Study on the Differential Shrinkage of Composite Prestressed Concrete Beam

Abstract

This paper describes the results of experimental studies made on the effects of differential shrinkage of the composite beams having the flange or the upper half portion cast on the precast prestressed beam. The cast-in-place concrete was made with artificial lightweight aggregates. In all thirty beam specimens were fabricated and the variables involved in the specimens were : shape of cross-section, amount of shear connecter, ratio of shear span to beam depth, and age at casting slab. Differences of shrinkage and creep characteristics between the cast-in-place lightweight concrete and the precast normal concrete were measured by using the control specimens. The differential shrinkage set up internal stresses in the composite construction and its effects on the cracking moment and on the ultimate strength of the composite beams were investigated and compared with the theoretical analysis. It is concluded that the differential shrinkage has so profound an effect that it should be taken into consideration in design, especially when the slab concrete is placed at a later time.