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.

Cables are the main load-bearing components of a cable bridge and typically composed of high strength steel wires with a galvanized coating or Galfan coating. Galfan steel wire has recently started to be widely used because of its better corrosion resistance than galvanized steel wire. The corrosion characteristics of the coating and the difference in the corrosion fatigue process of the two types of steel wire are unclear. To further improve the service performance and maintenance of cable bridges, this study investigated the corrosion characteristics of galvanized steel wire and Galfan steel wire through accelerated corrosion tests and established a time-varying model of uniform corrosion and pitting corrosion of high-strength steel wire. Then, a long-span suspension bridge was taken as the research object, and the corrosion fatigue degradation of the two kinds of steel wire under a traffic load was analyzed on the basis of traffic monitoring data. The results showed that the uniform corrosion of the two types of steel wire conformed to an exponential development trend, the corrosion coefficient of galvanized steel wire conformed to the normal distribution, and the corrosion coefficient of Galfan steel wire conformed to the Cauchy distribution. The maximum pitting coefficient distribution of the two kinds of steel wire conformed to the generalized extreme value distribution. The location parameters and scale parameters of the two distributions showed an exponential downward trend with the increase of corrosion duration. When the traffic intensity was low, the corrosion characteristics of the steel wire was the main factor affecting its service life, and the average service life of Galfan steel wire was significantly higher than that of galvanized steel wire. Under a dense traffic flow, the service life of the steel wire was mainly controlled by the traffic load, and the service life of Galfan steel wire was slightly improved. Effective anti-corrosion measures are a key factor for improving the service life of steel wire.

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.

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.

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.

To increase the authorization efficiency of overloaded customized transport vehicle (CTV), a serviceability limit state (SLS) reliability based permit checking method for concrete bridges is proposed through the optimization towards critical load effect ratio. In this procedure, the SLS reliability of crack width and the SLS reliability of concrete stress in tensile region are analyzed for reinforced concrete (RC) and prestressed concrete (PC) structures, respectively. The durability requirements and a unified reliable level can be concentrated reflected by the optimized critical load effect ratio. The results show that it is unreasonable to take a uniform target reliability index for all routes in permit checking of CTV, a stricter authorization criterion should be adopted for a higher expected authorization frequency. For a specific route level, a fluctuant variation of critical load effect ratio can be found with the increasing of bridge span. By introducing an ultimate limit state (ULS) based safety checking procedure, it is found that the SLS based permit checking criterion is crucial and determinative for the authorization of CTV instead of the ULS.