. In this study,the shear behavior of four reinforced girders with high strength vertical prestressed tendon were investigated,and furthermore the development law of damage for experimental girders,load-deflection relationship,average strain of web,vertical prestressed reinforcement stress,cracking load and shear bearing capacity were analyzed,respectively. Test results showed that when 3. 2MPa vertical compression stress was applied,critical inclined crack angle increased about 17°,the cracking load of girders with vertical prestressed force increased about 22% and the shear strength may increase about 30%. Whether vertical prestressed tendon was tensioned or not had little impact on the strain increment of shear reinforcement. The maximum stress in non-tension vertical steel bar was 713MPa at shear failure. However,it may reach 1440MPa after superposing the initial tension stress. After tensioning the vertical shear reinforcements, the strength of high strength shear reinforcement may be improved,and the inclined crack angle may increase. Therefore,compared to shear design of concrete beam with ordinary stirrup,the minimum spacing,the minimum reinforcement ratio and the initial tensile stress of vertical prestressed reinforcement should be suitably selected in practical engineering.