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Title: Structural Model for Interstory Drift Capacity of Flat Slabs without Shear Reinforcement

Author(s): C. E. Broms

Publication: Structural Journal

Volume: 117

Issue: 3

Appears on pages(s): 45-54

Keywords: flat slab; interstory drift; structural model; strut-and-tie model

Date: 5/1/2020

The model presented treats the relation between unbalanced moment capacity and the concurrent rotation of slab-column connections at interior columns of flat slabs without shear reinforcement. According to the theory of elasticity, unbalanced moment is transferred between slab and column by a combination of bending moment, torsional moment, and eccentricity of shear. Here a different approach is proposed; the flow of unbalanced moment forces is followed with a strut-and-tie-like model by which closed expressions for the relation between unbalanced moment and rotation can be formulated. It is demonstrated that the interstory drift capacity can be expressed as a function of the concentric punching capacity and the flexural stiffness of the slab adjacent to the column. Comparison with test results published in the literature demonstrates that the model can predict unbalanced moment capacity and drift capacity with good accuracy. Drift capacity curves for flat slabs with 120 and 240 mm (4.7 and 9.4 in.) effective depth are given for varying reinforcement ratios and column sizes. The curves clearly indicate that half-scale test specimens overestimate the interstory drift capacity for the corresponding prototype structure.


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