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The Cast ConneX® Scorpion™ Yielding Brace System™ (YBS) is a special class of concentrically braced frame. Just as in Special Concentrically Braced Frames (SCBF; AISC) / Moderately Ductile Concentrically Braced Frames (Type-MD CBF; CSA), the centerlines of YBS members that meet at a joint intersect at a point to form a complete vertical truss system that resists lateral forces. YBS have more ductility and energy absorption than SCBF / Type-MD CBF because overall brace buckling, and its associated strength degradation, is eliminated.
A YBS is composed of columns, beams and bracing elements, all of which are subjected primarily to axial forces. Braces of YBS are composed of a Cast ConneX® Scorpion Yielding Connectors™ connected to the end of a conventional W-Shape or HSS member. Scorpion Yielding Connectors have specially designed fingers which are intended to yield under seismic loading to dissipate energy while all other elements of the braced frame remain essentially elastic.
Engineers employing this system select Scorpion Yielding Connectors based on the desired activation load for the brace and then select a conventional W-Shape or HSS brace element based on capacity design requirements and on the desired axial stiffness of the brace assembly. In so doing, the yield force and elastic stiffness of each brace comprising a YBS can be independently tuned with this unique bracing system.
An additional benefit of the system is its unique post-yield response. At large deformations, Cast ConneX® Scorpion Yielding Braces™ exhibit post-yield strengthening and stiffening due to second-order geometric effects. This stiffening behavior allows for a better distribution of yielding in braces over a building’s height at large drift levels. In the event that deformations begin to collect in a single story, the system’s post-yield stiffening and strengthening will cause braces in adjacent stories to be activated, thereby reducing the likelihood of the formation of a “soft-story”. Neither of these advantages are available in systems which exhibit little or no post-yield stiffness.
The combination of high axial stiffness and low activation force also makes the YBS ideal for retrofitting existing seismically deficient reinforced concrete and steel moment-resisting frames. The high elastic stiffness of the system can reduce the drift levels of older buildings while lower activation forces reduce costly remediation of members, connections, and foundations. Furthermore, because all of the inelasticity in Scorpion Yielding Braces is confined to the Scorpion Yielding Connectors, engineers using the system have the flexibly to employ a wider range of brace configurations than can be accommodated with other hysteretic brace systems. For example, a single-bay, single-story X configuration can be employed to reduce the number of frames which are lost or obstructed; in the case of retrofit, this configuration can reduce the cost of the removal and replacement of building envelope and finishes.
Technical Publications
Development, Validation and Modeling of the new Cast Steel Yielding Brace System
(2012) Proceedings, 2012 Structures Congress, Chicago, USA
Authors: Gray, M.G., Christopoulos, C., Packer, J.A., and Lignos, D.G.
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Full-scale Testing of the Cast Steel Yielding Brace System
(2011) Proceedings, STESSA 2012 Conference, Santiago, Chile
Authors: Gray, M.G., Christopoulos, C., and Packer, J.A.
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Cast Steel Yielding Fuse for Concentrically Braced Frames
(2010) Proceedings, The 9th U.S. National and 10th Canadian Conference on Earthquake Engineering, Toronto, Canada
Authors: Gray, M.G., Christopoulos, C., and Packer, J.A.
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