Elimination of diagonal reinforcement in earthquake-resistant coupling beams through use of fiber-reinforced concrete

The design of reinforced concrete coupling beams in regions of high seismicity typically includes the use of diagonal bars designed to resist the entire shear demand, along with closely spaced transverse reinforcement to provide concrete confinement and diagonal bar support. While results from experimental investigations indicate that this design leads to stable behavior under large displacement reversals, the required reinforcement detailing is labor intensive and time consuming. One alternative that has been proven successful to simplify reinforcement detailing in coupling beams is the addition of discontinuous, deformed steel fibers to the concrete. Test results indicate that elimination of diagonal reinforcement, along with substantial reductions in confinement reinforcement over most of the beam span, are possible in coupling beams with span-to-depth ratios greater than or equal to approximately 2.2 when a tensile strain-hardening fiber reinforced concrete is used. Given the advantages of eliminating diagonal reinforcement in coupling beams, this new design was incorporated in high-rise structures in the State of Washington, USA, starting in the early 2010s. In this paper, a brief summary of relevant experimental results and the implementation of fiber reinforced concrete coupling beams in high-rise earthquake-resistant construction is provided