The steel-box girder with large cantilevers (named here as a cantilever steel-box girder), an innovative girder of a cable-stayed bridge, offers a unique solution by accommodating both highway and railway on the same deck. The width of the innovative girder is large, with the cantilever part constituting a significant portion of the entire cross section. The lateral-vertical deflection resulting from this large cantilever could not be ignored. Predicting the lateral-vertical deflection of the girder is crucial in ensuring the serviceability requirement during the operation. To address this issue, this study conducted a 1∶4.5 scale model test of the cantilever steel-box girder. The lateral-vertical deflection of the girder under the action of the vehicle and train load was investigated based on the model test. Furthermore, based on the lateral-vertical deflection patterns of the girder obtained by the model test, a simplified analysis model was developed to analyze the lateral-vertical deflection of the cantilever steel-box girder. The rationality of the simplified analysis model was validated by comparing it with the results of the model test. Moreover, the calculation technique for assessing the lateral-vertical deflection was derived based on the simplified analysis model. The calculation technique was categorized into three different situations in terms of the different positions of the live load. Finally, a parametric study was performed to understand the impact of the structural parameters on the lateral-vertical deflection of the girder using the calculation technique. The findings of this study could serve as a reference in the design of cantilever steel-box girders for cable-stayed bridges.

Interfacial bond properties between cast-in-place UHPC and NC for composite girder bridges: Experiments, analysis, and calculation methods

In this work, the deformation behavior of a long-span steel–concrete composite girder cable-stayed bridge under temperature loads and its subsequent impact on ballastless track systems were investigated. An integrated finite element model (FEM) of the bridge–track system was developed by taking the Taiziping Wujiang River Bridge (with a main span of 300 m) in Chongqing, China, as a case study. The model incorporates composite girders, pylons, stay cables, rails, and double-block slab tracks. Then, the integrated FEM systematically analyzed structural responses to various temperature loading scenario, namely uniform temperature change, differential temperatures among key components (girder, deck, pylons, and cables), and deck–girder temperature difference. The results show that the girder’s maximum vertical displacement linearly correlates with the temperature variations of the composite girder, upper pylon, and cables, with corresponding temperature sensitivity coefficients of 2.3 mm/°C, 2.78 mm/°C, and −5.8 mm/°C. While the ballastless track coordinates well with the composite girder in vertical deformation, the maximum longitudinal relative displacement occurs between rail and track at the ends of the bridge. Moreover, field monitoring data were used to establish a high-precision relationship between ambient temperature and structural temperatures of key components, enabling successful prediction of girder’s vertical deformation. The findings provide a theoretical basis for the control of thermal deformation during the operation and maintenance of similar long-span composite girder cable-stayed bridges.

Determining rational seismic systems for small- and medium-span girder bridges is a critical step in bridge seismic design. However, limited research has been conducted on the selection of seismic isolation systems, the definition of damage control objectives, and the formulation of associated design indicators. To support the selection of rational seismic systems, a comprehensive database of regional bridge structures along the Wenchuan–Barkam Highway in China was established. Leveraging this dataset, parametric OpenSees modelling, validated experimentally, and nonlinear time-history analyses were performed on numerous bridge samples to build an accurate probabilistic seismic demand surrogate model. This model employs machine learning algorithms to integrate multiple bridge design parameters and ground motion uncertainties. Furthermore, a systematic seismic system selection framework was developed based on fragility analysis, and its effectiveness was subsequently validated using prototype bridges. The findings indicate that an optimal seismic system selection approach should prioritise two primary limit-state objectives: ensuring rational seismic system design and controlling repairable earthquake-induced damage. Data-driven probabilistic seismic demand models and fragility assessments based on interpretability analysis were used to develop a rational seismic system selection procedure suitable for this type of bridge. This study proposes a data-driven, interpretable approach for seismic system determination, enhancing design efficiency.

Seismic performance of simply supported hot rolled shape steel–UHPC composite girder bridges under near-fault ground motions

Seismic fragility assessment of curved girder bridges under vehicle-induced risks: A specialized deep learning-based neural network approach

Life-cycle fragility analysis of near-fault simply supported and T-shaped girder bridges considering corrosion of piers

Prediction of flutter derivatives for closed-box bridge girder: A feature-fusion residual neural network algorithm

Inspection and capacity prediction of corroded steel bridge girders through 3D scanning, contour mapping, and experimental testing

3D point cloud skeleton-based method for bridge girder virtual trial assembly

The proposed model integrates four conflicting objectives—minimizing project duration, cost, energy consumption, and risk—into a unified decision-making platform. The Multi-Objective Teaching-Learning-Based Optimization (MOTLBO) algorithm is employed due to its superior convergence, solution diversity, and low parameter dependence. A real-world case study of a reinforced concrete girder bridge is used to validate the model, demonstrating its capability to generate 18 Paretooptimal solutions across varied execution modes.

