ABSTRACT
The enhancement of torsional resistance of building frames by the knee bracing system as an energy dissipator is corroborated by investigating the sensitivity of this type of framing to accidental torsion originated from uncertainties in the stiffness and strength of the bracing system. An expression to estimate the upper bound of the overall variation of the system stiffness is developed for statistically uncorrelated members. The results of a parametric study demonstrate the dependence of the accidental torsion arising from unforeseen discrepancies between actual and analytical stiffness and strength distributions on the type of resisting framing. The equivalent structural eccentricity caused by unbalanced yielding of the knee elements depends on the degree of the strength variation and the level of stiffness of the knee bracing system. More importantly is that the torsional translational coupling induced at high intensity level is less significant. The amplification of the induced torsion is probably prevented because of the existence of a strong restoring force from remaining elastic elements (MRF) in addition to the effect of the damping developed by the yielded knee element.
