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The prevention of non-uniform corrosion in steel bridges remains a global challenge. Addressing this gap, the present study investigates atmospheric corrosion in steel bridges and introduces a non-uniform corrosion rate prediction process based on micro-environments, including the temperature and relative humidity of the air near the steel bridge surface (TS and RHS) and the deposition of pollutants on the steel bridge (DP). Using a CFST arch bridge as a case study, this research examines the causes of non-uniform corrosion and explores effective protective measures. The findings reveal a maximum of 1.48 °C for the TS and 15.7% for the RHs in different parts of the arch ribs. Significant disparities of the DP are observed in different parts of the arch ribs. The largest DP at the upper chord is up to 44.3 mg/m2/day (mdd), and the smallest amount of deposition at the lower chord is close to 0 mdd. Under the influence of the aforementioned factors, significant non-uniform corrosion of the ribs was found, with the fastest corrosion rate being up to 18.5 μm/year and the slowest corrosion rate being close to 0 μm/year. Uneven pollutant deposition is the primary cause of the non-uniform corrosion of the CFST arch bridge. By conducting the regular cleaning of the ribs, non-uniform corrosion could be mitigated. [ABSTRACT FROM AUTHOR]

To investigate the controllability of sensitive cable forces during the construction phase of cable-stayed bridges, a novel optimization method is proposed, based on BP neural networks, which combines Gaussian process prediction with a simulated annealing-optimized particle swarm algorithm to determine the tolerance intervals of construction cable forces. Based on the analysis results of multiple linear regression, the variables for optimization are identified, and a mapping relationship between the sensitive cable forces and displacement values is established using a BP neural network. Subsequently, a Gaussian process model is constructed to delineate the relationship between cable forces and reliability, with a focus on the reliability of displacements during the construction phase of the cross-section, specifically targeting sensitive cable forces. Finally, a combination of the simulated annealing algorithm and the particle swarm algorithm is employed to optimize the tolerance intervals of the cable forces. To validate the effectiveness of the proposed optimization method, a case study is conducted on the tolerance interval optimization of cable forces using a three-tower steel box girder cable-stayed bridge. In this study, the construction cable forces are treated as optimization variables, while the reliability of displacements at both the main girder section and the tower's top section serve as the optimization objectives and constraint conditions. Under the premise of ensuring structural reliability, the accurate tolerance range for the stay cable forces during the construction phase of the cable-stayed bridge is obtained. The results indicate that the traditional PSO algorithm stabilizes after 26 iterations, whereas the hybrid intelligent algorithm reaches stability after just 13 iterations. In addition, the hybrid algorithm shows a significant increase in the objective function value during early iterations, demonstrating stronger optimization capability. This indicates that the optimization method exhibits better convergence and superior global optimization capability. It effectively improves the compatibility and controllability of the cable-stayed bridge construction process while simplifying the computational process. [ABSTRACT FROM AUTHOR]

To investigate the reasonable calculation value of the transverse design bending moment of a long-span cantilever box girder bridge deck under vehicle load, the plate beam model and beam element frame model were established according to the concept of load effective distribution width in the Chinese highway specifications. The local finite element model and full bridge model of a long-cantilever plate were established using the plate-shell element. The practical calculation formula and finite element analysis of the transverse bending moment of a bridge deck were studied. The results showed that the transverse bending moment of the long-cantilever plate calculated using Baider Bahkt formula slightly deviated from the calculated value of the plate-shell element, and the deviation between the calculated values of Baider Bahkt formula and Sawko formula was 7.72%. Baider Bahkt formula is more accurate than Sawko formula, which is recommended by the Chinese highway specifications. [ABSTRACT FROM AUTHOR]

