Bond, Development, and Anchorage of Reinforcement to Concrete

Project Summary

Research Programs:

Reinforcing steel must be anchored to and act in concert with the surrounding concrete for reinforced concrete to perform as an effective structural material. The University of Kansas has long been involved in research in the field of bond, development, and anchorage of reinforcement to with projects covering the effects of construction procedures, member geometry, coatings, reinforcement geometry, bar stresses, concrete strength, aggregate properties, cyclic loading, and anchorage method (hooks and headed bars). Notable work includes development of the ASTM A944 Beam-End test procedure, recognition of the role deformation geometry, as characterized by bar relative rib area, on bond strength, and the development of the ACI Committee 408 equations for bond strength, and development length and splice design of straight bars in tension. The ACI 408 equations have been shown to accurately characterize bond and development strength for concretes with compressive strengths up to 16,000 psi (110 MPa) and bars loaded to stresses in excess of 120 ksi (830 MPa).

Current active projects:

Anchorage of High-Strength Reinforcing Bars with Standard Hooks: The study will develop basic data on the anchorage of hooked high-strength reinforcing bars and use those results to formulate design criteria for reinforced concrete structures. The results of this study will be used by the design profession, code writers, and ultimately throughout concrete construction industry. The goal of the experimental phase of the study is to gain a firm understanding of the variation in hook strength as a function of bar size, concrete strength, member geometry, and transverse reinforcement. Emphasis will be placed on No. 5, No. 8, and No. 11 hooked bars tested at bar stresses of 60, 80, and 100 ksi (410, 550, and 670 MPa). A limited number of bars will be tested at stresses as high as 120 ksi (670 MPa). Concrete compressive strengths of 5000, 8000, 12,000, and 15,000 psi (35, 55, 83, and 105 MPa) will be used. The ranges in steel stress and compressive strength are needed to establish the performance of hooked bars across a broad range of material properties to help ensure that applications are not limited, as they now are, by a lack of data as a function of steel or concrete strength. The test results will be used to establish reliability-based design provisions.

Use of Headed Reinforcing Bars to Develop High-Strength Reinforcing Steel: The study will develop basic data on the anchorage of high-strength headed reinforcing bars and use those results to formulate design criteria for reinforced concrete structures. The study will include configurations and material properties that, while being necessary or advantageous for construction, are not addressed by the current design codes due to a lack of experimental results. Tests will include high-strength reinforcing bars, high-strength concrete, a broader range of head geometries than tested to date, group effects, and the effects of staggering the heads. Emphasis will be placed on No. 5, No. 8, and No. 11 hooked bars tested at bar stresses of 60, 80, and 100 ksi (410, 550, and 670 MPa). A limited number of bars will be tested at stresses as high as 120 ksi (670 MPa). Concrete compressive strengths of 5000, 8000, 12,000, and 15,000 psi (35, 55, 83, and 105 MPa) will be used. The test results will be used to establish a reliability-based design expression for the development length of headed bars and recommend code changes.