In the present study, using a square plan tall building models with various aspect ratios, characteristics of peak pressure coefficients, mean and fluctuating force coefficients and power spectra were systematically investigated through a series of wind tunnel tests. From the wind tunnel tests, the following were found. The peak pressure coefficients from the wind tunnel tests corresponded well to those from the AIJ-RLB (2015), and values prescribed in AIJ-RLB (2015) can be extended to the tall buildings with aspect ratio of 9.5. Mean force coefficients in X- and Y-axis increased with increasing aspect ratios, while fluctuating force coefficient CFX showed decreasing tendency and fluctuating force coefficient CFY showed increasing tendency with aspect ratio. Mean and fluctuating torsional moments were quite small and showed less variation when compared with force coefficients in translational directions. And, from the Den Hartog Criterion, it was found that aerodynamically unstable vibration could occur for tall buildings with aspect ratio larger than 3 for the current experimental conditions. Lastly, the shapes of power spectra of X-axis force coefficient SCFX(f) showed similar shapes regardless of aspect ratios, but for the power spectra of Y-axis force coefficient SCFY(f), peaks corresponding to the reduced frequency of 0.1 increased and became narrow band with increasing aspect ratios.
