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Aerodynamic shape of a closed-box girder plays an important role in the wind-induced stabilization of long-span suspension bridges. The purpose of this study is to investigate the effects of the combination of five aspect ratios and a downward vertical central stabilizer (DVCS) on nonlinear flutter and aerostatic behaviors of a super long-span suspension bridge with closed-box girders. Through conducting a series of wind-tunnel tests and nonlinear finite element analysis, the results show that the nonlinear self-excited forces and the critical wind speed ( U cr ) gradually increases as the increase of the aspect ratio ( i.e. the width to height ratios). Particularly, the application of 20% deck height DVCS could significantly increase the U cr for these aspect ratios, and the enhancement in the flutter performance of the bridge is more obvious for a relatively small aspect ratio. Furthermore, the installation of the DVCS could change the flutter divergence patterns of the bridge from soft flutter to hard flutter, especially for a small aspect ratio. In addition, the aerostatic force coefficients and torsional divergence critical wind speeds of the larger aspect ratio with DVCS are significantly larger than that without DVCS. A relatively small aspect ratio of the bridge has better aerostatic performance than that of a larger aspect ratio.

Traditional aerodynamic measures with fixed geometric shapes make it difficult to relieve the wind-induced vibration issues under the continuous expansion of bridge spans. Active aerodynamic control measures would be an alternative way to improve the wind vibration performance of long-span bridges. In this study, a bridge flutter control method based on active flaps was proposed, and the main girder-active flap-suspended aeroelastic model was designed to study the control effect. A pair of active flaps was installed on both sides of the box girder near the lateral fairings, and the movement signal of the main girder was detected using internal sensors. The two flaps move relative to the deck according to the preset equations of motion. This improved the flutter stability of the system with high effectiveness compared to traditional passive aerodynamic measures. By adjusting the gain coefficient in the motion function of the flaps and the phase difference between the flaps and the deck, the changing characteristics of the critical flutter wind speed were revealed with a deeper understanding of the relationship between the phase differences and gain coefficient of the active flaps and main girder. Studies have shown that the flutter performance of the deck-flap system is significantly affected by the phase difference and gain coefficient on both sides of the aerodynamic flap. The control law of the windward flap is relatively stable, but the control effect of the leeward flap is greatly affected by the movement of the windward flap.

In addition to common synoptic wind system, the mountainous terrain forms a local thermally driven wind system, which makes the mountain wind system have strong terrain dependence. Therefore, in order to estimate the reliable design wind speeds for structural safety, the samples for extreme wind speeds for certain return periods at mountainous areas can only come from field measurements at construction site. However, wind speeds measuring duration is usually short in real practice. This work proposes a novel method for calculating extreme wind speeds in mountainous areas by using short-term field measurement data and long-term nearby meteorological observatory data. Extreme wind speeds in mountainous area are affected by mixed climates composed by local-scale wind and large scale synoptic wind. The local winds can be recorded at construction site with short observatory time, while the extreme wind speeds samples from synoptic wind climate from nearby meteorological station with long observatory time is extracted for data augmentation. The bridge construction site at Hengduan Mountains in southwestern China is taken as an example in this study. A 10-month dataset of field measurement wind speeds is recorded at this location. This study firstly provides a new method to extract wind speed time series of windstorms. Based on the different windstorm features, the local and synoptic winds are separated. Next, the synoptic wind speeds from nearby meteorological stations are converted and combined with local winds to derive the extreme wind speeds probability distribution function. The calculation results shows that the extreme wind speed in the short return period is controlled by the local wind system, and the long-period extreme wind speed is determined by the synoptic wind system in the mountain area.

