GFRP-钢绞线复合筋与混凝土黏结机理及强度计算模型

Bonding mechanism and strength calculation model of GFRP-steel composite rebars embedded in concrete

GFRP-钢绞线复合筋不仅抗拉强度高、耐腐蚀性好、质量小,同时具有较高的弹性模量。复合筋的高强度能否得到充分发挥,一定程度上取决于其与混凝土的黏结性能。通过15组黏结试件的拉拔试验,分析对比筋材类型、直径、钢绞线体积率、保护层厚度和混凝土强度对FRP筋与混凝土黏结强度及破坏形态的影响。结果表明：复合筋与混凝土黏结强度较GFRP筋与混凝土黏结强度有一定的提高,且随着钢绞线体积率的增加而增大,但仍低于钢筋与混凝土的黏结强度;随着保护层厚度的增加,复合筋与混凝土黏结强度逐渐增大,试件的破坏形态由混凝土劈裂转为筋材拔出;混凝土强度的提高对黏结强度的增强作用较为显著。在试验的基础上,将筋材周围的混凝土作为带裂缝的弹性体,并考虑开裂部分混凝土的残余强度,根据混凝土环向应力的分布,建立了筋材与混凝土最大黏结应力计算模型。根据该计算模型和试验结果,引入黏结应力分布系数,建立了带肋FRP筋与混凝土黏结强度的计算方法,黏结强度计算值与试验值吻合较好。

GFRP-steel composite rebar has high tensile strength, good corrosion resistance, light weight, and high elastic modulus. Nonetheless, whether the high tensile strength of composite rebar could be made full use mainly depends on its bond strength with concrete. A total of 15 pull-out tests were conducted to investigate the effects of rebar type, rebar diameter, steel strand volume ratio, concrete cover thickness and concrete strength on the failure mode and bond strength of FRP bars embedded in concrete. The results show that the composite rebar has higher bond strength with concrete than the GFRP one. Although the bond strength of the composite rebar increases with increase in steel strand volume fraction, the strength is still lower than that of steel rebar. The bond strength is improved and the failure mode would change from concrete splitting to pullout of rebar with increase in concrete cover thickness. Also, the increase of concrete strength could improve the bond strength significantly. In addition to the experimental work, a calculation model for predicting the maximum bond stress of rebar in concrete was proposed by assuming that the adjacent concrete surrounding the rebar is an elastic body with cracks with residual strength. The model was developed according to the hoop stress distribution of the concrete surrounding the rebar. Finally, based on the proposed model and the test results, a design method for predicting the bond strength of ribbed FRP in concrete was presented by introducing a bond stress distribution coefficient. The predicted results for bond strength agree well with the test results.