1 BEAM HOOP REINFORCEMENT FOR LARGE CONCRETE SMRF BEAMS PRELIMINARY TEST RESULTS FOR BEAM 1 A project funded by the Pankow Foundation, Webcor Builders, ACI Foundation's Concrete Research Council, and the CRSI Foundation By Grigorios Antonellis, Tea Visnjic, Marios Panagiotou, and Jack Moehle University of California, Berkeley 25 January 2011 BACKGROUND Recent developments in the construction of high-rise buildings in the seismically active West Coast have resulted in construction of reinforced concrete special moment frame beams larger than was typical in past practices. The current Building Code requirements for these beams were written around prevailing practices from many years ago and, when applied to these new buildings, can result in hoop spacing as large as 12 inches in the beam plastic hinge zone (see ACI 318-08, Section 21.5.3.2). Some engineers have questioned the performance capability of these beams and have recommended Building Code changes to reduce the maximum hoop spacing. An ongoing research project at the University of California, Berkeley is investigating the requirements through a laboratory test program. TEST SPECIMENS (Figures 1 through 4) Two test beams have been designed and constructed to test current Building Code provisions and some proposed Code changes. The beams cantilever from a common reaction block that is anchored to the laboratory floor (Figures 1 and 2). The beams are tested by imposing displacement cycles (upward and downward) to simulate the effects of deformation reversals that occur during a major earthquake. Beam 1 (Figure 4) is designed to satisfy all provisions for special moment frame beams according to the current Building Code provisions. The beam hoops (No. 5 at spacing s = 11 inches) are each made up of three pieces; a stirrup with seismic hooks, a crosstie at the top to close the hoop, and an additional vertical crosstie to restrain longitudinal bars along the top and bottom faces. Volumetric confinement reinforcement ratio is ρ s = 0.31%, where ρ s = volume of vertical legs of hoops divided by volume of core. In Beam 2, the hoop spacing s is reduced to 6 inches, corresponding to a volumetric reinforcement ratio ρ s = 0.57%. Concrete is normal weight, using pea gravel (not crushed) as the maximum size aggregate, with target compressive strength of 5000 psi. All reinforcement is Grade 60.
BEAM HOOP REINFORCEMENT FOR LARGE CONCRETE SMRF BEAMS PRELIMINARY TEST RESULTS FOR BEAM 1
May 19, 2023
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