分缝护栏致空心板梁桥L型裂缝预应力控制方法研究

A Prestressing Approach to Control L-Shaped Cracks in Hollow Core Beam Bridge Induced by Joints in Cast-in-Situ Parapets

为提高护栏分缝桥梁的耐久性和承载力,以台金高速公路杨司高架桥预制空心板梁桥为背景,研究通过施加预应力控制因护栏分缝引起L型裂缝的有效性,并针对既有桥梁加固和新建桥梁设计提出通用的有效方法。采用Abaqus软件建立既有桥梁和新建桥梁的有限元模型,研究车道荷载作用产生的应力放大效应;分析预应力筋布置高度和长度对边梁梁底应力的影响及对既有桥梁护栏分缝导致的预应力损失;在此基础上,提出L型裂缝的预应力控制方法。结果表明:边梁应力放大系数随桥梁跨径和护栏高度的增加而增大,其取值范围为[1.42,2.14];预应力筋布置高度越低,边梁跨中梁底应力越大;预应力筋布置长度越短,既有桥梁梁底应力越大,对新建桥梁应力没有影响;分缝护栏对既有桥梁施加预应力产生损失,对新建桥梁不会产生预应力损失;在边梁跨中施加相应的预应力,可有效抵消跨中的应力集中效应,防止主梁跨中产生L型裂缝。

In the hollow core beam bridge,the joints in the cast-in-situ parapets are likely to induce stress concentration at the intersection of the parapets and edge beams,and further trigger L-shaped cracks in the edge beams.This study investigates the effect of applying prestressing tendons to control the L-shaped cracks in the edge beams,with the Yangsi Viaduct carrying a section of the Taizhou-Jinhua Expressway as a case bridge,and proposes a method suitable for both the existing bridge retrofit and new bridge design.The finite element models of an existing bridge and a new bridge were developed in Abaqus to examine the stress amplification effect under vehicle loads.The influence of the placement depth and length of prestressing tendons on the stresses in the bottom of edge beams as well as the prestress loss induced by the cast-in-situ parapets with joints in the existing bridge were analyzed.Subsequently,a prestressing approach to control the L-shaped cracks is proposed.It is concluded that the increase of the span lengths and parapet depths lead to the rise of the stress amplification factor of edge beam,and the latter should be between 1.42 and 2.14.For the existing bridge,the lower the placement depth and the shorter the placement length,the bigger the stresses in the midspan bottom of edge beam,while similar effects would not be in the new bridge.Applied with prestress,there will be prestress loss in the existing bridge,instead of new bridge.The stress concentration effect at midspan can be effectively counteracted by applying proper amount of prestress,to avoid the occurrence of L-shaped cracks.