Reliability analysis of a microwave tower for fluctuating mean wind with directional effect

The reliability analysis of a 75 m tall steel lattice tower is presented for the annual variation of mean wind velocity taken as a function of both mean wind speed and direction. A parametric study is also conducted in order to investigate the effect of different important parameters on the component and system reliability of the tower. Variation of the mean wind velocity is determined from the continuous records of the hourly mean wind speed and the hourly mean values of the two components of the wind velocity. Annual probability of maximum response of a component of the tower exceeding a threshold level is determined as the mean number of crossing per day of the velocity vector out of the safe resistance boundary surface defined as a function of mean wind speed and direction. Using the above method of analysis, reliability against allowable stress failure of critical members of the tower and the consequent, system reliability are determined for a number of parametric variations. It is shown that the probability of failure of the tower increases with the increase in the standard deviation of mean wind speed, the zero crossing rate and the correlation coefficient between the velocities in the two directions. Further, the variation of the probability of failure is found to be sensitive to the variation of the above parameters in the lower range of the threshold levels of stresses.