Determination of design moments in bridges constructed by balanced cantilever method

This paper introduces an equation to calculate the design moments in reinforced concrete (RC) bridges constructed by the balanced cantilever method. Through time-dependent analyses of RC bridges, considering the construction sequence and creep deformation of concrete, structural responses related to the member forces are reviewed. On the basis of the compatibility condition at every construction stage, a basic equation which can describe the moment variation with time in the balanced cantilever construction is derived. It is then extended to take into account the moment variation according to changes in construction steps. By using the introduced relation, the design moment and its variation over time can easily be obtained with only the elastic analysis results, and without additional time-dependent analyses considering the construction sequences. In addition, the design moments determined by the introduced equation are compared with the results from a rigorous numerical analysis with the objective of establishing the relative efficiencies of the introduced equation. Finally, a more reasonable guideline for the determination of design moments is proposed.