Large-Scale Testing of Steel Unbonded Braces for Energy Dissipation

Abstract

This paper outlines large-scale tests of tension/compression yielding braces (also called "unbonded braces") in support of their first applications in the United States. The core steel in these braces provides stable energy dissipation by yielding under reversed axial loading, while the surrounding concrete-filled steel tube resists compression buckling. The paper summarizes a series of tests on large-scale unbonded braces, having yield forces of 1200, 1600, and 2100 kN (270, 360, and 470 kips). Each brace was subjected to a cyclic loading pattern consistent with that used widely for testing steel beam-column connections. Additional tests explored the behavior of the braces under a near-field loading history, a displacement time history derived from a seismic analysis of an idealized 5-story building, and a low-cycle fatigue test.