Distortional buckling may occur for Cold-formed thin-walled steel lipped channel member except local buckling and overall buckling. The buckling of flange and lip are the important factor for the occurrence the distortional buckling. The different design codes have different design method for calculating plate buckling coefficient of flange and lip using the effective width method. So the effective width method in different codes are introduced and the load-carrying capacities of 100 lipped channel section compressive members collected from reference are computed using ‘Cold-formed steel structures (AS/NZS 4600:2005)’, ‘Supplementary rules for cold-formed members and sheeting(EN1993-1-3:2006)’, ‘North American specification for the design of cold-formed steel Structural Members(AISI-S100:2007)’, ‘Specification for the design of cold-formed steel structural members (AISI:1996)’ and ‘Technical code of cold-formed thin-walled steel structures’(GB50018-2002). The calculated results show that ‘Technical code of cold-formed thin-walled steel structures (GB50018-2002)’ and ‘Supplementary rules for cold-formed members and sheeting (EN1993-1-3:2006)’ are conservative and ‘Cold-formed steel structures (AS/NZS 4600:2005)’, ‘North American specification for the design of cold-formed steel Structural Members (AISI-S100:2007)’ and ‘Specification for the design of cold-formed steel structural members (AISI:1996)’ are unsafe. The elastic buckling stress of different lipped channel sections are predicted by finite strip program (CUFSM) and get the suggested calculation formula of plate buckling coefficient of flange according to regression Analysis. The calculated results using suggested plate buckling coefficient of flange are agree to test results.

According to anti-seismic design principle of strong column and weak beam, and of strong joint and weak member, reduced beam section (RSB) is often used to shift away plastic hinge from end of beam to the weaken region of the beam. The non-linear finite element models are established for concrete-filled steel square tubular column and reduced steel beam with holes in flange or in flange and web, considering geometric large deformation and material nonlinear. Comparison is made on load-displacement curves, the stress distribution of reduced beams, the ultimate load-carrying capacity, the ductility, and the energy-dissipating ability between analysis results of different RBS joints and experimental results. It shows that the stiffness and ultimate load-carrying capacity of new RBS joints are close to traditional RBS joint, the plastic hinge in the new joints with reduced beam section can be moved to the reduced region, and the new joints display good ductility, energy-dissipating ability and seismic behavior.

The thin-webbed I-shaped members are used as the basic members for beams and columns of steel buildings in order to increase utilization ratio of steel. The local buckling can occur for these members because of the large width-thickness ratio and these members have a substantial post-buckling strength which can be used. Different codes in China have different estimation method for substantial post-buckling strength of thin-webbed I-shaped members. So it is very necessary to establish the same calculation method to consider post-buckling strength for different china codes. In this paper the effective width estimation methods of technical specification for steel structure of light weight buildings with gabled frames (CECS 102-2002), code for design of steel structures (GB50017-2003), technical code of cold-formed thin-wall steel structures (GB50018-2002), America specification (AISC: 2005), European specification (E3-1.5:2006), and Winter equation are introduced simply. The effective area of thin-webbed I-shaped members with different width-thickness ratio in web and slenderness ratio are estimated using these codes. Comparison of these estimated results show that CECS 102-2002, GB50017-2003, AISC: 2005, Winter equation, and E3-1.5:2006 may be conservative or unsafe for members with different slenderness ratio or width-thickness ratio of web. GB50018-2002 is applicable for members with different slenderness ratio or width-thickness ratio of web without considering interaction between flange and web of members and can be used to estimate the effective area of thin-webbed I-shaped members. At the same time, the calculated method of post-buckling strength of thin-webbed I-shaped members in CECS 102-2002 and GB50017-2003 could use the same method as GB50018-2002.

According to anti-seismic design principle of strong column and weak beam, and of strong joint and weak member, reduced beam section(RBS) is often used to shift away plastic hinge from end of beam to weaken region of the beam. Reduced beam section with cut web are analyzed by non-linear finite element method(FEM) in this paper. Two kinds of effective suggested joints of reduced beam section(circled hole and long-circled hole) are put forward by comparing the results of mechanical behavior of reduced beam section with which of traditional RBS, including of ultimate load-carrying capacity, Von-mises stress distribution and the place of largest stress of beam end of the beam-column joints. A proposed seismic design method is put forward according to related chinese codes.