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 me mbers using strut-and-tie models incorporates lower-bound plasticity t heory, assuming the concrete and steel to be elastoplastic. Concrete, however; does not behave as a perfectly plastic material. To use the p lastic truss model, an efficiency factor is usually applied to reduce the effective concrete strength. An efficiency factor is proposed in t his paper for concrete strengths ranging from 20 to 100 MPa (2900 to 1 4,500 psi). The new efficiency relationship gives an improved correlat ion with experimental data when compared to existing relationships. Th e 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 qu antify the amount of secondary reinforcement required to avoid web spl itting failure.