Coupled Shear Wall with Fully Post-Tensioned Beams and Unbonded Reinforcing Bars at Toes

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Title: Coupled Shear Wall with Fully Post-Tensioned Beams and Unbonded Reinforcing Bars at Toes

Author(s): Steven M. Barbachyn, Yahya C. Kurama, Michael J. McGinnis, and Richard Sause

Publication: Structural Journal

Volume: 113

Issue: 6

Appears on pages(s): 1381-1392

Keywords: coupled shear walls; coupling beams; digital image correlation; earthquake-resistant structures; post-tensioning; reinforced concrete; seismic analysis; structural design; testing

Date: 11/1/2016

Abstract:
This paper describes the testing and behavior of a 40% scale coupled core wall structure with fully unbonded post-tensioned coupling beams and unbonded flexural (vertical) mild steel reinforcing bars below the wall pier toes. The specimen with C-shaped piers included the bottom three stories, a large portion of the tributary floor slabs, and the foundation of an eight-story prototype structure, and was tested under quasi-static reversed-cyclic lateral loads combined with tributary gravity loads. The elimination of mild steel reinforcement across the beam-to-wall interfaces was a significant simplification for construction. Ultimate failure of the structure was caused by low-cycle fatigue fracture (preceded by buckling) of the extreme flexural mild steel bars crossing the wall-to-foundation interfaces. This failure mode was significantly delayed (resulting in greater ductility capacity) because of the deliberate unbonding of the flexural bars crossing into the foundation below the wall pier toes. The coupling beams provided adequate and stable coupling to the structure throughout the test. The energy dissipation in the system was significantly above the minimum level prescribed by ACI ITG-5.1, demonstrating the adequacy of the design.