The Earthquake Engineering Online Archive

A study of seismically resistant eccentrically braced steel frame systems

Kasai, Kazuhiko; Popov, Egor P.

UCB/EERC-86/01, Earthquake Engineering Research Center, University of California, Berkeley, 1986-01, 309 pages (530/K245/1986)

Basic plastic theory for an eccentrically braced frame (EBF) force field and an ideal rigid-plastic displacement field are explained in the first part of this report. Based on these, a simple method for obtaining the lateral load-carrying plastic capacity of an EBF is proposed. Further, the proposed plastic theory is employed for various plastic problems of EBFs, where the accuracy of the theory is demonstrated by comparing results found using the theory with elastoplastic finite element analysis results. The second part of this report includes the effect of link inelastic deformation on both link and EBF behavior. Strain-hardening and various failures of the link are discussed. First, the experimental program for a subassemblage simulating EBF action is described. The observed cyclic behavior of different length links tested with or without simultaneously acting axial forces is reported. Next, the experimental results are analyzed with emphasis on the influence of the link length on the performance. Moment, shear, and axial force interaction, as well as the effect of strain-hardening on moment redistribution, energy dissipation, and flange and web buckling, are considered. Based on these results, the ultimate state design for cyclically loaded links is proposed. Further, a simple new criterion for web stiffener spacing to prevent premature cyclic web buckling is proposed using the secant modulus method based on experimental data for 30 links. The application of this criterion to an EBF ultimate state design is also discussed.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-86-01.pdf (9 MB)