Optimization of uplift capacity of transmission tower foundations

Abstract

Transmission tower lines using lattice towers and concrete foundations are the common practice in most of the countries all over the world. A significant amount of the cost of the transmission tower line is spent for the tower foundation construction. Uplift capacity of transmission tower foundation is determined based on the assumption that, the uplift force is resisted by the weight of the footing and the weight of the soil inside the volume of inverted frustum. Hence, the uplift capacity of the foundation is a major aspect of determining the dimensions of the tower foundation. However, the values of the frustum angle seem to be arbitrary and the failure pattern is more likely to be varied from the assumed pattern. Apart from that, the frustum angle is unsymmetrical for the inclined loadings. Further, the estimated uplift capacity shall also be reassessed according to the failure plane variations. As the first step of this study, a research survey was conducted on the available empirical methods of estimating the uplift capacity. Data were collected on transmission tower types and their foundation types based on different soil categories. This report will use PLAXIS; a finite element software to analyze the uplift capacity of transmission tower foundation. A comparison between the results from the software analysis and the capacities given by empirical methods is included in the report. An evaluation on the assumptions made on frustum angle, composition of uplift capacity to determine the uplift capacity of the transmission tower foundations is also given in the report. This analysis also includes the failure patterns, uplift capacity, composition variation of uplift capacity for different types of foundations used for transmission towers. Conclusively, this will evaluate and make a recommendation on determination the uplift capacity of transmission tower foundation, assumption of the frustum angle and the composition of the uplift capacity.