Exploring the Combined Use of Distributed Fiber and Deformed Bar Reinforcement to Resist Shear Forces

Project Information

Link to Latest Report: March 2023 Progress Report


Macro-synthetic fibers are often added to concrete mixtures as secondary reinforcement, designed to control shrinkage and temperature cracks and improve the durability of bridge superstructures. The addition of fibers to concrete improves the tensile behavior of the material, which leads to more durable concrete elements with increased ductility and better crack control. In addition to these desirable effects, the tensile strength of the fibers also contributes to the strength of the member, however this benefit is not included in current bridge design specifications. The lack of provisions regarding the use of macro-synthetic fibers as supplemental reinforcement is of detriment to the bridge construction industry because the use of fibers in PBEs and cast-in-place connections would result in a reduction of bar reinforcement and congestion, lighter members, smaller crack sizes, better distribution of localized stresses, and improved confinement and performance of member ends. 

Experimental data on the simultaneous use of deformed bars and distributed macro-synthetic fiber reinforcement to provide shear strength is limited, but the existing evidence suggests that the addition of fibers to beams containing deformed bar shear reinforcement improves the strength of the beams and can shift failure from brittle to ductile modes. While this limited test data suggests potential benefits of using fibers as supplemental reinforcement, the interactions and synergies between distributed fiber and deformed bar reinforcement in resisting shear is not well understood. To realize the full benefits of macro-synthetic polyolefin fiber-reinforced concrete (PFRC), additional experimental data and rational design guidelines are needed to predict the shear strength of members containing both macro-synthetic fibers and deformed bar reinforcement. 


The objective of the proposed research is the development of simple, rational design equations for the contribution of macro-synthetic fibers to the shear strength of reinforced concrete members containing at least the minimum shear reinforcement required by the AASHTO LRFD Bridge Design Specifications. The design equations will be based on a rational shear behavior model that will be developed as part of this work using the response of PFRC panel elements, subjected to in-plane loads (e.g., shear and axial tension or compression).


The project includes four tasks to achieve the stated research objective:

  • Task 1 – Literature review
    • An extensive review of past experimental research involving fiber-reinforced concrete will be completed, focusing on specimens that utilized deformed bar and macro-synthetic fiber reinforcement to resist shear forces.
  • Task 2 – Panel testing program
    • An experimental panel testing program will be completed investigating the interaction between distributed fiber and deformed bar reinforcement in resisting shear forces. This program will provide valuable data that is needed to build a shear behavior model in Task 3. The variables of interest within the experimental campaign will include fiber volume fraction, transverse deformed bar reinforcement ratio, and loading condition (concurrent shear and tension or shear and compression).
  • Task 3 – Code development
    • The results of the panel tests in Task 2, will be used to develop rational design recommendations that capture the potential beneficial interaction between deformed bar and distributed fiber reinforcement. These equations would add to, or modify, the steel contribution of the elements shear strength based on the interactions measured during the experimental testing program
  • Task 4 – Final Report
    • A final report, ABC-UTC Guide, and a 5-min video presentation will be prepared that summarize the methods used and the findings reached during the project.

Research Team:

Principal Investigator:  Travis Thonstad, Assistant Professor
Co-Principal Investigator:  Paolo Calvi, Associate Professor
Research Assistant: John Paul (JP) Gaston, Alexander Maldonado

Previous Progress Reports:
December 2022 Progress Report