Specifying Fixed-Base Columns or Pinned-Base Columns in Computer Analysis and Design of Steel Frames
Publication: Practice Periodical on Structural Design and Construction
Volume 26, Issue 1
Abstract
This paper addresses the application of support fixity condition of column bases in computer structural analysis and design of steel frames. All structural analysis software require input data to model the frames. Supports and connecting points are identified by joint or node numbers, members are identified by member numbers, and so on. The column bases are identified as support joints, and the degrees of freedom of all support joints must be specified. Most programs provide a default support condition as fixed, meaning fixed against all six degrees of freedom. The six degrees are displacement and rotation in the -, -, and -directions. A release command is used to release the restraint in any specified degree of freedom. It has been found that some engineers in some sectors of industry have been using incorrect column base support conditions for major steel frames, specifying pinned supports instead of the fixed supports in all their designs for years. This is equivalent to assuming that plastic hinges (full plastic moment) had already formed at the bottom of all columns before the frames were even applied with any loads. The results were safe design, but grossly overdesigned because the entire elastic range of moment resistance at all column bases were ignored. This paper describes the fixed and pinned supports and demonstrates with typical drawings and pictures of fixed and pinned supports commonly seen. Force distribution at typical anchor steel base plate (fixed support) is given with equation for applied moment. Test results for moment resistance of anchor base plates (fixed supports) are referred to. Several examples of actual major structures that were designed using a fixed-base connection and their life-long integrity under actual sustained service loads are given. Understanding of this paper should lead to a safe and economical design of steel structures.
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Data Availability Statement
No data, models, or code were generated or used during the study.
Acknowledgments
Disclaimer
The opinion written and expressed in this paper belongs to the author and is not necessarily that of McLaren Engineering Group to which the author is affiliated. Also, readers of this paper and engineers have to design and verify their own column base details for their projects. The details shown in this paper are specific for the specific projects discussed in this paper and solely for that purpose.
References
AISC. 1989. Specification for structural steel buildings, 5–135. Chicago: AISC.
Blodgett, O. W. 1982. Design of welded structures. Cleveland: James F. Lincoln Arc Welding Foundation.
Cook, R. A., and R. E. Klingner. 1992. “Ductile multiple-anchor steel-to-concrete connections.” J. Struct. Eng. 118 (6): 1645–1665. https://doi.org/10.1061/(ASCE)0733-9445(1992)118:6(1645).
Korn, A., and T. V. Galambos. 1968. “Behavior of elastic-plastic frames.” J. Struct. Eng. 94 (5): 1119–1142.
Reed, J. W. 1970. Window damage study of the Lubbock tornado. Albuquerque, NM: Sandia Laboratory.
Seniwongse, M. 1977. “Inelastic response of multi-storey building to tornadoes.” Ph.D. dissertation, Dept. of Civil Engineering, Texas Tech Univ.
Seniwongse, M. 1985. “Inelastic analysis of reinforced concrete and steel frames using beam and spring elements.” In Proc., Recent Advances in Structural Engineering, Japan-Thai Civil Engineering Conf., 703–723. Bangkok, Thailand: Engineering Institute of Thailand.
Seniwongse, M. 1991. “The construction of the new conference complex for the UN-ESCAP.” In Proc., 1991 Engineering Technology Symp., 475–489. Bangkok, Thailand: Engineering Institute of Thailand.
Seniwongse, M. 2007. “Evaluation and rehabilitation of concrete bridges in USA.” In Proc., 4th Int. Structural Engineering and Construction Conf. Melbourne, Australia: Univ. of Melbourne.
Seniwongse, M. 2012. “Actual steel moment frame behavior and computer models.” In Proc., 1st Australasia and South-East Asia Structural Engineering and Construction Conf. Perth, Australia: Curtin Univ. of Technology.
Seniwongse, M. 2019. “The basics of fixed connection in analysis and design of steel frames.” In Proc., 10th Int. Structural Engineering and Construction Conf. Chicago: Univ. of Illinois at Chicago.
Tan, C. T. 1975. “Inelastic response of high-rise buildings to tornadoes.” M.S.C.E. thesis, Dept. of Civil Engineering, Texas Tech Univ.
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© 2020 American Society of Civil Engineers.
History
Received: Mar 4, 2020
Accepted: Aug 12, 2020
Published online: Oct 31, 2020
Published in print: Feb 1, 2021
Discussion open until: Mar 31, 2021
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