混合配筋混凝土梁裂缝宽度试验及计算方法探讨

为了研究FRP筋与普通钢筋(HRB筋)混合配筋混凝土梁在受弯过程中的裂缝开展机理及其计算方法,设计制作8根混合配筋混凝土梁和3根普通钢筋混凝土梁.通过改变FRP筋种类、FRP筋直径、钢筋强度、FRP筋和钢筋配筋面积比以及截面配筋率等参数,对比分析试验梁抗弯承载力、裂缝分布、平均裂缝间距和裂缝宽度的变化规律.给出FRP筋与钢筋混合配筋混凝土梁抗弯承载力建议计算公式,并结合相关试验数据对其预测值和试验值进行分析,证明建议计算公式的精确性和合理性.根据传统的钢筋混凝土梁裂缝宽度计算理论,结合现有试验结果,对21根混合配筋混凝土梁的受弯开裂特性进行综合分析,提出正常使用阶段平均裂缝间距lm和受拉纵筋应变不均匀系数ψ的计算公式,修正裂缝宽度短期扩大系数τs,并在此基础上提出短期最大裂缝宽度的建议计算公式.结果表明:混合配筋混凝土梁正截面仍符合平截面假定;随截面配筋率的增大,混合配筋混凝土梁的平均裂缝间距和最大裂缝宽度均逐渐减小;单层配筋混合配筋混凝土梁的最大裂缝宽度比双层配筋大;平均裂缝间距建议计算公式精度较好;短期最大裂缝宽度建议公式的计算值与实测值吻合较好.相关研究成果可为混合配筋混凝土梁的设计提供一定的参考.

Experiment and Calculation of Crack Width of Concrete Beams Reinforced with Hybrid (FRP and Steel) Bars

To study the crack propagation mechanism and its calculation method for concrete beams reinforced with hybrid fiber reinforced polymer (FRP) and steel (HRB) bars during the flexural process, eight hybrid and three steel reinforced concrete beams were designed. The flexural capacity, crack distribution, average crack spacing, and crack width of test beams were compared and analyzed by modifying parameters such as the FRP type, FRP diameter, strength of steel bar, area ratio of FRP bars to steel bars, and cross-sectional reinforcing ratio. A model was then developed to calculate the flexural capacity. A comparison between the theoretical and test values verified the accuracy and rationality of the proposed formula. Based on the traditional crack theory of reinforced concrete beams, the flexural cracking characteristics of 21 hybrid reinforced concrete beams were analyzed. With the collected experimental data, the calculation formulas for average crack spacing l_m and non-uniform coefficient ψ of strain of the tensile stress bar under a serviceability limit state were put forward. The magnification coefficient derived from the short-term loading effect τ_s was corrected. Based on this, the proposed calculation model of the maximum short-term crack width was given. The results show that the cross section of hybrid reinforced concrete beam still meets the plane section assumption. With an increase in cross-sectional reinforcing ratio, the average crack spacing and maximum crack width of the hybrid reinforced concrete beam gradually reduced. The maximum crack width of the hybrid reinforced concrete beam with a single-layer reinforcement is greater than that of double-layer reinforcement, and the calculated precision of the average spacing of cracks is improved. The theoretical values of the proposed short-term maximum crack width are in good agreement with the test values, and thus, it can be used as a reference for hybrid reinforced concrete beam design.