To investigate the effect of combined end-and-shaft post-grouting on the vertical load-bearing performance of bridge-bored piles in the Dongting Lake area of Hunan, two post-grouted piles were subjected to bi-directional O-cell and top-down load tests before and after combined end-and-shaft grouting, based on the Wushi to Yiyang Expressway project. A comparative analysis was conducted on the bearing capacity, deformation characteristics, and load transfer behavior of the piles before and after grouting. This study also examined the conversion coefficient γ values of different soil layers obtained from the bi-directional O-cell test for bearing capacity calculations. Additionally, the characteristic values of the end bearing capacity, obtained from the bi-directional O-cell and top-down load tests, were compared with the values calculated using the relevant formulas in the current standards, which validated the accuracy of existing regulations and traditional loading methods. The results indicate that the stress distribution along the pile shaft differed between the two test methods. In the bi-directional O-cell test, the side resistance developed from the end to the head, while in the top-down load test, it developed from the head to the end. After combined post-grouting, the ultimate bearing capacity of the piles significantly increased, with side resistance increasing by up to 81.03% and end resistance by up to 105.66%. The conversion coefficients for the side resistance in silty sand and gravel before and after grouting are 0.86 and 0.80 and 0.81 and 0.69, respectively. The characteristic values of the end bearing capacity, as measured by the bi-directional O-cell and top-down load tests, were substantially higher than those calculated using the current highway bridge and culvert standards, showing increases of 133.63% and 86.15%, respectively. These findings suggest that the current standard formulas are overly conservative. Additionally, the measured values from the top-down load test may underestimate the actual bearing capacity of piles in engineering projects. Therefore, it is recommended that future pile foundation designs incorporate both bi-directional O-cell testing and combined post-grouting techniques to optimize design solutions. [ABSTRACT FROM AUTHOR]

The increasing use of cable-stayed bridges with steel box girders necessitates more sophisticated design approaches, as the diverse environments of bridge locations place higher demands on the design process. Determining a reasonable finished state is a critical aspect of bridge design, yet the current methods are significantly constrained. A new approach to optimizing the finished state is proposed. This method's practicality and efficiency are verified through a case study, analyzing how constraints on vertical girder deflection, horizontal pylon displacement, cable forces, and cable force uniformity affect the optimization outcome. The results show that convergence of the mixed-constraint quadratic programming model is achieved within 30 iterations, yielding an optimized finished state that meets the design criteria. The chosen constraint ranges are deemed appropriate, and the optimization method for the construction stage is thus demonstrably feasible and efficient. The multiplier path following optimization algorithm is computationally efficient, exhibiting good convergence and insensitivity to the problem size. Being easy to program, it avoids the arbitrariness of manual cable adjustment, enabling straightforward determination of a reasonable finished state for the cable-stayed bridge with a steel box girder. The vertical displacement of the main girder, the positive and negative bending moments, and the normal stresses at the top and bottom edges, as well as the positive and negative bending moments in the towers, are significantly influenced by the constraint ranges. The horizontal displacement of the pylon roof is significantly affected by the constraint ranges of both the main girder's vertical displacement and the pylon's horizontal displacement, while the remaining constraint ranges have a limited impact. [ABSTRACT FROM AUTHOR]

Compared with precast bent caps, high‐performance precast bent caps are shorter and lighter, a well‐designed precast bent cap can improve the construction rate, and guarantee an acceptable shear resistance capacity. Therefore, an ultra‐high‐performance concrete (UHPC) with a thin‐walled hollow bent cap suitable for short and medium spans was designed, and its mechanical performance was studied. Firstly, a UHPC bent cap model with a scale ratio of 1:3 was cast and used in a 4‐point loading test, and its crack propagation pattern, shear resistance capacity, and failure mode of the bent cap were revealed. Then, based on an ABAQUS finite element model verified by the experimental results, the influence of various design parameters on the shear performance of the UHPC bent cap was fully investigated, including longitudinal reinforcement ratio, stirrup ratio, web width, bottom thickness, and the thickness of the top and bottom plates. Finally, a prediction formula of shear bearing capacity suitable for different cross‐section types was developed based on the truss‐arch model. The results indicated that the bridging effect of steel fibers and diaphragm cloud restrained the generation and extension of cracks during the loading process, thus the UHPC bent cap showed good deformability and shear‐resistant capacity. Besides, the shear resistance capacity was improved by the increasing longitudinal reinforcement ratio, stirrup ratio, web width, and the thickness of the top and bottom plates. The accuracy and generalization ability of the established formula was validated by comparing the predicted results with the experimental results derived from this paper and relevant studies. The research can facilitate the application of UHPC and structure lightweight technology in bridge engineering. [ABSTRACT FROM AUTHOR]

