Researches On The Direct Methods In Calculating Vertical Capacity Of Cold-formed Steel Columns

Comparing with the overseas advanced level, our country is later in the research and application about the structural system of the cold-formed thin-wall steel residential building. For the ratio width-thickness of cold-formed thin-wall steel is bigger, element is easy to happen local buckling, distortional buckling or overall buckling when the structure bears the vertical load. The distortional bucking can be merged into local buckling calculation Current China Specification GB50018-2002 which is sometimes unsafe. There are no provisions for cold-formed thin-wall column with sheathing bracing in Current China Specification. At same times calculating process of effective section method becomes more and more cumbersome as section of cold-formed thin-wall column complex. So Current China Specification should be supplemented and improved. Based on relatively domestic and international existing research achievements the direct strength methods in calculating the vertical capacity of cold-formed thin-wall members between sheathing-bracing and non-sheathing-bracing is derived in order to promote design and application of cold-formed thin-wall steel member.1. This article introduces the characteristics of the cold-formed thin-wall steel residential buildings and the application of this structural system and the research status of the cold-formed thin-wall steel residential buildings system under the vertical force at home and abroad in recently years.2. Introduce the buckling modes of cold-formed thin-wall columns and the calculating methods of different buckling stresses. Based on Timoshenko beam stability theory the formula in calculating distortional buckling stress is derived. The law of distortional buckling stress relevant to parameters of section such as different section height and with or thickness is specially analyzed.3. Introduce basic principle of effective width and domestic and international technical code of effective section. The rational range of length of lip is given according to AISI. According to effective section method the direct strength methods in calculating the capacity of cold-formed thin-wall members without sheathing-bracing is derived, which is also specially analyzed. Using the effective section methods verify the direct strength method in calculating the capacity of the cold-formed thin-wall without sheathing bracing in validity and utility.4. Introduce failure modes of cold-formed thin-wall column with sheathing bracing (wall-column) and the calculating methods of different buckling stresses. The direct strength method in calculating the capacity of wall-column is also created, verified by effective section method in validity and utility.5. Test results verify the correctness of the finite element models of cold-formed thin-wall members without sheathing-bracing and with sheathing-bracing. The direct strength methods in calculating the capacity of the cold-formed thin-wall without sheathing bracing is verified in validity and utility by a large number of finite element analysis.Finally, on the basis of the above main conclusions is summed up and propose improved work in this paper according to recently research direction at home and abroad is also presented.