截面形式对R UHPC梁抗弯承载力的影响

为明确截面形式对UHPC抗拉强度在钢筋超高性能混凝土(R-UHPC)梁抗弯承载力贡献的影响,考虑实测得到的7种不同钢纤维掺量UHPC的抗拉和抗压性能,对矩形、箱形和T形R-UHPC梁进行抗弯承载力计算,构建并分析抗拉强度贡献率、抗压强度利用率等指标.结果表明:UHPC根据其硬化段长短和其极限应变与钢筋屈服应变的关系,可划分为U0、 U1和U2类材料. UHPC抗拉强度的贡献率与截面形式有关:矩形梁箱形梁T形梁,对U1和U2类UHPC的矩形梁或箱形梁,宜考虑其抗拉强度对梁抗弯承载力的贡献.材料设计时,若考虑UHPC抗拉强度的作用,宜采用U2类材料.截面设计时, UHPC抗拉强度的贡献,矩形梁应考虑,箱形梁可考虑, T形梁可不考虑,宜采用箱形、 I形或工形梁截面以提高抗拉强度贡献. UHPC抗压强度利用率,随纤维掺量的增大而下降,利用率在45.5%～60.2%范围.工程应用时,可应用UHPC-NC叠合梁或预应力UHPC梁以提高抗压强度利用率.

Influence of section shape on flexural capacity of R UHPC beam

The flexural capacity of rectangular, box and T-shaped reinforced ultra-high performance concrete (R-UHPC) beams was calculated and analyzed, and UHPC performance influence of 7 kinds of UHPC steel fiber content on flexural capacity was also considered, the indexes of contribution rate of tensile strength and utilization rate of compressive strength were conceived. The analysis results showed that 7 groups of UHPC can be divided into U0 class with non-hardening section or very short hardening section, U1 class with quite long hardening section but its limit strain was less than the yield strain of steel reinforcement, and U2 class with hardening section and its limit strain was greater than the yield strain of steel reinforcement. The contribution rate of UHPC tensile strength was related to section-shape: rectangular beam > box beam > T-beam. For rectangular or box UHPC beams of U1 and U2 class, the contribution rate of tensile strength should be considered to caculate flexural capacity of beams. In the engineering application, the utilization rate of compressive strength decreases with the increase of fiber content, the utilization rate was in the range of 45.5%~60.2%, and the utilization rate of compressive strength was low, UHPC-NC composite beam or prestressed UHPC beam was suggested in actual engineering. In material design, if the role of UHPC tensile strength was considered, UHPC should have corresponding tensile properties, and U2 class should be used. When U1 or U2 class were used in section design, the contribution rate of UHPC tensile strength should be considered for rectangular beam, box beam might consider but T-beam not consider.