Experimental Investigation of Eccentric Reinforced Concrete Beam-Column-Slab Connections under Earthquake Loading

The inelastic behavior of beam-to-column joints has been studied since 1960’s; however, there is still limited information on eccentric connections, in which the centerline of the spandrel beam does not coincide with the centroid of the column. In this experimental study, the seismic behavior of three 3/4- scale eccentric beam-column-slab subassemblies was investigated. The main design parameters were selected as the eccentricity, normal beam width, and column section aspect ratio. The eccentricity between the centerline of the spandrel beam and centroidal axis of the column was selected as a design variable because some buildings with eccentric spandrel beams exhibited extensive damage during earthquakes and previous tests of planar (two-dimensional) specimens indicated early deterioration of joint shear strength for these types of structures. The main design variable for the column was the section aspect ratio (width vs. depth) to examine if the entire joint region of the rectangular column works under applied shear loading as effectively as a square column. Each specimen was tested twice. First, lateral loading was applied in the plane of the spandrel beam, then the specimen was rotated 90 degrees and the loading was applied in the plane of the normal beam that is perpendicular to the spandrel beam. The major design variable for the normal beam was its width, which was larger than the width of the supporting column for the last test specimen, to investigate the confinement of the joint region provided by the wide normal beams, and the transfer of moment from the wide beam to the column by a previously loaded spandrel beam. The experimental results indicated that when exterior connections have the floor system with slab and beams spanning in two perpendicular directions, the influence of the spandrel beam eccentricity on the seismic behavior of the joint region changes significantly. When the specimens were compared to previous tests, it was observed that the damage in the joint region was not as severe, the specimens have full hysteresis curves with high energy dissipation capacities, and the deterioration of joint shear stiffness and strength were delayed due to the additional torsional stiffness resulting from the use of a floor system