| The triangle tower has three struts and its triangle-shaped transverse cross section is parallel to the ground. At present the high voltage electricity is transmitted through quadrangle towers. Compared with the quadrangle tower, the triangle tower made with 60 degree steel angle not only has a higher loading capacity with less restraint stress, temperature stress, and windage but also is more stable in structure and saves space, where the potential of materials can be fully used. However, the triangle tower made with 60 degree steel angle is rarely seen in the projects of electricity transfer tower. So far, the systemic theoretical analysis, numerical calculation, and experimental measurement study have not been conducted to find out the mechanical properties of 60 degree steel angle and triangle cross-section tower. Therefore, it is of significance in theoretical innovation and practical value to conduct the study on the mechanical properties of 60 degree steel angle and triangle cross-section tower and apply the research findings in the projects of electricity transfer tower and wind turbine tower when solving its key mechanical problems.Considering the bending instability and the flexural-torsional buckling, the stability theory of thin-walled member torsion is used to address the overall instability of 60 degree steel angle and the expression about the critical buckling load is derived. Regarding the mechanical performance about the local stability in 60 degree steel angle, the critical load and the finite element numerical simulation result are first calculated through the Rayleigh-Ritz method before the contrastive analysis is conducted on the results. Meanwhile, the reference value related to the constraint coefficient of 60 degree steel angle members under the axial compression is obtained. According to the equistability principle, the calculation expression that can be applied to the width-to-thickness ratio limitation value of 60 degree steel angle is derived. Moreover, the contrastive analysis is conducted between the calculation expression of 60 degree steel angle and the corresponding design approach and computational formula mentioned in Design Code for Steel Structures, US Design Guidelines, and Technical Regulations for Structural Designs of Overheard Transmission Line.In order to study the influence of the tower cell over the axial force of principal member, diagonal member, and transverse member, the cell models of both the triangle tower and the quadrangle tower made with 60 degree steel angle are first established before the expressions of axial force for principal member, diagonal member, and transverse member under the impact of axial force, shearing force, bending moment, and torque, the displacement expression of the cell under the impact of the bending moment, and the torsion angle expression of the cell under the impact of the torque are derived. Meanwhile, the expression to calculate the overall rigidity and stability is also derived to study the optimization methods of the triangle tower and the quadrangle tower so that the optimum foot distance and floor height of the triangle tower are calculated and the corresponding calculation software gets designed. The buckling modes were established for legs or diagonal bracings of the double-supporting bracing under the large transverse deformation. The two buckling modes(mode I and mode II) of the double-supporting bracing were studied as well as its relationship with structure sizes and transverse deformations of legs or diagonal bracings. The transition threshold values between the two buckling modes were presented and the values were checked by buckling experiments.To verify the mechanical performance of 60 degree steel angle and triangle cross-section tower, this paper adopts the numerical simulation and experimental measurement in the research.In terms of the numerical simulation: Firstly, the model of finite element numerical simulation is established through the finite element analysis software ANSYS to conduct the eigenvalue buckling analysis to the equilateral angle steel with the internal angle of 60 degree, verifying the validity of the critical buckling load and the expression of the width-to-thickness ratio limitation value for 60 degree steel angle. Secondly, the finite element models of 60 degree steel angle triangle tower and 90 degree steel angle quadrangle tower are established to conduct the geometric nonlinearity calculation and the eigenvalue buckling analysis. The results of numerical calculation match the experiment results relatively well, verifying the validity of the theoretical expressions. Thirdly, the 18 m two-circuit tangent tower and the 18 m single circuit angle tower are selected as the research objects in this paper. Since each tower produces different bending moments and torques under various working conditions, the Fortran calculation procedure is compiled and the maximum bending moment and torque of main members and diagonal members for each storey in the tower are obtained through circulation under the corresponding working conditions, with the aim of finding out the worst load working condition for main member and diagonal member of the tower. In the design of triangle towers, the foot distance of tower bottom, the slope of the tower body, number of floors, and floor height of the triangle tower and quadrangle tower are set the same value, and the size of each member bar for the triangle tower is calculated through the initial optimization in accordance with the principle that the total consumable items are the same. The axial force of main member and diagonal member for two types of towers under the worst load working conditions is calculated through the finite element analysis and the maximum stress of these two types of tower are also compared and analyzed. Fourthly, triangular cross section is given wind load calculation methods of wind turbine tower. For a given wind turbine model, triangular cross section design of wind turbine tower is given. Hot spot stress method is used to check wind turbine tower of advocate material and oblique material joints, oblique and oblique joint weakness into a strengthIn terms of the experimental measurement: The real model tests of triangle cross-section double circuit angle tower and tangent tower are conducted in the outdoor test base. The experiment value of the main member of tower body conforms to the finite element value. Moreover, the experiment value also matches the finite element value well when it comes to the diagonal member and transverse member with a higher measured absolute value. The rationality of the triangle tower theory is verified through the comparative analysis of experimental measurement and finite element calculation. |
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