Identification of aerodynamic admittance functions of a flat closed-box deck in different grid-generated turbulent wind fields

Abstract

Wind tunnel tests of synchronous measurements of the buffeting lifts and moments on six separated strips of a motionless 1:45 scale sectional model of a flat closed-box bridge deck were carried out in three turbulent flow conditions. The longitudinal and vertical components of turbulent wind speed were also measured synchronously with the buffeting forces at the positions just over the windward edges of the six strips. Three typical methods, including the auto-spectral method based on the measured auto-spectrum of buffeting force (auto-spectrum method), the cross-spectral method based on the measured cross-spectra between buffeting force and fluctuating turbulence components (cross-spectrum method), and the colligated least square method based on a colligated residue of the above-mentioned auto- and cross-spectra (colligated least square method), were then used, respectively, to identify the aerodynamic admittance functions of the flat closed-box deck. The aerodynamic admittance function components of a buffeting force with respect to the longitudinal and vertical components of fluctuating wind speed were effectively separated using the colligated least square method while only a weighted average value, often called the equivalent aerodynamic admittance function, was obtained using the auto-spectrum method. Meanwhile, the reproduced auto-spectra of the buffeting forces had very high accuracies when the aerodynamic admittance functions identified with the colligated least square method were employed, but deviated significantly from the measured ones when the aerodynamic admittance functions identified with the cross-spectrum method were used. Furthermore, the influence of the span-wise position of the wind probe on the values of aerodynamic admittance function module was confirmed to be very small. Finally, the aerodynamic admittance function components with respect to the longitudinal and vertical fluctuating wind speeds were found to be significantly affected by both the intensities and integral scales of the oncoming turbulence wind.

Modeling and simulation of bridge-section buffeting response in turbulent flow

“…Aerodynamic admittances were traditionally obtained from wind tunnel experiments, and several test strategies report successful results, see, e.g., 9,10,11,12,13,14,15 However, as the majority of these methods measure forces over a wider segment than the flow integral length scale, span-wise coherence of the turbulence and buffeting forces must be considered. As discussed in, 16,15 this introduces some uncertainty in the estimation of admittance functions. Whereas methods based on pressure strips do not have these problems, they do instead suffer from inaccuracies of the pressure integration.…”

Refined Time‐Domain Buffeting Analysis of a Long‐Span Suspension Bridge in Mountainous Urban Terrain

“…Of particular interest is the square of the module of the AAF |χ (ω)| 2 , which can be obtained in the frequency domain by considering the power spectra of the fluctuating wind and aerodynamic forces. Conventionally, the experimentally tested AAF is based on an equivalent assumption [18,[31][32][33][34][35] that the admittance of a buffeting force due to the longitudinal turbulence (u) equals that due to the vertical turbulence (w).…”

Span-wise coherence of fluctuating forces on twin bridge decks and the turbulence effect

“…In Figure 2(a), two DTC initium data processors were used since one processor can be connected to eight scanners. The data transmission frequency from the processors to the computer was as high as 1200 Hz per channel (Yan et al, 2018). The maximum sampling frequency of the pressure measure system was decided by the scanning rate of one scanner, which kept 300 Hz in this study (20,000/64 ' 312 Hz).…”