Ductile Fuses for Special Concentrically Braced Frames

Abstract

The behavior of Fuse Elements subjected to load reversals is explored for potential use in Steel Concentrically Braced Frames. Two fuse elements are investigated through experimental and computational analyses. The use of these fuse elements allows the braces to yield in a ductile manner while limiting the damage to the brace elements and the connections. Both fuse elements are intended to maintain frame strength under repeated cycles beyond yield both in tension and compression, providing balance between the tensile and compressive lateral load resistance across the building in the direction of the braced frame which helps prevent the accumulation of inelastic drifts in one direction. The first fuse element system consists of a reduced brace section with oval cutouts and is designated by the letters RXS. The tensile capacity of the fuse element is mainly a function of the cross sectional area whereas the fuse compressive capacity depends not only on the fuse cross sectional area but also on the fuse length. Experimental results showed that the response of the RXS fuse to the loading history was rather poor mainly because of its limited energy dissipation capacity. This fuse system is highly sensitive to eccentricities on axial loading and it is not suitable for the intended applications, although it provided valuable information for the development of the second fuse system presented. The second fuse element is a brace composite element that consists of steel bars embedded in a polymer matrix that is confined by carbon fiber reinforced polymer. The letters BCE designate this second system. The tensile capacity is provided by the steel bars, similarly the buckling capacity is also provided by the steel bars but due to the slenderness of the bars, a confined polymer matrix is provided to improve the stiffness of the system under compressive loads. The polymer matrix is confined by a Carbon Reinforced Polymer layer. The BCE fuse system has the ability to dissipate energy without loss in strength up to very large inelastic deformations. Experimental results showed that damage to the BCE fuse was very limited even at unit deformations beyond 3%, indicating that the fuse has remarkable toughness under load reversals. The BCE fuse exhibited great potential as an energy dissipation device. The biggest benefit of the composite fuse is its inherent toughness. The fact that the fuse bars can be easily replaced after large inelastic deformations is another significant advantage. Even though the fuse was subjected to large inelastic deformations, there was virtually no loss in strength in tension and compression, and there was no meaningful overstrength in compression.