大跨PC刚构桥采用预制RPC柱降低跨中长期下挠技术研究

Research of the Technology of Laying out Precast RPC Column to Reduce Long-time Mid-span Sag of Large Span PC Rigid Frame Bridge

跨中长期下挠是大跨PC刚构桥通病,至今无法有效解决,而受压混凝土徐变是跨中长期下挠的最主要因素。鉴于活性粉末混凝土(RPC)经热养护后强度高、收缩极小、徐变系数小的特点,提出在刚构桥受压高应力区(负弯矩区箱梁底板、跨中顶板)加入预制RPC柱形成局部RPC-NC(普通混凝土)复合截面的技术措施来减少其跨中长期下挠。依托实际工程设计预制RPC柱的布置方案,同时利用有限元软件分析加入预制RPC柱对于全桥受力和变形的影响。结果表明预制RPC柱能明显降低负弯矩区结构转角和箱梁底板普通混凝土的压应力,从而大幅减小结构长期徐变下挠。最后对RPC的面积比例以及RPC的长度进行参数分析以期得到最为合理的RPC布置。

Long-term mid-span sag is a common disease among long-span rigid frame bridges,which can＇ t be effectively solved so far, while creep of compressive concrete is the most important factor of the long-term mid-span sag. In view of the fact that reactive powder concrete （RPC） has high strength, almost no shrinkage, small creep coefficient after heat curing, a method of adding precast RPC column into area of high compressive stress of the rigid frame bridge （the bottom plate of the negative mo- ment region and mid-span roof of the middle span） to form RPC-NC （ Normal Concrete） composite section is proposed to solve above problem. Based on actual project, layout scheme of prefabricated RPC column used in actual bridge is put forward, and then the influence of precast RPC column on the whole bridge stress and mid-span deflection is analysed by finite element software. The results demonstrate that adding precast RPC obviously reduce the rotation of the negative moment region and stress of concrete of the bottom plate, thus significantly decreasing long-term mid-span sag of the rigid frame bridge. Finally, thearearatio of RPC and the length of the RPC has been analysed as parameters in order to get the most reasonable layout of the RPC.