TORSIONAL VIBRATION AND STABILITY OF WIND-EXCITED TALL BUILDINGS WITHECCENTRICITY

This paper describes an experimental investigation in wind tunnel of t orsional vibration and stability of a tall square cross-section buildi ng 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 developed in the wind tunnel. The eccentric buil ding model was tested by using an aeroelastic test rig designed for pu re torsional vibration. The probability distribution of torsional peak response, aerodynamic damping and excitation spectrum were examined t o determine torsional ''citation and response characteristics. It was found that with a 10% geometric eccentricity ratio the tall square bui lding was susceptible to torsional vibration. There was also a signifi cant increase in the maximum mean response. For the open country terra in unstable torsional vibration due to vortex shedding was observed in which lock-in type large amplitude twist angular displacement occurre d. Increase in turbulence associated with the city terrain, however, e ffectively mitigated torsional lock-in excitation.