The data of 302 highway bridge catastrophic collapses occurring in China between 2000 and 2014 due to human causes were collected and statistical analyses were conducted from various viewpoints including accident stages (during construction or service), casualties (death or injury), location, time, life span, bridge type, and primary causes behind the accidents. Six representative collapse cases were expounded on to find out their individual peculiarities. These cases encapsulated serious problems in Chinese highway bridge engineering, including design, construction, maintenance, and management, among others. A concise review of highway bridge collapses due to human causes in China was presented. Some typical abnormal phenomena, such as those concerning entities involved in the Chinese highway bridge engineering industry, were analyzed and highlighted. Suggestions were put forward to urge all related parties to obey rules and laws to reduce and avoid bridge collapse accidents. The lessons from the...

The nonlinear flutter featured by the limit cycle oscillation (LCO) is a typical aeroelastic phenomenon for bluff decks and/or streamlined decks at large incidence angles. In this study, the flutter characteristics of a streamlined deck were investigated by using comprehensive wind-tunnel tests, and a nonlinear mathematical model was introduced to model the aeroelastic behavior of the nonlinear torsional flutter oscillation. The nonlinear aerodynamic force is the major source of the nonlinear flutter. The nonlinear flutter LCO corresponds to a state in which the energy absorbed by the linear damping and the energy dissipated by the nonlinear damping are balanced within an oscillation period. On the basis of the instantaneous amplitude and instantaneous frequency calculated by using the normalized Hilbert transform, a system identification method was developed to simultaneously extract the linear and nonlinear aerodynamic parameters. The efficacy of the nonlinear mathematical model and the identification accuracy of aerodynamic parameters were validated by two examples. The sensitivities of aerodynamic parameters to the signal length were studied, and the corresponding causes were revealed. The linear aerodynamic damping parameter and structural damping ratio are the dominant parameters for determining the critical flutter wind speed. For the nonlinear torsional flutter, a practical approach was proposed to predict the critical reduced wind speeds and the LCO amplitudes with different structural damping ratios, and its accuracy was verified by comparing the experimental results.

Because of the significant position of long-span cable-supported bridges in land transportation, the typhoon wind effects on these slender structures attract intensive attention in engineering communities. This paper presents a study about the wind effects on a kilometer-level cable-stayed bridge during Typhoon Haikui. The Sutong Cable-Stayed Bridge (SCB) with a main span of 1,088 m is taken as the research object and the structural health monitoring system (SHMS) works as a medium to provide valuable full-scale measured data. The wind characteristics, e.g., turbulence intensity, gust factor, turbulence integral scale, and power spectral density (PSD), of the severe typhoon are firstly analyzed in a statistical point of view. Specifically, the variation of turbulence PSDs in different stages is described and compared among cases at different altitudes. Then, the dynamic properties of the structure are identified with the random decrement technique, and the amplitude-dependent features are discussed. Moreover, the relationship between structural dynamic responses and the wind velocity is analyzed with a comparison to the results from the wind tunnel test. Since a significant variability is captured in structural buffeting responses, the response surface methodology (RSM) is employed to investigate influential variables in a statistical framework, which is further utilized to predict the wind-induced dynamic responses considering the variability. The observations and findings are expected to provide references for the wind-resistant analysis and design of super-long-span cable-stayed bridges.

With the specific objective of exploring the surface pressure characteristics and further revealing the torsional vortex-induced vibration (VIV) mechanisms of a bridge deck with a particular geometry, numerous simultaneous pressure measurement campaigns were performed in a wind tunnel for aerodynamic-countermeasure–modified and unmodified sections of a section model at different angles of incidence under the conditions of smooth or turbulent flow. The mean and fluctuating pressure distributions, instantaneous pressures at typical instants, dominant pressure frequencies, pressure phase differences at the dominant frequency of individual pressure measurement taps, and the correlation coefficients among local and global torsional moments were studied, revealing the origins and mechanisms of torsional VIVs. The results demonstrate that the angle of incidence, flow conditions (smooth or turbulent), and installation of a spoiler exert significant effects on the surface pressure distributions, hence affe...

The mechanical stiffness and damping coefficients of a spring-suspended deck section model in still air are conventionally assumed to be constants and can be extracted through free decay vibrations. The extracted stiffness and damping coefficients, indeed, include both mechanical and aerodynamic components. In this study, the vertical and torsional single-degree-of-freedom (SDOF) free decay vibration tests of two typical bridge deck section models were carried out in still air to study the nonlinear vibration characteristics of the sections. SDOF motion equations of the section models were developed on the basis of the equivalent linearization theory. A system identification procedure was developed to extract the amplitude-dependent frequency and damping ratio from the measured acceleration responses. The efficacy of the equivalent linearization and the identification accuracies of the mechanical and aerodynamic parameters were verified by an example. The mechanical parameters (stiffness and damping ratio) and aerodynamic parameters [added mass (or moment of inertia), and damping ratio] of the spring-suspended systems were extracted separately. The aerodynamic damping was found to be the major damping source for the spring-suspended system. The influences of the initial condition, mass (or moment of inertia), vibration frequency, and amplitude on the mechanical and aerodynamic parameters and nonlinearities were thoroughly investigated. The aerodynamic parameters were more sensitive to the vibration amplitude than were the mechanical parameters. The conclusions advance a better understanding of the nonlinear vibration characteristics of bridge deck section models in still air.