Evaluation of bridge exterior girder rotation during construction

Abstract

During bridge construction, many loads affect its behavior and can be critical to its future performance. The screed machine and the fresh concrete loads acting on the overhang portion of the deck slab are very significant since they cause unbalanced eccentric loads, resulting in deflection of the overhang and rotation of the exterior girders. Moreover, as the concrete has not hardened yet, the deck slab formwork deflects, causing a non-uniform slab thickness, transversely. Other issues, such as a reduction in steel rebar cover, poor rideability, and local buckling in the girders, can occur from this. Many temporary bracing systems are currently used to prevent the rotation of the exterior girder due to construction loads, such as transverse and diagonal ties, timber blocks, and temporary cross bracing at the exterior panels. However, recent studies show that these bracing systems are not effective enough, and more efficient methods will be needed to solve this problem. The goal of this research is to find the most significant geometrical parameters that affect the rotation of the exterior girders under construction loads. Six parameters were considered in this study: the girder’s section properties, the unbraced length, the overhang width, the number of girders, the girder spacing and the diaphragm’s section properties. SAP2000 software was used to develop the Finite Element models to carry out the parametric study. The rotation of the exterior girders was recorded at the middle of the span at three locations (the top flange, the center of the web and the bottom flange). The results showed that the most significant variables to the rotation of the exterior girder were the girder’s section properties, the unbraced length, and the overhang width. Based on these three parameters a regression model is developed to predict the rotation value with an average error of 9.7%.