Vortex-induced vibration (VIV) occurred on Humen Bridge starting from May 5th, 2020. The direct reason was that the water-filled barriers were placed along the two edges of the bridge deck upper surface, which destroyed the streamlined aerodynamic shape configuration and, therefore, vortices were generated along the bridge section. With the help of several portable monitoring devices, wind speeds, structural motion, and airflow at the wake of the bridge section can also be recorded separately. After removing the barriers, subsequent VIV was continuing due to the decreased structural damping. The amplitude was smaller than the initial case, but still exceeded the threshold defined in Chinese bridge specification. The spoiler was proposed to be installed on the handrail to mitigate vortex and suppress VIV. The Doppler LiDAR detected that the vortex frequencies had been distorted after installing the spoiler, and bridge motion also had dramatically reduced to below the threshold when the wind climate kept as a similar condition when previous VIV happened. Therefore, the bridge administrative agency and local government decided to reopen Humen Bridge after ten days of closure.

In structural health monitoring (SHM), variations of structural dynamic properties are paramount to indicate the health status of structures. Structural dynamic properties are time variant due to various long-term effects (e.g., structural deterioration) and periodic effects (e.g., periodic variations of temperature, humidity, and traffic). Sometimes periodic effects will interfere with the quantification of long-term effects. Though important, there are still limited research studies aiming to distinguish these two effects. Given the amount of SHM data, it is possible to solve the issue from a data-driven perspective. This article proposes a time series decomposition methodology to divide the time series of structural dynamic properties into long-term parts, multiscale periodic parts, holiday parts, and error parts. We extract the 10-year dynamic properties of a long-span bridge using the fast Bayesian FFT identification algorithm and choose two dynamic modes of that bridge as examples to explain how our proposed methodology works. We use the long-term parts to extract the rules of structural deterioration. The multiscale periodic parts are utilized to find the relationships with the periodically varying ambient conditions (i.e., temperature and humidity) in different time scales (i.e., yearly, weekly, and daily). Then, the long-term and periodic effects can be distinguished. For the long-term effects, the modal frequencies tend to decrease but the damping ratios seem to increase. For the periodic effects, we find that the increment of temperature will lead to the decrease of both modal frequencies and damping ratios. The variations of modal frequencies induced by deterioration and temperature are of the same amplitudes. The variations of both modal frequencies and damping ratios are not significantly related with humidity. This article could provide references for damage detection and safety assessment for similar bridges.

As the typical span of suspension bridge increases and multi-tower suspension bridges are developed, the linear flutter theory cannot meet the design requirements of modern flexible bridges, and the study of nonlinear flutter of bridges becomes necessary. The author discovered the flutter-mode transition phenomenon in a full-bridge aeroelastic model wind tunnel test of the Maanshan Bridge; that is, the bridge vibration was transformed from first-order anti-symmetric torsion mode (A-T-1) to first-order symmetric torsion mode (S-T-1) and diverged when the flutter critical wind speed was approached. A vertical bending mode acted as a medium for energy transfer between A-T-1 and S-T-1. This phenomenon greatly increased the critical wind speed of flutter, and therefore it is interesting to study its mechanism. Starting from the nonlinear nature of the bridge structure itself, this paper discusses the mechanism of the flutter-mode transition phenomenon, and analyzes the typical characteristics of flutter-mode transition of Maanshan Bridge in depth. A nonlinear discrete mathematical model of the Maanshan Bridge is built, and the transition between the vertical bending mode and torsional mode of the bridge is realized. Adopting the Mathieu function theory and based on the single-degree-of-freedom vibration equation of the Maanshan Bridge corresponding to each mode, the evolution between A-T-1 and S-T-1 is realized, the mechanism of which is also explained.

The advancement of construction techniques and high-performance sustainable materials enables the increase of span length for arch bridge. It is of great importance to study the theoretical ultimate span length of arch bridge. Based on the parabolic and catenary arch axes, the analytical solutions of ultimate span length of arch bridge are solved using theoretical derivation accounting for the strength, in-plane stability and out-plane stability conditions, respectively. Then, the use of high-performance concrete, reactive powder concrete and high-strength steel is considered to study the relationship between theoretical ultimate span length and rise-span ratio as well as material strength for concrete and steel arch bridges. The results show that the theoretical ultimate span length derived by catenary arch axis is smaller by about 2–6% than that obtained by parabolic arch axis, but the difference is insignificant. When the rise-span ratio is 1/5, the theoretical ultimate span length for concrete arch bridge using R200 reactive powder concrete can reach 2000 m (2161 m for catenary arch axis and 2099 m for parabolic arch axis) while the main span of steel arch bridge using Q690 high-strength steel can be longer than 2500 m (2948 m for catenary arch axis and 2865 m for parabolic arch axis).

