CFRP筋钢骨混凝土组合梁受弯性能

Flexural Behavior of CFRP Reinforced Concrete Encased Steel Composite Beams

为研究CFRP(Carbon Fiber Reinforced Polymer/Plastic)筋钢骨混凝土组合梁的抗弯性能,试验设计了3片CFRP筋钢骨混凝土组合梁,其中对比参数包括不同弹性模量的受拉主筋和不同CFRP筋配筋率,通过静载试验得到了钢骨混凝土组合梁在应变、挠度、裂缝开展以及抗弯承载能力等方面随着荷载增加的变化规律。研究结果表明:随着荷载的增大,工字钢与混凝土之间的滑移也会增大,从而导致钢骨混凝土组合梁加载点截面应变沿梁高方向会出现不符合平截面假定的情况;提高受拉主筋的弹性模量可以提高主梁抗弯刚度、抗裂性能以及耗能能力;CFRP筋钢骨混凝土组合梁在工字钢下翼缘屈服之后的强度储备比相同抗弯承载力的普通钢筋钢骨组合梁要大,且耗能能力提高约1.36倍;当受拉主筋与混凝土接触面积相同时,增加组合梁的配筋率,可以延缓CFRP筋钢骨混凝土组合梁的裂缝开展,提高组合梁的整体抗弯性能和耗能能力。采用梁的纯弯曲计算理论推导了开裂弯矩公式,并结合试验结果引入开裂弯矩影响系数对计算公式进行了修正,其中普通钢骨混凝土组合梁的开裂弯矩影响系数取0.73,CFRP筋钢骨混凝土组合梁的开裂弯矩影响系数取0.43。结合试验,对比研究国内外规范中有关钢骨混凝土组合梁极限承载能力的计算结果,表明《钢骨混凝土结构技术规程》(YB 9082—2006)、《组合结构设计规范》(JGJ 138-2016)和美国规范《Guide for the Design and Construction of Concrete Reinforced with FRP Bars》(ACI-440-1R)的计算结果均比试验结果偏小;而《劲性钢筋混凝土结构设计指南》(CH 3-78)与《钢-混凝土组合梁设计原理》得到的计算值与试验值吻合相对较好。研究成果可为同类型钢骨混凝土组合梁的设计和规范编制提供参考。

To investigate the flexural performance of carbon fiber-reinforced polymer/plastic(CFRP) reinforced concrete encased steel composite beams, three steel reinforced concrete composite beams with CFRP bars were designed in this study. The comparison parameters included the main tensile bars with different elastic moduli and reinforcement ratios of the CFRP bars. The variation trends of the strain, deflection, crack development, and flexural bearing capacity of the steel-reinforced concrete composite beams with increasing load were determined through a static load test. The results indicate that the slip between the I-beam and concrete increases with the increase in load, leading to the non-conformance of the strain of the steel-reinforced concrete composite beam along the beam height direction with the plane section assumption. The flexural rigidity, crack resistance, and energy dissipation capacity of the test specimens can be improved by increasing the elastic moduli of the main reinforcement. The strength of the steel-reinforced concrete composite beams with CFRP bars following the yielding of the lower flange of the I-beam is greater than that of ordinary steel reinforced steel composite beams with the same flexural capacity, and the energy dissipation capacity is greater by 1.36 times. When the contact area between the main tensile reinforcement and concrete is maintained constant, increasing the reinforcement ratio of the composite beams can delay the crack development of the steel-reinforced concrete composite beams with CFRP bars, thereby improving the overall flexural performance and energy dissipation capacity of the composite beams. Based on the pure bending calculation theory of the beams, the cracking moment formula was derived, and the cracking moment influence coefficient was introduced to modify the calculation formula. The cracking moment influence coefficient of the ordinary steel-reinforced concrete composite beams is 0.73, and that of the CFRP-reinforced steel reinforced concrete composite beams is 0.43. Combined with the test in this study, the calculation results of the ultimate bearing capacity of the steel reinforced concrete composite beams according to domestic and foreign codes were compared and studied. The results indicate that the calculation results of the technical specifications for the steel reinforced concrete structures(YB 9082—2006), the code for the design of composite structures(JGJ 138—2016), and the American Code guide for the design and construction of concrete reinforced with FRP bars(ACI-440-1 R) are smaller than the test results. However, the calculated values from the design guidelines for reinforced concrete structures(CH 3-78) and design principles of steel-concrete composite beams are in good agreement with the experimental values. Thus, the study findings provide a reference for the design and specification compilation of the same type of steel-reinforced concrete composite beams.