Tortional Vibration of Along-Wind Excited Structures

A method for analyzing the torsional vibration of along-wind excited structures is presented. The method is based on random vibration concepts and yields the expected maximum translational and torsional responses of a single-mass structure. The approach is similar to the gust factor method. Aerodynamic admittance functions are derived which are used to estimate the spectral density function of the random torque and the cross-spectral density function of the force and torque acting on the structure. These are required for estimating the structure's translational and torsional mean square responses. Results for several examples indicate that the dynamic torsional response increases as follows: as the width of the structure's exposed face increases, as the structural or geometric eccentricity increases, and as torsional natural frequency decreases.