Experimental investigation of wind-induced loading on a tall building under downburst-like outflow conditions

This study investigates the aerodynamic effects of three downburst-like outflows: translation, gust front, and transient, on a Commonwealth Advisory Aeronautical Research Council (CAARC) building model using pressure-based measurements conducted in a Multi-Fan Wind Tunnel (MFWT). Each outflow was designed to replicate distinct physical phases of downburst-like outflow, facilitating detailed analysis of mean and fluctuating surface pressures, global and local aerodynamic forces, and spectral characteristics across building elevations. The study introduces a unified experimental framework to systematically compare these outflow types under controlled, repeatable inflow conditions. The translation outflow exhibited coherent low-frequency loading associated with the lateral sweep of the gust. The gust front produced more uniform and steady aerodynamic forces governed by consistent shear inflow. By contrast, the transient outflow generated highly localised stagnation pressures, intensified lateral suction, and elevated torsional excitation near the roof level, reflecting the abrupt rise of velocity and impingement of the shear layer. Spectral analysis of across-wind forces and torsional moments revealed height-dependent energy distributions, with transient flows showing the broadest frequency range. Dynamic Amplification Factor (DAF) analysis revealed significant temporal variability in load amplification across outflow types. These results collectively demonstrate that wind loading under downburst-like flows is governed not merely by peak gust intensity, but by the short-duration unsteady nature of the inflow, with DAFs reaching up to 2.18, thereby necessitating tailored structural design strategies responsive to each outflow regime's dynamic effects.