To consider aeroelastic instabilities of prismatic high-rise buildings in strong winds, i.e., vortex induced oscillation or galloping, unsteady aerodynamic forces must be investigated as the external forces acting on building. From this point of view, wind tunnel experiments were performed to obtain the information of fluctiating pressures on side face of a building, which is subjected to the forced harmonic oscillation with a fundamental linear mode in a boundary layer. This paper presents the characteristics of fluctuating pressures on the side face of a square oscillating in the transverse direction. The phase angle between the fluctuating pressure and the displacement of the prism showed positive value near the resonant velocity. The total work done by unsteady aerodynamic pressures suddenly jumped up from negative to positive near the immediate change of the work.
