体外预应力无腹筋超高性能混凝土梁的抗剪性能试验探索

Experimental study on shear behavior of externally prestressed ultra-high performance concrete beams without stirrups

为研究超高性能混凝土(Ultra-high performance concrete,UHPC)无腹筋梁的抗剪性能,本次试验共制作9根体外预应力无腹筋UHPC梁,试验参数包括预应力的大小、剪跨比、纵向配筋率和钢纤维掺量,通过四点加载方法分析试验构件的破坏形态、开裂强度和极限强度。试验结果表明:无预应力无腹筋UHPC梁在剪跨比为1.0加载时发生弯曲破坏,设置钢绞线25%极限强度张拉值使无腹筋UHPC梁的正截面抗弯能力得到强化,弯矩增幅为157%,使试验梁从弯曲破坏转变为剪切破坏。张拉25%和40%控制应力的UHPC梁的开裂荷载分别提高了1.2倍和2.6倍,有效抑制了裂缝的形成。体外预应力张拉40%控制应力,剪跨比为1.0和1.5时UHPC梁均发生剪切破坏,但是剪跨比增大至2.0时,UHPC梁发生弯曲破坏,受压区混凝土压溃。规范中的抗剪公式均低估了体外预应力无腹筋UHPC梁的抗剪承载力,其斜截面抗剪强度的实验值与计算值之比的平均值分别为2.28和3.21。

In order to study the shear behavior of ultra-high performance concrete(UHPC)beams without stirrups,9 externally prestressed UHPC beams without stirrups were fabricated.The experimental parameters included the level of prestress,shear span-to-depth ratio,longitudinal reinforcement ratio and volume fraction of steel fibers.Four-point loading method was used to obtain the failure patterns,cracking strength and ultimate strength.The results show that the non-prestressed UHPC beam under the shear span-to-depth ratio of 1.0 suffers from flexural failure.However,the flexural resistance of the normal section of UHPC beam is strengthened by a prestressing tension of 25%ultimate strength of the strands,resulting in an increase of the flexural moment by 157%and turning into a shear failure.Compared with non-prestressed UHPC beam,the cracking loads of UHPC beams tensioned by 25%prestress and 40%prestress increase by 1.2 times and 2.6 times,respectively,which effectively inhibit the formation of cracks.The UHPC beams with 40%prestress under shear span-to-depth ratio of 1.0 and 1.5 fail in shear.However,when the shear span-to-depth ratio increases to 2.0,the UHPC beam suffers from a flexural failure,which leads to concrete crushing in the compression zone.The formulae of the codes underestimate the shear capacity of the externally prestressed UHPC beams,since the average ratios of the experimental shear capacity to the calculated one of the inclined section are 2.28 and 3.21,respectively.