Yozo Fujino

This paper describes an investigation into vortex-induced vibration (VIV) and the influence of the Reynolds number (Re) on the aeroelastic behavior of a suspension bridge tower with corner cuts. The analysis focuses on the Osman Gazi Suspension Bridge tower, which has a corner-cut ratio of 0.13D and center-to-center spacing of 4.56D. Three-dimensional numerical simulations were conducted using the Large Eddy Simulation (LES) method across a wide Re range from 3×10³ to 1×10⁷. The results showed that at low Re (Re ≤ 1×10⁴), the Strouhal number remained nearly constant at 0.18, followed by a sharp increase to 0.22 for Re between 9×103 and 1.25×10⁴. Flow simulations showed distinct flow regimes and revealed mechanism behind the Strouhal number change at different Re. Proper Orthogonal Decomposition (POD) analysis revealed that pressure fluctuations were widely distributed at low Re but became localized near the leeward corners above Re = 1×10⁴. These results confirm that the sudden jump in Strouhal number is strongly related to changes in flow separation and vortex dynamics as the Re increases. The CFD simulations provide a detailed explanation and a rational interpretation of the wind tunnel test results, particularly at lower Re. Re dependency of Strouhal number has significant implications for accurate prediction of resonant wind speed associated with VIV occurrence. The study demonstrates effectiveness and limitation of corner-cuts as aerodynamic countermeasure is strongly dependent on Re and turbulence intensity. In transitional Re regimes, corner cuts may cause abrupt changes in the Strouhal number and shift the lock-in wind speed into critical ranges rather than suppressing VIV.

Safety assessment of vehicles crossing highway interchanges during earthquakes by reliability-based numerical simulations is presented in this paper. The assessment was performed for two limit states: vehicle rollover and sideslipping accidents. Simulations were conducted using three-dimensional finite element models of two existing highway interchanges consisting of straight and curved bridges under site-specific earthquakes. Effects of curved bridges radii, levels of earthquake, vehicle type, driving velocity, and road surface conditions on the safety limit states of five types of vehicles, namely, sedan-type, SUV, small-box truck, bus, and large truck, were investigated and clarified in the Monte Carlo simulation.

This paper describes techniques for detecting bearing malfunction directly from the seismic response of the bridge using wavelet transform time-varying identification. Instantaneous frequency of continuous wavelet and detail components of discrete wavelet transform are utilized as structural features, and they characterize isolation bearing condition via statistical clustering technique. Accuracy and efficacy of the techniques were verified in numerical simulations using analytical and finite element models. The techniques were implemented on seismic records from long-term monitoring of multi-span continuous-girder isolated bridge. Results demonstrate that wavelet-based features can effectively characterize the condition of the isolation bearing directly from seismic responses of girder and piers.

This paper describes a numerical study on the vehicle instability when crossing curved highway bridge during an earthquake. Analytical framework using two-axle vehicle dynamics model is developed to describe vehicle vibration when moving under seismic excitation from the curved bridge girder. The model includes out-of-plane and in-plane motion along with the effect of curved girder with specific radius, camber angle and longitudinal grade. Two criteria for critical vehicle stability are evaluated namely the rollover and sideslip stability. As case study, numerical simulations were conducted using three-dimensional finite element model of an elevated highway junction consisting of four curved sections and two straight sections. Effects of curved bridge radii, level of earthquake, vehicle velocity and driver reaction on the vehicle stability were investigated. It was found that a vehicle moving on a curved bridge during earthquake has a larger possibility for rollover and sideslip instability than a vehicle moving on a straight section for the same driving velocity and level of earthquake. Results of simulations demonstrate that normal forces on vehicle’s wheels are significantly influenced by the curved bridge effects, steering angle, effect of road camber at the curved section. These conditions contributed to reduction of normal forces on vehicle’s wheels and increased the risk of vehicle instability.