桥梁结构施工中，在一些部位和某些施工阶段必须设置预留变形。钢筋混凝土与预应力混凝土简支梁在预制时，依据其结构变形特点，应分别把预制底模板做成上拱与下挠的曲线，以期全桥完成以后，尽量减少大梁变形造成的不良影响。 Bridge structure construction, in some parts and some stages of construction must be set aside for deformation. In the prefabrication of reinforced concrete and prestressed concrete simply supported beams, according to the deformation characteristics of the structure, the precast bottom formwork should be made into the curves of the arch and the flexure respectively so as to minimize the adverse effects caused by the deformation of the girder after the completion of the full bridge.