Research On Mechanical Property Of Double-depth Steel Storage Rack

Double-depth storage rack is a type of storage rack designed to be placed side by side in two rows.It has the advantages of simple structure and higher storage capacity than ordinary storage rack.However,in terms of both theoretical research and practical application,the research on steel storage rack in China lags far behind the developed countries.Not to mention double-depth storage rack that have come into people's sight in recent years.Its technical reserve is very lagging behind.Firstly,this paper introduces the structure characteristics and force transfer mechanism of doubledepth storage rack,the mechanical behavior of the traditional double-depth storage rack is analyzed by calculation example.It's found that the local moment of the columns is large and the lateral stiffness of the back-tension system can't be effectively transmitted to the first depth under the seismic action.Secondly,the layout methods of new "K" type and "Z" type braces and the improvement schemes of replacing closed section columns in back-tension area,adding axillary braces in back-tension area and thickening short beams are put forward respectively.At the same time,the advantages and disadvantages of the schemes are analyzed through calculation example and engineering experience.Thirdly,based on the software SSFD,which was developed earlier by the research group,combined with the structural characteristics and the structural improvement schemes proposed in this paper,the design module and parametric design module of the double-depth storage rack were compiled.Finally,using SSFD software,the effects of parameters such as axillary bracing angle,beam height difference,number of back-tension,back-tension arrangement,back-tension layer height and horizontal bracing arrangement on the mechanical properties of double-depth storage rack are analyzed.The parameterization results are summarized,and the reference opinions on the structure layout and principles of double-depth storage rack are put forward.The main conclusions are as follows:(1)In the traditional design,the columns of sheet-column system will produce large local moment under lateral seismic action.Under the action of the axial force in the short beam and the diaphragm short beam,the column connected with the short beam will produce larger local moment at the joint,which will lead to the increase of the internal force of the column.(2)In the traditional design,the lateral stiffness of the back-tension system can't be effectively transmitted to the first depth under longitudinal seismic action,resulting in poor lateral resistance and poor integrity.Because of the poor torsion resistance of open section columns,the rectangular lattice stiffness is small and easy to deform.Under the longitudinal seismic action,the two depths columns can't deform synergistically,which makes the lateral stiffness of back tension can't be transferred to the first depth,resulting in the poor lateral resistance of the first depth and the poor integrity of the doubledepth storage rack.(3)The layout method of new "K" type and "Z" type braces can reduce the local moment of columns under transverse seismic action.By arranging the intersection of the short beam,the diaphragm short beam and the braces,the braces can provide lateral support for the short beam and the diaphragm short beam,offset part of the axial force and reduce the local moment of the column.Meanwhile,the "Z" type braces is adopted to arrange the two depths braces without strict mirror symmetry.(4)The improvement measures of replacing closed cross-section column in back-tension area and adding axillary brace in back-tension area can effectively transfer most horizontal loads in the first depth to back-tension system,but the improvement effect of short beam thickening scheme is not obvious.Replacing the closed section columns in the back-tension area improves the torsional behavior of the columns in the back-tension area.Adding axillary braces in the back-tension area can form a local trusslike structure system to enhance the stiffness of the rectangular lattice.The method of adding axillary braces in back-tension area is more economical and less difficult than that of replacing closed section columns.(5)The double-depth storage rack design module of SSFD software combines the proposed structural improvement schemes with the traditional storage rack,which can accurately,conveniently and efficiently realize the establishment,calculation and parametric analysis of the finite element model of the double-depth storage rack.(6)In double-depth storage rack,it is suggested that the axillary bracing angle should be set between 30 and 60 degrees,the height difference of beams should be set at about 150 mm.When 20 rows of double-deep shelves are evenly arranged with back-tension,the number of standard and side layouts should not be less than 10 rows and 8 rows respectively.When the total number of back-tension is fixed,it is suggested that the maximum number of continuous layouts of standard and side backtension should not be less than four rows.Horizontal braces on both sides of back-tension and backtension are more suitable for side double-depth storage rack.It is more suitable to use 2 times of the cargo compartment height for the back-tension layer height.