The non-stationarity of the realistic wind velocity field strongly influences the wind effects on structures. Related researches are limited since it is difficult to simulate the non-stationary win...

The reinforcement design is the most critical and time-consuming process in structural design of hyperbolic cooling tower (HCT) shell due to the complicate internal force distributions and arbitrary direction of wind load. The internal forces of a representative HCT under different loads, including gravity, wind, thermal actions of winter and summer, horizontal and vertical earthquakes with reasonable load values, were illustrated individually and compared systematically. It was found that all the internal forces follow uniform or simple latitude distribution except the wind effects and, therefore, the structural reinforcement design is an easy process when wind load is excluded. However, the participation of wind load make it unpredictable where the most unfavorable internal force condition locates in latitude direction. It is even inevitable that many wind directions must be involved to combine with other loads in reinforcement design calculation. In this study, a virtual uniform distribution is proposed to replace the actual irregular distribution of wind effects, and then, the design calculation procedure is simplified greatly because the multiple wind direction involvement and calculation on the whole latitude shell are both avoided. Meanwhile, the incensement of reinforcement amount got from the simplified procedure is about only 2% and the distribution is more reasonable.

In this study, with the help of the three-degree-of-freedom random forced vibration device developed independently by Tongji University, high-precision measurement of bridge aerodynamic force under large torsional amplitude was realized, and a potential energy spectrum was established in consideration of the energy evolution and amplitude effect that varies with reduced velocity. As a result, a new research strategy for nonlinear flutter of bridge girders is proposed. Taking the Old Tacoma Narrows Bridge as an example, the mechanism of nonlinear vibration phenomena at post-flutter state was analyzed, and the wind-induced instability path of the bridge and its potential development path were deduced. The results show that flutter response can be divided into two components according to the energy spectrum. One component is related to the aerodynamic effect, and the other component is related to the mechanical damping ratio effect, which is helpful for studying the relationships between the mechanical damping ratio and bifurcation phenomena of bridge flutter. At the collapse of the Old Tacoma Narrows Bridge, both the aerodynamic nonlinearity and variations of the mechanical damping ratio with vibration amplitude have important contributions to the post-flutter behavior of the bridge in terms of energy effects. Variations of the mechanical damping ratio in torsion with amplitude greatly improve the flutter performance of the bridge. Thus, the development path of the structural displacement response depends on the competitive relationships among the structural torsional damping ratio, structural rigidity, and oncoming wind velocity.

Buffeting’s importance is highlighted in the case of super-long bridges. It remains unclear how buffeting will perform and whether the traditional methods still apply when bridge’s span is approaching its upper limitation. To figure out this, a full aeroelastic model testing has been carried out with the span arrangement 2000+5000+2000 m. A comparison with the existing bridges reveals the similarities and differences. It shows vertical and torsional buffetings are important for a 5000 m bridge while lateral response is almost static. Fundamental modes contribute most kinetic energy. With the increasing of wind speed, the aerodynamic coupling effect becomes prominent while the structural coupling effect keeps limited. Afterwards, four analytical methods, namely SRSS and CQC, with and without self-induced forces, are used for the buffeting displacements. The calculation indicates the multi-mode (CQC) analysis is still applicable on a 5000 m bridge but the mode-by-mode (SRSS) method is risky since the neglection of aerodynamic coupling effect. Parameter analysis shows aerodynamic admittance function and force coherence are decisive while the cross terms are of secondary importance. Since all data is experimentally measured, the reliability of analytical results can be ensured.

