Torsional vibration and stability of wind-excited tall buildings with eccentricity

This paper describes an experimental investigation in wind tunnel of torsional vibration and stability of a tall square cross-section building with eccentricity between building elastic and geometric centres. 1:400 scale wind models of natural wind flow over open country and city centre terrains were deve3oped in the wind tunnel. The eccentric building model was tested by using an aeroelastic test rig designed for pure torsional vibration. The probability distribution of torsional peak response, aerodynamic damping and excitation spectrum were examined to determine torsional excitation and response characteristics. It was found that with a 10% geometric eccentricity ratio the tall square building was susceptible to torsional vibration. There was also a significant increase in the maximum mean response. For the open country terrain unstable torsional vibration due to vortex shedding was observed in which lock-in type large amplitude twist angular displacement occurred. Increase in turbulence associated with the city terrain, however, effectively mitigated torsional lock-in excitation.