Seismic Inelastic Design of Steel Structures by Spectrum Analysis and Equivalent Damping

Abstract eng:
This paper presents a new method for the seismic design of steel structures. The method involves the use of equivalent modal damping for predefined deformation limits and spectrum analysis and modal synthesis for the calculation of the design base shear of the structure. All the work of dissipation due to material and geometric nonlinearities is converted into work of dissipation due to linear damping. Design curves providing equivalent damping ratios as functions of period for the first few modes as well as design accelerations as functions of period for given equivalent damping are constructed using numerical data coming from a large number of plane steel moment resisting frames excited by various long duration seismic motions. The proposed design procedure is illustrated by means of the seismic design of a steel moment resisting framed structure and is checked by means of non – linear inelastic dynamic analysis. It is concluded that the presented design method can be viewed as a more rational and effective alternative of the force based method of current seismic codes with equivalent modal damping values playing the role of the behaviour or strength reduction factor.

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