Designing a bridge is a complex endeavour, involving multiple variables, limitations and requirements. The design process often includes high-fidelity analyses that are computationally expensive, and the internal working tools of the analysis software are often unknown. This limits the applicability of conventional numerical optimization, especially due to time constraints. As a mean to reduce the computational burden, surrogate modelling may be applied. Surrogate models are constructed on the basis of observed results from the computationally expensive high-fidelity analyses, and serves as a fast approximation of unobserved regions in the design space. If probabilistic surrogates are applied, the probabilistic element may be exploited in the optimization phase, resulting in a scheme known as Bayesian optimization. In this article, it is described how to derive a constrained Bayesian optimization scheme in the process of bridge design, where both the goal and constraints are approximated using probabilistic surrogates. The article also presents a case study where constrained Bayesian optimization is applied to a three-span post-tensioned concrete girder and the results are compared to conventional surrogate-based optimization. The results from the case study show that the Bayesian optimization schemes converge after about six iterations, significantly faster than the conventional surrogate optimization scheme, with a consistently higher relative improvement—providing a faster and more confident process for surrogate-based optimization. [ABSTRACT FROM AUTHOR]

This study introduces an innovative approach for identifying surface defects in underwater bridge structures through the fusion of deep learning and three-dimensional point cloud. The method employs a U2-Net neural network enhanced with residual U-blocks to effectively capture defect features across scales and merge multiscale underwater image attributes to produce significant probability images for defect detection. By leveraging three-dimensional digital image correlation techniques, the method reconstructs the bridge pier surfaces' physical dimensions from point cloud, enabling precise defect contour and size recognition. The fusion of deep learning's semantic segmentation with the accurate dimensions from point cloud significantly improves defect detection accuracy, achieving pixel accuracies of 0.943 and 0.811 for foreign objects and spalling and exposed rebars, respectively, and an Intersection over Union of 0.733 and 0.411. The method's millimeter-level precision in point cloud reconstruction further allows for detailed defect dimensioning, enhancing both the accuracy and the quantitative measurement capabilities of underwater bridge inspections, and shows promise for future advanced applications in this field. [ABSTRACT FROM AUTHOR]

To protect two adjacent and parallel bridges, this study proposes a double-pier linkage-type flexible guided anticollision device (DPLT-FGAD). LS-DYNA (version R13.1.1) software was used for numerical simulations, and the finite-element model was verified using test data. The synergistic force effect between the two piers and the energy conversion relationships within the system under different ship impact cases, including variations in angle, location, velocity, and ship type, were examined. Additionally, the protective effect of DPLT-FGAD was highlighted by comparing cases with DPLT-FGAD to those without steel wire rope coils (SWRCs), without an anticollision device, and with a single-pier flexible guided anticollision device. The results reveal that the SWRC is crucial to ensure that the double piers jointly resist the ship impact. Compared with the ship impacting the triangular area of the DPLT-FGAD, the pier is safer when the ship impacts the side area. As the ship impact velocity decreases or the tonnage of the full-loaded ship reduces, the forces on the double piers become more balanced. The DPLT-FGAD significantly enhances the impact resistance of a single pier while simultaneously protecting the ship. [ABSTRACT FROM AUTHOR]

