Simplified design method of cold-formed steel columns with built-up box sections

Cold-formed steel (CFS) profiles with a wide range of cross-section shapes are commonly used in building construction industry. Nowadays several cross-sections can be built using the available standard single sections (C, U, Σ, etc.), namely open built-up and closed built-up cross-sections. This paper reports an extensive experimental investigation on the behavior of single and built-up cold-formed steel columns at both ambient and simulated fire conditions considering the effect of restraint to thermal elongation. The buckling behavior, ultimate loads and failure modes, of different types of CFS columns at both ambient and simulated fire conditions with restraint to thermal elongation, are presented and compared. Regarding the buckling tests at ambient temperature it was observed that the use of built-up cross-sections ensures significantly higher values of buckling loads. Especially for the built-up cross-sections the failure modes were characterized by the interaction of individual buckling modes, namely flexural about the minor axis, distortional and local buckling. Regarding the fire tests, it is clear that the same levels of restraint used in the experimental investigation induce different rates in the generated restraining forces due to thermal elongation of the columns. Another conclusion that can be drawn from the results is that by increasing the level of restraint to thermal elongation the failure of the columns is controlled by the generated restraining forces, whereas for lower levels of restraint the temperature plays a more important role. Hence, higher levels of imposed restraint to thermal elongation will lead to higher values of generated restraining forces and eventually to lower values of critical temperature and time.

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Experiment and Design Method on Cold-Formed Thin-Walled Steel Lipped Channel Columns with Slotted Web Holes Under Axial Compression

The Open Civil Engineering Journal ◽

10.2174/1874149501711010244 ◽

2017 ◽

Vol 11 (1) ◽

pp. 244-257 ◽

Cited By ~ 2

Author(s):

Xingyou Yao

Keyword(s):

Finite Element Method ◽

Finite Element ◽

Ultimate Strength ◽

Test Results ◽

Distortional Buckling ◽

Steel Columns ◽

Cold Formed Steel ◽

Thin Walled ◽

Shell Finite Element ◽

The Web

Background: Cold-formed steel structural sections used in the walls of residential buildings and agricultural facilities are commonly C-shaped sections with web holes. These holes located in the web of sections can alter the elastic stiffness and the ultimate strength of a structural member. The objective of this paper is to study the buckling mode and load-carrying capacity of cold-formed thin-walled steel column with slotted web holes. Methods: Compression tests were conducted on 26 intermediate length columns with and without holes. The tested compressive members included four different kinds of holes. For each specimen, a shell finite element Eigen-buckling analysis and nonlinear analysis were also conducted. The influence of the slotted web hole on local and distortional buckling response had also been studied. The comparison on ultimate strength between test results and calculated results using Chinese cold-formed steel specification GB50018-2002, North American cold-formed steel specification AISI S100-2016, and nonlinear Finite Element method was made. Result: Test results showed that the distortional buckling occurred for intermediate columns with slotted holes and the ultimate strength of columns with holes was less than that of columns without holes. The ultimate strength of columns decreased with the increase in transverse width of hole in the cross-section of member. The Finite element analysis results showed that the web holes could influence on the elastic buckling stress of columns. The shell finite element could be used to model the buckling modes and analysis the ultimate strength of members with slotted web holes. The calculated ultimate strength shows that results predicted with AISI S100-2016 and analyzed using finite element method are close to test results. The calculated results using Chinese code are higher than the test results because Chinese code has no provision to calculate the ultimate strength of members with slotted web holes. Conclusion: The calculated method for cold-formed thin-walled steel columns with slotted web holes are proposed based on effective width method in Chinese code. The results calculated using the proposed method show good agreement with test results and can be used in engineering design for some specific cold-formed steel columns with slotted web holes studied in this paper.

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