Wind-induced vibrations of tall buildings certainly change wind effects on the structures, which is the so-called aero-elastic effect. To date, the approach to identify the aero-elastic effect is still sparse. In this paper, a bi-axial forced vibration device is developed to evaluate the aero-elastic effects of tall buildings via wind tunnel tests. The device can simulate the first-order bi-axial vibration of building models. Furthermore, the surface pressure and the top displacement of the oscillating model can be synchronously measured. The aerodynamic damping ratio and aerodynamic stiffness were identified through analyzing the aero-elastic force acting on the oscillating model. The effects of aero-elastic parameters on wind-induced responses and equivalent static wind loads of a 347 m tall building were examined and analyzed. The results show that for a return period of 100 years, the aerodynamic damping is positive while the aerodynamic stiffness is negative. Aerodynamic stiffness is much smaller than the structural stiffness and therefore it has a negligible effect on natural frequency of the building. Considering the aero-elastic effects, the maximum top displacement and acceleration decrease by approximately 4% and 10% respectively, and meanwhile, the base shear and base moment induced by equivalent static wind loads decrease by approximately 1%. This investigation indicates that wind tunnel test using such kind of biaxial forced vibration device is an effective approach to identify aero-elastic parameters of tall buildings and even other tall slender structures.

Introduction

The aerodynamic elastic effects induced by aero-elastic parameters, especially by aerodynamic damping ratio, should be considered when evaluating wind-induced responses of tall slender buildings with low frequency and damping ratio [1,2]. Currently, there are mainly two types of methods to investigate the aero-elastic effect by wind tunnel tests: the aero-elastic test [2–۷] and the forced vibration test [8–۱۱]. In the former method, the aerodynamic damping ratio is identified based on the random structural responses. The results from this method, however, are highly discrete. Moreover, the results identified by different technique are varied, and meanwhile, the identified results greatly depend on the selection of sample [1]. Compared with the aeroelastic wind tunnel tests, the forced vibration wind tunnel tests possess a number of advantages including large signal-to-noise ratio, simple recognition algorithm and high recognition stability [12]. In the late 1980s, Steckley [12] designed a pivot mode activator, based on which a pendulum model can perform harmonic vibrations around the bottom axis with a given frequency and amplitude. This device was the first one to be used to identify aerodynamic elastic parameters of tall buildings. The influence of the harmonic motion with different amplitudes and frequencies on aerodynamic force coefficients and spectra of tall buildings with a square section was analyzed by a multi-point pressure measurement wind tunnel test in Canada [9].