Patch loading and improved measures of incremental launching of steel box girder

Yandangshan Bridge is a tied-arch bridge of double-line railway with a (90 + 90) m continuous steel box girder and passes over a very busy highway in China. The incremental launching of the steel box girder of this bridge is a challenge for bridge builders, mainly because of the patch loading caused by large self-weight, large camber, unsymmetrical and flexible temporary transverse beams. Due to on-site working conditions, many commonly used measures cannot be taken for the launching of this bridge. The launching process is simulated using finite element method. The results have shown that significant local stress concentration would occur in the web plate and bottom plate of the girder if no improved measures are applied. The influencing factors of the stress concentration are studied. Four measures to reduce the local stress of the girder are presented and put into practice: to add two slide shoes on every pier; weld six short launching noses at the diaphragm of leading end of the box girder; pre-lift the 6 slide shoes on one temporary pier at different positions to eliminate part of the deflection of the temporary transverse beams, and use special adjustable slide shoes in one span. The whole launching process has been monitored and the measured stress and deformation coincide with the results of finite element analysis. Good effects have been obtained by applying the four improved measures. The incremental launching of the steel box girder of Yandangshan Bridge has been successful.

► Based on FEM results stress concentration would occur in the girder during launching.
► Stiffness of rubber bearing affects the level of stress concentration of the girder.
► Deformation of temporary beams influences the distribution of reaction on one pier.
► Steel supporting blocks can decrease the maximum stress of the girder obviously.
► Four improved measures are presented and good effects have been obtained.