Document Type : Structural Earthquake Engineering
The use of passive control systems is widely considered as a reliable approach for controlling earthquake vibrations in steel structures. First, under frequently occurring low to moderate earthquakes, the structure should have sufficient strength and stiffness to control deflection and prevent any structural damage. Second, under rare and severe earthquakes, the structure must have sufficient ductility to prevent collapse. For this case, significant damage of the structure and non-structural elements is acceptable. In this paper, the performance and the lateral stiffness of a new eccentric and knee bracing system named Eccentrically Knee Brace (EKB) is investigated. The stiffness of eccentrically knee braced frames (EKBs) is difficult to calculate by hand because they are indeterminate and have significant shear, flexural and axial deformations in different members. EKB stiffness is important for design, because it is used to compute story drifts and the knee and link rotations, which have prescribed limits. This note presents an equation for the stiffness of an EKB story in terms of the design story shear, frame geometry, and beam depth. The equation is independent of specific member sizes, making it useful for determining appropriate geometry in design. The equation is developed numerically and verified with experimental data from code compliant. One application of the equations is the estimate of the beam depth required to ensure a link or knee will satisfy inelastic rotation limits.