Torsional excitation and interference effects of tall buildings with structural eccentricity

This report describes an experimental investigation in wind tunnel of torsional excitation of a tall square building with structural eccentricity and torsional interference effects on the eccentric building response from neighbouring buildings of different sizes. The eccentric building model was an aeroelastic model of pure torsional motion and the interfering building models were rigid. Tests were carried out in 1:400 scale wind models of natural wind flow over open country and city centre terrains developed in the wind tunnel. The probability distribution of peak response, aerodynamic damping and torsional excitation spectrum were examined to determine torsional excitation and response characteristics. It was found that the tall square building with a 10% geometric eccentricity ratio was more susceptible to torsional motion and vibration, compared with one without eccentricity. There was a significant increase of maximum mean responses, and an unstable torsional vibration due to vortex shedding was also observed in which large amplitude twist angular displacement occurred. With interference effects from a small square interfering building, the torsional response of the eccentric building was enhanced by a factor of up to 4.6 in the open country terrain due to resonant buffeting. The critical location of the interfering building was found to be dependent on the size of the interfering building and the eccentricity position of the eccentric principal building relative to wind incidence.