Study of Seismic Behavior of SCBF with "Balanced Bracing"

Abstract eng:
Bracing members in concentrically braced frames are specially designed to undergo plastic deformations and dissipate hysteretic energy through successive cycles of inelastic buckling in compression and yielding in tension while force controlled elements, such as beams, columns and connections should remain elastic to ensure the gravity load resistance of the frame. Design of a brace for buckling usually requires bigger sections than tension, while due to tension action of brace, the connections and other members should be designed for tensile strength of brace element. In chevron braced frames, beams in bracing frame should possess adequate strength to resist the unbalanced vertical forces due to unequal axial capacity of braces in tension and compression. This result in very big size beams, much stronger than would be required for other brace configurations. This paper describes an innovative brace member, Balanced Bracings, which intend to decrease the difference between tensile and post-buckling strength of braces. To do so the idea of RBS (Reduced Beam Section) in moment resisting frames is implemented in concentrically braced frames. Decreasing steel area in a limited length and at a specific location will result in a reduction in tensile capacity of the brace while it’s buckling load and post buckling behavior is not affected significantly. Location and shapes of reduced area in brace are investigated by analytical studies that take into account the possibility of local buckling. The use of balanced bracing result in smaller unbalanced vertical forces on floor beams in chevron configuration, and also smaller design force for gusset plates.

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