SHRINKAGE STRESS ANALYSIS OF CONCRETE SLABS IN A MULTI-STOREY BUILDING CONSIDERING INTERNAL AND EXTERNAL RESTRAINTS

Shrinkage strains of concrete slabs in a multi-storey building are restrained internally by reinforcement bars as well as externally by supporting members such as columns or walls. These strains may induce tensile stresses in concrete members and lead to cracks due to excessive shrinkage stress. In this study, a practical shrinkage stress analysis method for application to concrete slabs in a multi-storey building is proposed. The proposed approach considers both internal restraint of reinforcement bars and external restraint variations resulting from construction sequence. The shrinkage stress due to external restraint is obtained by multiplying the relaxation coefficient by the elastic shrinkage stress. The additional shrinkage stress due to internal restraint is obtained by the residual strain calculated via a linear elastic analysis for external restraints. A verification example was comparatively analysed using the proposed method and a commercially available analysis program that is capable of time-dependent analysis of concrete. The results of a 10-storey sample building suggest that the internal restraint due to reinforcement considerably increases the shrinkage stress at slabs under loose external restraint. Copyright (C) 2008 John Wiley & Son, Ltd.