Bridges, Tunnels and other Transportation Structures
During the construction of concrete deck slabs in bridges, the overhang portion of the deck slab is usually subjected to unbalanced eccentric loads. These loads are mainly the result of the weight of the screed machine and the freshly poured concrete. The screed machine is used to finish the deck slab concrete surface, and usually it rests on the overhang formwork edges, which results in torsional moments in the exterior girders. Hence, deflection of the overhang and excessive rotation of the exterior girder occurs. These deflections causes many issues such as instability of the superstructure during the construction, non-uniform deck slab thickness, poor rideability in the future and reduction in reinforcement steel cover. Many DOTs in the US are facing this problem, and there is no specific approach or method in AASHTO to target this issue. However, some DOTs have requirements to limit the rotation of the exterior girder, and they also suggest simplified approaches to estimate this rotation. The bridge girders are stabilized during the construction through permanent lateral bracing system represented by diaphragms or cross-bracing. During the construction contractors tend to use temporary bracing systems such as timber blocks, transverse and horizontal ties or other systems to resist these unbalanced loads. However, investigations showed that even with these measures, rotation values in the exterior girders that exceed DOTs limits are recorded. Skewed girder bridges are very common in the US, where they provide an efficient and economical solution to overpass a specific obstacle. However, with bridge skewness, the lateral bracing system layout can follow different patterns or orientations. Diaphragms or cross-frames can be parallel to the angle of the skew or it can be perpendicular to the girders lines in a staggered or non-staggered layout. These different layouts can affect the distribution and the transition of lateral loads significantly. The purpose of this study is to find the effect of different lateral bracing system layouts in different bridge skewness on the rotation of the exterior girders under construction loads. Finite Element models of bridges with different skewness and layouts are developed to examine this phenomenon. The scope of the research is skewed steel girder bridges subjected mainly to screed machine and fresh concrete weight loads. The findings of this research should provide designers and contractors a better understanding of the effect of the diaphragms layout in skewed bridges on the rotation, and also promotes the most optimum layout in different skewness.