Exterior wide beam–column connections in existing RC frames subjected to lateral earthquake loads

Abstract

In this paper, the seismic performance of reinforced concrete exterior wide beam–column connections with shallow spandrel beams lightly reinforced for torsion and moderate levels of gravity loads was investigated experimentally. The study focuses on existing frames designed and detailed according to construction practices used over ten years ago in the moderate-seismicity Mediterranean area. The results can be useful for assessing the seismic vulnerability of older structures and orienting seismic retrofit alternatives. Two 3/5 scale test models representative of exterior sub-assemblages in a prototype six-story building were subjected to gravity-load levels typical of those acting during an earthquake, and quasi-static cyclic lateral loads until failure. The performance was studied in terms of strength, displacement, ductility and energy dissipation capacity. The data are analyzed in conjunction with the results of previous tests. The specimens exhibited a “strong column–weak beam” type of flexural yielding mechanism. The average drift ratios at first yielding of the wide beam longitudinal reinforcement, δ y o , and at failure, δ u , were 2.2% and 4.5% respectively; the displacement ductility ratio μ was approximately 2.2. Comparison to similar connections without added gravity loads showed that moderate levels of gravity loading increased δ y o by about 40%, and decreased by a similar percentage the value of μ and the energy dissipated in each half cycle of displacement expressed in terms of an equivalent viscous damping ratio. Finally, two approaches for estimating the wide-beam flexural capacity are examined.