Effect of Axial Restraint on Mechanical Behavior of High- Strength Concrete Beams

This study was performed to verify the effect of restraint of axial deformation (that is, thermal and time-dependent volume change after concrete placing and axial elongation due to lateral loading) on mechanical behavior of high-strength concrete beams. For this purpose, the characteristics of concrete beams (the development of the restrained stress and the mechanism of crack formation due to the restrained stress and so forth) were studied on the basis of the experiments and numerical analyses of the data for highstrength concrete beams at an early age. When a high-strength concrete member is axially restrained, a crack might propagate in the member not demolded at an early age. This is caused by a drop of temperature that results from the hydration heat of cement and autogenous shrinkage and not by drying shrinkage, which would not have started as yet. The restrained stress of a member is accurately obtained by calculating the externally restrained force and the steel stress. The maximum restrained stress is determined by the cracking strength of concrete. It is concluded that the additional restrained stress is released and the axial rigidity of member is reduced with formation of additional cracks.