Ballastless tracks have a high smoothness, but the corresponding laying requirements are strict. Therefore, the maximum span of cable-stayed bridges that can accommodate ballastless tracks is 392 m. For laying ballastless track structures over larger spans, the deformation characteristics of long-span, cable-stayed bridges under complex loads are incompletely understood, and the interaction between them and long-span track–bridge structures is unclear. The influence of the wavelength of the cosine wave on the track–bridge mapping of different orbital structures was explored. The wavelength characteristics of vertical deformation under complex loads were investigated. The track–bridge integrated model for the cable-stayed bridge was established to analyze the mapping relationship between the rail and the bridge and the wavelength characteristics of deformation. Based on the mapping relationships and the wavelength characteristics of deformation, the train–track–bridge dynamics simulation model was simplified. The results show that, when the minimum wavelength of bridge deformation surpassed 6 m, 10 m, and 16 m, the rail deformation in the ballasted track, the longitudinal-connected track, and the unit slab-type ballastless track accurately mirrored the deformation of the bridge. For the span of bridges ranging from 200 m to 600 m, the wavelength of vertical deformation ranged from 21 to 1270 m under complex loads. During local loads, the vertical deformation below the 200 m wavelength constituted a significant proportion near the pie. Considering the influence of the deformation on the train vibration response, the train–bridge dynamic coupling model can be employed to treat the track structure as a load to reduce the complexity of the model and enhance the calculation efficiency. [ABSTRACT FROM AUTHOR]

According to the mechanical characteristics of joints in steel–concrete composite bridge decks under the combined bending and shear, improved joint details with simple structure and convenient construction were studied, including lapped U-bars, lapped headed bars, and lapped hook bars. In order to test the mechanical properties of the three joint details and compare them with the existing lapped/welded linear bars, the tests of five specimens were carried out. The cracking load, ultimate load, failure mode, crack pattern, and reinforcement strain were analyzed. The test results showed that the joint with lapped U-bars and hook bars exhibited ductile failure, while the joint with lapped headed and lapped/welded linear bars exhibited brittle failure. The cracking load of the five specimens was basically the same. The crack first occurred at the interface of pre-cast concrete and wet joints. When the ultimate bearing capacity was reached, the vertical main cracks were generated near the interface of the lapped U-bars, lapped hook bars, and welded linear bars specimens. The diagonal cracks were generated at the wet joint of the lapped headed bars specimen and lapped linear bars specimen. The lapped U-bars specimen had the highest bearing capacity, which was 22.8%, 14.2%, 50.4%, and 32.1% higher than the capacities of the lapped headed bars, lapped hook bars, lapped linear bars, and welded linear bars specimens, respectively. The load–deflection curves and crack mode obtained from the FEM of the lapped U-bars joint specimen were consistent with the test results. The bearing capacity of the FEM (351.3 KN) was 1.8% less than the test result (357.6 KN), which indicates that the bearing capacity calculated by the finite element model is reliable. There are 80 models with varying lap lengths and concrete strengths. The self-organizing migrating algorithm was used to fit the coupling effect of lap length and concrete strength. Based on doubly reinforced beam flexural capacity formulas, a bearing capacity calculation for lapped U-bars joint was proposed. The mean value of the formula calculation result and the finite element result ratio is 1.03, and the variance is 0.0004. [ABSTRACT FROM AUTHOR]

Curved continuous steel box girders are extensively utilized in bridge construction due to their efficiency and environmental benefits. However, in regions with significant temperature fluctuations, temperature effects can result in cumulative deformation and stress concentration, which may severely impact structural safety and durability. This study examines the structural response of curved continuous steel box girders with five spans under diverse temperature conditions and also develops a comprehensive parameterized thermodynamic numerical model. The model assesses the influence of cross-sectional shape parameters, including the number of cross-sectional box chambers, diaphragm thickness, and height-to-width ratio, as well as longitudinal structural parameters such as planar configurations, width-to-span ratio, and support arrangements, along with the arrangement of stiffening ribs on the temperature-induced effects in the girders. The results indicate that optimizing the width and eccentricity of support stiffeners to 30% and 25%, respectively, in support plate size can significantly alleviate local temperature-induced stresses. Additionally, variations in longitudinal and transverse stiffeners manifest minimal impact on thermal performance. These findings provide a theoretical foundation for improved design and construction practices, offering practical design recommendations to mitigate temperature effects and enhance the longevity and safety of such structures. [ABSTRACT FROM AUTHOR]

