Research on Nose-Less Incremental Launching Construction Technology for Long-Span Steel Box Girders

Incremental launching construction is currently one of the most commonly used methods for the construction and erection of steel box girders. With the rapid development of bridge construction engineering technology in China， the incremental launching construction technology without a launching nose has begun to be applied. Compared with the traditional incremental launching method with a launching nose， the front end of the nose-less method is directly the steel girder itself， and the advantages of utilizing a lightweight launching nose and an internal nose beam structure are forfeited. This causes the steel girder to transition earlier from a cantilever state to a simply-supported or continuous state during the construction process， increasing the risk of permanent deformation and overturning of the steel girder. To gain a more comprehensive understanding of the nose-less incremental launching construction technology for steel box girders， a systematic analysis and research on this technology and its quality control methods were conducted in the steel box girder installation project of the Anhai Bay Extra-large Bridge on the Fuzhou-Xiamen Railway. First， an analysis was conducted on the characteristics and challenges of the nose-less incremental launching construction technology for steel box girders. Subsequently， the stress conditions during the nose-less incremental launching process were examined. Calculations were performed to determine the anti-overturning coefficient， stress distribution， and deflection magnitude of the steel girder under various construction conditions. Based on these analyses， key technical points and quality control measures for nose-less incremental launching were proposed. Finally， by analyzing monitoring data from the incremental launching process， it was verified that implementing the following measures ensured construction safety and achieved compliance with the required finished bridge alignment： controlling incremental launching steps， monitoring girder deformation and stress， and adding counterweight balancing. The nose-less incremental launching technology and quality control methodology presented in this study can reduce frequency of structural system transitions in the steel girder， elimination of fabrication， installation， and dismantling procedures for launching noses or auxiliary facilities， and enhance safety reliability and cost-effectiveness.