UTILIZATION OF STEEL FIBERS IN DIAGONALLY REINFORCED CONCRETE COUPLING BEAMS AS ADDITIONAL TRANSVERSE REINFORCEMENTS
HYUN-DO YUN, SEOK-JOON JANG, SUN-WOO KIM, WAN-SHIN PARK
The purpose of this study is to investigate the feasibility of using hooked-end steel fibers as additional transverse reinforcements such as cross ties and leg bars for diagonally reinforced concrete (DRC) coupling beams aligned vertically over coupled special structural walls. Three 1/3-scale short beams were made and tested under cyclic shear in a double curvature condition. All specimens have the same reinforcement configuration except for transverse reinforcing details and the clear span length-to-section depth ratio (ln/h) of 2.0. Reinforced concrete (RC) coupling beam (RC-CB) was designed with full confinement of diagonally reinforced concrete beam section based on the seismic design provisions of the ACI 318-14 Code. To improve the constructability without sacrificing strength and ductility, the fiber contents in the FRC0.75-CB and FRC1.50-CB specimens replacing additional transverse bars with steel fibers were 0.75% and 1.50% at volume fraction, respectively. Test results revealed that additional transverse reinforcement in the diagonally reinforced coupling beams have a significant effect on the cracking and structural behaviors. For diagonally reinforced coupling beams with only hoops and without crossties and legs of hoop, the addition of steel fiber at volume fraction of more than 0.75% to concrete provides equal cracking and structural behaviors as compared to those of diagonally reinforced coupling beam with full confinement details.
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