| On the basis of the research results of the National Natural Fund Project "the mechanical coupling mechanism of the light quantized bionic box girder of large crane structure",the following research is carried out in this paper for the buckling of gantry crane longitudinal rib stiffened plate buckling:On the basis of the limited formula for Moment of inertia of stiffened rib in "Design rules for cranes",the expression of height' hs ' and thickness 'bs' of rectangular rib relation,rigid rib minimum height ' h0 ' expression are derived,multiple sets of curves are obtained.The significance of h of rectangular rib is:When the motherboard size and the number of rib are fixed,there is a minimum value of ' ho' rigid rib height,when the height of the rib is less than ho,the rib is flexible,when the height is more than h0,there is always a minimum thickness value of the ribs that makes rib rigid,h0 and motherboard aspect ratio of a had significantly positive correlation.One of the necessary conditions for rigid ribs is that the coordinate of the cross section(hs,bs)falls on the right side of the right branch of curve.The stiffeners are simplified as three edges simply supported and one edge free sheet,based on a hypothesis of the bearing capacity of the rib stiffened plate is equal to the district's bearing capacity,a relation which makes ribs rigid is derived and the relation curves is obtained,this curve is one of the boundaries of the rigid domain,in the rigid domain,the stiffened plate buckling mode for mode two(rib rigidity,grid buckling)or mode three(rib buckling with grid).A rbuck expression was presented relative buckling ratio used to characterize the rib and the motherboard,rbuck value can be used to distinguish structural instability modes in mode two or three mode,when the rbuck value is less than 1,the instability mode is considered as mode two,when rbuck is greater than 1,the instability mode is considered as mode three.Based on rbuck expression and finite element method,a group of boundary rib section coordinates are obtained which make ribs absolute rigid,according to these coordinates,a boundary curve of absolute rigid domain in whch structural instability mode is mode two is fitted.The solid stiffened plate model is compared with the shell element model and the Timoshenko energy method.,the results show that when the rib cross-sectional area and moment of inertia are fixed,stiffened plate bearing capacity increases with the increase of the width of the contact with the motherboard of the rib.With the decrease of the width of the motherboard,rib contact area influence on the carrying capacity of the structure is higher,in the contact width larger,contact line of the shell model will not reveal the actual contact between the ribs and the motherboard simulation.Similarly,when the rib contact width is large,Timoshenko method based on the shell theory is no longer applicable,at this time,the structure can be solved by the compression column model or the solid element model.The moment of inertia of rib uniform value(L.Jun)is used to characterize the strengthen effect of ribs' moment of inertia to motherboard per unit width of the contact range,the results show that when the width is larger,the effect of reinforcing rib on the motherboard is stronger.To explore the influence of web length width ratio on the optimum distance between rib and compression flange under bending,compared with the standard,it is found that when the length and width are relatively small,the optimum distance h1 is always fluctuating in the(1/5?1/4)ho range,which is in accordance with the specification.When the aspect ratio increases,h1 also increases,while the(1/5?1/4)h0 is still used in the specification,and the local stability is maintained by adding short transverse reinforcement.It is suggested that when the wheel extrusion stress is not included,it can be determined according to the different aspect ratio to enhance the bearing capacity of the structure. |
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