farmer
Seismic Demands on Steel Braced Frame Buildings with Buckling-Restrained Braces by 1
2
Rafael Sabelli, Stephen Mahin and Chunho Chang
3
Abstract
This paper highlights research being conducted to identify ground motion and structural characteristics that control the response of concentrically braced frames, and to identify improved design procedures and code provisions. The focus of this paper is on the seismic response of three and six story concentrically braced frames utilizing buckling-restrained braces. A brief discussion is provided regarding the mechanical properties of such braces and the benefit of their use. Results of detailed nonlinear dynamic analyses are then examined for specific cases as well as statistically for several suites of ground motions to characterize the effect on key response parameters of various structural configurations and proportions.
Introduction
Steel moment-resisting frames are susceptible to large lateral displacements during severe earthquake ground motions, and require special attention to limit damage to nonstructural elements as well as to avoid problems associated with P-∆ effects and brittle or ductile fracture of beam to column connections [FEMA, 2000]. As a consequence, engineers in the
US have increasingly turned to concentrically braced steel frames as an economical means for resisting earthquake loads. However, damage to concentrically braced frames in past earthquakes, such as the 1985 Mexico [Osteraas, 1989], 1989 Loma Prieta [Kim, 1992], 1994
Northridge [Tremblay, 1995; Krawinkler, 1996], and 1995 Hyogo-ken Nanbu [AIJ/Kinki
Branch Steel Committee, 1995; Hisatoku, 1995; Tremblay, 1996] earthquakes, raises concerns about the ultimate deformation capacity of this class of structure.
Individual braces often possess only limited ductility capacity under cyclic loading [Tang,
1989]. Brace hysteretic behavior is unsymmetric in tension and compression, and typically exhibits substantial
2
Rafael Sabelli, Stephen Mahin and Chunho Chang
3
Abstract
This paper highlights research being conducted to identify ground motion and structural characteristics that control the response of concentrically braced frames, and to identify improved design procedures and code provisions. The focus of this paper is on the seismic response of three and six story concentrically braced frames utilizing buckling-restrained braces. A brief discussion is provided regarding the mechanical properties of such braces and the benefit of their use. Results of detailed nonlinear dynamic analyses are then examined for specific cases as well as statistically for several suites of ground motions to characterize the effect on key response parameters of various structural configurations and proportions.
Introduction
Steel moment-resisting frames are susceptible to large lateral displacements during severe earthquake ground motions, and require special attention to limit damage to nonstructural elements as well as to avoid problems associated with P-∆ effects and brittle or ductile fracture of beam to column connections [FEMA, 2000]. As a consequence, engineers in the
US have increasingly turned to concentrically braced steel frames as an economical means for resisting earthquake loads. However, damage to concentrically braced frames in past earthquakes, such as the 1985 Mexico [Osteraas, 1989], 1989 Loma Prieta [Kim, 1992], 1994
Northridge [Tremblay, 1995; Krawinkler, 1996], and 1995 Hyogo-ken Nanbu [AIJ/Kinki
Branch Steel Committee, 1995; Hisatoku, 1995; Tremblay, 1996] earthquakes, raises concerns about the ultimate deformation capacity of this class of structure.
Individual braces often possess only limited ductility capacity under cyclic loading [Tang,
1989]. Brace hysteretic behavior is unsymmetric in tension and compression, and typically exhibits substantial
References: AISC (American Institute of Steel Construction), Seismic Provisions for Structural Steel Buildings, Chicago, 1997. Technology in Structural Engineering: Proceedings of the 2000 Structures Congress & Exposition, May 8-10, 2000, Philadelphia, Pennsylvania, American Society of Civil Engineers, Reston, Virginia, 2000 Clark, P., et al., Evaluation of design methodologies for structures incorporating steel unbonded braces for energy dissipation, 12th World Conference on Earthquake Engineering, Proceedings, New Zealand Society for Earthquake Engineering, 2000, Paper No FEMA (Federal Emergency Management Agency), 1997 NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures, Washington, 1997. FEMA, Recommended Seismic Design Provisions for New Moment Frame Buildings Report FEMA 350, Federal Emergency Management Agency, Washington DC, 2000. FEMA, State of the Art Report on Performance Prediction and Evaluation (FEMA-355F), Federal Emergency Management Agency, Washington, DC, 2000. Association of California, Structural Engineers Assn. of California, Sacramento, 1995, pages 21-40 Rotterdam, 2000, pages 403-409 ICBO (International Conference of Building Officials), Uniform Building Code California, 1997. Behaviour of Steel Structures in Seismic Areas: STESSA 2000, Balkema, 2000, pages 33-38. Khatib, I. and Mahin, S., Dynamic inelastic behavior of chevron braced steel frames, Fifth Canadian Conference on Earthquake Engineering, Balkema, Rotterdam, 1987, pages 211-220 Engineering, Univ. of Michigan, Ann Arbor, Oct. 1992, 290 pages Ku, W., Nonlinear analyses of a three-story steel concentrically braced frame building with the application of buckling-restrained (unbonded) brace, Dept. of Civil and Environmental Engineering, University of California, Berkeley, Calif., 1999. Krawinkler, H. et al., Northridge earthquake of January 17, 1994: reconnaissance report, Vol. 2 -- steel buildings, Earthquake Spectra, 11, Suppl. C, Jan. 1996, pages 25-47. Arbor, Apr. 1987, 226 pages. Document SAC/BD-99/01, SAC Joint Venture, Sacramento, CA, 1999. Osteraas, J. and Krawinkler, H., The Mexico earthquake of September 19, 1985 -- behavior of steel buildings, Earthquake Spectra, 5, 1, Feb Research Report UMCEE96-21, Dept. of Civil Engineering, Univ. of Michigan, Ann Arbor, 1996. Ann Arbor, 1997. FEMA/EERI Professional Fellowship Report, 2001 (in preparation). Saeki, E.; et al. Analytical study on unbonded braces fixed in a frame (in Japanese), Journal of Structural and Construction Engineering (Transactions of AIJ), 489, 1996, pages 95-104 SEAOC (Structural Engineers Association of California), Draft Provisions for BucklingRestrained Braced Frames, Sacramento, CA, 2001. Somerville, P. et al., Development of Ground Motion Time Histories for Phase 2, SAC Background Document SAC/BD-97/04, SAC Joint Venture, Sacramento, CA, 1997. September 8-10, 1992, San Diego, CA, [Applied Technology Council], 1994, pages 27-39 Wada, A Earthquake Engineering Research Center, University of California, Dec. 1999, pages 279-289 Watanabe, A