Limiting Compressive Stress in Strut

AASHTO LRFD provide an equation (5.6.3.3.3-1) for the effective strength of concrete struts based on the tests of Vecchio and Collins (1982) on large concrete panels under uniform stresses and deformations.

where ε₁ is the average principal tensile strain in the concrete in the direction of the concrete strut. The tensile strain is determined by considering the strain conditions of the concrete and reinforcement in the vicinity of the strut. If a steel tie crosses a concrete strut, the steel strain reduces the capacity of the concrete strut to resist compressive stress. Assuming that the principal compressive strain in the strut at failure is 0.002 and that the tensile strain in the steel tie is ε_s, the principal tensile strain required by compatibility becomes

where α_s is the smallest angle between the tie and the strut.

Calculation of principal tensile strain ε₁

Reference

1. American Association of State Highway and Transportation Officials (2014) AASHTO LRFD Bridge Design Specifications, 6th Edition, Washington D.C., USA.
2. Vecchio, F. J. and Collins, M. P. (1982) The Response of Reinforced Concrete to In-plane Shear and Normal Stresses, Publication No. 82-03, Department of Civil Engineering, University of Toronto, Canada.