装配式预应力混凝土小箱梁桥病害分析及优化设计

Analysis of Deteriorations of Precast Segmental Small Box Girder Bridge and Modification Design

装配式预应力混凝土小箱梁桥在使用过程中,箱梁的腹板、顶板、底板、横隔板、桥面铺装等部位常出现不同程度的开裂,削弱了其耐久性和安全性。通过大量工程实例,结合部颁通用图分析认为,上述病害的产生与箱梁板件厚度、横隔板设置、保护层厚度、负弯矩区预应力钢束锚固构造、普通钢筋配置、施工质量以及超载等因素相关。以石首长江公路大桥引桥及接线桥为背景,针对以上因素提出相应的优化措施以减少相关病害的出现。以通用图中26 m宽路基、4×25 m先简支后连续小箱梁为例,量化分析优化前、后设计性能的改善,结果表明:优化后的小箱梁在承载能力、抗裂性能、结构刚度等方面均有所提升。这些优化措施已应用于石首长江公路大桥引桥及接线桥。运营情况表明,优化措施对提高装配式预应力混凝土小箱梁桥的使用性能和改善其耐久性起到了很好的作用。

In the service period of the precast segmental PC small box girder bridge,diverse cracks are likely to grow in the web,top and base plates,diaphragms and deck pavement of the box girders,which undermine the durability and safety of the bridge.Based on the analysis of a large number of engineering cases and the standard drawings suggested by the Ministry of Transport,the deteriorations are attributed to multiple factors,including the thickness of box girder plates,locations of diaphragms,concrete cover thickness,anchorages of prestressing tendons in the negative bending moment zone,placement of normal reinforcement,construction quality and overload.Taking the approach and access bridges of Shishou Changjiang River Highway Bridge as examples,the modification measures were taken to address the aforementioned influential factors.Based on the 4×25 m small box girder bridge in the standard drawings,which comes into being through a systematic transformation from a simply-supported structure to a continuous structure during construction and is with 26 m-wide subgrade,the improvement of the design performance of the bridge after modification was quantitatively analyzed.It is shown that after modification,the load bearing capacity,cracking resistance,structural stiffness of the small box girder are all improved by a certain degree.These proposed measures have been implemented on the approach and access bridges of Shishou Changjiang River Highway Bridge.The service condition of the bridge proves that the design modification measures exert positive effect on the improvement of serviceability and durability of the precast segmental PC small box girder bridge.