Search

This paper reports details of a numerical study undertaken to evaluate seismic response factors for steel eccentrically braced frames (EBFs) using the FEMA P695 methodology. Six archetypes were designed by making use of the current U.S. specifications, and their behavior was assessed by making use of nonsimulated collapse models. Results indicate that the current values of response factors result in designs with higher collapse probabilities than expected. Two modifications were developed to bring the collapse probability of these archetypes to acceptable levels. The first modification is on the deflection amplification factor while the second one is on the response modification coefficient. Six archetypes were redesigned using the proposed modifications and reevaluated using the FEMA P695 methodology. The results indicate that the proposed modifications are adequate to satisfy the target collapse probability. Maximum and cumulative link rotation angles were observed to be less than the predefined limits.

The paper reports an analytical study on the design overstrength of steel eccentrically braced frames (EBFs). The study aimed at examining the influence of geometrical factors and seismic hazard on the design overstrength of EBFs. Pursuant to this goal a computer program which facilitates EBF designs was developed. The algorithm of the program adopts the lightest uniform frame design and library of link-beam-brace sub-assemblages concepts. The design output from the program was compared with published solutions and the results indicate that the algorithm developed as a part of this study is capable of providing lighter framing solutions. A parametric study was conducted using the developed computer program. The results indicate that the frames considered in this study have on average higher overstrength values when compared with the codified value even without considering potential increases due to material overstrength and strain hardening. The design overstrength was found to be influenced primarily by the link length to bay width ratio and the bay width, and secondarily by the building height and seismic hazard level.

Abstract: A study has been undertaken to evaluate the similarities and differences between the steel building design specifications used in the United States and Europe. Expressions for nominal strength presented in the AISC-360 Specification and the Eurocode 3 Specification were compared for fundamental limit states. In particular, rules for cross-section classification, tension members, compression members, I-shaped members subjected to flexure, I-shaped members subjected to shear, and fasteners were studied. Results of the investigation revealed that, in general, both specifications provide nominal capacities that are close to each other. Significant differences were reported for some limit states such as flexure in I-shaped members with non-compact flanges, shear and lateral torsional buckling in I-shaped members, and bearing strength at bolt holes. In this paper, the details of the comparative study are presented along with observations that are useful for practicing engineers.