超高韧性水泥基复合材料控裂钢筋混凝土复合梁正截面承载力计算

Calculation of flexural capacity for crack-control UHTCC/RC composite beams

采用拉应变可达3%～5%、极限受拉破坏时平均裂缝间距和平均裂缝宽度仅为1～2mm和60～100μm的超高韧性水泥基复合材料(UHTCC)替换普通钢筋混凝土梁受拉区的部分混凝土材料,可提高结构的耐久性。针对该类UHTCC/RC复合梁,在假定UHTCC和混凝土之间界面粘结很好和平截面假设成立的前提下,根据平衡方程给出了其整个受力过程中考虑UHTCC起裂后拉应力增加部分影响的弯曲承载力理论解析公式,结合所完成的12个UHTCC/RC复合梁弯曲试验结果,进行了对比。结果表明,理论解析公式和UHTCC按理想弹塑性受拉模型推导的理论简化公式计算值比较接近,最大误差不超过10%。本文提出的正截面承载力计算方法可为该类复合梁的承载力设计提供参考。

Uhra-high toughness cementitious composite （UHTCC） is a new class of fiber reinforced cementitious material and possesses remarkable tensile strain capacity of up to 5% -5% and a unique crack dispersion capacity with the average crack width of 60-100 μm at tight crack spacing of merely 1-2mm. Past studies show that utilizing UHTCC to replace a part of concrete in tension region of ordinary reinforced concrete beam to serve as crack-controlled layer is an effective method to improve durability of structures. In this paper, the flexuraI response of UHTCC/RC composite beams were investigated. Under the assumption of perfect bond between UHTCC and concrete material together with plane section assumption, analytical formulae for calculating flexural capacity at any loading moment were given based on a pair of equilibrium equations, in which the contribution from sustaining higher load after tensile initial cracking in UHTCC material was considered. Using the experimental data of a total of 12 UHTCC/RC composite beams, the feasibility of the suggested formulae was examined. The comparison shows that flexural load-carrying capacity calculated by the proposed analytical formulae is close to that by simplified analytical formulae in which tensile stress strain relation in UHTCC is modeled using ideal elasto-plastic model and the maximum error is no more .than 10%. The present study provides a useful reference for the design UHTCC/RC composite beams in future practical engineering applications.