To accurately assess the temperature action and effect of steel-concrete composite girder bridges in plateau and cold areas, this paper investigated nearly 50 years of historical meteorological data from 26 meteorological observation stations in the Tibet region of China. Based on the most unfavorable extreme meteorological data at each meteorological station, a finite element model was used to analyze the temperature field of the composite girder. The most unfavorable values of temperature were obtained. The regional differences in temperature actions at different meteorological stations were analyzed, and the isotherm maps of the extreme values of the uniform temperature and thermal gradients were further obtained based on spatial interpolation methods in the ArcGIS program. The study shows that the uniform temperature is significantly affected by the climatic environment, and the isotherm maps provide a visual representation of the geographic distribution pattern of temperature extremes. The maximum and minimum uniform temperatures in Tibet range from 18.28 °C to 42.27 °C and from −41.07 °C to 4.71 °C respectively. The maximum regional difference of positive and negative thermal gradient reaches 11.32 °C and 7.69 °C respectively. The temperature effects calculated using the most unfavorable values of the isotherm map are all more unfavorable than the specification calculations. In particular, the tensile stress of the concrete under the positive thermal gradient reaches 2.91 MPa, which exceeds the standard value of the tensile strength of concrete. This is a significant risk factor for cracking. The compressive stress of the steel girder under a negative thermal gradient reaches 19.35 MPa, which represents a 136% increase compared to the specified value. This increase elevates the risk of instability in the steel girder. [ABSTRACT FROM AUTHOR]

In order to promote the development of bridge assembly technology and accelerate the application of rectangular steel-tube–concrete composite truss bridges, this study focuses on the Yellow River Diversion Jiqing Main Canal Bridge as the engineering example and conducts a numerical analysis of a rectangular steel-tube–concrete composite truss bridge. Based on the results of the analysis, structural optimization is achieved in three dimensions—structural design, construction methods, and force analysis—leading to the establishment of key design parameters for through-type ultra-high-performance rectangular steel-tube–concrete composite truss bridges. The results show that filling the hollow sections with ultra-high-strength concrete can significantly enhance the load-bearing capacity. Additionally, employing prestressed concrete components addresses the bending and tensile load capacity challenges of composite structures, thus maximizing the material strength advantages. The proposed preliminary design scheme incorporates prestressed PBL-reinforced tie rods filled with ultra-high-performance concrete with optimal design parameters, such as high span ratios, wide span ratios, and ideal segment lengths, are suggested to ensure that the strength, stiffness, and stability comply with relevant standards. While ensuring that the structure meets safety, applicability, and durability criteria, the preliminary design scheme reduces steel usage by 23.5%, concrete usage by 11.6%, and overall costs by 17.29% compared to the original design. The proposed design demonstrates distinct advantages over the original in terms of mechanical performance, construction efficiency, economic viability, and durability, highlighting its promising application potential. [ABSTRACT FROM AUTHOR]

With the rapid development of bridge construction, environmental concerns have become increasingly prominent. Low-carbon, green, and sustainable bridge engineering has emerged as an inevitable trend. A comprehensive carbon emission calculation system is key to achieving low-carbon bridges. This study proposes a rapid calculation and analysis system for bridge carbon emissions (Building Information Modeling–Life Cycle Assessment, BIM-LCA). This system, using the bridge information model as a carrier, calculates and manages data on material consumption, machinery, transportation, and energy throughout the bridge's life cycle. It then calculates the carbon emissions for each stage. This system simplifies the complex and cumbersome data collection and analysis processes found in traditional methods while also making the carbon emissions across the full bridge life cycle more accessible and visible. Being applicable to all types of bridges, this system can provide insights and a basis for decision-making in the early design stages and during construction and operation to support carbon reduction. Ultimately, it promotes low-carbon, environmentally friendly, and sustainable bridge engineering development. [ABSTRACT FROM AUTHOR]

