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.

中文翻译：

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活动脚手架体系PC箱梁桥开裂机理及对策

摘要 使用可移动脚手架系统（MSS）建造的PC箱梁桥的底板中发现了严重的纵向裂缝。本文研究了这些裂缝的形成机制和预防措施。建立了MSS建造的PC箱梁的线性和非线性有限元模型，分析了开裂原因。线弹性数值结果表明，在所有载荷的共同作用下，底板内的风管孔附近会产生较大的横向拉应力，从而导致开裂。较大的横向应力主要是由纵向筋特别是腹板中的筋受拉引起的，管道附近截面的减小导致应力集中。根据施工顺序采用非线性-塑性模型模拟了与钢筋张拉相关的开裂过程，进一步验证了钢筋在腹板中的主导影响。提出并讨论了防止开裂的措施。在底板中设置横向筋对降低横向应力和防止开裂是有效的。然而，其他建议的措施在一定程度上降低了底板中的应力，因此无法完全避免开裂。