The nonlinear vortex-induced vibration of a rectangular section with an aspect ratio B/D = 6 is investigated in this study, aiming at explanation of the phenomenon of double lock-in ranges. First, numerical results by two-dimensional CFD simulation are compared with experimental results; then flow field characteristics, aerodynamic loadings and structural motion properties are presented and discussed; finally, an energy-trapping-based model for motion stability is brought forward, based on which the observed aeroelastic phenomena are discussed. The present study shows the motion-induced lock-in range is able to be explained qualitatively with the proposed principle describing the free-oscillation stability. Within the motion-induced lock-in range, the 1-DOF system can experience two motion components. The dominance of the free vibration fueled by feedback lift can dwarf or even eliminate the vortex-shedding-induced motion. Further, it is demonstrated that the phase angle between the lift and motion velocity, instead of the load amplitude, dominates the motion stability.

This paper reviews the development of forced motion apparatuses (FMAs) and their applications in wind engineering. A kind of FMA has been developed to investigate nonlinear and nonstationary aerodynamic forces considering the coupled effects of multiple degrees of freedom (DOFs). This apparatus can make section models to vibrate in a prescribed displacement defined by a numerical signal in time domain, including stationary and nonstationary movements with time-variant amplitudes and frequencies and even stochastic displacements. A series of validation tests show that the apparatus can re-illustrate various motions with enough precision in 3D coupled states of two linear displacements and one torsional displacement. To meet the requirement of aerodynamic modeling, the flutter derivatives of a box girder section are identified, verifying its accuracy and feasibility by comparing with previously reported results. By simulating the nonstationary vibration with time-variant amplitude, the phenomena of frequency multiplication and memory effects are examined. In addition to studying the aerodynamics of a bluff body under large amplitudes and nonstationary vibrations, some potential applications of the proposed FMA are discussed in vehicle-bridge-wind dynamic analysis, pile-soil interaction, and line-tower coupled vibration aerodynamics in structural engineering.

A framework was proposed to identify a comprehensive set of aerodynamic admittance functions for bridge decks. The contributions of the cross-spectra between longitudinal and vertical wind velocity components and between turbulence components and gust-induced forces were embedded in the identification procedure. To facilitate application of the identified functions in engineering practice, the concept of an equivalent aerodynamic admittance function was introduced and numerically validated. The equivalent aerodynamic admittance functions of a set of streamlined and bluff cross sections were identified experimentally in a wind tunnel. Buffeting analysis of a bridge deck was carried out and the response predicted using the identified aerodynamic admittance functions compared well with the measured response. In addition, a sensitivity analysis was performed to delineate the influence of aerodynamic and structural parameters on the buffeting response, thereby demonstrating the significance of the proposed identification framework.

Over recent years there has been considerable development in bridge engineering. Thirty-two bridge projects have received IABSE Outstanding Structure Awards during the past two decades in recognition of the most remarkable, innovative, creative, or otherwise stimulating structures. Several creative structural forms have been created such as two twin-box girder suspension bridges, three spatial main cable suspension bridges, six multi-main-span cable-supported bridges and one cable-stayed and suspension hybrid bridge. Various innovative material combinations have been developed and used in two steel truss and PC flange composite girder bridges, one butterfly web extradosed bridge, one multiple material strength bridge and one long-life concrete cable-stayed bridge. Some remarkable functional technologies have been invented for two remarkable movable bridges, two innovative cable-stayed bridges, two extreme seismic function cable-supported bridges and two environmental coordination bridges. Many stimulating bridge projects have been awarded as Winners or Finalists including three extradosed bridges, four arch bridges, two cable-stayed bridges and four sea-crossing bridges. The innovation and creation of recent bridge engineering has been recognised by IABSE Outstanding Structure Award reflecting the creative structural forms, the innovative material combinations, the remarkable functional technologies and the stimulating bridge projects.

