Elimination of Intermediate Stiffeners in Box Link Beam of Eccentrically Braced Frames Using Low Yield Point Steel

The eccentrically braced frame has more ductility in comparison with concentrically braced frame and more lateral stiffness in comparison with moment resisting frame and involves the advantages of both moment frame and concentrically braced frame. Because of these reasons, this system has gained popularity in the last decades. I shaped and box-shaped beams are two usual link beams. In cases that lateral braces are hard to provide at both ends of the link beam, box link beam has some advantages comparing to the I-shaped beam because of its high torsional stiffness. Using transverse stiffeners in Box link beams, delays local buckling and leads to higher buckling stability and energy dissipation in links but increases the cost of construction and decreases the velocity of execution. In this research, low yield point steel, as a new material in seismic design of steel structures, has been used as web of link beam in order to enhance local buckling stability of links and eliminate intermediate stiffeners. Using low yield point steel in the web of link beam makes it possible to increase links web thickness and lowers the compactness ratio of the web as a result. Because of low yield stress, high ductility, and strain hardening, low yield point steel prevents buckling and fracture and increases energy dissipation of structure but using of low yield point steel as link web, leads to the about triple value of over-strength in comparison with usual steels that should be considered in the design of force-controlled members based on link beam capacity. According to this research, using Low yield point steel with a compactness ratio less than 16.5 and without intermediate stiffeners as link web, eliminate local shear buckling. Also using Low Yield Point steel in link beam may lead to a higher response modification factor.