Search Results (65)

During the fabrication of prestressed concrete beams, the quality and positional accuracy of the laid corrugated ducts (or prestressing ducts) directly influence the load-bearing capacity and durability of the beams. However, traditional manual inspection is inefficient, highly subjective, and difficult to achieve full coverage. To address this problem, this paper proposes an automated detection method that integrates improved YOLOv11-based pose estimation, robust curve fitting, and image stitching techniques. The method automatically identifies duct positions and evaluates laying quality. By incorporating the SE channel attention mechanism and the SPPFCSPC multi-scale pooling module, the SC-YOLOv11 model is developed, which significantly enhances the detection accuracy of slender corrugated pipe key points in environments with dense rebar occlusion. The RANSAC algorithm is employed to fit curves to the predicted key points, effectively suppressing the influence of outliers. Furthermore, the SIFT algorithm is used for precise stitching of drone-captured segmented images, which are then transformed into a unified front orthographic coordinate system of the entire box girder via perspective transformation, enabling accurate reconstruction of the corrected 2D layout of corrugated ducts across the full beam. Ablation experiments using 5-fold cross-validation demonstrate that SC-YOLOv11 improves mAP₅₀ and mAP_50–95 by 2.6% and 1.2%, respectively, with statistical significance (paired t-test, p < 0.01). The model achieves a per-image inference time of 6.37 ms, with 4.34 M parameters and 8.1 GFLOPs, meeting real-time requirements. In a 30 m prefabricated box girder field application, the measured section trajectory fitting curves of the corrugated ducts were compared with the design alignment, successfully identifying two abnormal locations where the laying deviation exceeded the allowable threshold. Cross-validation with on-site inspector records shows that over 92% of the measurement points agree within ±10 mm. This method achieves a fully automated analysis chain from key point detection and curve fitting to deviation quantification, providing an efficient, non-contact, and traceable intelligent tool for quality control of bridge prestressed systems. Full article

There are different degrees of cracks in prestressed concrete (PC) beams, especially the transverse cracks in the bottom plate and the vertical cracks in the web of prestressed concrete box girders, which will reduce the bearing capacity of the structure. In order to clarify the evolution law of cracks in prestressed concrete box girders after cracking, a 25 m prestressed concrete box girder was poured and a full-scale model test was carried out. At the 1/4 span position of the test beam, the test beam was cracked in 19 steps to 1900 kN. Then at the 3/4 span position, the test beam was cracked in 18 steps to 1800 kN, and after that the bending load test was carried out in 17 steps to analyze the influence of existing cracks on the bending cracks of the test beam. Combined with fractal theory, the evolution law of cracks, the development law of fractal dimensions, and their relationship under different loading conditions were analyzed. The results showed that the crack distribution of the test beam satisfies self-similarity and had fractal characteristics in a statistical sense, which could reflect the process of crack occurrence, propagation and damage, and could quantify the crack shape. The fractal dimension of cracks gradually increased with the increase in concentrated load on the test beam, and the fractal dimension of cracks had a linear relationship with the concentrated load. The crack propagation process of the concrete beam reflected the fractal dimension increasing process; that is, the crack damage evolution process of test beam was a dimension increasing process, and the fractal dimension of crack distribution increased linearly with the applied load. The functional relationship between prestressed concrete crack width and fractal dimension was constructed, which provided a new path for bridge safety evaluation. The research results provide engineering reference for the cause analysis and maintenance treatment of similar bridge cracks. Full article

In order to produce long-span precast bridge members and reduce the transport pressure of precast members, the lightweight design of bridge components has become a key area of research. In this study, utilizing retard-bonded prestressing technology and high-strength concrete, a full-scale thin-walled box girder measuring 30,000 mm in length and 1600 mm in height was designed and fabricated. A shear test with a shear-span ratio of 2.5 was conducted to investigate the failure mode and shear carrying capacity. Subsequently, an Abaqus finite element (FE) model was established and validated with experimental data. Based on the FE model, numerical investigations were conducted to examine the influence of bonding between prestressed steel strands and concrete, stirrup ratio, web thickness and bottom flange thickness at the end of the box girder, concrete strength and length of UHPC end zone on the shear performance of thin-walled box girder. The results indicate that the retard-bonded prestressed box girder exhibits acceptable mechanical performance. Additionally, intensifying the ends of the box girder with ultra-high-performance concrete (UHPC) can further reduce the wall (i.e., web and bottom flange) thickness of the girder, enhance its shear carrying capacity, and achieve lightweighting. This discovery provides new insights into the lightweight design of bridge components. Full article

