| The use of cold-formed thin-walled steel structures has increased rapidly in recent years due to significant development of material science and improvements of manufacturing technologies. An important tendency of cold-formed steel structure is the application of more slender structure members and elements with higher strength. At present, cold-formed steel members with thickness less than 2mm have been widely used into practice projects. However, Chinese current national standard Technical code of cold-formed thin-walled steel structures can only be applied to calculate and design the cold-formed thin-walled steel members with thickness between 2mm and 6mm. The calculation and design methods for cold-formed thin-walled steel members less than 2mm thick have been not included in and there are no standards for cold-formed thin-walled steel members less than 2mm thick design and calculation in China yet. Cold-formed steel eccentrically-compressed columns less than 2mm thick and self-drilling screw connections are systemically researched in this thesis.Firstly, a series of experimental research on cold-formed eccentrically-compressed columns were carried out. 66 cold-formed steel members, including lipped-channels and combined I sections, were tested in this experimental research. Besides this, the widely used finite element software, ANSYS, was also employed for analysis. Based on experimental investigation and numerical analysis, calculation methods for the strength of eccentrically-compressed columns present in the codes or specifications of China, Australia/New Zealand and North American were compared and investigated. The research result shows that the calculation formulas of Chinese current national standard Technical code of cold-formed thin-walled steel structures can be used to calculate the strength of cold-formed steel eccentrically-compressed columns with thickness less than 2mm. A simplified calculation method for combined I section eccentrically-compressed columns was also proposed. Besides these, reliability analysis was also done to further verify the applicability of the channel calculation formulas of Chinese code.Secondly, a series of shear tests have also been conducted on self-drilling screw connections. The factors influencing the shear behavior of the connections, the number of screws, screw patterns, screw spacing, edge distance, sheet material included, were investigated. The findings of the research demonstrated the existence of "Group Effect" in the connections including more than one screw, which means that the assumption that the connection strength for a multiple screw connection is proportional to the number of screws in the connection, as the calculation method in Chinese current national standard Technical code of cold-formed thin-walled steel structures have based on, would result in an unconservative estimate for the shear capability of connections including more than one screw. Based on experimental study and existing research fruits, a modified calculation formula has been proposed in this paper. The shear strength of the specimens calculated via the modified calculation formula, in which both "Group Effect" and screw spacing influence were took into account, agreed well with the experimental result and the rationality of the modified calculation formula was verified thus. |
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