Research On The Mechanical Performance Of Quartet-Steel-Tube Built-Up Columns And Plate-Circular Hollow Section Joints In Transmission Towers

Transmission lines are important infrastructure to ensure energy supply and support national economic development,of which the UHV transmission lines have a pivotal role.Since the existing transmission tower has not meet the construction needs of transmission lines with large span length,the designers have proposed quartet-steel-tube built-up column transmission tower to solve such construction problem.Since it is the first attempt to apply the quartet-steel-tube built-up column and plate-CHS joint in the transmission tower,there are many problems to be solved:(1)How to calculate the elastic and elastic-plastic stability bearing capacity of the built-up column;(2)Whether the failure mode and stress distribution of quartet-steel-tube built-up plate-CHS joints differ from those of conventional plate-CHS joints,and how to determine the bearing capacity of such joints;(3)What the influence that the batten types and its joint-slippage have on the ultimate bearing capacity of built-up columns and plate-CHS joints.The main research of this paper means to unfold the above problems:(1)The mechanical performance of the quartet-steel-tube built-up column in transmission tower was studied,and the bearing capacity calculation method was proposed;(2)According to the structural characteristics of the quartet-steel-tube built-up plate-CHS joint,the mechanical performance of local and overall joints were studied.The calculation formulas for bearing capacity were fitted by parametric analysis,and the bearing capacity calculation method was proposed;(3)Based on the component method,a joint-slippage model was proposed.The structural analysis of transmission tower considering jointslippage was realized,and the effect of bolt-slippage on the bearing capacity of the quartet-steeltube built-up column and plate-CHS joint was studied.Joint-slippage significantly affects the stiffness of transmission towers.Based on the component method,a joint-slippage model,which is appliable for tower structure analysis,was proposed in this paper.Then,the model was applied in structural analysis of a new type of transmission tower with asymmetric structural stiffness to verify the applicability of the jointslippage model and the analysis method considering joint-slippage.In the research of the built-up column,chord-checking method considering initial bending and eccentricity was proposed.Then,the applicability of calculation methods was discussed by comparing with finite element analysis.The results show that the equivalent slenderness ratio method considering the shearing of the batten is more suitable for the built-up column of transmission tower,and the chord-checking calculation is not necessarily carried out when the slenderness ratio of the chord meets the standards.In the research on the quartet-steel-tube built-up plate-CHS joints,they were simplified to Kjoints and DK-joints by separating.Firstly,considering the structural characteristics of the built-up plate-CHS joints,the mechanical performance of K-joints and DK-joints,that subjected to large eccentric force(named SGK-0,SGDK-0),was researched by parametric finite element analysis that based on the equivalent forces model of plate-CHS joint.Accordingly,achieve the ultimate bearing capacity formulas of the joints,and conduct the comparative analysis between the joints with and without large eccentric force.Then,a new toroidal deformation model for planar K-joints with 1/4 annular ribbed plate was proposed.With the ring-generator separation model and the virtual work principle,derive the ultimate bearing capacity formula of planar K-joints with 1/4 annular ribbed plate.Furthermore,the mechanical performance of K-joints and DK-joints considering the supporting of battens in the built-up plate-CHS joints(named SGK-1,SGDK-1,SGK-2 and SGDK-2)was researched by parametric finite element analysis,and the ultimate bearing capacity formulas of the joints were also derived.Combined with the research of SGK-0 and SGDK-0,the influence of batten type on the deformation,failure mode,stress distribution and ultimate bearing capacity of K-joints and DK-joints in the built-up plate-CHS joints were analyzed.Based on the above researches,a calculation method for the ultimate bearing capacity of the built-up plate-CHS joints was proposed.And the comparative analysis with finite element analysis and relevant test results was conduced to verify that the proposed calculation method can well predict the ultimate bearing capacity of the quartet-steel-tube built-up plate-CHS joints.Finally,the main research results and innovation points are summarized,and further research directions are proposed.