GFRP筋钢纤维高强轻骨料混凝土梁受弯性能试验研究

完成了9根配GFRP筋和1根配钢筋的高强轻骨料混凝土梁受弯性能试验，观察其破坏过程与破坏形态，分析了纤维掺量、纵筋类型、配筋率及纵筋直径等参数对试件承载能力、弯矩-跨中挠度曲线、裂缝宽度等受弯性能的影响，采用美国ACI 440.1R-15、中国GB 50608—2010和加拿大CSA S806-12、ISIS-M03-07等规范中的建议模型，通过开裂弯矩、承载力、挠度和裂缝宽度等参数评估了各国规范对该类构件的适用性。结果表明：随配筋率的增大，试件破坏模式依次表现为受拉破坏、平衡破坏和受压破坏，受压区破坏面贯穿骨料内部，较为光滑；掺入钢纤维能够有效抑制混凝土裂缝开展，延缓构件刚度退化，使开裂弯矩平均提高51.71%，承载力平均提高22.10%；增大GFRP筋配筋率能够提高构件刚度，但GFRP筋直径变化对试件变形及裂缝宽度无显著影响；GFRP筋梁开裂后刚度退化较配钢筋的对比试件迅速。各国规范计算结果表明：受拉破坏试件承载力计算结果较离散，且均偏于不安全；对于平衡破坏和受压破坏的试件预测结果均偏于保守，有足够安全储备。考虑轻骨料和钢纤维对构件刚度退化规律的影响，修正有效惯性矩并给出建议挠度计算模型，计算结果与试验结果吻合较好。

Flexural behavior of steel fiber-reinforced high-strengthlightweight aggregate concrete beams reinforcedwith glass fiber-reinforced polymer bars

Nine beams reinforced with glass fibre-reinforced polymer (GFRP) bars and one beam reinforced with steel rebars fabricated using high-strength lightweight aggregate concrete were tested. The experimental results in terms of flexural strength, deflection, crack width, and failure mode were presented and the influences of parameters, including steel fiber content, type of reinforcement, reinforcement ratio and bar diameter, were discussed. The equations recommended by the design codes ACI 440.1R-15, GB 50608—2010, CSA S806-12 and ISIS-M03-07 were employed to assess the flexural behavior in terms of cracking moment, ultimate moment, deflection, and crack width of the test beams. The test results show that FRP rupture failure, balanced failure, and concrete crushing failure are sequentially obtained as the reinforcement ratio constantly increases. The failure surfaces in the compression zone cross the interior of the aggregates and are relatively smooth. Adding steel fibers improves the rigidity and restrains the propagation of the cracks of the specimens. Besides, the cracking moment and load carrying capacity are increased by 51.71% and 22.10%, respectively, due to the addition of fibers. Increasing the GFRP reinforcement ratio increases the stiffness of the beams, while GFRP bar diameter has a marginal effect on the deflection and cracking behavior. Furthermore, the beams reinforced with GFRP bars exhibit more rapid stiffness degradation compared to their steel reinforced counterparts. The equations recommended by the design codes overestimate the strength of specimens without adequate reinforcement and the theoretical results are scattered. However, the strength of beams failed by concrete crushing are underestimated. The formula for effective moment of inertia was modified considering the effects of lightweight aggregate and steel fiber on the rigidity degeneration of the beams. The theoretical values calculated by the recommended equation agree well with the test results.