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The Earthquake Engineering Online Archive - (Nisee e-library)
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.
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Design of links and beam-to-column connections for eccentrically braced steel frames
Popov, Egor P.; Malley, James O.
UCB/EERC-83/03, Earthquake Engineering Research Center, University of California, Berkeley, 1983-01, 67 pages (530/P65/1983D)
This report has been prepared to be Chapter 11 of the upcoming "ASCE Manual on Beam-to-Column Building Connections," under review by members of the Monograph Task Committee of the Committee on Structural Connections of the ASCE Structural Div. The chapter first introduces the concept and points out some of the advantages of eccentrically braced frames (EBFs) for seismically resistant steel construction. A brief exposition of some of the available design procedures for such frames is provided. An approach is given for appraising the performance of the active links, i.e., beam segments between braces and/or columns, for achieving a stiff elastic structure together with an indication of the ductility demands placed on the links at extreme cyclic overloads. Suggestions for link length selection are made based on experimental results with some 28 full-sized isolated links. Some of the obtained results in these experiments are described and selected hysteretic loops for cyclic loadings are given. Illustrated in this chapter are suggested details for the following items: link-column connections, link-brace connections, and spacing and sizing of link-web stiffeners. Possible applications of EBFs in nonseismic design are also pointed out.
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Design considerations for shear links in eccentrically braced frames
Malley, James O.; Popov, Egor P.
UCB/EERC-83/24, Earthquake Engineering Research Center, University of California, Berkeley, 1983-11, 126 pages (530/M224/1983)
This study addresses three aspects of shear link behavior critical to the economical design of an eccentrically braced frame which employs shear links: the sensitivity of link behavior to the imposed loading history, the link-column connection detail, and the web stiffener design and details. Results for twelve full-size shear link specimens are presented. Each of the specimens was designed to investigate specific shear link response characteristics. Four specimens were tested with stiffener details which differed significantly from those of previous experiments and early design applications. Another set of four specimens were designed and tested with widely varying loading histories. A set of four specimens which employed conventional moment resisting connection details were also tested. The qualitative and quantitative results of these experiments are compared and analyzed using energy dissipation capacity as a major parameter. Test conclusions and design recommendations are presented. A practical method for web stiffener design is developed which considers both the axial force and bending rigidity requirements which shear link web stiffeners must satisfy. An example of the method is given in an appendix. A design procedure for eccentrically braced frames which employ shear links is outlined, based on the major considerations of shear link design. This procedure includes recommendations on the determination of structural configuration, member sizes, link-connection details, and web stiffener sizes and details. The suggested connection and stiffener details are illustrated.
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Structural steel bracing systems: behavior under cyclic loading
Popov, Egor P.; Takanashi, Koichi; Roeder, Charles W.
UCB/EERC-76/17, Earthquake Engineering Research Center, University of California, Berkeley, 1976-06, 81 pages (515/P65/1976)
A survey is made of existing literature on the performance of steel braced frame structures under cyclic excitations. Particular emphasis is placed on inelastic behavior under extreme credible excitations which may occur during a severe earthquake. The experimental and analytical studies of the behavior of an individual brace are described. The effect of the individual braces on the behavior of the entire structural system is then brought out. The behavior of a concentrically braced frame is discussed with respect to dynamic response to given excitations as well as its quasistatic hysteretic behavior under cyclic load. The advantages and limitations of the two possible approaches to design and correlations are indicated. The overall problem is very complex and has not been completely resolved, but a number of plausible design concepts have been advanced. These are reviewed in the report. Most of these are based on static methods of analysis and are intended to assure good dynamic performance of the structure. These approaches are not a substitute for dynamic analysis, but they help simplify the design procedure. Several design concepts, such as the eccentrically connected braced frame, show that braced frames can perform well under extreme excitations. Finally, the limitations of current knowledge are summarized and recommendations for further research are made.
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Inelastic buckling of steel struts under cyclic load reversals
Black, R. Gary; Wenger, W. A.; Popov, Egor P.
UCB/EERC-80/40, Earthquake Engineering Research Center, University of California, Berkeley, 1980-10, 174 pages (530/B538/1980)
Cyclic axial loading experiments simulating severe seismic conditions are described for 24 structural steel struts of sizes and shapes typically employed as braces in small to moderately large steel buildings. The cross-sectional geometries of the specimens were also chosen to model the larger, heavier struts. Six of the 24 members were pinned at one end and fixed at the other, while the remaining 18 were pinned at both ends. The range of cross-sectional shapes included wide flanges, double-angles, double-channels, structural tees, thin- and thick-walled pipes, and thin- and thick-walled square tubes. The responses of the specimens are evaluated and special attention paid to the effects of cross-sectional shape, end conditions, and slenderness ratio using hysteretic envelopes. While investigating the major parameters that influence a member's performance under cyclic loading, some important properties were recognized and quantified. Reduction factors were developed, which can account for the Bauschinger effect and initial curvature of struts. These factors can be used with an American Iron and Steel Inst. code-determined load to estimate the deteriorating compressive capacity of a strut during a few consecutive cycles of full inelastic load reversals. Some design recommendations are made for builtup members likely to experience severe load reversals.
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Seismic moment connections for moment-resisting steel frames
Popov, Egor P.
UCB/EERC-83/02, Earthquake Engineering Research Center, University of California, Berkeley, 1983-01, 61 pages (530/P65/1983S)
This report has been prepared to be Chapter 6 of the forthcoming "ASCE Manual on Beam-to-Column Building Connections," under review by members of the Monograph Task Committee of the Committee on Structural Connections of the ASCE Structural Div. The chapter provides an overview of the state of the art for the design of steel moment connections for high seismic risk regions. The need to design such connections to remain ductile when subjected to full-load reversals is indicated first. The generally accepted approach of "strong columns-weak girders," i.e., designing the joints to develop inelastic activity in the connections and beams rather than in the columns, is adhered to throughout. A major section is devoted to presentation of experimental results to illustrate the observed behavior of beam-to-column connections and column panel zones under severe cyclic loadings simulating extreme seismic conditions. Procedures are given for seismic moment joint calculations pertaining to flange beam connections, web connections, and panel zone design. Typical seismic moment connections of beam-to-column flanges as well as to webs and column splices are illustrated. The chapter concludes by identifying those problems requiring further research.
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