Cyclic Response of Sloped Extended End-Plate Moment Connections

Abstract

Bolted extended end-plate (BEEP) moment connections are extensively recommended in design standards to be used as a prequalified beam-to-column connection in steel portal frames and special moment frame buildings. These standards assume that in such a connection, the beam is perpendicular to the steel column or that the slope angle of the steel beam is very small. To expand the engineering applications of BEEP connections in large-slope angle buildings, in this study, three one-sided specimens at half scale with 0°, 15°, and 30° slope angles, respectively, were designed and tested under cyclic loading. All dimensions of these specimens were identical, except the slope angles of their steel beams. The experimental results showed that the maximum rotation angles of these sloped BEEP connections exceeded 0.05 rad, and they were remarkably larger than those of other types of sloped rigid-moment connections tested by Mashayekh and Uang. However, the force concentration that occurred in the flange at the heel location was similar to that observed by them, and it led to the development of brittle fractures. Particularly, with the increase in the slope angle, the force concentration tended to become more severe. Three strengthening schemes for reducing the force concentration and enhancing the deformation capacities of the sloped BEEP connections subjected to the extremely rare earthquake, i.e., less than 2% probability of exceedance in 50 years, were evaluated using the finite element approach. These were Scheme I: stiffening the rib in the acute-angle zone, Scheme II: employing a reduced beam section (RBS) connection, and Scheme III: forming a curved web cut in a non-RBS beam. The analytical results showed that the three schemes decreased the von Mises stress level in the acute-angle zone of the connection web. Scheme I enhanced the initial rotation stiffness, flexural strength, and deformation rotation capacity. For Scheme II, a RBS configuration was employed, which effectively improved the connection rotation capacity, whereas it decreased the flexural strength of the sloped BEEP connection. Scheme III without a reasonable design led to a degradation of the hysteretic performance, moderate rotation capacity, and low flexural strength. Therefore, Schemes I and II leading to much better seismic behavior than Scheme III are recommended.