Behavior of reinforced concrete deep beams with openings strengthened with steel fibers

Abstract
Strut-and-Tie models are effective in designing reinforced concrete structures with discontinuity regions where linear stress distribution is not valid. Deep beams are typically short girders with a large point load or multiple point loads. These point loads, in conjunction with the depth and length of the members, contribute to a member with primarily discontinuity regions. ACI 318-08 Building Code Requirements for Structural Concrete provides a method for designing deep beams using either Strut-and-Tie models (STM) or Deep Beam Method (DBM). Large openings in reinforced concrete (RC) deep beams generally interrupt the load transfer by concrete struts and cause a sharp decrease in strength and serviceability. The reinforcement detailing of these deep beams based on strut-and-tie models (STMs) can be complex and, very often, these models may not predict the failure mechanism of deep beams due to localized damages. The main objective of this paper is to study Steel Fiber Reinforced Concrete (SFRC), offered as an alternative material, to the cumbersome and iterative steps involved in strut-and-tie (STM) methodology. Additionally, a similar reinforced concrete (RC) specimen was tested under the same controlled condition designed with classical strut-and-tie model design methodology reinforced using conventional steel bars. In this investigation, three types of steel fibers, and three percentage of steel fibers, and two aspect ratios were aiming to show the effect of these parameters on the behavior of concrete deep beams.
Material testing was conducted on the materials used in the large scale specimens to ensure that the actual material mechanical properties were known for the analysis. Computer Aided Strut and Tie (CAST) software was used to quantify the experimental data obtained from the controlled conditions testing. The eight beams were compared and contrasted throughout the study to show the effect of fiber on the behavior of deep beams. This study provides information on the viability of using steel fiber reinforced concrete in complex D-regions in structural elements.