预应力UHPC-RC无腹筋组合梁足尺模型抗弯试验及极限弯矩计算研究

Flexural Test on Full-Scale Prestressed UHPC-RC Composite Girder Specimen Without Web Reinforcement and Ultimate Bending Moment Calculation

为了解预应力UHPC-RC无腹筋组合梁(简称组合梁)的抗弯性能,以2座组合梁桥实际工程为背景,分别制作25 m长工字形组合梁及30 m长箱形组合梁足尺模型进行抗弯试验,研究组合梁在弯曲荷载下的裂缝发展形态、荷载~挠度曲线及不同截面高度应变等。结果表明:2种组合梁最终受弯破坏时,1条主裂缝快速发展为贯穿弯曲裂缝,组合梁裂缝细密;荷载~挠度曲线较为饱满,刚度折减较普通预应力混凝土梁明显推迟,结构性能更为优良;开裂前组合梁截面受力发展满足平截面假定,出现主裂缝后逐渐不满足平截面假定。为考虑组合梁截面在极限状态不满足平截面假定的情形,基于UHPC材料本构关系,提出采用体外预应力筋极限理论推导组合梁极限弯矩计算方法,并将该方法与平截面假定理论计算结果及试验结果进行对比。结果表明:提出的组合梁极限弯矩计算方法较平截面假定理论计算方法能更好地反映结构受力。

This paper presents the methods to calculate the flexural performance of the prestressed UHPC-RC composite girder without web reinforcement(the composite girder for short).Two existing composite girder bridges were used as prototypes,based on which mockups of a 25 m-long I-girder bridge and a 30 m-long box girder bridge were prepared for flexural tests,to study the load bearing behavior of the composite girder under bending loads,and the key issues included the crack propagation trend,load-deflection curves and the relationship between the location of cross-section and strain.It is shown that when the two mockups failed,a dominant crack grew to be a through flexural crack,and the cracks in the structure were dense.The load-deflection curves are smooth,the rigidity reduction is significantly delayed compared to conventional prestressed concrete girders,and the load bearing performance of the structure is better.When there are no cracks,the load bearing performance of the composite girder satisfies the plane section assumption,while fails when there appear dominant cracks.Supposing that the cross-section of the composite girder does not satisfy the plane section assumption under ultimate bending moments and considering the constitutive relations of UHPC material,it is suggested to utilize the ultimate theory of external prestressing tendons to derive the method to calculate the ultimate bending moments,and the results were compared with the test results and the caculations following the plane section assumption.The verification reveals that the presented method to calculate the ultimate bending moments reflects the load bearing condition of the structure better than that of the plane section assumption theory.