The Relative Stiffness of Steel Eccentric Braced Frame with Dual Vertical Links

The most important characteristics of building frames can be abbreviated in stiffness, strength and ductility. Moment frames have ductile behavior and low stiffness; therefore, the main reason in using the lateral bracing systems is their considerable stiffness. Eccentric bracing systems are considered as ductile frames, while satisfying the required stiffness. The lateral stiffness of conventional eccentric configurations have been calculated previously. In this research, the lateral relative stiffness of eccentrically braced frame with dual vertical links (EBF-DVL) is calculated analytically. EBF-DVL has two parallel vertical links which are welded to the floor beam at the top and to one horizontal link at the bottom. In order to provide the required equations for obtaining the stiffness, the slope-deflection equations are used by considering the effects of shear deformations. The results show that EBF-DVL has a high relative stiffness and by adjusting the lengths of vertical and horizontal links, it is possible to achieve the stiffness even more than the stiffness of eccentric bracing with horizontal link between two diagonal braces. Although an increase in either the moment of inertia or shear area of the vertical link leads to an increase in the lateral stiffness of the system, the effective interval for increasing the moment of inertia of the vertical links is to be limited to approximately half of the column moment of inertia and the corresponding value for increasing the shear area is approximately 60% of the shear area of the column.