Strength of Concrete Struts in Three-Dimensional Strut-Tie Models

The design of structural concrete using strut-tie models requires establishing the effective strength of concrete struts, ensuring sufficient anchorage of reinforcing bars in nodal zones, and the geometric compatibility of the strut-tie model within the member geometry. In this paper, a consistent and general method applicable to three-dimensional (3D) strut-tie models is presented. The proposed method includes the effects of 3D stresses associated with tensile strains in reinforcing bars crossing a strut, strut length, deviation angle between strut orientation and compressive principal stress flow, compressive strength of concrete, and degree of confinement provided by reinforcement. The proposed method is implemented and then verified using data from 115 reinforced concrete pile caps tested to failure.