Seismic behavior of reinforced concrete column-to-steel beam (RCS) connections with special configurations.

Abstract

This study was aimed at evaluating the seismic behavior of composite joints between R&barbelow;einforced C&barbelow;oncrete (RC) columns and S&barbelow;teel (S) beams (RCS) with the following two configurations: (1) RC column substantially wider than the steel beam, and (2) roof level T-configuration. The main objective of the study on the behavior of RCS joints with wide columns was to evaluate the effective width of joints with band plates and/or embedded steel columns for shear force transfer. The effective width of RCS joints was evaluated by comparing the results from two connections previously tested by Parra and Wight (2000), in which the RC column width was 2.4 times the width of the steel beam flange, to the results obtained from two nearly identical specimens tested in this investigation, but with a column-to-beam width ratio of 3.6. Test results indicated that a 50% increase in column width led to an approximately 50% and 30% increase in joint strength for the specimens with steel columns and band plates, respectively. Based on these observations, the use of a 2:1 horizontal projection from the edges of the steel column flange closest to the compression flange of the steel beam is recommended for estimating the outer panel width in RCS joints without band plates. For connections with band plates the outer panel width may be taken as 16 times the band plate thickness. The seismic behavior of roof T-joints was investigated through the testing of two beam-column subassemblies under displacement reversals. The primary variable investigated was the anchorage of column longitudinal bars in the connection. The column bars in the first specimen were anchored with mechanical anchors, which had twice the bar diameter, plus an anchorage length of 12 bar diameters before the anchors. This specimen exhibited a stable response up to 4.0% drift, the displacement at which a bar anchorage failure occurred. Thus, the anchorage length before the mechanical anchors for the second specimen was increased to 20 bar diameters and a larger bearing area for the mechanical anchors was provided through steel channel sections running transversely above the top flange of the steel beam. The behavior of the second specimen was characterized by large column inelastic rotations and limited joint damage. The experimental results showed that an anchorage length of 20 bar diameters for bars with mechanical anchors, in combination with band plates and a joint stirrup volumetric ratio of 0.5%, are adequate for ensuring proper column bar anchorage and a stable T-joint behavior under displacement reversals. Also, the mechanical anchor area must be such as to limit concrete bearing stresses to 2<italic>f'_c</italic>. Further, test results suggest that the shear strength of RCS roof T-joints can be estimated as 50% of that predicted for an interior connection with the same detailing.