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The effects of tempering holding time at 700°C on the morphology, mechanical properties, and behavior of nanoparticles in Ti-Mo ferritic steel with different Mo contents were analyzed using scanning electron microscopy and transmission electron microscopy. The equilibrium solid solution amounts of Mo, Ti, and C in ferritic steel at various temperatures were calculated, and changes in the sizes of nanoparticles over time at different Mo contents were analyzed. The experimental results and theoretical calculations were in good agreement with each other and showed that the size of nanoparticles in middle Mo content nano-ferrite (MNF) steel changed the least during aging. High Mo contents inhibited the maturation and growth of nanoparticles, but no obvious inhibitory effect was observed when the Mo content exceeded 0.37wt%. The tensile strength and yield strength continuously decreased with the tempering time. Analysis of the strengthening and toughening mechanisms showed that the different mechanical properties among the three different Mo content experiment steels were mainly determined by grain refinement strengthening (the difference range was 30–40 MPa) and precipitation strengthening (the difference range was 78–127 MPa). MNF steel displayed an ideal chemical ratio and the highest thermodynamic stability, whereas low Mo content nano-ferrite (LNF) steel and high Mo content nano-ferrite (HNF) steel displayed relatively similar thermodynamic stabilities.

We have analyzed the effect of the final rolling temperature on the morphology, mechanical properties, carbide nanoparticle size, and dislocation density of Ti-Mo ferritic steel. The microstructure was mainly composed of equiaxed ferrite, ultrafine ferrite, and polygonal deformed ferrite, whose three proportions were affected significantly by the final rolling temperature. The change trend of the mechanical strength was in line with the dislocation density under different finishing rolling temperatures, whereas the ferrite grain size change trend was the opposite. There were various types of nanoparticle precipitation in the test steels: interphase precipitation, dispersion, dislocation precipitation, and deformation-induced precipitation. The optimum mechanical properties were obtained at a final rolling temperature of 900 °C. Quantitative analysis showed that the effect of the final rolling temperature on the yield strength was mainly because of dislocation and precipitation strengthening. The toughening mechanism is attributed to the fine grain strengthening of nanoparticles in austenite stage and the precipitation strengthening of ferrite stage.

Stability of the closely star-battened member of a power transmission tower were researched in this paper, a theoretical analysis was conducted for the buckling mode of the closely star-battened member by different plate batten arrangements. The analytical method of the buckling capacity on the closely star-battened member was proposed here considering an arrangement type of the plate batten and they are compared with the results of a full-scale test. The conclusions are follows: the flexuraltorsional buckling did not happened for the closely star-battened member; the flexural buckling need to be calculated only after the strength reduction factor was considered; the stability-bearing capacity of the closely star-battened member of the line-shape type batten is slightly less than that of the cross-shape type batten; the stability-bearing capacity of the closely star-battened member can be improved when the number of bolts in the plate batten increases in a suitable extent; and the stability-bearing capacity calculated and test results agree well with each other when the stability-bearing capacity analytical method of the closely star-battened member was used to analyze the full-scale test tower. The experimental results show the calculation method is reasonable.

To include the effects of the joint zones efficiently, firstly a chord member considering the joint zones is seen as a combination of three beams with different sections and its element stiffness matrix is derived; Secondly, based on the statistically geometrical properties of the joint zones and chord members in service, the coefficients in the element stiffness matrix of the varied section beam element related to the moments and shear forces greatly increase more than 70%, while the coefficients related to axial forces only increase less than 2%. Therefore, along with the other two inherent mechanical properties of member structures, it is essential to include the effects of the joint zones. Finally, the results by the finite element models where the chord members and the joint zones are simulated by four methods are compared, which proves the efficiency and the accuracy of the varied section beam element.

