| Angle steel transmission tower is one of the most commonly used transmission tower types worldwide.We use bolts to connect main materials,oblique materials,and auxiliary materials.Under the influence of natural disasters such as storms and snowstorms,the collapse accidents of transmission tower frequently occur,causing great safety hazards and economic losses.In order to accurately calculate the ultimate capacity of the entire structure,it is first necessary to accurately calculate the ultimate capacity of the components at the component level.Material nonlinearity,geometric nonlinearity,initial geometric defects,residual stress,eccentric connections are key factors.Angle steel transmission tower is one of the most commonly used transmission tower types worldwide.We use bolts to connect main materials,oblique materials,and auxiliary materials.Under the influence of natural disasters such as storms and snowstorms,the collapse accidents of transmission tower frequently occur,causing great safety hazards and economic losses.In order to accurately calculate the ultimate capacity of the entire structure,it is first necessary to accurately calculate the ultimate capacity of the components at the component level.Material nonlinearity,geometric nonlinearity,initial geometric defects,residual stress,eccentric connections are key factors.A program for the ultimate yield surface of the angle steel section is written.Through parameter analysis,the angle steel whose size is ∠120mm×80mm×12mm(short-lengthto-length ratio 0.64)is selected as the representative of the unequal-leg angle steel.Also,we perform polynomial fitting on the representative angle steel’s ultimate limit yield surface to ensure smoothness and continuity.Then the ultimate yield surfaces of crosssections,H-sections,T-sections,box-sections,thin-walled square steel sections,rectangular sections and other commonly used sections in engineering are solved.Through comparative analysis,it is found that with the gradual increase of the normalized axial force,the ultimate yield surface of the cross-section will shrink at a faster and faster rate,and the symmetry axis position,extreme point and shape of the ultimate yield surface are all related to the symmetry axis of the section.The plastic hinge theory is combined with the ultimate limit yield surface of the angle steel to analysis the material nonlinearity.Based on the ultimate limit yield surface fitted above,the plastic reduction matrix is derived and a new way to refine it is proposed.The correction method is used to make up for the defect that the plastic hinge method cannot simulate the plastic development process.The initial geometric defects were added when the finite element geometric model is established,and the CRC tangent modulus is used to consider the influence of residual stress.The basic idea of the rigid body criterion is used to analysis the geometric nonlinearity of the structure,the deformation of the element is regarded as a combination of rigid body displacement and natural deformation.Combining the above methods,the calculation program is written,and the correctness of the method and the program is verified through typical calculation examples.The single-angle steel struts under axial compression(Type A),one end eccentric compression(Type B),and both ends eccentric compression(Type C)under common engineering slenderness ratios are calculated.Through comparative analysiswith tests and specifications,it is found that 16 units are the ideal number of units for calculating the ultimate bearing capacity of single angle compression bars,and whether torsion constraints are added at both ends of the member has little effect on the calculation of single angle compression bars.The angle steel whose size is∠80mm×6mm in the A,B,and C working conditions are analyzed.The load carrying capacity of the A working condition is the highest when λ≤140,and the carrying capacity of the C working condition is the lowest.whenλ≥140,the bearing capacity of the angle steel struts under the three working conditions is very close.Factors such as material strength,section form,initial bending,residual stress and other factors will have a certain impact on the ultimate bearing capacity of single angle steel struts.Refer to the existing test,the beam element stiffness matrix with rigid arms is used to solve the eccentric connection problem of angle steel,and calculate three common transmission tower inter-node models when the main material axial force and lateral thrust(tension-compression ratio-0.2)are applied.Through calculation and analysis,Through calculation and analysis,it is found that although more node numbers are required for modeling with coupling node constraints,the calculation results are accurate,and when the capacity of the auxiliary materials is sufficient,the presence of the auxiliary materials is very important.But the arrangement of auxiliary materials has little effect on the bearing capacity. |
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