Dicleli and Mehta 2009
The authors propose and perform an analytical study of a retrofit to a chevron braced frame. An energy-dissipating element is placed between the braces and the connecting beam. Nonlinear static pushover, time-history, and damage analysis are conducted and the results compared between a chevron braced frame and the retrofitted chevron braced frame. The energy-dissipating element can either be an HP or W section.
System Concept
The goal of this system is to prevent the buckling of the braces by yielding another element first. The HP section at hand is composed of stocky plates that can undergo large inelastic deformations and failing in shear from the axial forces of the braces. The system is meant to be replaceable so that the existing structure is not affected. With this is mind, it is important that the fuse element take most of the energy so that the rest of the structure does not experience any buckling or damage.
Analytical Study, Results, and Discussion
The authors performed an analytical study of this system including buckling instability of the braces. The behavior of the system with the braces as the main energy-dissipating system is compared to the system with the fuse element connecting the braces to an overhead beam as the main energy dissipater. Imperfections are introduced into the brace model to allow for buckling. The analytical study examined the systems with varying numbers of stories, as well as brace slenderness, to see what roles these played in the energy-dissipating abilities of each system.
It was found that adding fuse elements reduces the brace sensitivity to slenderness, preventing the braces from buckling. It was also found that the lateral strength of the frame is maintained because the braces do not buckle, when the fuse element is added to the brace connection.
It is noted that the fuse elements are much more effective with low levels of ground motion and low number of stories. The fuse elements do not go far past yielding with high motions, although inter-story drifts are still only 60% of the chevron braced frames without fuse element retrofits. These can be attributed to the combination of elastic stiffness of the braces with the energy-dissipating capabilities of the fuse elements.
Reference
Dicleli, M. and Mehta, A. (2009). "Seismic Retrofitting of Chevron-Braced Steel Frames Based on Preventing Buckling Instability of Braces," International Journal of Structural Stability & Dynamics, 9.2, pp. 333-356.