Behavior of Concrete Deep Beams with High Strength Reinforcement

The Strut-and-Tie modeling technique is a widely accepted design approach for reinforced concrete deep beams. However, there are significant differences between various design code implementations for this technique with respect to the reinforcement tie influences on the capacity of adjacent concrete struts. Furthermore, each design code specifies different limits on the maximum permitted stress in the ties. Since high-performance reinforcement continues to gain wider acceptance in industry practice, it is necessary to validate existing design approaches, including Strut-and-Tie modeling, for the mechanical properties of these new materials. An experimental campaign was conducted to understand the performance of large-scale reinforced concrete deep beams constructed with high strength longitudinal reinforcement. Test results from six beams are presented, where primary test variables included the shear-span-to-depth aspect ratio and the longitudinal reinforcement ratio. All specimens included a constant quantity of transverse reinforcement. Testing was conducted under a four-point bending configuration, on specimens with cross-section 300 mm wide x 607 mm high. Specimens failed either by shear-compression, or by a flexural mode of longitudinal reinforcement yielding or crushing of the flexural compression zone. The results showed that the member capacity decreased as the shear-span-to-depth ratio increased, and as the longitudinal reinforcement ratio decreased. It was possible to design members to efficiently exploit the high strength reinforcing steel using Strut-and-Tie modeling techniques according to CSA A23.3-04 and ACI 318-05 provisions.