Bearing Capacity Assessment and Maintenance Scheme Optimization on a 220kV Transmission Tower with Foundation Settlement

Abstract

Finite element model of a 220kV transmission tower was established in general software ANSYS. The constrained method of the freedoms of tower foots with foundation settlements was proposed. According to the monitoring data of the non-uniform settlement, the relative settlement values were applied at the tower foots as displacement loads. By considering the relative position relationship between the wind direction and the settlement direction, the foundation settlement case can be combined with the design wind load case and the design ice load case, and structural analysis of the transmission tower totally includes 32 cases. The stresses of the main members and diagonal members at the tower head and tower body were calculated and assessed for different load cases. Optimization on the angle between staying wire and the ground was carried out. The reducing efficiency of stresses by using staying wires for two angles between the staying wires and the ground was compared. Introduction Effected by the surface settlement of the goaf, the foundation of the transmission pole and tower will be destroyed by settlement, inclination or slip [1-4]. Then with the variation of the leg opening and height difference of the transmission tower legs, the transmission tower structures will bear high additional loads, and part body or whole body of the tower structure may break down [6-9]. Deformations of the foundation have brought serious threat to the safe operation of the power grid. Limited values of the uniform foundation settlement for the towers with different heights are specified in the design technical regulations. Limited values for foundation with non-uniform settlement, inclination and slip aren’t specified. The healthy state evaluation of the tower with foundation deformation hasn’t been researched sufficiently. Prototype test on the transmission tower with foundation deformation is very costly and difficult to be realized. It is necessary to analyse the member forces of the transmission tower with foundation settlement. In this paper, finite element model of a 220kV transmission tower was established in general software ANSYS. The constrained method of the freedoms of tower foots with foundation settlements was proposed. By considering the relative position relationship between the wind direction and the settlement direction, the foundation settlement case can be combined with the design wind load case and the design ice load case, and structural analysis of the transmission tower totally includes 32 cases. The stresses of the main members and diagonal members at the tower head and tower body were calculated for different load cases, which can bring technical suggestions for the maintenance scheme of the transmission towers with foundation settlements. Optimization on the angle between staying wire and the ground was carried out. 4th International Conference on Computer, Mechatronics, Control and Electronic Engineering (ICCMCEE 2015) © 2015. The authors Published by Atlantis Press 391 Analysis model A 220kV tangent transmission tower is selected for the structural analysis with foundation settlement. Bearing capacity of the tower agrees with the requirement of the working load cases including wind load, accreted ice load and installation load etc. The design wind velocity is 30m/s at 15m reference height and the design ice thickness is 10mm. Total height of the tower is 58.5m. The vertical and horizontal spans of conductors and ground wires are 175m and 225m, respectively. The type of the conductor and the ground wire is 2×LGJQ-240 and GJ-70. The outlines of the transmission tower are presented in Fig.1. Fig.1 Outlines of the transmission tower Fig.2 FEA model The general FEA software ANSYS was applied for the tower structural analysis with foundation settlement. The leg members and the main members of the tower are simulated by BEAM4 element. The diagonal members are simulated by LINK8 element [8-9]. The secondary members are ignored in the FEA model. The connection between the main members and the diagonal members is hinged. The finite element analysis (FEA) model of the transmission tower and the global coordinate system are shown in Fig.2. Tower foot numbers and the wind directions are illustrated in Fig.3. The absolute settlement values, the relative settlement values as well as the constrained conditions in FEA model are listed in Table 1. The non-uniform settlement case is illustrated in Fig.4. For the non-uniform settlement of foundation, one of the four tower foots is fixed, the other three foots are settled by the relative settlement values in Table 1. 4991 mm 66 63 m m Line direction N S W E Wind direction