Steel Fibers Show Promise As ‘Rebar Decongestants’

(ENR.com) A structural engineer is poised to be the first to use steel fibers as structural reinforcing in the lateral-force-resisting system of a concrete-framed high-rise in a seismic zone. The application, designed to reduce reinforcing-steel congestion in shear-wall link beams and, perhaps, in shear walls themselves, is based on recent successful performance tests of SFRC link beams at the University of Michigan, Ann Arbor.
Shear walls in high seismic regions are typically heavily congested. Link beams, which occur above wall openings, are especially challenging; they require large diagonal bars that are known to be difficult and time-consuming to place.  “Steel fiber promises to solve this problem,” says Cary Kopczynski, president of the Bellevue, Wash.-based structural firm that bears his name. The engineer has designed two, 40-story towers in Seattle using SFRC link beams. Thanks to the recession, both are on hold.  Steel fiber can reduce about 40% of link-beam rebar, Kopczynski says. It also allows smaller-diameter, more bendable diagonal bars to exit the beam horizontally in shorter lengths. “This is huge,” he says. “Many, if not most, link-beam problems will be solved with elimination of the long, heavy diagonal-bar tails that conflict with adjacent wall steel.”  Kopczynski may also use steel fiber throughout the walls at lower levels of both buildings, depending on the timing of usable design information resulting from the University of Michigan tests. For some shear-wall applications, “we believe SFRC will also provide strength, stiffness, ductility and buildability benefits to the entire shear-wall system,” he says.  A net cost reduction of 20% to 30% over conventional link beams is possible, says Kopczynski. Depending on the number of link beams per floor, schedule improvement can be anywhere from nothing to very significant. “A full day per floor would not be unreasonable,” he says.  Read More...


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