Full-scale Investigations on Free Standing and Guyed Lattice Towers
Lattice steel towers are used for a number of diverse purposes, namely, telecommunications, radio and television broadcasting, observation, power transmission and lighting supports, etc. The need to design a lattice tower for resonant dynamic response due to wind load arises when the natural vibration frequency (fundamental frequency) of the structure is low enough to be excited by the turbulence in the natural wind.
Full-scale investigation on a 52 m tall free standing lattice tower has been carried out using anemometers, accelerometers and strain gauges to measure wind characteristics and structural dynamic response characteristics.
- The GRF values for measured base bending moment are found compare well with those obtained from the IScode (with and without f) and AS code (with gB and with gu) and fall between these codal values. Hence, it is necessary to consider the `f’ value in the evaluation of GRF values based on the IS code, irrespective of the terrain category.
Guyed masts are used for wireless communication, meteorological measurements, and recently, even for power transmission. The behaviour of the mast is non-linear due to its slenderness and compliant ‘guy-support’ system. The guys also exhibit nonlinear behaviour especially at low values of pretension due to possible multimodal excitations and dynamic response to wind turbulence. Full-scale investigations on a 50 m tall guyed lattice tower has been carried out using anemometers and accelerometers to measure wind characteristics and dynamic response characteristics.
- The r.m.s. values of displacements evaluated for the measured wind speeds using the patch load patterns suggested by Davenport and Spalding, which avoid complex non-linear transient dynamic analysis of guyed masts for evaluation of peak fluctuating responses, were observed to be comparable to the measured values observed during the measurement programme.