To support the seismic optimization of long-span bridges in regions of high seismicity, this study evaluates the seismic performance of continuous rigid-frame box-girder bridges with different web configurations. A continuous box-girder bridge with corrugated steel webs (CSWBGB) having a main span of 105 m was analyzed and compared with two control models: a continuous box-girder bridge with flat steel webs (FSWBGB) and a conventional prestressed concrete box-girder bridge (PCBGB). Finite element models of the three web types were developed using MIDAS/Civil, and seismic responses were evaluated using the response spectrum method with geometric nonlinearity incorporated; the analyses were conducted under E1 and E2 ground motion intensities (corresponding to a 63% probability of exceedance in 100 years and a 2% probability in 50 years, respectively, as specified in the Chinese seismic design code). Displacement, axial force, and shear force responses were systematically compared among the three configurations. The results show markedly different seismic responses despite the bridges having similar fundamental frequencies. In the longitudinal direction under seismic excitation, the CSWBGB exhibited larger axial displacement than the FSWBGB, yet its peak axial force and shear force decreased by 13% and 18%, respectively, indicating that the greater axial deformation helps relieve internal force demands. Under transverse E1 seismic action, the CSWBGB displayed smaller lateral displacements than both the FSWBGB and the PCBGB. Compared with the CSWBGB, the PCBGB experienced an 11% larger longitudinal displacement and a 43% higher peak axial force, reflecting its relatively limited seismic performance. These findings demonstrate that the CSWBGB not only provides lighter self-weight than the PCBGB but also offers enhanced transverse stiffness, which results in smaller lateral displacements and lower peak shear forces—thus achieving an optimal balance between lightweight design and structural strength. Although the CSWBGB shows strong potential for practical application, its longitudinal displacement response should be carefully controlled in design. Full article

Real-time monitoring of surface cracks in reinforced concrete (RC) beams is critical to structural safety and service performance evaluation. Current structural crack monitoring still faces prominent scientific and technical bottlenecks: conventional unidirectional sensors cannot achieve multi-directional collaborative sensing, rigid piezoelectric materials exhibit poor compatibility with the large deformation of concrete, and there is a lack of quantitative mapping relationships from sensing signals to crack parameters, making it difficult to simultaneously measure crack width, angle, and morphology. This paper presents a novel ring-shaped piezoelectric sensor based on polyvinylidene fluoride (PVDF) and an annular piezoelectric sensing mechanism for real-time monitoring of crack angle, width, and morphology. The sensor incorporates a laminated structure with four strip sensing units for multi-directional strain detection. Experiments were conducted on RC beams under various loading conditions, and finite element analysis was performed using COMSOL Multiphysics. An innovative crack damage index (B) was introduced to assess structural damage quantitatively. Results demonstrate high sensor sensitivity and stable output. Voltage signals increase both with crack width and crack angle, showing responses of 0.045 mV, 0.041 mV, and 0.023 mV for crack angles of 60°, 45°, and 30°, respectively, at a crack width of 9 mm. Strong consistency between experimental and simulation data validates the effectiveness of the mechanism in monitoring the direction, width, and types of cracks. The crack damage index B exhibits a positive correlation with the structural stress response, enabling a quantitative assessment of damage. This study is applicable to the prestressed concrete box girders and T-beams commonly used in large-span bridges, which are typically with a main span of 20–50 m, a beam length of 6–30 m, a section height of 1.2–2.5 m, and designed for Grade C35–C50 concrete. The findings provide a practical foundation for real-time crack monitoring in large-scale bridge beam members. Full article

