城市隧道敞口段封闭改造方案探讨

Discussion on Closure Reconstruction Scheme for Open Section of Urban Tunnel

对既有工程进行功能提升、结构改造是在工程实践中经常遇到的问题,本文以某隧道改造工程为例,对既有U型槽结构的敞口封闭方案进行分析探讨。根据封闭后结构的使用需求,结合景石荷载,分析发现承载力已不是结构设计的主要控制指标,而体现结构舒适度指标的自振频率随着跨径的增大降低明显,变为主要控制指标在分析工程现场特点的基础上确定本工程需采用预制梁,但预制混凝土梁自重大,导致运输安装困难,自振频率低,在不考虑特种荷载的情况下也难以满足使用需求;钢箱梁和钢混组合梁均可满足使用需求,两者基频相当,钢箱梁的承载能力略优于钢混组合梁,可根据工期和工程投资情况酌情选用。

Functional upgrading and structural renovation of existing projects are often encountered in engineering practice.Taking the renovation project of one tunnel as an example,this paper makes an analysis and discussion on the open closure scheme of existing U-shaped groove structure.According to the use demand of the rebuilt structure and the special load,it is found that the bearing capacity is not the main control index in the structure design,but the natural frequency reflecting the structural comfort index decreases obviously with the increase of span,and becomes the main control index.According to the site characteristics of the project,it is determined that prefabricated beams should be used in this project.But the prefabricated concrete beams are self-weight,which makes it difficult to transport and install,and the natural vibration frequency is low.It is also difficult to meet the use requirements without considering the special loads;Steel box girders and steel-concrete composite beams can meet the requirement.Their fundamental frequencies are the same,and the bearing capacity of steel box girders is slightly better than that of steel-concrete composite beams.Engineers could select one according to the construction period and project investment.