How Safe Are Our Large, Lightly Reinforced Concrete Beams, Slabs, and Footings?


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Title: How Safe Are Our Large, Lightly Reinforced Concrete Beams, Slabs, and Footings?

Author(s): Michael P. Collins and Daniel Kuchma

Publication: Structural Journal

Volume: 96

Issue: 4

Appears on pages(s): 482-490

Keywords: beams (supports); footings; one-way slabs; shear properties

Date: 7/1/1999

The current ACI shear design procedures can be very unconservative if applied to large, lightly reinforced members because these procedures do not recognize that as the size of such members increases, the shear stress required to cause failure decreases. This paper describes an extensive experimental investigation aimed at evaluating the significant parameters that influence the magnitude of this size effect in shear. It was found that the reduction in shear stress at failure was related more directly to the maximum spacing between the layers of longitudinal reinforcement rather than the overall member depth. High-strength concrete members displayed a more significant size effect in shear than normal strength concrete members. Some simple modifications to the ACI shear design procedures are suggested that will result in a more consistent level of safety across the possible range of concrete strengths and member sizes.