doi:10.3850/9789628014194_0065

ABSTRACT

The long-term effects of shrinkage often give rise to serious cracking problems in reinforced concrete buildings with large floors. To identify the problematic areas, shrinkage movement analysis can be carried out by finite element method with proper creep and shrinkage models using step-by-step time integration. The typical multi-storey building considered is constructed in stages and the construction period for each floor and the supporting columns is 20 days. The time-dependent stresses and strains of the building are studied with respect to various parameters including the number of bays, number of storeys and time lag of the staged construction sequences.

Results of multi-bay frame models show that the restrained shrinkage stress increases with the number of bays in the frame. However, results of the shear-wall frame show that the first floor slab has the maximum shrinkage stresses and is therefore subjected to the most severe cracking. The stress initially decreases with height until it reaches its minimum value roughly at the upper quarter height of the building and then the stress increases again. The trend continues up to the roof. Furthermore, results of shear-wall building show that the shrinkage stresses at the lower floors may exceed the tensile strength of concrete even though late-cast strips are provided, implying that measures such as provision of anti-crack reinforcement may be required.

Keywords: Building frames, Creep, Reinforced concrete, Serviceability, Shrinkage, Simplified method.

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