Abstract The significant load disparity between the two decks of a cable-stayed bridge with separated unequal-width decks results in complex asymmetric static effects in the jointed dual-pylon. To investigate the structural behaviour and reliability of the jointed dual-pylon under asymmetric loads, a 1:30 scaled model test and numerical simulation were conducted based on the world's first road-railway same-level cable-stayed bridge with jointed pylons. The test results indicate when the unbalanced horizontal force of the jointed dual-pylon structure reaches its maximum during the service phase, the stress at the dual-pylon connectivity node remains relatively low, indicating good shear resistance of the dual-pylon connectivity node. Structural failure occurs when the load reaches 1.82 times the maximum shear stress at the tower column merging section, and the railway beam will experience severe cracking and stiffness degradation, ultimately leading to loss of bearing capacity. The calculation results further reveal that under the combined action of dead load, full-span moving load, and lateral wind load, the minimum calculated nonlinear stability coefficient of the dual-pylon connectivity node is 1.65. Moving load and longitudinal wind load have minimal impact on the nonlinear stability coefficient, and the dead load and lateral wind load primarily govern the failure of the dual-pylon connectivity node.

Abstract The second-order blind identification (SOBI) and its variants have been extensively explored for output-only modal identification of civil structures under varied excitations. At the core of these methods is the matrix joint approximate diagonalization (JAD) technique, while their efficiency and accuracy are largely determined by how the target-matrices for JAD are constructed from multi-channel structural responses. This study first formulates the JAD framework for structural identification, where different techniques in formulating the target-matrices are summarized and mathematical tools to conduct JAD are also presented. Then two novel ways stemming from conventional identification methods are presented as alternatives to construct the target-matrices for ambient identification, to maintain a low-order formulation and even avoiding the formation of covariance matrix. Subsequently, in view of the large number of candidate target-matrices which are analytically usable, a guiding principle is proposed for selecting reliable target-matrices, where the closeness of the eigenvectors of the target-matrices are compared beforehand, therefore eliminating of distorted target-matrices and also improving the efficiency of the subsequent JAD. The proposed techniques are applied to modal identification of the Donghai Bridge from monitoring data and the proposed JAD-based methods are compared in this context. The results suggest the effectiveness of the proposed techniques and also provide a performance evaluation of these methods.

Abstract Pile spacing significantly influences the dynamic response of coastal pile foundation bridges, particularly under complex loading conditions. This study presents a novel methodology for optimizing the distribution of piles within a nine-pile cap and evaluates the effects of varying pile spacings on the dynamic fluid-structure interaction. An experimental investigation was conducted to assess the dynamic response of three scaled bridge specimens with pile spacings of 2.5D, 2.0D, and 1.5D (where D is the pile diameter) under combined current-wave forces during seismic events. The acceleration and displacement responses were measured using the innovative Reality Water Structure Earthquake Interaction Test (RWSEIT) system. The results revealed that reduced pile spacing (1.5D) led to a significant increase in both acceleration and displacement responses, indicating higher vulnerability under dynamic loading. In contrast, wider spacing (2.5D) demonstrated improved stability, with reduced displacement and acceleration, thereby enhancing the overall structural resilience. The analysis also highlighted the critical role of water depth, current velocity, and wave properties in modulating the dynamic response. Complementary 3D numerical models were developed using the Finite Element DIANA Software, and the numerical results closely matched the experimental findings, thereby validating the model’s accuracy. These insights contribute to more sustainable infrastructure design, aligning with global efforts to enhance the resilience and longevity of coastal structures while minimizing environmental impact. These findings provide crucial insights into the fluid-structure interactions of coastal bridges, offering practical guidance for the design and assessment of deepwater pile foundations under seismic and hydrodynamic forces.

