Study of Causes and Preventive Measures of the Support System Settlement Accident during Cast-In-Situ Bridge Construction: A Case Study

The failure of the support system is one of the primary reasons for bridge failures during construction. Existing research on support system failures primarily focused on falsework, with less attention given to other components such as Bailey beams, transverse beams, and steel pipe piles. This study focused on an incident where the support system of a cast-in-situ box girder bridge experienced settlement due to the failure of Bailey beams, transverse beams, and steel pipe piles. To thoroughly analyze the accident's causes, a multiscale elastic-plastic finite-element model of the support system was developed based on the actual on-site layout. By combining the results of the finite-element model with comprehensive on-site data, it was found that the support system settlement accident was caused by a series of construction errors, including the incorrect placement of the Bailey beams, excessive vulnerability in the steel pipe piles' support positions, and inadequate welding strength between the transverse beams. To prevent similar accidents from recurring, the design, construction, and supervisory parties should collectively ensure the consistency between design and construction and increase their attention to potential stress concentrations in certain components of the support system. When the possibility of stress concentration exists, Bailey beams should be reinforced with vertical or diagonal struts depending on their actual support positions, while steel pipe piles should be reinforced with annular steel plates higher than 500 mm. This study focuses on an incident where the support system of a cast-in-situ box girder bridge experienced settlement due to the failure of Bailey beams, transverse beams, and steel pipe piles. These failures were primarily caused by inconsistencies between design and construction and a lack of attention to potential stress concentrations in certain components of the support system. In fact, the differences between design and construction are widespread and are one of the primary reasons for the failure of support systems during bridge construction. Therefore, the design, construction, and supervisory parties should work together to reduce the occurrence of such situations. Designers need to identify the most critical assumptions made during calculation and communicate these assumptions clearly to the construction team through a checklist. Construction and supervisory parties should implement these assumptions as much as possible and promptly report when they cannot be met. Furthermore, more attention should be given to potential stress concentrations in the support system. This requires designers to be aware of the limitations of beam element models when analyzing stresses at connection points. When stress concentrations are inevitable, the methods proposed in this study can be used to reinforce Bailey beams and steel pipe piles.