Strut Strength and Failure in Full-Scale Concrete Deep Beams

There has been some recent debate about the actual behavior and performance of some components of strut-and-tie models, specifically struts. This research aims to shed additional light on the behavior and performance of struts. Five full-scale concrete deep beams with two different shapes (rectangular and truss-like) were tested under a three-point load setup. The shear span-to-effective depth ratio (a/d) for the specimens were 1 and 1.6, which led to strut angles of 30 and 45 degrees. All the specimens were simply supported vertically and reinforced with bonded or unbonded bars horizontally. The results indicate that the truss-like specimens have substantially more capacity compared to the rectangular specimens with similar dimension. The unbonded rein forced beam results were similar to bonded results. The ultimate shear strength obtained from the experimental tests was compared with strut-and-tie method (STM) estimates using current design codes to evaluate their safety and accuracy.