Effect of Hoop Reinforcement Spacing on the Cyclic Response of Large Reinforced Concrete Special Moment Frame Beams.

摘要

Recent developments in the construction of high-rise buildings in the highly seismic regions of the United States have resulted in construction of reinforced concrete special moment frame beams that are larger compared to those used previously. Governing building code requirements (ACI 318-08) for these beams were introduced in ACI 318-83 and are based on prevailing practices and technical knowledge from that period. When the existing provisions are applied to the larger beams that are now prevalent, hoop spacing can be as large as 305 mm (12 in.) in the beam plastic-hinge zone. An experimental study was conducted to explore the effectiveness of the ACI 318-08 provisions and to identify needed changes for ACI 318-11. Two large special moment frame beams were constructed and tested. The beams were 1219 mm (48 in.) deep by 762 mm (30 in.) wide, and constructed of normal-weight aggregate concrete having target compressive strength of 34 MPa (5000 psi). Longitudinal reinforcement consisted of five No. 36 (11) ASTM A706 Grade 60 bars at top and bottom faces. Transverse reinforcement consisted of No. 16 (5) hoops, where each hoop set was made up of a stirrup closed by a crosstie with an additional vertically oriented crosstie. Center-to-center spacing of hoop sets was either 279 mm (11 in.) or 152 mm (6 in.). The beams were subjected statically to cyclic displacement reversals to simulate effects of earthquake-induced deformations.