The design of nonflexural members with normal and high-strength concretes

Over the last two decades significant technological advances have been made in the development of high-strength, high-performance concrete. Concretes with compressive strengths greater than 70 MPa (10,000 psi) are now commonly used in many structures. The design of nonflexural members using strut-and-tie models incorporates lower-bound plasticity theory, assuming the concrete and steel to be elastoplastic. Concrete, however; does not behave as a perfectly plastic material. To use the plastic truss model, an efficiency factor is usually applied to reduce the effective concrete strength. An efficiency factor is proposed in this paper for concrete strengths ranging from 20 to 100 MPa (2900 to 14,500 psi). The new efficiency relationship gives an improved correlation with experimental data when compared to existing relationships. The three main failure modes for nonflexural members are yielding of the tension tie, crushing of the concrete strut, and web splitting. Each of the failure modes is discussed and a truss model is developed to quantify the amount of secondary reinforcement required to avoid web splitting failure.