Simplified design moment equations in concrete bridges constructed by special bridge construction method

Abstract

This dissertation introduces simple, but effective, equations to calculate the dead load and tendon moments in reinforced concrete (RC) bridges constructed using the Free Cantilever Method (FCM) and Movable Scaffolding System (MSS). 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 and equilibrium equation at every construction stage, basic equations which can describe the moment variation with time in construction methods are derived. These are then extended to take into account the moment variation according to changes in the construction steps. By using the introduced relations, 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 equations are compared with the results from a rigorous numerical analysis with the objective of establishing the relative efficiencies of the introduced equations. In addition, this dissertation introduces a relation to determine the span ratio between exterior and interior spans, which is required in the preliminary design stage of bridges constructed by balanced cantilever method. On the basis of the numerical results obtained by rigorous time-dependent analyses and by the simple equations introduced, the moment distribution along the spans and its variation with the construction sequence are reviewed, and a recommendation for a rational design is suggested. First, a relation for the initial tendon force is derived on the basis of an assumption that no vertical drift occurs at the far end of a cantilever beam due to the balanced condition between the self-weight and the cantilever tendons. In advance, the determination of an effective span ratio is foll...