Effective Strength of Strut – FIB

ReferenceComite Euro-International du Beton (2010) CEP-FIP Model Code 2010, International Federation for Structural Concrete (fib), Lausanne, Switzerland.

Effective Strength of Strut – Eurocode 2

ReferenceEuropean Committee for Standardization (2004) Eurocode 2: Design of Concrete Structures, Brussels, Belgium.

Effective Strength of Strut – ACI 318-14

Effective Strength Coefficients of Concrete Strut
The reinforcement required by above table is related to the tensile force in the concrete due to the spreading of the strut. Reinforcement placed to resist the splitting force restrains crack widths, allows the strut to resist more axial force, and permits some redistribution of force.Above Figure shows two layers of reinforcement crossing a cracked strut. This reinforcement will help control cracking in a bottle-shaped strut and result in a larger strut capacity than if this distributed reinforcement was not included.Often, this distributed reinforcement is difficult to place in structures such as pile caps. If this reinforcement is not provided, the value of βs=0.60λ should be used.
ReferenceAmerican Concrete Institute (2014) Building Code Requirements for Structural Concrete (ACI 318M-14) and Commentary(ACI 318RM-14), Farmington Hills, Michigan, USA.

Effective Strength of Strut – AASHTO LRFD 2014

Limiting Compressive Stress in StrutAASHTO 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 εs, the principal tensile strain required by compatibility becomes
where αs is the smallest angle between the tie and the strut. Calculation of principal tensile strain ε1

ReferenceAmerican Association of State Highway and Transportation Officials (2014) AASHTO LRFD Bridge Design Specifications, 6th Edition, Washington D.C., USA.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.