Seismic response of diagonally reinforced coupling beams with headed bars

Ductile coupled walls are important elements in resisting seismic loads in tall buildings. Ductile coupling beams must possess excellent energy absorption characteristics and significant ductility. Coupling beams with small span-to-depth ratios typically utilize diagonal bars to resist the shear and flexure. The present method for the confinement of the diagonal reinforcement requires closely spaced seismic hoops. This type of coupling beam is difficult to assemble and has several areas of congested steel bars. To simplify construction and ease the steel congestion, it is proposed that the confinement of the diagonal bars be provided by headed bars.Two full-scale coupling beam specimens, one with confining hoops and one with headed bar confinement, were tested under reversed cyclic loading at McGill University. Both specimens contained identical diagonal bars and distributed reinforcement and were constructed from the same batch of concrete. The responses of the specimens were compared with respect to the general hysteretic responses, including ductility, energy absorption and load sustainability. The specimen using headed bar confinement performed as well as, or better than the specimen with seismic hoops. The ease of construction and excellent performance of the specimen containing headed bars make this type of confinement a viable alternative for ductile coupling beams