Mechanisms and Countermeasures for Cracking in PC Box Girder Bridges Constructed by Movable Scaffolding System

Abstract Severe longitudinal cracking has been found in the bottom slabs of PC box girder bridges constructed using a movable scaffolding system (MSS). This paper examines the mechanisms of and prevention measures for these cracks. Linear and nonlinear finite element models of a PC box girder constructed by MSS were built to analyse the causes of the cracking. Linear-elastic numerical results show that a large transverse tensile stress occurs near the duct holes in the bottom slab under the combined action of all loads, which leads to cracking. The large transverse stress is primarily caused by the tension of longitudinal tendons, especially the tendons in the web, and the reduction of cross section near the ducts results in stress concentrations. The cracking process related to the tensioning of tendons is simulated using a nonlinear-plastic model according to the construction sequence, further verifying the dominant influence of tendons in the web. Prevention measures for the cracking were proposed and discussed. Setting transverse tendons in the bottom slab shows effective in reducing the transverse stresses and preventing the cracking. However, stresses in the bottom slab are reduced to some extent by the other proposed measures, by which the cracking cannot be totally avoided.