Shear Capacity of Fiber Reinforced Concrete Based on Plasticity of Concrete: A Review


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Title: Shear Capacity of Fiber Reinforced Concrete Based on Plasticity of Concrete: A Review

Author(s): Gordon B. Batson and Alber G. Youssef

Publication: Special Publication

Volume: 142


Appears on pages(s): 141-166

Keywords: beams (supports); compressive strength; limit state design; fiber reinforced concretes; plasticity; reinforcing steels; research; shear properties; stirrups; structural design; tensile strength; Materials Research

Date: 1/1/1994

The effectiveness of steel fibers as shear reinforcement to replace and/or augment conventional stirrups in concrete beams with flexural reinforcement has been demonstrated by Batson, et al. (1972), J. Craig (1984), and other researchers. The current thinking within ACI Committee 544 is to adjust the limiting values of the empirical equations for shear design in ACI 318. However, a rational basis for the design or analysis of steel fibers as shear reinforcement has not been developed. Possible approaches can be based on the plasticity of concrete, Chen (1978) and Nielsen (1984); and limit state analysis and the modified compression field theory, Marti (1986) and Collins (1984). Test data for flexural reinforced concrete beams using steel fibers as the shear reinforcement match the lower bound solution for the shear strength as a function of the shear span-depth ratio, based on limit states analysis of concrete by Nielsen and Braestrup (1978) and Kemp and Al-Safi (1981). The test data agree well with the theoretical predicted strength, assuming the steel fiber concrete is rigid-plastic with a modified Coulomb failure criterion for the yield condition, no tensile strength, and the compressive strength is the effective compressive strength. The plasticity assumption for steel fiber reinforced concrete is supported by research reported on its torsional strength by Narayanan et al. (1979 and 1983), in which the torsional strength was best predicted by the Nadai's "sand heap" plastic model for a variety of steel fiber volumes in the concrete. The random distribution of the steel fibers at relatively close spacing provides a very ductile mode of failure that is in good agreement with strength theories based on plasticity theory and limit states. The initial test results suggest that a rational design procedure for the shear strength of steel fiber concrete can be based on a modified compression field theory that will be accepted by design engineers. This paper briefly reviews the current thinking on shear design of beams using steel fibers as the shear reinforcement, plastic material response of steel fiber concrete, and test data that agrees with the plasticity properties and limit theorems proposed by Nielsen and Braestrup and by Kemp and Al-Safi for reinforced and prestressed concrete beams without shear reinforcement.