This study reports the development of a Ti- and Mo-bearing ferritic steel precipitation-strengthened by nanometer-sized carbides. The steel showed an ultimate tensile strength of 995 MPa, a tensile elongation of 20 pct, and a hole-expanding ratio of 44 pct. The precipitation of nanometer-sized carbides in this steel during isothermal transformation at 873 K, 898 K, and 973 K (600 °C, 625 °C, and 700 °C) for 60 minutes was investigated in detail. The contributions of various strengthening mechanisms were analyzed, and the maximum contribution from the nanometer-sized carbide precipitates was estimated to be about 430 MPa.

This paper adopts three different grids to conduct numerical simulation of flow field around an angle member by CFD. The two-dimensional incompressible Navier-Stokes equation is solved. The pressure velocity coupling adopts the SIMPLE algorithm and the pressure discretization adopts the standard algorithm. Both the momentum equation and turbulence model adopt the second-order windward scheme, and the time term adopts the second-order implicit scheme. The aerodynamic coefficients of angle member and the flow field are obtained by different grids, and through comparison, it is found that the grid mode has a very small impact on the CFD results, and the differences between different grid modes can be ignored. In respect of CFD simulation of flow field around angle member in transmission tower, it is recommended to adopt the partitioned structured grids and the partitioned mixed grids in order to enhance the simulation ability of the grid under multiple working conditions. If the angle member is irregularly shaped, the partitioned mixed grids are preferred.

Considering the structural characteristics of transmission towers, four sections of cold-formed angles with different slenderness ratios and constrained types were selected for the experimental and numerical study. Experiments and finite element analysis for the ultimate loads of the compression cold-formed angles were carried out. The finite element model well predicts the buckling behaviour of the cold-formed members. For the axial compression members, the load-strain curves as well as the ultimate loads were analyzed, and the experimental ultimate loads were compared with those of calculated by the applicable standards. It shows that the applicable standards aren’t adaptive to the strength design of the compression cold-formed members in transmission towers. Through the analysis of the experimental and FEA results, the fitting curve of the stability coefficients for the cold-formed members in transmission towers was determined. The ultimate loads calculated by the fitting curve are well agreed with the experimental values, especially for the members with relatively low slenderness ratios. Some modification suggestions were proposed for the calculation of the ultimate load for the axial compression cold-formed angle. Experimental analysis on the cold-formed members of the other five constrained types was completed, and the modification formulas of the slenderness ratios for members of different constrained types were obtained.

Ice shedding from conductors may easily induce electrical and mechanical accidents, which cause a serious threat to the safe operation of transmission lines. In this paper, a 3D finite element model of tower-conductor-ground wire-insulator system was established in ANSYS, and the dynamic responses of ice shedding under different cases were analyzed for a transmission tower-line system. The computed jumping heights are in excellent agreement with the experimental values of a two span conductors model. Many variables were considered in the ice-shedding simulations that include tower-line coupled effect, phase combination of the ice-shedding conductors, thickness of the accreted ice, length of the ice-shedding span as well as elevation difference. Influences of all the variables on the dynamic responses of jumping heights, loads at the end of insulators and the forces of transmission tower were studied. Ice-shedding simulations of an actual 500 kV transmission line section which experience failure under ice shedding in 2008 were performed. The results show that stress ratios of members at the tower head under design ice thickness exceed the limiting values when the amount of shedding ice is large. For ice shedding at the top phase conductors, the jumping height and unbalanced tension at the end of insulator can be reduced by applying interphase spacers in triangular arrangement. The tower is in a safe state under the load of the design ice thickness. In order to prevent ice-shedding accidents, interphase spacers should be used, and the weak members at the tower head should be strengthened according to the calculated load values at the end of insulators.