The long-span bridges in coastal region of China exposed to the challenge of typhoon-induced flutter instability with the continuous increase the span length and flexibility of bridges. A Monte- Carlo-technique-based framework to analyse the flutter fragility long-span bridges subjected to typhoon winds is developed. A 3D typhoon boundary layer wind field model and a geographically- weighted-regression (GWR) -based stochastic track model are proposed to generate a large quantity of synthetic tracks around the bridge site before achieving the typhoon wind hazard curves at the height of the bridge deck. The flutter critical wind speed of the bridge is derived accounting for the structural modal and damping randomness as well as experiment-induced errors of aeroelastic flutter derivatives. The typhoon-induced flutter failure probabilities of the bridge are then predicted and compared with code-suggested target reliability indices.

A bridge wind resistance database has been built based on the wind tunnel testing results of 20 long-span bridges. The artificial intelligence models for identifying aerostatic coefficients and flutter derivatives of close box girders are trained and developed via machine learning methods, including error back propagation neural network based on Levenberg-Marquardt algorithm and gradient boosting decision tree. The identification of the aerostatic coefficients can be achieved with high accuracy. For flutter derivatives, the model can also explore the underlying distribution of dataset. In this way, the present research work can make the identification of aerodynamic parameters separated from tedious wind tunnel test and complex numerical simulation to some extent. It can also provide a convenient and feasible option for expanding data sets of aerodynamic parameters. In addition, it can help determine the appropriate shape of the box girder cross-section in preliminary design stage of long-span bridge and provide the necessary reference for the aerodynamic shape optimization by modifying local geometric features of the cross-section to evaluate the influence of the aerodynamic shape on flutter performance.

The cosine function and two modulation functions are separately selected to generate the time- varying mean wind and fluctuating wind speed, and their effects on nonlinear buffeting responses of a super long-span suspension bridge were investigated in this paper. Firstly, two non-stationary wind speeds models were validated by the classical power spectrum density, and could effectively simulate the non-stationary characteristics. Secondly, the time histories and RMS values of three displacement responses of the bridge deck under two non-stationary wind speeds with three different values of 𝛾𝛾 and 𝜃𝜃 were compared, respectively. Results show that the torsional and lateral displacement responses under the non-uniform modulation function are larger than those under the uniform modulation function. Moreover, the RMS values in three displacement responses of the deck gradually become larger with the increase of 𝛾𝛾 or the decrease of 𝜃𝜃.

The vector form intrinsic finite (VFIFE) method is a new and promising structural analysis technique that has many advantages as compared with the conventional finite element method (FEM) in analyzing the complex behaviors of a structure. However, despite the popularization of its application in civil and infrastructure engineering, there is no available unified general analysis framework for it, which limits the applications and developments of VFIFE. This work develops and implements a platform (termed openVFIFE) based on a new proposed object-oriented framework to facilitate the development and application of the vector form intrinsic finite method as well as the efficient and accurate analyses of complex behaviors for civil structures. To validate the platform, a series of numerical examples are conducted. Furthermore, to extend the applications of VFIFE, the nonlinear dynamic and collapse processes of a transmission tower under earthquake load are studied using openVFIFE. The results of these numerical examples simulated by the developed truss or beam elements are consistent with theoretical solutions, previous research or conventional finite element models. The failure modes of the transmission tower under earthquake load simulated by the platform is consistent with those observed in real cases. In addition, the results of nonlinear dynamic analyses of the transmission tower show that the computational efficiency of the proposed platform is 6-10 times higher than that of the conventional finite element method. The results provide sufficient evidence to prove the accuracy and efficiency of the proposed platform in the static, dynamic and elastoplastic analyses of truss and frame structures, especially in the structure analysis characterized by strong geometry nonlinearity. It is noteworthy that in addition to the link and beam elements, further work is undergoing on implementing more elements, such as shell and solid elements. The openVFIFE also allows researchers who are interested in this topic to put their creative ideas into this platform and continuously improve the completeness and applicability of the VFIFE method.