免拆超高性能混凝土模板钢筋混凝土梁的受力性能及短期刚度研究

通过4根采用免拆超高性能混凝土(UHPC)模板的钢筋混凝土(RC)梁与2根RC梁的对比试验,研究UHPC模板与后浇混凝土界面的黏结性能、保护层厚度对免拆UHPC模板RC梁的抗弯刚度和承载力的影响,结果表明:达到峰值荷载时,经过拉毛处理的预制UHPC模板与后浇混凝土界面未出现滑移;峰值荷载后至受拉钢筋达到其极限拉应变时,预制UHPC模板与后浇混凝土界面出现轻微剥离;保护层厚度为10 mm的免拆UHPC模板RC梁的抗弯刚度和承载力略高于保护层厚度为20 mm的梁;但在峰值荷载后,前者较后者的底部模板与后浇混凝土界面处较早地出现沿界面滑移;综合考虑,建议该类梁的保护层厚度取20 mm较为合理。采用有效惯性矩法,基于平截面假定,建立了免拆UHPC模板RC梁的截面开裂弯矩和抗弯刚度计算式,计算值与试验值吻合较好。

Mechanical behavior and immediate stiffness of RC beams with UHPC permanent formwork

In order to investigate the effects of concrete cover thickness and the bonding property between ultra-high performance concrete（UHPC） formwork and post-cast-in-place concrete on flexural stiffness and bearing capacity of RC beams with UHPC permanent formwork, four RC beams with UHPC permanent formwork and two ordinary RC beams were tested. The results show that under the peak load of the beam, no slip can be observed between prefabricated UHPC formwork and post-cast-in-place concrete. The interface between prefabricated UHPC formwork and post-cast-in-situ concrete is slightly peeled off when the steel bar reaches ultimate tensile strain of 0.01. The flexural stiffness and bearing capacity of UHPC formwork RC beams with concrete cover thickness of 10mm are higher than those of beams with concrete cover thickness of 20mm. However, after the peak load the slip cracks along the interface between the bottom formwork and the post-cast-in-place concrete of the former beams appears earlier than that of the latter ones. Therefore, the thickness of 20mm is more reasonable for the concrete cover. Based on the assumption of the section remaining plane, the formulas of the cracking moment and stiffness of RC beam with UHPC permanent formwork were established using the effective inertia moment method. The calculated values are in good agreement with the experimental values.