# Spectral Characteristics of Fluctuating Aerodynamic Forces Acting on Rectangular Prisms
###### Abstract  
The present work is devoted to the role of boundary layer turbulence on the spectral characteristics of fluctuating wind loads on large aspect-ratio rectangular prisms. Seven rectangular rigid models with different side ratios (1/4-4) were created, and simultaneous pressure experiments were conducted under the boundary layer turbulence flows. Using the measured data, the power spectrums of the fluctuating aerodynamic forces were calculated, and then, the spectral characteristics under different turbulent boundary layer flows were analyzed. In contrast to the typical power spectrum model, the main factors affecting the spectral characteristics of the fluctuating aerodynamic loads are presented and discussed in this study. The power spectrum of the rectangular prism was significantly impacted by the turbulent wind field, primarily because higher turbulence intensity levels result in a lower spectral peak and a wider spectral bandwidth, which also redistributes spectral energy. In particular, the effect on the spectral properties of across-wind fluctuating loads was stronger, and the turbulent disturbance modified the lateral separation flow structure, causing the reattachment phenomenon to occur earlier on rectangular prisms with small side ratios, which effectively altered the spectral properties. Thus, a normalized across-wind fluctuating wind load spectrum model is proposed, taking into account the effects of incoming turbulence, the side ratio, vortex shedding, separation reattachment flow-induced spectral bandwidth changes, and high-frequency fluctuations. 20  
loads are evolving into a design control element, and in-depth investigations of wind effects are especially crucial given the current prevalence of'super tall' building developments. Therefore, thorough research using efficient research techniques is required to understand the spectral characteristics of fluctuating aerodynamic forces on high-rise buildings with large aspect ratios. It is now generally accepted that along-wind fluctuating wind loads are generally straightforward and mainly determined by the along-wind turbulence component [1; 3; 5; 14]. [PERSON] [15] created and improved the calculation method for along-wind loads and wind-induced responses, based on the quasi-constant theory and strip assumption; they produced the influential gust factor method that served as the theoretical framework for later studies. The gust load factor approach, or a variant of it, can be utilized to precisely determine the wind-induced response and equivalent static wind load of a building based on the [PERSON] wind vibration theory [16; 17]. Overall, it can be argued that the spectrum properties of along-wind fluctuating loads are mostly compatible with the along-wind fluctuating velocity component, and studies in this area are generally well established. As a'super tall' building's height increases, the across-wind loads and wind-induced response frequently outweigh the along-wind direction, and they take control of the structure's design [3; 6; 7; 9; 18; 19; 20]. The more complicated, across-wind loading, aerodynamic mechanism is primarily affected by a confluence of vortex shedding, separation and reattachment flow, incoming turbulence, and aeroelastic excitation [7; 8; 9; 20; 21]. The applied aerodynamic forces caused by incoming turbulence and wake excitation, and the self-excited forces caused by the structure's air-bounce effect, comprise the two halves of the across-wind load [3; 6; 7; 11; 18; 19; 20; 21; 22]. Currently, rigid model pressure measurements, base high-frequency dynamic balance force testing, or fluid numerical computations are the main methods used to examine the across-wind fluctuation pressure spectral properties [9; 11; 19; 20; 23]. The across-wind fluctuating load spectrum and the basal bending moment spectrum were obtained experimentally by [PERSON] [6], [PERSON] [19], [PERSON] [10], and [PERSON] [20].