Consideration of Shear Deformations for Slender Concrete Beams


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Title: Consideration of Shear Deformations for Slender Concrete Beams

Author(s): Admasu S. Desalegne and Adam S. Lubell

Publication: Special Publication

Volume: 284


Appears on pages(s): 1-18

Keywords: reinforced concrete, slender beams, reinforcement, deflection, shear deformation.

Date: 3/1/2012

The ACI 318-08 design code provides a direct computation method for deflection control of slender reinforced concrete beams. This method is based on the Navier-Bernoulli theory where shear deformations are presumed to be minimal. Using a database of twenty slender reinforced concrete beams with shear reinforcement, this paper reports on an analytical study which compared the service deflection predictions from the ACI 318-08 model, with predictions from a proposed MCFT-based sectional analytical deflection model and two MCFT-based numerical models, namely Response-2000 and VecTor2. The MCFT-based models all consider the deflection resulting from shear deformations in addition to the Navier-Bernoulli deflections. Emphasis in the study was placed on deflection predictions at the equivalent serviceability limit state for slender concrete beams longitudinally reinforced with either conventional or high strength steel and transversely reinforced with conventional stirrups. The results indicate that the ACI 318-08 deflection model can underestimate the service deflections by a large margin, especially for members with high transverse reinforcement ratios. The MCFT-based models gave results in better agreements with the test values for the full range of parameters studied. The average test-to-model deflection ratios were 1.77, 1.44, 1.50 and 1.09, and coefficients of variation were 23% 17%, 14% and 18%, for the ACI 318-08, Response-2000, VecTor2 and proposed MCFT-based sectional deflection models respectively.