Advanced Steel Construction

Vol. 5, No. 1, pp. 33-48 (2009)


MODIFIED ELASTIC APPROACH FOR STABILITY DESIGN OF IN-PLANE FRAME COLUMNS

 

Hou Hetao 1, 2, 3* and Li Guoqiang 3

1 Associate Professor, School of Civil Engineering, Shandong University, Jinan, Shandong, China

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2 Postdoctor, Laiwu Steel Group Limited, Laiwu, Shandong, China

3 Professor, School of Civil Engineering, Tongji University, Shanghai, China

 

Received: 16 October 2007; Revised: 25 December 2007; Accepted: 29 December 2007

DOI:10.18057/IJASC.2009.5.1.3

 

ABSTRACT:

In order to overcome the limitations of the current Chinese Code for Design of Steel Structures (GB50017-2003), such as the second-order analysis of the structures and the effective length method used in stability check of steel frame columns, one modified elastic approach for analysis and check for ultimate loading-carrying of steel frames is outlined and compared to the current Chinese Code method. The second-order elastic moments in a Steel frame can be easily determined according to the first- order elastic analysis of the steel frame under vertical loads and lateral loads respectively. Such second-order moments are more accurate than those determined from the current Chinese Code method. By accounting for the initial geometric imperfections of the structural system and its component members directly within a second-order elastic analysis, the need for effective length or buckling solutions is eliminated, and the effective length K-factors can be set to be one. This paper also provides a rational means of complete frame classification that overcomes the limitations and paradoxes of the well known alignment charts for braced and unbraced frames. Simple criteria are presented that define the partially braced frames, as well as the minimum lateral bracing required by frames to achieve non-sway buckling mode. Case studies are drawn to show the detailed design procedures of the modified elastic approach. The case study covers a set of portal frames and single-bay, three-story frames. The results from the case studies are summarized to demonstrate the accuracy and validity of the approach for evaluation of the ultimate loading-carrying capacity of steel frame columns. Comparisons are made to the results from rigorous distributed plasticity of analyses. In conclusion, the modified elastic approach presented is an efficient, reliable, practical method and therefore to be recommended for general design practice.

 

Keywords:Steel frame column; second-order analysis; criteria of frame classification; notional lateral load; structural stability; modified elastic approach.

 

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