Effect of Reduced Brace Section on Behavior of SCBF Bracings

摘要

Energy dissipation in concentrically braced frames is achieved by successive cycles of inelastic buckling in compression and yielding in tension and force controlled elements, such as beams, columns and connections should remain elastic to ensure the gravity load resistance of the frame. Braces are usually designed for compression which results section areas that are more than required by 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, the 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. In this paper effect of Reduced Brace Section on behavior of displacement control braces, which intend to decrease the difference between tensile and post-buckling strength of braces, is described. Decreasing area of the steel section in a limited length and at a specific location will result in a reduction in tensile yielding capacity of the brace while it's buckling load and post buckling behavior is not affected significantly. Tensile yielding force is related to the reduced area of the brace while its post yielding tensile capacity is also related to the length of the reduced section. Minimum change in buckling and post buckling response was derived from the proposed arrangements of reduced sections. Linear and nonlinear response of the reduced section braces in tension and compression is studied by analytical methods under monotonic and cyclic loading. Braces with reduced section are considered as a type of balanced bracing which results smaller design forces for gusset plates and beams in chevron bracings.