基于可靠度的GFRP筋混凝土梁抗弯承载力设计方法

Reliability-based design method for ultimate load-bearing capacity of GFRP reinforced concrete beams under flexure

为解决混凝土结构中的钢筋锈蚀问题,采用玻璃纤维增强复合材料(Glass Fiber-Reinforced Polymer,GFRP)筋替代钢筋是一种行之有效的方法。由于GFRP筋的线弹性力学特性,GFRP筋混凝土(GFRP-RC)梁的弯曲破坏模式为脆性破坏(受拉破坏或受压破坏),钢筋混凝土梁的设计方法将不适用于GFRP-RC梁,因此有必要开展基于可靠度的GFRP-RC梁抗弯承载力设计方法研究。基于已有文献数据,系统收集和整理了相关设计参数的统计信息。在考虑荷载组合、配筋率、材料强度等关键参数影响的基础上,建立了3432根GFRP-RC梁的设计空间。采用Monte Carlo模拟对GFRP-RC梁抗弯承载力极限状态开展了可靠度分析。结果表明:受拉破坏时,根据《纤维增强复合材料建设工程应用技术规范》(GB 50608-2010)设计的梁的可靠指标(β=4.08～4.50)高于脆性破坏的目标可靠指标(β_T=3.7);受压破坏时,根据《纤维增强复合材料建设工程应用技术规范》GB 50608-2010设计的梁的可靠指标(β=3.08～3.39)低于β_T。基于上述分析,以不同弯曲破坏模式下的梁均达到(β_T=3.7)为目标,校准了GFRP筋材料分项系数(γ_f=1.3),并改进了受压破坏控制截面的GFRP筋极限应力计算公式。

Substitution of steel reinforcements with glass fiber-reinforced polymer （GFRP） bars shows great promise to solve the problem of durability in reinforced concrete （RC） structures. Due to the linear elastic mechanical properties of GFRP bars, the brittle failure （tensile failure and compressive failure） is unavoidable in GFRP-RC beams under flexure. Thus, the design provisions developed for concrete structures with steel bars are not necessarily applicable to those with GFRP bars. In this paper, a reliability based design approach for GFRP-RC beams under flexure is presented. Firstly, statistics of random variables in load and resistance model are obtained from literature. Then, a design space of 3432 GFRP-RC beams covering a wide range of design scenarios are considered to conduct stochastic simulation with respect to the ultimate flexural strength. The simulating results show that the reliability index （β=4.08-4.50） obtained from current Chinese Code is higher than the target reliability index （βT=3.7） for tension controlled sections. However, the reliability index （β=3.08-3.39） obtained is far lower than the target reliability index for compression controlled sections. Finally, to achieve the reliability index （βT=3.7） for all possible flexural failure modes, the GFRP partial material factor is suggested as 1.3 based on the reliability analysis, and a new equation of ultimate stress of GFRP bars in compression controlled sections is revised.