Optimization of Closure Jacking Forces in Multispan Concrete Rigid-Frame Bridges

Abstract

Creep, shrinkage, and temperature drops will shorten the main girder and create additional internal forces in the piers of continuous rigid-frame bridges. Horizontal jacking forces can be applied at the ends of a closure segment before casting to improve the stress state in the piers. Multispan continuous rigid-frame bridges have several closure segments and usually have different jacking forces. In general, the determination of the optimal jacking forces is relatively difficult because of their compound effects on the bridge piers. In this study, multiobjective linear programming was used to calculate the jacking forces by selecting the stress in the piers as the objective function in the service stage and the stresses at the various construction stages as constraints. The minimum tensile stress in the piers was obtained by an iterative process that allowed for the creep effect of the jacking forces to be included in the calculations. The results obtained show that the proposed method is convenient for design, and the appropriate jacking forces can be determined to minimize detrimental long-term effects. Creep caused by jacking forces was found to affect pier stress significantly. In comparison, jacking forces were found to have a smaller effect on the internal stresses of the main girder. Calculation results show that if jacking force is not applied, the long-term effect of creep will generate large stress variations between the top and bottom of the piers and may cause cracking. However, when jacking force is applied, stresses in the piers in the service stage are relatively uniform.