With the increasing demand for highway transportation, the structural integrity of ageing bridges has become a critical concern. Transverse steel connections (TSCs) offer distinct advantages in economic efficiency and rapid construction. This study introduced a novel H-shaped TSC and proposed arrangement improvements to reduce costs. A field loading test on a four-span continuous multi-box girder bridge showed that the H-shaped TSC increased vertical bending frequency by 16.2% and reduced peak girder deflection by 5.7%. A finite element (FE) model, built in ABAQUS and validated by test results, was used for parametric analyses. Results indicated that structural form and vertical height had negligible effects, while steel consumption was the dominant factor; efficiency dropped significantly when the cross-sectional area fell below 12.5%. A systematic TSC design methodology was developed and validated, providing a practical framework for optimising arrangement and configuration. These findings offer recommendations for reinforcing multi-box girder bridges.

Prestressed concrete (PC) girder bridges are essential in modern bridge engineering. Traditional design methods are time-consuming and labour-intensive, often failing to produce economically or structurally superior schemes. Optimisation techniques automate the design process, enabling optimal designs. However, challenges remain, including limited optimisation research on long-span girder bridges, high computational intensity of finite element analyses (FEAs) during optimisation, a tendency to get trapped in local optima, insufficient attention to structural performance, and a lack of interpretability for optimal designs. In this paper, a hybrid-heuristic machine learning-based framework is proposed, applied innovatively to the optimisation of long-span PC girder bridges. The framework incorporates optimisation objectives focused on cost and stress indicators. Within this framework, a support vector regression (SVR) model replaces traditional FEA, enhancing optimisation efficiency. Additionally, a hybrid-heuristic algorithm, combining simulated annealing and particle swarm optimisation (SA-PSO), is incorporated for the global optimum. The shapley additive explanations (SHAP) approach is integrated to clarify relationships between the objective and variables, providing interpretability for the optimal design. This framework is validated on a PC rigid-frame bridge. Results indicate it rapidly achieves optimisation, balancing structural performance and economic efficiency with strong interpretability. Furthermore, the framework demonstrates potential for future research and engineering practice beyond bridges.

— Steel Box Girder (SBG) bridges represent a widely used structural solution for both straight and curved bridges of moderate spans, owing to their high torsional rigidity, significant bending resistance, and rapid construction characteristics. This study provides a comprehensive theoretical comparison of the preliminary proportion limits, shear resistance design strength, and flexural resistance design strength in both positive (sagging) and negative (hogging) moment regions of SBG bridges. The comparison encompasses major bridge design specifications (BDS), including those of the American Association of State Highway and Transportation Officials (AASHTO), the Egyptian Code of Practice (ECP 207 – Part 6), and the European Standard Eurocode 3 (EC-3). The objective of this work is to develop a clear understanding of the design provisions, highlighting both similarities and differences among these internationally recognized standards. By analyzing the design criteria adopted in each code, the study aims to enhance familiarity with their respective requirements and ensure that the highest possible levels of structural efficiency and safety are achieved in the design of steel box girder bridges.

To address issues such as web and bottom plate cracking and insufficient bending capacity in in-service prestressed concrete box girder bridges, this study proposes internal prestressing and section enlargement composite reinforcement. Firstly, taking a bridge of Shenhai Expressway as the background project, the combined reinforcement method is designed and the reinforcement effect is analyzed by MIDAS/Civil. Secondly, through numerical analysis, the influence of the bond shrinkage of self-compacting concrete with different mix ratios on the stress of the web of the original box girder is analyzed, and the interface between the new and old concrete is carried out. The analysis of the loss of the new prestress on the bonding surface of the new and old concrete is carried out by parameters such as the interface planting rate, the interface shear stiffness and the reinforcement structure. Furthermore, the theoretical calculation method of prestress loss rate of new and old concrete bonding interface is obtained. The results show that the flexural capacity of the normal section of the main beam is significantly improved after reinforcement, and the surplus coefficient is 1.18, which meets the requirements of the secondary safety level, and the mid-span deflection is improved by 34.28%, which verifies the effectiveness and feasibility of the combined reinforcement method. When the content of fly ash is 54%, the bond shrinkage strain and shrinkage stress of self-compacting concrete are reduced to the lowest level, which has the least influence on the existing box girder structure. It is suggested that the reinforcement ratio between the new and old concrete interface is 0.6%, and the interface roughness is 0.9 mm, which can increase the shear resistance of the new and old concrete interface and effectively reduce the transfer loss of prestress at the interface. Error analysis shows that the proposed semi-empirical calculation method has high accuracy with a deviation of less than 10%.

