预应力RPC-NC叠合梁疲劳裂缝宽度的计算方法

为研究预应力活性粉末混凝土（RPC）-普通混凝土（NC）叠合梁的疲劳开裂性能,以中国铁路32 m T型梁为原型,制作了4根部分预应力RPC-NC叠合试验梁进行静载试验和等幅弯曲疲劳试验,对试验梁在不同次数疲劳加载下的裂缝数量、裂缝宽度、裂缝间距等开裂发展情况进行分析.以平截面假定为基础,考虑开裂截面处钢筋的疲劳应变增大系数,基于黏结滑移理论推导处于疲劳稳定阶段时RPC-NC叠合梁的裂缝间距及裂缝宽度,提出考虑RPC疲劳抗拉性能及RPC与钢筋间疲劳黏结性能的计算方法.同时为便于设计应用,在铁路规范提供的裂缝宽度计算公式的基础上,引入考虑RPC疲劳抗拉性能影响和循环荷载引起的疲劳扩大影响的系数,得到适用于预应力RPC-NC叠合梁裂缝宽度的计算式.将通过两种方法得到的计算结果和本文试验结果进行对比发现,基于黏结滑移理论的疲劳裂缝宽度计算方法和修正后的铁路规范计算公式均能较为准确地计算预应力RPC-NC叠合梁进入疲劳稳定阶段后的最大裂缝宽度.

Calculating methods for crack width of prestressed RPC-NC composite beam under fatigue loads

To study the fatigue cracking performance of prestressed reactive powder concrete-normal concrete (RPC-NC) composite beams, four identical model beams were designed and produced by taking the 32-m span T-girder of Chinese railway as the prototype. Static test and constant amplitude fatigue test were carried out on the beams. The number of cracks, crack widths, and crack spacing of the model beams at different cycles were analyzed. Based on the plane-sections hypothesis, the magnified factor of strain in the rebars at crack sections was considered under cyclic loads. Tensile property of RPC and bonding property between RPC and rebar under fatigue loads were discussed, and calculation methods for crack spacing and crack width of RPC-NC composite beams at stable stage of fatigue were deduced based on the bond-slip relationship. For the convenience of design and application, by taking account of the influence of RPC tensile property and the amplification effect caused by cyclic loads, the formula applicable to the crack widths of prestressed RPC-NC composite beams was obtained on the basis of the formula provided by the railway codes of China. The comparison between experimental and calculation results obtained by the two methods show that the maximum crack width of prestressed RPC-NC composite beams can be accurately calculated.