部分无黏结复合筋混凝土梁变形能力研究

Deformation capacity of concrete beams reinforced by partially unbonded composite bar

钢-连续纤维复合筋(SFCB)由内芯钢筋和外侧复合材料(FRP)组成,具有高耐久、可控的屈服后二次刚度等优点。由于FRP的极限延伸率较低,SFCB混凝土构件的极限状态往往由FRP断裂应变控制。为了提高SFCB混凝土梁的变形能力,针对变化无黏结长度的SFCB混凝土梁进行了试验研究,结合数字图像相关技术(DIC)测量了构件表面位移场,研究了无黏结长度对SFCB混凝土梁变形能力、承载能力的影响。结果表明:随着无黏结长度增大,SFCB混凝土梁的裂缝高度、宽度和间距逐渐增加,受压区混凝土将更早被压溃;SFCB混凝土梁的屈服后刚度与开裂后刚度的比值比较稳定,约为22%;跨中设置无黏结段后,跨中混凝土表面平均应变依然符合平截面假定;适当设置无黏结段有利于降低受拉筋材应变,提升SFCB混凝土梁的抗弯承载能力和变形能力。

The steel-fiber-reinforced polymer(FRP)composite bar(SFCB)consists of an inner steel bar and an outer fiber composite material,and has the advantages of high durability and controllable post-yield stiffness.Owing to the relatively low ultimate elongation rate of FRP,the ultimate state of SFCB-reinforced concrete members is typically determined by the fracture strain of FRP.To improve the deformation capacity of SFCB-reinforced concrete beams,this study experimentally investigated SFCB-reinforced concrete beams with a varying unbonded length.The displacement field of the concrete beams was measured using the digital image correlation(DIC)technique,and the influence of the unbonded length on the deformation capacity and bearing capacity of the SFCB-reinforced concrete beams was investigated.The results reveal that,as the unbonded length increased,the crack height,width,and interval of the SFCB concrete beams gradually increased,and the concrete in the compression zone collapsed earlier.The ratio of the post-yield stiffness to the post-crack stiffness of the SFCB beams was relatively stable,that is,approximately 22%.The average strain of the concrete surface at mid-span still obeyed the plane-section assumption when the unbonded section was set at mid-span.Appropriately setting the unbonded length is beneficial in reducing the strain of the mid-span tension-bars and improving the flexural bearing capacity and deformation capacity of SFCB concrete beams.