Ductile steel beam-to-column connections for seismic resistance

The strength and ductility of steel frames depend strongly on the behavior of their beam-to-column connections. The fracture of beam-to-column connections of steel buildings in the Northridge Earthquake generated concern about the reliability of current design and construction technology on steel connections. There is an urgent need to find a reliable method to retrofit these connections and to use it for the design of new buildings. A simple method is proposed here to enhance the ductility of beam-to-column connections. On trimming the beam flanges slightly, the ductility of the connection can be improved greatly. Experimental study of the newly designed connections under cyclic load shows that the ultimate strengths are almost unaltered, whereas the stiffness is decreased only slightly. However, the plastic rotational capacity can be increased several times. Moreover, the fracture proneness of connections due to welding sensitivity and stress concentration from abrupt geometry alternation can be minimized and the energy dissipation capacity can be improved. A shaking table test of a steel frame designed according to the proposed connection method also behaves better than that of a conventional moment-resisting frame.