榕江大桥矮塔斜拉桥次边跨施工方案比较

Comparison of Subsidiary Side Span Construction Schemes for Extradosed Bridge of Rongjiang River Bridge

结合混合梁矮塔斜拉桥——榕江大桥工程实例,针对其70m次边跨钢箱梁,拟定了桥面吊机悬拼法(方案1)和支架法拼装(方案2)2种施工方案,分析2种方案在施工阶段受力安全性、经济性、施工控制难易性方面优缺点;建立了2种施工方案的全桥施工过程有限元分析模型,对主要施工控制指标进行计算。特点分析和计算结果表明:2种施工方案结构应力均在允许范围,技术上均可行;在施工阶段结构安全性方面,方案2中结构应力较方案1有利,其边跨和次边跨提前完成为主跨单悬臂悬拼施工钢箱梁提供良好的锚固和压重作用;在施工经济性方面,方案2中钢材和小型吊机投入量较方案1多,但方案1中次边跨桥面吊机利用率低,其成桥后需第二轮调索,两者综合成本相差不大;在施工控制难易性方面,方案2中次边跨主梁线形控制较方案1容易且精度高,但两方案主跨主梁累计位移差别较大,应在确定钢箱梁安装线形前明确施工方案。

The Rongjiang River Bridge is the hybrid girder extradosed bridge with the longest main span in the world.For this study,two construction schemes were designed for the erection of its 70 mlong subsidiary side span steel box girders,including the scheme of cantilever assembly by derrick cranes（Scheme 1）and assembly carried out on scaffoldings（Scheme 2）.The advantages and disadvantages concerning the load bearing safety and economic performance of the two schemes in the construction stage as well as the construction control conditions were analyzed.The finite element analytical models of the whole bridge using the two construction schemes were established to calculate the main construction control indexes.The analysis of the characteristics of the two schemes and the results of the calculation demonstrate that the structural stresses of the bridge under the two construction schemes are within the allowed range and the two schemes are technically feasible.In terms of the structural safety during the construction process,Scheme 2is superior to Scheme I regarding structural stress,the erection of the side spans and the subsidiary side spans are possible to be finished in advance,which can in turn provide sound anchoring and counterweight effect for the single-cantilever assembling construction of the main span steel box girder.When it comes to the construction economy,a larger amount of steel and more small-scale lifting cranes would be used in Scheme 2than in Scheme 1,but the derrick cranes used to the erection of subsidiary spans in scheme 1has lower application rate,and second round cable force adjustment is a need after the completion of the bridge.For the construction control,the main span geometry control in Scheme 2is easier and can reach higher level of precision than that of in Scheme 1,but the difference of accumulated displacement errors of the main span girder between the two schemes is great,therefore,the construction scheme should be laid out before the erection geometry of the steel box girder is determined.