This paper proposes a site-specific traffic load model for long-span multi-pylon cable-stayed bridge. Structural effects are primarily investigated based on influence lines, which are identified as either global effect (GE) or partial effect (PE) depending on the effective influenced region. GEs are further categorised as sensitive effect (SE), insensitive effect (ISE) or less sensitive effect (LSE), considering sensitivity to unbalanced traffic loading. Three on-bridge traffic states are simulated, and Weibull extrapolations are utilised to predict the extreme responses. These responses are analysed and compared with several design codes. Results indicate the maximum response is only 75% of the value calculated based on the design code of China (D60), and even lower than other codes. The responses show strong positive correlation with traffic parameters of annual average daily traffic volume and heavy vehicle proportion, and the on-bridge traffic states have significant influence on the responses. Further, the identified effects of ISE, SE and LSE present different responses, which indicate specific load models are needed accordingly. Finally, a site-specific traffic load model consisting of load form, loading pattern, multi-lane factor and load value is recommended, which gives an accurate illustration on the structural effects and traffic responses.

Traffic micro-simulation is the newly developed approach for loading calculation of long span bridges. The approach is quite precise, but computationally expensive to consider the full extent of traffic loading scenarios during a bridge lifetime. To address this shortfall, an efficient multi-scale traffic modelling approach is proposed. The proposed approach uses micro- and macro-simulation with different load model varieties (LMVs), or fidelities (levels of detail) of traffic loading in different bridge regions, to achieve optimal computation efficiency while maintaining the precision of loading calculation. Metrics of influence line (IL) characteristics, such as degree of nonlinearity, are proposed to evaluate the appropriateness of the choice of LMV, and standards of the metrics are also investigated to quantify the implementation of LMVs on bridge IL regions in the multi-scale modelling. Finally, two typical ILs are used along with random traffic modelling to study the feasibility of the proposed approach. It is shown that the multi-scale modelling approach proposed here achieves high computational efficiency and accuracy, which is significant for the massive traffic load simulation for lifetime bridge load effect analysis.

The antisliding safety of the middle saddle is a key issue for the design of three-pylon suspension bridges. Vehicle load is the main adverse effect, especially unsymmetrical vehicle load. A general mechanical model on the saddle sliding behavior is reviewed and proposed, and then characteristics of load responses of the main cable are investigated to explore a simplified live load computational method. Based on the deterministic approach from codes and a reliability-based approach, the antisliding safety of the middle saddle is discussed and assessed for the Taizhou Yangtze River Bridge, which has two symmetrical spans of 1,080 m. The study shows that geometric nonlinearity caused by dead load has a big effect on the load responses of the main cable, so it must be included in the design. Further, the maximum difference between the geometrically linear and nonlinear cases due to live load is up to 12.71%, whereas in all conditions, the balanced static friction coefficient is smaller without consid...

Several bridges now require widening owing to the continuous development of road transport. However, the standard of traffic load in design specifications has been enhanced. Consequently, old bridges may not meet the safety requirements of current design specifications and, therefore, must be reconstructed or retrofitted. However, the old structures in widened bridges carry fast-lane traffic loads, which are relatively low due to uneven multilane traffic loads. This paper reports a case study conducted on a Chinese highway widening project for comprehensively evaluating the structural safety of multislab widened bridges using code-based deterministic and reliability-based probabilistic approaches. In the deterministic evaluation, previous and current Chinese bridge designs and other national codes were employed. Meanwhile, in the probabilistic assessment, an uneven multilane truckload modeling was implemented based on site-specific traffic data. Subsequently, bridge safety under normal traffic conditions with all lanes open and occasional traffic conditions with lane closure was investigated. The results indicate that most old slabs, especially those closer to medial dividers, are unsafe under the current Chinese design specifications. However, a site-specific assessment under normal traffic conditions indicates that these old slabs possess adequate security reserves, except that the side slab close to the junction requires safety. Further analyses conducted with occasional traffic conditions demonstrated that closing fast lanes does not affect the safety of slabs. Conversely, closing slow lanes significantly affects the safety of inner old slabs, which should be prohibited or addressed with strict weight restrictions. These results can be beneficial for future bridge widening projects.