Abstract Round-end hollow reinforced concrete (RC) tall piers have been widespreadly utilized for railway bridges in river valleys and mountainous regions. The post-earthquake damage state of such bridge piers differs significantly from that of traditional short-to-medium piers. To investigate the seismic performance and failure mode of RC round-end hollow tall piers, a finite element model was developed using the OpenSees platform and calibrated against previous test results. Subsequently, incremental dynamic analysis (IDA) and modal pushover analysis (MPA) were conducted to obtain bending moment and curvature distributions as well as damage ranges for piers subjected to different intensities of ground motion. The results indicate that: The RC round-end hollow tall piers subjected to strong ground motions can crack up to 75% and 80% of its height according to IDA and MPA, respectively. The MPA incorporating mode coupling up to the third order is capable of predicting crack distribution of the pier as demonstrated in this study. Furthermore, it is recommended that the damage range of the pier be considered as a primary control indicator in seismic design.

Abstract Surface damage detection in concrete structures is critical for maintaining structural integrity, yet current object detection algorithms often struggle in low-light environments. To address this challenge, this study proposed a methodology that integrates image enhancement and object detection networks to improve damage identification in such conditions. Specifically, we employ the self-calibrated illumination (SCI) model to reconstruct low-light images, which are then processed by an improved YOLOv5-based network, YOLOv5-GAM-ASFF, incorporating a global attention mechanism (GAM) and adaptive spatial feature fusion (ASFF). The performance of YOLOv5-GAM-ASFF is evaluated on a dataset of concrete structure damage images, demonstrating its superiority over YOLOv5s, YOLOv6s, and YOLOv7-tiny. The results show that YOLOv5-GAM-ASFF achieves a mAP@0.5 of 79.1%, surpassing the other models by 1.3%, 3.3%, and 5.8%, respectively. This approach provides a reliable solution for surface damage detection in low-light environments, advancing the field of structural health monitoring by improving detection accuracy under challenging conditions.

Abstract An iced suspension bridge hanger has an altered aerodynamic shape, potentially causing various types of wind-induced vibrations. A wind tunnel experiment was performed, based on the DenHartog galloping theory, to study the wake galloping of the iced suspension bridge hangers at different hanger spacings. The results revealed that, for iced pin joint hangers, the pneumatic characteristics of the leeward hanger are more stable when the hanger spacing is in the 4.8D ≤ L ≤ 6.2D range. The range of wind attack angle corresponding to the negative value of the DenHartog coefficient increased gradually with the increase in hanger spacing. For iced straddling hangers, the effect of lift must be considered when the static wind load of iced straddling hangers is calculated. The DenHartog coefficients of iced hangers under different hanger spacings all exceeded the -1.0 specified in the code for Wind Resistance Design of Highway Bridges (JTG/T3360-01–2018). The aerodynamic characteristics of iced leeward hangers were more stable when the hanger spacing was A × B = 8D × 4D. Therefore, measures should be taken to increase the rigid vibration-damping frame and improve the critical wind speed of the hangers to avoid vibration in iced hangers.

Timely and effective detection of surface defects on bridges is crucial for ensuring public transportation safety and extending the lifespan of bridges. Traditional bridge defect detection primarily relies on manual inspections, which are highly subjective, inefficient, and exhibit a significant rate of undetected issues. Moreover, there is a lack of effective detection methods for bridges located in special areas, such as large-span canyon bridges. To address these challenges, this study focuses on the Chishi Bridge in Chenzhou, Hunan Province, China, which is the largest multi-tower concrete cable-stayed bridge in the world with high piers. First, we designed a fully automated detection system for one-stop intelligent maintenance operations. Second, our system integrates a bridge damage detection algorithm guided by fractal geometric features. This algorithm is an improvement based on the classic object detection algorithm YOLOv7 (You Only Look Once), incorporating the SimAM and CARAFE attention mechanisms to enhance damage feature recognition, accurately identifying and assessing various defects on the underside of the bridge. The proposed method achieves an average mean precision (mAP) of 87.24% and reduces inference time by 15%, demonstrating significant improvements in both accuracy and efficiency compared to the baseline. Overall, this significantly enhances the level of intelligent defect detection for the Chishi Bridge, ensuring safe and stable operation while showcasing considerable economic production value. [ABSTRACT FROM AUTHOR]

