高强钢筋UHPC梁抗弯性能及承载力试验研究

Experimental Study on Flexural Behavior and Bearing Capacity of UHPC Beams Reinforced with High-Strength Steel Bars

为研究高强钢筋超高性能混凝土(UHPC)梁的抗弯性能,以配筋率和钢筋等级为参数,设计制作6根HRB500级高强钢筋和3根HRB400级普通钢筋UHPC梁进行梁体抗弯性能试验研究。试验采用三分点对称加载,根据试验结果分析试验梁的破坏模式、荷载~挠度曲线、裂缝扩展和延性;考虑UHPC受拉贡献进行折减(受拉区等效应力折减系数取0.5),提出正截面承载力简化计算方法,并与试验结果进行对比。结果表明:少筋梁和超筋梁呈脆性破坏,适筋梁呈延性破坏,破坏过程包括无裂缝、裂缝扩展、钢筋屈服和破坏4个阶段;UHPC梁承载力随配筋率的增大而增大,其最小配筋率建议取1.0%;对于HRB500钢筋UHPC梁,界限配筋率约为8.10%,合理配筋率建议取2.5%~5.0%,此范围内的UHPC梁具有较好的延性;UHPC初裂取决于基体的抗拉能力,受配筋率和钢纤维的影响较小,而最大裂缝宽度0.05 mm和0.2 mm时名义拉应力与配筋率基本呈线性正相关;提出的正截面承载力简化计算公式具有较高的计算精度和适用性。

To study the flexural behavior of the ultra-high performance concrete(UHPC)beams reinforced with high-strength steel bars,6 specimens of UHPC beams with high-strength steel bars(HRB500)and 3 specimens with normal steel bars(HRB400)were prepared,taking the reinforcement ratio and reinforcement grade as the main parameters.Each specimen was loaded symmetrically at three points,and based on the test results,the characteristics of the specimen was discussed,including failure mode,load-deflection curve,crack propagation and ductility.Considering the inherent tensile strength of UHPC,the tensile stress in the tension zone should be reduced,with an equivalent tensile stress reduction coefficient of 0.5,as such,the simplified formula to calculate the load bearing capacity of the normal cross-section is proposed,and the calculated and test results were compared.It is shown that the beams either with steel bars below the required level or surpassing the required level exhibit brittle failure,and the beams with appropriate amount of steel bars exhibit ductile failure,which experience the four stages of no crack,crack propagation,steel bar yielding and failure.As the reinforcement ratio increases,the load bearing capacity of the UHPC beam is improved,and the minimum reinforcement ratio recommended is 1.0%.For the UHPC beam with HRB500 steel bars,the critical reinforcement ratio is about 8.10%,and the effective reinforcement ratio is about 2.5%to 5.0%,in this range,the UHPC beam owns good ductility.The appearance of initial cracking in UHPC beam is depended on the tensile strength of the beam,with subtle relation to the reinforcement ratio and steel fibers.When the maximum crack widths reach 0.05 mm and 0.2 mm,the nominal tensile stress and reinforcement ratio are basically in linear correlation,proving that the proposed simplified formula to calculate the load bearing capacity of normal cross-section bears high calculation precision and applicability.