Yonghui An

Aerodynamic admittance functions (AAFs) are a key parameter determining the accuracy of buffeting analysis in long-span bridges. However, the presence of barriers and central gap complicates the aerodynamic response of in-service twin-box decks, thereby increasing uncertainties in AAF identifications when relying solely on traditional wind tunnel tests (WTTs). To improve the identification accuracy and reliability, the AAFs of a twin-box deck with barriers are investigated here by combining active wind tunnel tests, large eddy simulations (LESs), and field validations. Firstly, the AAFs in narrow-banded sinusoidal gusts are identified by combining the WTTs using the active gust generator and LESs. Then, the strongest wind event at the bridge site recorded over the service life of the bridge is simulated using LESs using a synthetic inflow to identify the AAFs under the action of broad-banded turbulent wind. The effects of barriers on AAFs are isolated by comparing the results obtained on the bare deck with those on the in-service geometry. Finally, time-domain buffeting analysis using four 1-h strong wind events is performed to validate the identified AAFs. Results show that the AAFs identified from active WTTs match well with LESs under both sinusoidal gusts and turbulent inflows, with values notably exceeding the Sears function and quasi-steady value of 1. The increase in AAFs caused by barriers is primarily attributed to reduced lift coefficient derivatives. Buffeting analysis using identified AAFs shows good agreement with field measurements, providing practical guidance for AAF identifications and buffeting estimations of in-service long-span bridges.

The aerodynamic characteristics of a pitching flat plate encountering periodic gusts represent a fundamental problem in the field of aerodynamics and have motivated the development of theoretical gust-loading models. However, experimental validation of these models remains challenging, as it requires specialized facilities such as the active gust generator and forced-vibration system. Therefore, numerical methods that allow precise control of prescribed gust inflows and pitching motion are needed as a useful complement to experimental approaches. Aiming to validate the theoretical aerodynamic models and clarify the gust–motion interactions, this study investigates the unsteady lift and moment of a pitching flat plate in various periodic gusts using Unsteady Reynolds-averaged Navier–Stokes (URANS) simulations. Three types of periodic gusts in longitudinal, vertical, and bidirectional directions are synthetically generated to validate the Greenberg theory, the combined Theodorsen–Sears theory, and the combined Greenberg–Sears theory, respectively. Nine gusty inflow cases are considered to examine the effects of pitching amplitudes and gust characteristics on aerodynamic components and flutter derivatives (FDs). The URANS results match all three theoretical models at small pitching amplitudes. However, significant deviations occur at larger pitching amplitudes, particularly as increased vertical gust intensity breaks up the leading-edge vortices and generates strong secondary vortices, which in turn shift the phase of motion-induced moment and reverse the critical FD A2* from positive to negative. This study provides guidance for numerical simulations and aerodynamic models of an oscillating body subjected to gusts.

The vortex-induced vibrations (VIVs) of curved cable-stayed bridges differ from those of straight bridges due to two key factors. First, the superelevation introduces deck asymmetry and alters the effective angle of attack, leading to mechanisms responsible for VIVs that remain unclear. Second, spatial curvature modifies wind yaw angles and induces coupled vertical-torsional VIVs, complicating the mode shape correlation factor (MSCF) and making it challenging to assess VIVs solely from a straight sectional model. Investigating these effects through wind tunnel tests (WTTs) requires costly multiple sectional models, while fluid–structure interaction (FSI) simulations of in-service decks demand high computational burdens due to the fine mesh required for modeling barrier configurations. In this study, the effects of superelevation are investigated by combining sectional models, WTTs, and FSI simulations using two-dimensional (2D) unsteady Reynolds-averaged Navier–Stokes (URANS) and three-dimensional (3D) improved delayed detached eddy simulation (IDDES). Zero-thickness baffles are employed to model the barriers and accelerate simulations. Furthermore, the spatial curvature effects and MSCF are clarified by comparing sectional and full curved model WTTs. Results show that 2D URANS overestimates VIVs due to the inability to capture inner recirculation regions on the deck's lower surface, while 3D IDDES agree well with WTTs. Superelevation has unfavorable effects on VIVs by generating strong secondary vortices downstream of the central barrier at certain yaw angles, leading to conditions that might increase VIV amplitudes with respect to standard decks. The MSCF of 1.28 is recommended for coupled vertical-torsional VIVs, providing practical guidance for evaluating curved bridge VIVs using simplified sectional models.

Significant asynchrony exists between the extreme sectional temperature differences (STDs) of the high-speed railway (HSR) box girder and the ballastless track slab. Structural flexural deformation analysis based solely on univariate extreme temperature gradient may lead to distortion and redundancy. To address this issue, a method based on the maximum entropy principle is proposed for the unbiased estimation of the combined representative STDs for the box girder and track slab. Firstly, a model transforming spatial temperature measurements from multiple points into a one-dimensional equivalent linear STD for the structure is established. Secondly, an unbiased fitting method is proposed for the estimation of extreme STD based on the maximum entropy principle. Using measured data samples, the optimal marginal distributions for the univariate values are fitted. Thirdly, based on long-term measured temperature of the box girder and track slab system, a method for determining the combination coefficients of extreme STDs over multiyear return periods is proposed. The study reveals that due to the differences in structure size and shielding effect, the magnitude and seasonal pattern of the STD of box girder are significantly different from those of track slab. The joint exceedance probability model of the STDs of box girder and track slab, fitted using the maximum entropy principle, can quantitatively characterize the time lag effect of their temperature fields over multi-year return periods. Compared to the traditional extreme value analysis models, the proposed method based on maximum entropy principle can provide a more unbiased probability distribution function without making any distribution assumptions in advance. The proposed method can be used to determine the combined STD effects of HSR box girder and track slab, improving the accuracy of temperature effect analysis and providing support for more economical and safer service of HSR.