In recent years, many bridge collapse accidents have been attributed to the passage of extra heavy trucks (EHTs, gross weight $\ge 80\mathrm{t}$ ) in numerous countries. Compared with the standard traffic loads in design specifications, the actual characteristics of EHTs are very difficult to predict because they may be specific to the management, charge policy, or other properties of the route. In a previous publication, the authors researched the characteristics and dynamic impact of EHTs on Chinese expressways. In the current study, long-term traffic monitoring data were statistically analyzed to identify the key characteristics of EHTs on Chinese first-class highways. Based on the EHT scenarios extracted from the weigh-in-motion (WIM) data, which can be used to record the traffic information of moving vehicles, a comprehensive simulation analysis was conducted by an in-house advanced dynamic bridge–traffic interaction model on five typical simply supported T-beam bridges. The bridge response and dynamic impact factors (DIFs) of EHTs were numerically investigated, and reasonable expressions for calculating the DIFs were proposed. Finally, the load effect calibration under EHTs was performed when the road surface condition was average. These findings can be used as additional references for bridge codes and safety assessment by practicing engineers.

Damage detection of highway bridges is a significant part of structural heath monitoring. Conventional accelerometers or strain gauges utilized for damage detection have many shortcomings, especially their monitoring gauge length being too short, which would result in poor damage detection results. Under this circumstance, long-gauge FBG sensors as a novel optical sensor were developed to measure the macro-strain response of the structure. Based on this sensor, many derived damage detection methods were proposed. These methods exhibit various characteristics and have not been systematically compared. As a result, it is difficult to evaluate the state of the art and also leads to confusion for users to select. Therefore, a strict comparative study on three representative methods using long-gauge FBG was carried out. First, these methods’ theoretical backgrounds and formats were reformulated and unified for better comparison. Then, based on validated vehicle–bridge coupling simulation, these methods’ performances were tested through a series of parametric studies including various damage scenarios, vehicle types, speeds, road roughness and noise levels. The precision and reliability of three methods have been thoroughly studied and compared.

Recently, the occurrence frequency of extra-heavy trucks (EHTs, gross weight $\ge 80\mathrm{t}$ ) in China has significantly arisen due to the increasing demand of heavy freight transportation. Load characteristics, such as traveling speed, axle weight, and axle distance, of EHTs are different from those of normal traffic loads and vary by region. In the present study, the site-specific load characteristics of EHTs are analyzed based on weigh-in-motion (WIM) data measured from two typical routes of China. Then, the EHT load cases are extracted and a bridge–vehicle simulation is conducted. Finally, the bending capacities of small- to medium-span bridges are assessed. It is found that more attention should be paid to the site-specific load characteristics of EHTs because they are significantly different among different routes. The focused small- to medium-span bridges under EHT load can satisfy the safety requirements and the safety reserves of the bending capacity of such bridges on Chinese highway, which are higher than those of Chinese expressways under EHT load.

This article presents a new method for structure assessment based on weigh-in-motion data and simulation analysis. The focus is particularly on the simply supported hollow slab bridges and extra-heavy truck (gross truck weight ≥ 80 t) from the right tail of weigh-in-motion data. The dynamic models of truck types are refined, and the coupling relationship between truck and multi-girder bridge are determined. A self-developed bridge–truck analysis system is established by separate iteration and is used in the simulation analysis of extra-heavy truck load cases. The truck load effect is first analyzed by a comparison with code values. The load rating index is introduced for the structure safety assessment; meanwhile, the key parameters, for example, the dynamic amplification factor, are optimized. The results show that the maximum load effect level of extra-heavy truck is obviously higher than the design vehicle load effect, and the average level is approximate to or a little higher than the latter. The displacements due to extra-heavy truck are seriously transfinite, while the structural stiffness can meet the requirement of serviceability. Both the proposed method and Chinese code method are used to assess the structure safety of hollow slab bridges. The maximum value of load rating index ranges from 0.69 to 0.78 and the average value is 0.53–0.67. The hollow slab bridges have not yet reached the ultimate limit state and have a safety redundancy under the extra-heavy truck load. The loading indices of MOCAT are close to the average values of load index of this study, but lower than those of the maximum values. Some extreme loading conditions may be thoughtless in the proposed safety assessment method by MOCAT.

An empirical modeling of nonlinear aerodynamic force during aeroelastic instabilities, that is, vortex-induced vibration (VIV), galloping and flutter, is necessary in the estimation of vibration responses. Previous works on single-degree-of-freedom (SDOF) models suggest that nonlinear forms (Van der Pol or Rayleigh types) differ from section to section, which causes difficulty in practical application. Analytical evidences in this study have clarified that Van der Pol-type and Rayleigh-type models are equivalent in the amplitude-dependent aerodynamic damping; their difference lies in the higher-order harmonic responses. An identification algorithm of aerodynamic parameters is proposed to improve the robustness of aerodynamic parameters and guarantee the equivalence of both model types. Wind-tunnel tests of typical aeroelastic instabilities indicate that higher-order harmonic responses are small for VIV, galloping, and early-stage flutter instability when compared with the fundamental components due to weak nonlinearity. Van der Pol-type and Rayleigh-type models are both applicable until the flutter amplitude grows excessively large. It is clear that both model types are suitable for any section shape when use the proposed method of aerodynamic identification, and thus can be treated as a universal model for estimating the vibration amplitudes of nonlinear aeroelastic instabilities.

Customized transport vehicles (CTVs) are usually required to travel along the bridge centerline at low speed. However, emergency situations might occur on the bridge during the passing of a CTV and result in partial closure of the traffic lane. To investigate whether the CTV could pass over multigirder bridges in a manner of lateral eccentric load, five critical CTVs were extracted from long-term recorded data, and the dynamic simulation analysis of 360 different CTV load cases was accomplished. Bending bearing safety assessments of small-to-medium-span multigirder bridges under lateral eccentric CTV loads were conducted and the applicability of specified axle weight limits analyzed by using a load rating method, in which the partial factor of CTV load effect is optimized considering the balance between failure cost and benefit. The results show that when the lateral eccentric distance is not greater than 2.5 m, all safety indices are lower than 0.879 and the bending bearing capacities of multigirder bridges are deemed to meet safety requirements. The safety indices of bridges under fully loaded critical CTVs are lower than 0.977, and the specified CTV axle weight limits are applicable when the lateral eccentric distance reaches 2.5 m. To prevent the structure from entering the plastic stage, the lateral eccentric distances of C-IV and C-V, which denote the fourth and fifth vehicle type, are suggested to be less than 2.0 m when they pass over prestressed T-beam bridges.