Abstract
This paper presents the results of an experimental investigation comprising 55 tests on cold-formed high strength steel Z-sections having different stiffened flanges undergoing web crippling. The test specimens were brake-pressed from high strength zinc-coated grades G450, G500 and G550 structural steel sheets. The material properties of the cold-formed steel Z-section specimens were obtained by tensile coupon tests. The experimental program consisted of 4 series of Z-sections having different stiffened flanges, web slenderness, material strengths, bearing lengths and subjected to different loading conditions. The loading conditions were End-Two-Flange (ETF), and Interior-Two-Flange (ITF) loadings as specified in the North American Specification for cold-formed steel structures. The web crippling test strengths and load–displacement relationships of the Z-section specimens were obtained from the tests. The loading condition and bearing length had a considerable effect on the web crippling test strengths. The presence of lips of the Z-sections increased the web crippling test strengths of the specimens loaded under ITF loading condition. The web crippling test strengths were compared with the design strengths calculated using the current North American Specification and European Code for cold-formed steel structures. In addition, reliability analysis was performed to assess the reliability of the design rules. Generally, it is found that the predictions obtained from the North American Specification are unconservative for most of the cold-formed high strength steel Z-section specimens, except for the specimens with unstiffened flanges loaded under ITF loading condition, while the European Code conservatively and reliably predicted the web crippling strengths for all the Z-section specimens loaded under ETF and ITF loading conditions. A modification of the constants used in the European Code design equations is proposed in order to provide more accurate and reliable web crippling design strengths.
Published Version
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