Experimental Testing of a Replaceable Brace Module for Seismically Designed Concentrically Braced Steel Frames

Abstract

For a seismically designed concentrically braced frame with hollow structural sections as braces, the typical connection design consists of a slotted brace that is field welded to a gusset plate. During an earthquake, the brace is expected to buckle out-of-plane and the gusset plate is expected to yield. This makes it difficult to repair or replace the brace and connection, and the out-of-plane brace buckling caused by this connection can also damage surrounding walls and cladding, with potential life safety implications. This paper proposes an alternative connection that is expected to result in reduced erection costs by avoiding site welding, and also to simplify structural repairs following a major earthquake by confining all damage to a replaceable brace module. Additionally, the new connection causes the brace to buckle in-plane during a seismic event, reducing the potential for damage to the surrounding walls and cladding. This paper discusses large-scale quasi-static cyclic testing of eight brace modules with two variations of the new connection, one with a single-shear eccentric splice and the other with a double-sided concentric splice. All tested specimens had the desired failure progression and buckled in-plane, as intended. Bolt slip in the connection had very little effect on the overall force-deflection response after the brace compressive strength degraded to less than the slip load. The brace module was replaced after each test without observable damage outside the module. Although both connection variations behaved in a desirable manner, the single-shear eccentric splice was preferred because of the simpler constructability and improved performance.