体外预应力节段式UHPC无腹筋梁抗剪性能试验研究

Experimental Study on Shear Behavior of Externally Prestressed Segmental UHPC Beam without Stirrup

体外预应力节段式超高性能混凝土(UHPC)无腹筋桥梁由于其施工工业化水平高且构造简单,得到广泛地关注,但其抗剪性能研究尚不成熟,相关规范也相对滞后。为了研究体外预应力节段式UHPC无腹筋梁的抗剪性能,开展了静力破坏试验,共制作了5根体外预应力节段式UHPC无腹筋梁、2根体外预应力节段式UHPC有腹筋梁和1根体外预应力整体式UHPC无腹筋梁,选取了剪跨比、钢纤维掺量、箍筋间距为研究参数进行试验。结果表明:接缝张开后梁刚度明显下降;添加钢纤维的试验梁的裂缝多而密;钢纤维的掺入可以提高梁的开裂强度、极限强度和裂后性能,2%钢纤维掺量的梁开裂强度比1.5%和0%掺量的增大8.20%和1.16倍;配箍筋的梁在钢纤维失效后箍筋开始受力,并且很快达到屈服,箍筋的存在可以提高梁极限承载力,无腹筋梁的极限承载力比箍筋间距为150 mm和75 mm的梁低15.9%和19.6%。采用AASHTO GSCB INTERIM-2003标准中计算干接缝节段式梁的折减系数0.85。在不考虑安全系数的情况下,法国规范NF P 18-710中UHPC梁抗剪承载力计算公式可以准确地预测含钢纤维体外预应力节段式UHPC无腹筋梁的抗剪强度,其试验值和预测值比值的平均值为1.04,标准差为0.28。

Externally prestressed segmental UHPC beams without stirrups has attracted extensive attention because of its high level of construction industrialization and simple structures,but its shear performance study is not mature and the standards update stagnantly.In order to study the shear performance of segmental UHPC beams without stirrups,5 externally prestressed segmental UHPC beams without stirrups,2 externally prestressed segmental UHPC beams with stirrups and 1 externally prestressed monolithic UHPC beam without stirrups are fabricated.The shear-to-depth ratio,steel fiber content and stirrup spacing are selected as the research parameters.The result shows that(1)the stiffness of the beam decreases obviously after the joint is opened;(2)there are many and dense cracks in the test beam with steel fiber;(3)the crack strength,ultimate strength and post-crack performance of the beams can be improved by steel fiber addition,the cracking strength of beams with 2% steel fiber content is 8.20%and 1.16 times higher than that of beams with 1.5% and 0% steel fiber contents;(4)the stirrup begins to bear force after the steel fiber fails,and soon reaches yield,the existence of stirrup can improve the ultimate bearing capacity of the beam,the ultimate bearing capacity of beams without stirrup is 15.9% and 19.6% lower than that of beams with stirrup spacing of 150 mm and 75 mm.The AASHTO GSCB INTERIM-2003 standard is used to calculate the reduction factor of 0.85 for the dry-jointed segmental beams.With no consideration for safety factor,the formula for calculating the shear capacity of UHPC beams in French standard NF P 18-710 can accurately predict the shear strength of externally prestressed segmental UHPC beams without stirrup,the average value of the ratio of experimental value to predicted value is 1.04,and the standard deviation is 0.28.