UHPC局压性能试验研究与承载力计算公式

Experimental research on local compression performance and bearing capacity calculation formula of UHPC

预应力超高性能混凝土(UHPC)结构具有轻型化、跨度大等优点,为了探明其锚固区的受力性能,以钢纤维长径比、局压面积比与钢纤维掺量为变量,开展了18个带中心孔道的UHPC棱柱体试件的局压试验,得到了局压承载力以及荷载-位移关系。试验结果表明:UHPC试件局压开裂荷载一般为局压极限荷载的45%~78%,局压破坏之前有较长的裂缝发展过程;局压受力可分为压密、弹性变形、外围混凝土及其与楔形体界面的裂缝发展、破坏四个阶段;钢纤维长径比分别为65与80的两组UHPC试件局压承载力、局压刚度相差均较小;UHPC试件弹性变形阶段核心混凝土竖向柔度和相对压陷的竖向柔度随局压面积减小而增大;当钢纤维掺量分别从1%增至2%和2%增至3%时,UHPC试件局压承载力增幅达12.9%~14.4%和5.3%~7.4%,局压刚度亦随纤维掺量增加而增加。UHPC局压承载力的计算仍可采用普通混凝土局压承载力公式的形式,但相关系数取值有所不同;按该文给出的方法取值,计算值与试验结果吻合较好。

The prestressed ultra-high performance concrete(UHPC)structure has the advantages of light weight and large span.In order to investigate the mechanical performance of its anchoring zone,with the steel fiber aspect ratio,local-compression area ratio and steel fiber content taken as variables,local-compression tests on 18 UHPC prism specimens with central holes are carried out,so that the local-compression bearing capacity and the load-displacement relationship of the specimens are obtained.Experimental results disclose that the local-compression cracking load of UHPC specimens is generally 45%to 78%of the local-compression limit load,and there is a long process of crack development before the local-compression failure.Under the local-compression,the specimens experience four stages:compaction,elastic deformation,crack development of peripheral concrete and its interface with wedge,and failure.The difference between the two groups of UHPC specimens with steel fiber length-to-diameter ratios of 65 and 80 respectively is small in the local compressive bearing capacity and local compressive stiffness.The vertical flexibility of the core concrete and the vertical flexibility of the relatively compressed concrete in the elastic deformation stage of the UHPC specimens increase with the decrease of the local compression area.When the content of steel fiber is increased from 1%to 2%and from 2%to 3%,the local compressive bearing capacity of UHPC specimens increases by 12.9%to 14.4%and by 7.4%to 7.6%,and the local compressive stiffness also increases with the content of steel fiber.The formula of calculating the local-compression bearing capacity of ordinary concrete is still applicable to that of UHPC,but the values of the correlation coefficient are different.By taking values using the proposed method,the calculated values agree well with our test results.