Research On The Bearing Capacity Of Cold-formed Thin-walled C-shaped Members With Web Openings

In recent years,cold-formed thin-walled steel building has been vigorously promoted in China.Its advantages of fast construction and low cost are favored by the masses.In order to facilitate the installation of water,electricity,heating and ventilation pipeline,it is necessary to open holes in the web of cold-formed thin-walled steel members.At present,there is no specific calculation formula for the bearing capacity of cold-formed thin-walled steel members with web openings in China’s code,and only constructional measures are adopted to the regulation.Therefore,the calculation of the bearing capacity of high-strength and ultra-thin cold-formed thin-walled steel members with web openings has important academic significance and engineering value.In this paper,the bearing capacity and failure mechanism of the members with and without openings under axial load is compared by the method of combining experiment and finite element.Then,according to the material parameters measured in the actual experiment,considering the most unfavorable initial geometric imperfection,the influence of the opening parameters on the axial load-bearing capacity of the member is investigated.The corresponding calculation suggestions of axial compression bearing capacity reduction factor are put forward.The influence of opening parameters for the compressionbending members with web openings in the floor beam bearing both axial load and transverse uniform load on the web,and the compression-bending members in the wall frame system bearing both axial load and transverse uniform load on the flange is investigated.The main achievements are as follows:(1)The axial compression experiment of 11 LQ550 high strength cold-formed thin-walled C-shaped members with no opening and web openings were carried out to analyze the influence of different opening numbers and sizes on the actual bearing capacity of short,medium and long members.The experiment results show that: the bearing capacity of members was reduced by the openings,the more the number of openings,the lower the bearing capacity.There are three kinds of buckling modes in the experiment,which are: the local buckling of web and flange;interactive buckling of local buckling of web and distortion buckling of flange and lips;interactive buckling of distortion buckling of flange and lips,overall bending deformation of web and local buckling.(2)The finite element models were established according to the material properties and size of the measured members,and the experiment processes were simulated.The validity and reliability of the finite element modeling and analysis technology were verified.Then the most unfavorable initial imperfections are found by the verified finite element method.It is found that the most unfavorable initial geometric imperfections are the composite I-type distortional buckling,the local web bulging and the overall bending around the weak axis.Considering this initial geometric imperfection,the influence of opening form,opening size,opening number,opening center position and opening spacing on the axial compression bearing capacity of the members is studied.The results show that the opening form has no obvious influence;the larger the opening size and opening number,the lower the bearing capacity of the members;the influence of opening position and opening spacing on the bearing capacity is small.Based on a number of experiment and finite element calculation results,the formula of axial compression capacity reduction factor considering the effect of opening is proposed.(3)By using the finite element method,considering the most unfavorable initial geometric imperfection,the influence of opening parameters on the members subjected to axial load and transverse uniform load on the web is analyzed.The results show that the members are prone to O-type distortional buckling of flange and crimped composite plates,local web bulging and overall bending around the weak axis.The results show that the bearing capacity of cold-formed thin-walled C-shaped members is greatly affected by the opening size and the number of openings.The larger the opening size or the number of openings,the greater the reduction of the bearing capacity and the lower the reduction of the bearing capacity.The location and spacing of openings have little effect on the bearing capacity of cold-formed thin-walled Cshaped members.(4)The finite element method is used to analyze the influence of opening parameters on the members subjected to axial load and transverse uniform load on the flange.With the increase of the size and the number of openings,the bearing capacity of the members decreases monotonously,and the reduction is large.The results show that the bearing capacity of the member changes sinusoidal when the opening position moves from bottom to top,and the bearing capacity of the member is relatively low when the opening position is opposite to both ends of the span.The effect of opening spacing on the bearing capacity of the member is also obvious,which makes the opening concentrated in the span of the members.The smaller opening spacing makes the bearing capacity lower when the opening is concentrated in the middle of the members.