Full-Scale Experimental Assessment of Steel-Encased Buckling Restrained Braces

Abstract eng:
Dissipation of seismic energy through large plastic deformations in ductile elements is a key approach to provide structural safety in strong earthquakes. Steel buckling-restrained braces (BRBs) offer significant energy dissipation capability by nondegrading plastic response of the internal steel core in tensile and compressive deformation cycles. Seismic performance of BRBs is affected by several factors such as the core-restrainer gap, the stiffness of the restraining system, and the interfacial friction between the core and the restrainer. This paper presents the results of 12 full-scale tests on BRB specimens made with an all-steel simple-to-fabricate restrainer jointed by high strength bolts. A simple hinge detail is also introduced at the brace ends to reduce the flexural demand on the framing components. The effects of interfacial friction between the core and the restrainer, gap size, loading history, bolt spacing, and local stiffness of the restraining mechanism are verified in these tests. Two practical pressure-sensitive UHMW polyethylene and PTFE tapes, and a graphite-based dry film lubricant are used as debonding material between the restrainer and the core. The influence of fast loading rates on axial resistance and low cycle fatigue life of BRB is examined through successive application of real-time seismic deformations histories. The performance of the brace member is also qualified under typical long-duration subduction inter-plate earthquakes. Internal restrainer thrust forces are evaluated using series of instrumented bolts. It is shown that insufficient strength can lead to significant strong-axis core buckling and subsequent loss of loading bearing capacity of BRB member in compression.

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