Prestressing is critical in prestressed concrete (PC) bridges, where improper design not only wastes material but may ultimately compromise serviceability or even cause structural collapse. Traditional design methods, often cumbersome and code-oriented, typically yield suboptimal solutions. While existing optimization studies mainly target cost minimization, they exhibit several limitations. These include insufficient attention to structural stress performance, resulting in suboptimal mechanical behavior, as well as a lack of research on long-span girder bridges, which involve inherent complexities in both structural behavior and construction processes. Moreover, applications of multi-objective evolutionary algorithms (MOEAs) remain scarce in bridge optimization. To address these gaps, this paper innovatively proposes a multi-objective prestressing optimization method for long-span PC girder bridges, simultaneously considering cost and stress performance. Focusing on long-span continuous girder bridges, the method aims to minimize tendon usage while achieving uniform distribution of stress safety degree. Constraints incorporate code-specified stress and configuration requirements. The Non-dominated Sorting Genetic Algorithm II (NSGA-II) is employed to handle multi-objective, discontinuous, and nonlinear optimization challenges. The proposed method is applied to an actual bridge, demonstrating its feasibility and effectiveness. Additionally, comparison with a single-objective optimization confirms that the proposed method provides a more balanced and effective scheme.

To facilitate accelerated bridge construction and reduce the cost of bridge design and construction, a cold-formed steel composite bridge girder has been suggested recently as an economical alternative. The new technology for the composite bridge girder includes a cold-formed steel plate and either a precast or cast-in-place reinforced concrete (RC) slab. Previous research on cold-formed steel concrete composite girders has introduced two new shapes for short-span bridge girders: a cold-formed steel tub girder and a folded plate girder system. No study has been conducted on the impact of shape on the static structural behavior of cold-formed composite girders for short-span bridges. This paper investigated the behavior of the cold-formed steel composite girders with different shapes in terms of ductility, stiffness, the ultimate failure load, crack resistance, and interfacial slip. Four shapes were carried out in this research: tub, open-box, and double C with and without lips. Six simply supported girder specimens were designed, fabricated, and subjected to static load tests. The results showed that the cold-formed steel double C lipped girder increased the ultimate load by 12.12% compared to the cold-formed steel tub girder. Additionally, the initial stiffness of the cold-formed steel double C girder increased by 21% compared to the cold-formed steel tub girder. The open-box shape specimen can effectively improve the cracking resistance of cold-formed steel composite girders compared to the cold-formed steel tub girders.

Abstract To address key challenges in traditional composite bridges—such as complex mechanics, weak interface bonding, and cracking in negative moment zones—this study investigates a double-deck, double-girder steel-concrete composite continuous curved bridge. Integrating theoretical, numerical, and practical approaches, a collaborative design theory and complete construction technology system are established. Optimization criteria for the upper double-girder-crossbeam system and shear connections are proposed to enhance interface force transfer and achieve stiffness-matched stress redistribution, improving deck collaboration. For crack control in negative moment zones, a two-stage construction-operation control method combined with steel-UHPC reinforcement forms a comprehensive anti-cracking system. A lightweight lower-deck structure and a 3D adjustable suspension system are designed, supported by a 3D (vertical-transverse-longitudinal) vibration control strategy to optimize spatial mechanical performance. Additionally, an innovative integral hoisting technique for prefabricated decks and girders improves construction efficiency and quality control. Validated through a real project, the research provides a technical scheme covering structural selection, cross-section layout, joint design, and construction, significantly improving load-bearing capacity, economy, and buildability. This promotable technology system advances composite bridges toward higher performance and intelligence, offering an innovative solution for complex spatial bridge structures.

Comparison of the seismic fragility of reinforced concrete continuous girder bridges considering near-field and far-field earthquake sequences

In structural health monitoring (SHM) projects, sensor placement is critically linked to the uncertainty of identification outcomes, directly determining the reliability of monitoring results. Although existing studies predominantly focus on the relationship between sensor configurations and uncertainties in modal parameter identification, the influence of actual structural changes on identification uncertainty remains underexplored. This paper proposes an adaptive sensor placement strategy for bridge SHM systems, tailored to accommodate varying structural health states. Leveraging a Bayesian two-stage system identification framework, optimal sensor layouts were independently determined for each phase with distinct objectives and subsequently integrated. During the modal identification stage, optimal sensor positions were selected by minimizing modal parameter uncertainty to ensure robust identification. In the subsequent phase, sensor locations were dynamically adjusted to maximize sensitivity to structural changes through quantification of discrepancies between measured parameters and analytical models. A composite objective function was formulated to harmonize these dual priorities. Numerical simulations on a simply supported beam demonstrate that the proposed sensor arrangement concurrently reduces parameter identification uncertainty and preserves sensitivity to structural variations. Field validation on a 60-m continuous girder bridge confirms the method’s practical efficacy. The strategy is applicable to both aging structures (with localized damage or repair histories) and newly constructed facilities. Notably, when integrated with environmental vibration testing techniques, it enables operational-phase sensor reconfiguration to target emerging damage zones, thereby ensuring sustained SHM system reliability and prioritized monitoring of critical regions during long-term service.