Seismic Analysis and Design of Type FR Steel Frames Using Displacement-Based Design and Advanced Analysis

Abstract

Current design office methodologies for seismic design of steel moment frames include forced-based methods for calculating equivalent lateral forces and a static elastic analysis. Research has revealed erroneous assumptions in forced-based methods and proposes that displacement-based methods, due to modeling inelastic systems, result in more reasonable lateral force distributions. Additionally, LRFD1 member design interaction equations implicitly account for geometric and material non-linear effects. This philosophy does not satisfy compatibility between the actual inelastic member response and the elastic system as assumed by conventional elastic analysis.

Displacement-based lateral force distributions in combination with a second-order inelastic static analysis that sufficiently determines the limit state strength and stability of a structural system, or "Advanced Analysis," is advantageous to the design of steel moment frames. Second-order geometric and inelastic effects are directly accounted for in the analysis. This allows engineers to predict actual frame behavior with greater accuracy and results in a more efficient and economical frame. Another advantage is that force reduction factors outlined in current seismic codes are not required since the frame is designed for inelastic behavior. This approach eliminates discrepancies between initially assumed force reduction factors and final frame ductility capacity. Also, individual member capacity checks outlined in design specifications are similarly not required.

The goal of this research is to advance the validity and accuracy of displacement-based design methods and Advanced Analysis for the engineering of seismic resistant steel moment frames. This research will allow the development of alternate seismic analysis and design procedures, as well as refined practical methods that can be incorporated in a design office.

1) Manual of Steel Construction – Load and Resistance Factor Design, American Institute of Steel Construction