Application of weathering and cold-formed steel in transmission lines can reduce steel consumption and environmental pollution. Some advances in the studies on the weathering and cold-formed steel in transmission tower are introduced. Firstly, corrosion-resistant tests of weathering steel samples under different simulating technical atmospheres were carried out separately for 240 hours. It shows that the corrosion degree of joint samples is higher than that of single chip samples, and the corrosion-resistant performance of weathering steel is superior to common carbon steel. The corrosion-resistance of weathering steel meets with the requirement of transmission tower. Secondly, experiments and finite element analysis for cold-formed angles and a 220kV prototype tower were completed, and the stability coeffi-cient fitting curves as well as the modification formulas of slenderness ratio for cold-formed members were determined. According to the structural characteristics of transmission towers, four sections of cold-formed angles with different sections and slenderness ratios were selected in this study. The finite element model well predicted the buckling behav-iour of the cold-formed members. Ultimate loads calculating by the fitting curve were well agreed to the experimental values, especially for the members with small slenderness ratios. Weight of the cold-formed steel tower can be reduced by more than 5 percent after considering the strength enhancement. Cost of the weathering and cold-formed steel transmission tower is nearly equivalent to that of hot-rolled steel tower with hot galvanizing.

Some advances on tower destruction mechanics of overhead transmission lines and prevention technologies in ice disasters are introduced. Firstly, based on the numerical and experimental study on the tower-line system with ice-shedding and broken of conductors, dynamic responses of the tower-line system were obtained, and the unbalanced tensions as well as the uplift loads were proposed. Secondly, study on the bearing capacity of K type joints with an included angle less than 30 degree was completed. The first ultra high voltage (UHV) steel tubular cup type tower in the world was designed for transmission lines in heavy icing area, and the prototype test was carried out in the UHV tower test station. Thirdly, the bearing capacity and the destruction modes of transmission towers with galloping conductors were studied. A practical calculation method of the galloping loads was obtained. A constructional measure realized by the bolt strengthen technology were proposed for the transmission towers in the galloping area with high intensity. Lastly, the structural reinforcement technologies of the transmission towers after ice disaster were developed, especially for the enhancement of design standards and reinforcement technology for main members of transmission towers. Keywords: Transmission tower; Accreted ice; Load characteristic; Destruction mechanics; Reinforcement.

The overall stability and local stability of legs on UHV transmission steel tubular tower are controlled by the slenderness ratio and the diameter-thickness ratio of steel bar respectively. 8 typical steel tubular towers with double circuit transmission lines on the same tower in 1000kV transmission project of Anhui Province – Shanghai (the 1000kV Huainan to Shanghai transmission line, the PROJECT as called hereby in this paper) are chosen to set up the finite element model of beam-bar mixed element and calculate the stress of legs under consideration of the effect of bending moment of bar end. The result shows the effect degree of bending moment of bar end to the stress of legs is be closely related to its slenderness ratio. The law between slenderness ratio and stress is obtained by calculation and analysis. The local buckling will occur when the diameter-thickness ratio of round section of steel tubular tower is beyond a limit. Basing on this analysis result and comparison between the domestic design standard and the foreign design standard, the value of diameter-thickness ratio of round section of steel tubular tower is suggested. This study result provides references and proofs for the structural optimization of UHV Transmission Steel Tubular Tower.

Application of weathering and cold-formed steel in transmission lines can reduce steel consumption and environmental pollution. Some advances in studies on the weathering and cold-formed steel in transmission tower are introduced. Firstly, corrosion-resistant tests of weathering steel samples under different simulating technical atmospheres were carried out separately for 240 hours. It shows that the corrosion degree of joint samples is higher than that of single chip samples, and the corrosion-resistant performance of weathering steel is superior to common carbon steel. The corrosion-resistance of weathering steel meets with the requirement of transmission tower. Secondly, experiments and finite element analysis for cold-formed angles and a 220 kV prototype tower were completed, the stability coefficient fitting curves as well the modification formulas of slenderness ratio for cold-formed members were determined. Ultimate loads calculating by the fitting curve were well agreed to the experimental values, especially for the members with small slenderness ratios. Weight of cold-formed steel tower can be reduced by more than 5% percent after considering the strength enhancement. Cost of weathering and cold-formed steel transmission tower is nearly equivalent to that of hot-rolled steel tower with hot galvanizing. So application of this new style steel can bring great social effects and economic returns. The research results provide important reference to the application of weathering and cold-formed steel in transmission tower.