考虑黏结-滑移效应的FRP筋混凝土受弯构件裂缝宽度计算方法

Study on Calculation Method of Crack Width of FRP Rebar Reinforced Concrete Flexural Members Considering Bond-slip Effect

由于纤维增强聚合物(FRP)筋的弹性模量较低,FRP筋混凝土梁的设计状态通常采用其在正常使用极限状态下的裂缝宽度来控制,故准确预测最大裂缝宽度对FRP筋混凝土梁的设计及应用至关重要。FRP筋混凝土梁裂缝宽度的计算公式依然沿用我国《纤维增强复合材料建设工程应用技术规范》(GB 50608—2010)中的半经验计算公式,计算结果偏小。相较于经验公式,基于应力传递的数值计算模型可以充分反映开裂混凝土和FRP筋之间应力重分布的复杂特性。因此,在综合考虑FRP筋与混凝土间的黏结-滑移效应、裂缝间混凝土拉伸硬化效应以及材料非线性本构关系等问题的基础上,建立了FRP筋混凝土梁裂缝宽度计算的数值模型。数值分析中采用了两种黏结应力-滑移本构模型,通过对比可得,本构模型的选取对计算结果具有较大的影响。将数值模型计算结果与试验结果和按规范中公式计算的结果进行对比后发现:试验梁纯弯区短期平均裂缝宽度的模型预测结果与试验结果较为接近,两者比值的均值为0.92;按修正后的公式计算,结果更精确。

Due to the low elastic modulus of fiber reinforced polymer(FRP) rebar, the design state of FRP rebar reinforced concrete beams is usually controlled by the crack width under the serviceability limit state. Therefore, accurate prediction of the maximum crack width is very important for the design and application of FRP rebar reinforced concrete beams. The formula for calculating the crack width of FRP rebar reinforced concrete beams still follows the semi-empirical calculation method in China′s Technical Code for Construction Engineering Application of Fiber Reinforced Composite Materials(GB 50608—2010), and the calculation result is small. Compared with the empirical formula, the numerical calculation model based on stress transfer can fully reflect the complex characteristics of stress redistribution between cracked concrete and FRP rebar. Therefore, the numerical model for calculating the crack width of FRP rebar reinforced concrete beams is established based on the comprehensive consideration of the bond-slip effect between concrete and FRP rebar, tension-stiffening effect of concrete between cracks, and nonlinear constitutive relation of materials. Two kinds of bond stress slip constitutive models are applied in the numerical analysis. The comparison shows that the selection of constitutive model has great influence on the calculation results. The results of the numerical model are compared with the test results and the results calculated according to the formula in the code. It shows that the model prediction result of the short-term average crack width in the pure bending area of the test beam is close to the test result, and the average value of the ratio between the two is 0.92. According to the revised code formula, the calculation results are more accurate.