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Farmington Hills, Mich. — The ACI Foundation’s Concrete Research Council (CRC) completed a new research product — Evaluation of Seismic Behavior of Coupling Beams with Various Types of Steel Fiber-Reinforced Concrete. Gustavo J. Parra-Montesinos, University of Wisconsin – Madison, Madison, Wis., served as the project’s principal investigator.

Traditionally, coupling beams between special structural walls (shear walls) are reinforced with diagonal bars that are “woven” together with dense transverse reinforcement. The “woven” design, which comes from research conducted in the 1960s and 1970s, is difficult to construct. The ACI Foundation’s Concrete Research Council (CRC) and several other financial supporters funded the research to evaluate the use of FRC (Fiber-Reinforced Concrete) to allow the design of coupling beams that no longer require the use of diagonal bars.

A total of six FRC mixtures were evaluated, using three types of hooked steel fibers and three different fiber volume fractions. The material properties of the various FRCs were evaluated using four-point bending tests, direct tension tests, and compression tests. Eight FRC coupling beams were tested under large displacement reversals.

The experimental data from the research were used to develop design guidelines for FRC coupling beams linked to material performance criteria. The proposed coupling beam design results in less congested reinforcing bar configurations—a benefit to owners, designers, and contractors.

These new provisions could be used to develop a code change proposal to ACI Committee 318, Structural Concrete Building Code. “Linking coupling beam drift and shear stress capacity to FRC bending performance obtained through a standard ASTM test is expected to further facilitate adoption of the proposed FRC coupling beam design by structural engineers,” stated Parra-Montesinos. “Such a link could also serve as the basis for future design provisions to be proposed to ACI Committee 318.”

Adding the FRC design option to the current code provisions would translate into simplified and more straightforward construction, saving construction time, financial resources, and labor — creating a positive impact on the concrete construction industry. The results of this research were presented at the 16th World Conference on Earthquake Engineering, January 9-13, 2017, in Santiago, Chile.

More information about this research product is available at www.concreteresearchcouncil.org.