Abstract Fire pose more severe threat to steel truss bridge girders as compared to common steel plate and box bridge girders. To deeply clarify failure mechanism of fire exposed steel truss bridge girders, this paper presents an investigation on fire performance of composite steel truss bridge girders simultaneously subjected to structural loadings and hydrocarbon fires. A numerical model, developed using the computer program ANSYS, is validated dependent on fire test to trace fire behavior of a typical through-type composite steel truss bridge girders under different hydrocarbon fire exposure conditions. The analysis is applied to evaluate influence of potential fire exposure scenarios occurred in bridge structures, including fire exposure lanes on bridge deck and fire exposure length beneath bridge, on temperature and structural response in steel truss bridge girders. The results shows that fire exposure lanes on bridge decks and fire exposure length beneath bridge has a significant influence on fire performance of steel truss bridge girders. Fire exposure on all lanes and side lanes can cut down fire resistance highly as compared to fire exposure on mid-lanes. The composite steel truss bridge girders exhibit special multi-hinge failure modes when fire exposure under bridge. Further, the composite steel truss bridge girders exposed to side-lane fire exhibit significant transverse torsional deformation. The established failure criteria dependent on structural deflection limit states, chord deformation and strength can be applied to evaluate fire resistance of actual composite steel truss bridge girders under realistic fire exposure scenarios. Limiting the minimum clearance of passage on bridge deck and increasing fire protection measures in upper portion of trusses can effectively improve fire resistance of through-type composite steel truss bridge girders. Some predominant design strategies closely related to oil tanker trucks traversing composite steel truss bridge girders are proposed to minimize probability of fire incidents on bridge and keep integrity of structure in the case of fire to the maximum extent possible.

Abstract The objective of this study is to examine the dynamic response behavior of a long-span cable-stayed bridge with ultra-high piles subjected to near-fault ground motions, comprehensively considering deep-water, sedimentation, local site, and wave-passage effects. Firstly, a 3D finite element (FE) model of the long-span cable-stayed bridge with ultra-high piles (Approximately 105 m) and a tower height of 216.4 m was established using Midas software. The deep-water, sedimentation, local site, and wave-passage effects were synthetically considered in this FE model. The FE model incorporates the sag effect of the stayed cable and the pile-soil interaction, enabling a detailed seismic analysis. Secondly, the examined near-fault ground motions with long-period velocity pulses were selected from the PEER database according to the design acceleration response spectrum with a fortification intensity of VIII degrees. Finally, nonlinear time history analyses of the selected long-span cable-stayed bridge, subjected to spatial near-fault ground motions including local site effect and wave-passage effect, were conducted, and the responses of critical design sections and points in structures were examined and evaluated. The results demonstrate that long-period velocity pulses can significantly affect the structural responses, while deep-water and sedimentation effects do not have a significant impact on the dynamic responses of long-span cable-stayed bridges. For the local site effect, the softer the soil at the support site and the greater the difference in soil conditions at the support, the larger the structural response. Regarding the wave effect, the structural response will increase or decrease depending on the magnitude of the wave speed and the span length between towers.

Abstract Fabricated ballastless track has witnessed increasingly wide application in large-span bridges of municipal railways. The current ballastless track standard is applicable to bridges with a main span of 200 m to 400 m. For the main span is longer than 400 m, it is necessary to ensure the travelling safety and comfort on the fabricated tracks. In this study, static and dynamic analysis models of train-track-bridge are established to explore the influence of complex ambient temperature changes and concrete shrinkage and creep on bridge deformation, followed by the analysis of the deformation coordination between long-span bridge and fabricated ballastless tracks, thereby revealing the dynamic response of the train-track-bridge system under the complex influence of temperature. The results show that when a train runs at a speed of 160 km/h, the existing ballastless track design standard is still applicable to a bridge span of 688 m. Compared with CRTS type III track, the adoption of the novel prefabricated ballastless track on long-span urban bridges provides higher safety and greater comfort, with comprehensive power performance improved by more than 10%. This design comprehensively takes into account the deformation coordination and dynamic performance of the rail bridge, providing a basis for the design and application of fabricated ballastless tracks on long-span bridges of urban railways.