Interference effects on the response of a tall building model

Abstract

A model of a simple building of rectangular planform and elevation (CAARC Standard Model) has been tested in a simulated atmospheric shear flow. The model was rigid but was mounted on two mutually perpendicular pairs of torsion bars which allowed the model to vibrate with two degrees of freedom with linear mode shapes; external electromagnetically controlled damping was applied. Mean and r.m.s. amplitudes of the longitudinal and lateral displacements were measured whilst each of four related models was situated upwind but offset to one side of the dynamic model. The tests were made for reduced wind speeds between 5 and 14 1 2 with logarithmic decrements of between 1% and 8%. Additionally one set of tests was made with the models yawed through 30° relative to the wind. Mean longitudinal displacements generally experienced a shielding effect, but in some cases there was a measurable overspeed effect. Fluctuating longitudinal displacements were generally enhanced by the interference effects from the wakes of the upwind models. The fluctuating lateral displacements were reduced by the presence of the upwind models at reduced wind speeds around 10, at which the isolated dynamic model experienced peak response amplitudes. However at lower reduced wind speeds of around 6, the lateral displacements were enhanced by the presence of the wake from the upwind models. These effects varied in detail, dependent on the particular geometry of the upwind model, but it has been shown that, for a given geometry and reduced wind speed, the relative change in the response amplitude is independent of the applied damping.