Abstract
This paper discusses some of the findings arising from long-term monitoring of the wind effects on a transmission tower located on an exposed site in South-West England. Site wind speeds have been measured, together with the foundation loads at the base of each of the four legs. The results show good correlation between the wind speeds and leg strains (loads) for a given wind direction, as expected for wind speeds in excess of 10 m/s. Comparisons between the measured strains and those determined from the UK Code of Practice for lattice towers (BS8100), for the same wind speed and direction show that the Code over-estimates most of the measured foundation loads by a moderate amount of about 14% at the higher wind speeds. This tends to confirm the validity of the Code for assessing design foundation loads. A finite element analysis model has been used to examine the dynamic behaviour of the tower and conductor system. This shows that, in the absence of the conductors the tower alone has similar natural frequencies of approximately 2.2 Hz in the both the first (transversal) and second (longitudinal) modes, whilst for the complete system the conductor oscillations dominate, giving similar frequencies of approximately 0.1 Hz for both the first and second modes.