Time-dependent analyses of segmentally constructed balanced cantilever bridges

Abstract

Segmentally constructed concrete cantilever bridges often exhibit larger deflections than those predicted by the design calculations. The slender and long spans in combination with the fact that permanent loads are only partially compensated for by prestressing are reasons for the large deflections that increase during the life time of the bridge, although at a decreasing rate. The rate of drying shrinkage may be one reason for the accelerating displacement of cast-in-place bridges. The construction of continuous spans instead of introducing joints has both comfort and durability advantages. The continuous span is however more complicated to design, and secondary restraint moments due to creep, shrinkage and thermal effects develop at the connection. The results of analyses of the stepwise cast-in-place construction of a balanced cantilever bridge with time-dependent material properties show both higher deflection than those originally assumed in the design calculations and high stresses in the webs due to stressing of the tendons in the bottom flange. The analyses show significant effects of creep during cantilevering and of a non-uniform drying shrinkage rate on the continuous bridge.