Structural Response of Lattice Steel Masts

The wind excitation induces fluctuating stresses with randomly varying amplitudes around mean deformation states leading to fatigue damage accumulation. For the design of such structures, it is important to study their dynamic behavior and fatigue damage under wind excitation. In the present work structure has been modeled with two node space truss element. Equivalent static wind loads has been calculated as per IS 875-1987(part3). The corresponding joint deflections, forces in each member and, base reactions has been computed. The eigen value analysis was performed to get natural frequencies and mode shapes of the tower. The natural frequencies up to ten modes have given, and the first four mode shapes were plotted. The wind velocity is considered as stationary zero mean random process superimposed over mean velocity. The mean velocity profile has been described by a logarithmic law, while Kaimal power spectral density (PSD) function of the wind fluctuation has been used to describe the random component. The cross-spectral density of wind fluctuation at different elevations has been found by using coherence, function.