Discussion of “Ammann on Tacoma Narrows”

Ammann, O. H.; Ellis, Charles A.; Frankland, F. H.

doi:10.1061/taceat.0006184

Cited by 1 publication

(6 citation statements)

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“…This Strouhal number closely matches the non-dimensional natural frequency of f nat h/U = 0.1-0.105 at n m = 10 (figure 4a), indicating that the vortex shedding behind a stationary deck triggers the natural frequency at n m = 10 (wavelength of λ z = L z /5). This wavelength is similar to what was observed during the vertical vibration of the TNB (Ammann et al 1941).…”

Section: Natural Frequencies Of the Tnbsupporting

confidence: 87%

“…The wavelength of the torsional vibration is λ z = L z (figure 10c). The peak frequencies of these vertical and torsional vibrations are fh/U = 0.103 (0.78 Hz) and 0.025 (0.19 Hz), respectively, which are similar to the recorded data (0.60-0.63 and 0.18 Hz, respectively) of Ammann et al (1941) considering the uncertainty of the measurement at that time.…”

Section: Fluid-structure Interactionsupporting

confidence: 83%

“…U c /( f nat B) = 4 by Matsumoto, Shirato & Hirai (1992), 3.55 by Scanlan (1999), 3.6-4 (instability analysis) and 4 (numerical simulation) by Larsen (2000), 4 by Szabó et al (2020) and 3.5-4.4 by Hu et al (2022). It is also noteworthy that Ammann et al (1941) obtained U c /( f nat B) = 4 for a two-dimensional H-section (wind tunnel test), but failed to obtain a reasonable critical wind speed for a 1 : 234 scale full model of the TNB. The lowest Reynolds number at which vortex shedding occurs behind a stationary deck cross-section is obtained as Re cr = 89 by performing additional two-dimensional simulations.…”

Section: Further Study Of the Vertical And Torsional Vibrationsmentioning

confidence: 84%

“…In the early morning, the bridge deck showed a vertical vibration with a wavelength of 2L z /9 or L z /5 at a frequency of 0.60-0.63 Hz, where L z is the length of the bridge deck. The vertical vibration changed abruptly to a torsional one around 10:00, and the bridge oscillated at 0.23 Hz with the angular amplitude reaching up to 45 degrees right before the collapse at 11:00 (Ammann, von Kármán & Woodruff (1941); see also Olson, Wolf & Hook (2015) for a brief summary of the incident).…”

Section: Introductionmentioning

confidence: 99%

“…In those studies, how the vibration was initiated was not investigated but an initial vibration was prescribed. Previous experimental studies (Ammann et al 1941;Scanlan & Tomko 1971;Hu, Zhao & Ge 2022) and numerical ones employing three-dimensional fluid-structure interaction (Szabó, Györgyi & Kristóf 2020) also prescribed the initial motions of the bridge models. Abbas, Kavrakov & Morgenthal (2017) summarized the aerodynamic analysis techniques and numerical and experimental methods for flutter stability analysis of long-span cable-supported bridges.…”

Section: Introductionmentioning

confidence: 99%

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Vertical and torsional vibrations before the collapse of the Tacoma Narrows Bridge in 1940

et al. 2022

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We perform a three-dimensional direct numerical simulation of flow over the Tacoma Narrows Bridge to understand the vertical and torsional vibrations that occurred before its collapse in 1940. Real-scale structural parameters of the bridge are used for the simulation. The Reynolds number based on the free-stream velocity and height of the deck fence is lower ( ${Re}=10\ 000$ ) than the actual one on the day of its collapse ( ${Re}=3.06 \times 10^{6}$ ), but the magnitude of a fluid property is modified to provide the real-scale aerodynamic force and moment on the deck. The vertical and torsional vibrations are simulated through two-way coupling of the fluid flow and structural motion. The vertical vibration occurs from the frequency lock-in with the vortex shedding, and its wavelength and frequency agree well with the recorded data in 1940. After saturation of the vertical vibration, a torsional vibration resulting from the aeroelastic fluttering grows exponentially in time, with its wavelength and frequency in excellent agreement with the recorded data of the incident. The critical flutter wind speed for the growth of torsional vibration is obtained as $3.56 < U_c / (f_{nat} B) \le 4$ , where $U_{c}$ is the critical flutter wind speed, $f_{nat}$ is the natural frequency of the torsional vibration and $B$ is the deck width. Finally, apart from the actual vibration process in 1940, we perform more numerical simulations to investigate the roles of the free-stream velocity and vertical vibration in the growth of the torsional vibration.

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Section: Natural Frequencies Of the Tnbsupporting

confidence: 87%

Section: Fluid-structure Interactionsupporting

confidence: 83%