预应力RPC-NC叠合梁弯曲疲劳性能试验分析

为研究预应力活性粉末混凝土(RPC)-普通混凝土(NC)叠合梁的弯曲疲劳性能,以中国铁路32 m跨度T型梁为原型,设计并制作了4根完全相同的缩尺模型RPC-NC叠合梁,其中1根梁进行静载试验另外3根梁进行等幅疲劳试验.对试验梁在不同疲劳加载循环下的正截面应变分布、受压区NC应变变化、裂缝发展、疲劳挠度及刚度发展的变化规律进行了分析,并将疲劳加载后未发生疲劳破坏的叠合梁、未经历疲劳加载的叠合梁以及相同结构尺寸和配筋情况下的普通混凝土梁的静力弯曲性能进行对比.结果表明:和普通混凝土适筋梁相同,RPC-NC叠合梁的疲劳破坏由非预应力纵筋疲劳断裂引起;在疲劳荷载作用下,截面应变沿截面高度始终近似呈线性分布,RPC-NC叠合梁正截面变形符合平截面假定;疲劳加载结束后,未发生破坏的RPC-NC叠合梁和疲劳加载前相比延性有所下降,但仍大于未经历疲劳加载的普通混凝土梁.根据试验结果,拟合得到试验梁与疲劳加载循环次数有关的刚度退化公式,可为RPC-NC叠合梁的设计提供一定的参考.

Experimental analysis on bending fatigue performance of prestressed RPC-NC composite beam

To study the flexural fatigue performance of prestressed reactive powder concrete (RPC)-normal concrete (NC) composite beams, four identical reduced-scale model beams were designed and produced on the basis of a 32 m span T-girder of Chinese railway. One of the beams suffered static load and others were under bending fatigue test. Strain distribution in normal section, strain variation in compressed NC, crack propagation, and the development of fatigue deflection and stiffness were analyzed. Furthermore, flexural property of the composite beams without failure after fatigue loading were compared with the composite beams that did not experience fatigue loading and the NC beams with identical structural size and reinforcement condition. Results show that fatigue failure of prestressed RPC-NC composite beams was caused by the fatigue fracture of non-prestressed longitudinal bars, which was the same as balanced-reinforced NC beam. Strain in normal section was always approximately linear with the height of the section under fatigue load, which means the plane section assumption can be applied to prestressed RPC-NC composite beams. Flexural ductility of the composite beams without failure after fatigue loading declined compared with the composite beam before fatigue loading, while it was still greater than NC beam. Stiffness degradation formula of test beams related to fatigue loading cycles was obtained by fitting experimental data, which can be a reference for the design of prestressed RPC-NC composite beams.