Simplified seismic code design procedure for friction-damped steel frames

This paper describes the development of a proposed seismic design procedure for friction-damped steel structures, which employs the lateral force prov isions used in many modern building codes. Closed-form expressions are firs t derived that relate the normalized response of a single degree of freedom friction-damped system with the system parameters, such as bracing stiffne ss ratio, damper slip ratio, and frame member ductility. A parametric analy sis is then used to reveal that the seismic displacement of a friction-damp ed frame can be controlled by combining the frame stiffness with the bracin g stiffness of the friction damper component, while the seismic force can b e controlled by the damper slip force. A force modification factor (equival ent to the code R-factor) and displacement estimate for a friction-damped s ystem are next determined. The single degree of freedom results are subsequ ently used to develop expressions for dealing with the multi degree of free dom situation, which permits the seismic lateral force design procedure ado pted by many current building codes to be applied to friction-damped system s. The proposed procedure allows the frame response to be controlled so tha t the displacement can be limited to small magnitudes and the overall struc tural shape to an essentially straight-line deformation. Design examples il lustrate that friction-damped frame systems are economical and offer a bett er overall response performance than that provided by conventional systems under the design earthquake.