Comparison of Steel Fibers and Transverse Steel Reinforcement for Shear Capacity in Reinforced Ultra High Performance Concrete Beams

Abstract

Ultra high performance concrete (UHPC) is a class of cementitious composites comprised of a mortar mix containing a relatively large percentage of cement and short, randomly disbursed fibers. Its high strength and ability to maintain narrow crack widths lend the material to a wide range of applications. When reinforced with deformed steel bars, proper care in design is required to make efficient use of both the longitudinal steel in tension and UHPC fracture toughness in compression. Recent studies have shown that a high reinforcement ratio combined with a low fiber volume fraction leads to increased ductility and a favorable, gradual failure path. The objective of this research is to study the response of steel reinforced UHPC beams (R/UHPC) with a high shear demand from both a high reinforcement ratio (above 4%) and low shear span-to-depth ratio (near two). Four small scale R/UHPC beams were experimentally tested. Transverse steel reinforcement ratio and steel fiber volume fraction were varied. Experimental results show that more narrow stirrup spacing with a lower fiber volume allowed the R/UHPC beams to more fully utilize the longitudinal steel properties in tension and UHPC properties in compression. Additionally, results