Abstract

Reinforced Concrete coupled walls consist of two or more walls connected by short beams referred to as coupling beams. The coupling action provided by these beams leads to increased lateral stiffness and strength compared to isolated walls. During a seismic event, these coupling beams also represent a source of energy dissipation through inelastic deformations. In order to ensure adequate deformation capacity during earthquakes, a combination of diagonal bars and heavy confinement reinforcement is typically used in reinforced concrete coupling beams. This reinforcement scheme, although it has been proven effective to ensure adequate seismic behavior of coupling beams, is costly and difficult to construct.

As an alternative to the use of intricate diagonal and transverse reinforcement detailing in coupling beams, the use of strain-hardening, high-performance fiber reinforced concrete was investigated. The use of a ductile material both in tension and compression diminishes the reliance on diagonal and transverse reinforcement for shear resistance and ductility, substantially simplifying coupling beam construction. The proposed design was evaluated through a series of tests on isolated coupling beams with length to total depth ratios ranging from 1.75 to 3.3. In addition, two four-story coupled walls incorporating precast fiber reinforced and regular reinforced concrete coupling beams were tested under lateral displacement reversals. Fiber reinforced concrete was also used at the base of one of the coupled wall specimens in order to reduce the amount of transverse reinforcement in the boundary regions of the coupled walls. Test results indicate that strain-hardening, high-performance fiber reinforced concrete contributes significantly to both shear strength and deformation capacity of coupling beams. A reduction of approximately 60% in the amount of diagonal reinforcement was achieved in short coupling beams, while a total elimination of diagonal bars was found to be possible in slender coupling beams (i.e. aspect ratio of 3.3). Coupling beam drift capacities exceeded 5% under a shear stress in the order of 0.8-1.0√f’c (MPa). At the system level, coupled walls with precast fiber reinforced concrete coupling beams exhibited a drift capacity greater than 3% with superior damage tolerance compared to regular concrete coupled walls.