Strengthening existing structures and bridges allows us to continue using them, increase their reliability, resistance, durability and extend their service life instead of demolishing them and replacing them with new ones. This helps to reduce CO₂ (decarbonization). The use of prestressed CFRP strips represents the use of new modern materials and new technology for strengthening existing bridges. The paper is focused on the use of prestressed CFRP strips for strengthening a concrete bridge made of precast prestressed box girders as the most suitable strengthening alternative in a given case. This is a technology that is more commonly used for strengthening structures, but it is not common to use this technology for strengthening bridges. There are relatively few examples of using this technology for strengthening bridges, also because these are dynamically loaded structures. The paper firstly presents the diagnostics and calculation of the load-carrying capacity of the railway bridge on a narrow-gauge railway line in Štrbské Pleso, Slovakia, and then the strengthening of the given bridge. The bridge is located in the mountains of the High Tatras in the northern part of Slovakia and bypasses two local roads. The bridge was made from the precast prestressed post-tensioned box girders of six single spans. The visual inspection, diagnostics, and verification of real dimensions and material characteristics were requested. The non-destructive and semi-destructive methods of testing were used to determine the geometrical and materials’ properties. After that, the calculation of the load-carrying capacity was done. For this purpose, a numerical 3D FEM model was created. For determining the load-carrying capacity, the standard approach, given in Eurocodes, was used according to provisions, which take into account the modified (lower) reliability levels and their adequate partial safety factors. From the calculation, it follows that the bridge should be strengthened. The strengthening of the superstructure was done using prestressed CFRP strips in the lower part of the box girders. This is one of the first applications of this modern method of strengthening, not only in Slovakia but in Central Europe as well. Full article

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%. Full article

Seismic design for multi-span simply supported to continuous (SSC) bridges is complicated by the vulnerability of continuity joints and the interaction between substructure stiffness and superstructure dynamics. Although Lead Rubber Bearings (LRB) are standard in current practice, the optimization of their spatial layout to balance displacement demands against force mitigation is often overlooked. This study evaluates the efficacy of hybrid bearing configurations that integrate LRBs with sliding bearings on the same pier. Using a 3D finite element model of a representative five-span prestressed concrete box girder bridge, 20 distinct layout schemes utilizing five different types of LRBs were systematically evaluated under El-Centro ground motions. Results show that a hybrid bearing configuration outperforms uniform isolation strategies. The fundamental efficacy of the proposed hybrid layout configuration is rooted in the establishment of a spatial stiffness gradient. This configuration concentrates hysteretic energy dissipation centrally while releasing transverse edge constraints. This also results in a higher seismic reduction rate for the transverse pier bottom bending moment compared to the longitudinal direction in the same pier. Compared to the non-isolated baseline, this hybrid scheme achieved a maximum reduction of 67.4% and 90.0% in longitudinal and transverse pier bottom bending moments, respectively. Main girder displacements, while increased by isolation, remained strictly within safe serviceability limits (peak 174.8 mm). This study provides a cost-effective optimization strategy for the seismic resilience design of SSC bridges. Full article

Since a significant part of the Italian territory was not seismically classified until 2003, most existing bridges have been designed—for decades—disregarding earthquake-induced excitations. In fact, this means that load-bearing devices and shear keys of presently in-service infrastructures may not be up to current codes, both in terms of resistance and displacement capacity. Robust investigations are hence required for verifications and possible retrofit. In this study, the seismic behaviour of a case study post-tensioned concrete bridge built in the 1980s is numerically analysed. The examined structure is 440 m long and composed of nine spans, built with precast segments using the balance cantilever construction method. The deck is divided into two parts connected by a hinged joint in the middle of the central span, obtained with three shear keys and originally designed to allow for thermal expansion only. Most importantly, the mid-span hinge, the end joints and the bearing devices were originally designed without considering the effects of seismic action. In order to preliminarily investigate the performance of devices and joints, the case study bridge is analysed by means of non-linear dynamic time history simulations, formulating different hypotheses about the non-linear behaviour of the load bearings. Forces and displacements over time are obtained for a set of seven accelerograms, and maximum values are compared to the capacity of the bridge devices. Results are then critically discussed. Full article

In this study, the dynamic responses of railway bridges generated by both blast motions and earthquakes are comparatively studied. A numerical model of a three-span continuous prestressed concrete (PSC) box girder bridge, a representative type of railway structure, was developed to investigate its dynamic performance. Dynamic analyses were conducted under two blast-induced ground motions and four earthquake ground motions, and the structural responses at the girder top were employed to evaluate the dynamic behavior of the railway bridge. The results indicate that the blast-induced bridge responses are relatively small compared to the earthquake-induced bridge responses (2–3% of the bridge response). This implies that the blast vibration limit provided in the Korean standard manual could be excessively conservative when applied to the railway bridges. Also, the results show that the blast vibration limit should be revisited, with a consideration of different structures and conditions. Full article

To mitigate thermal cracking in concrete box girders during construction, this study introduces an inversion method for thermal parameters by integrating machine learning with finite element simulation. The research aims to accurately identify key thermal parameters—thermal conductivity k, total hydration heat Q₀, convection coefficient h, and reaction coefficient m—through an efficient and reliable data-driven approach. An orthogonal experimental design was used to construct a representative sample database, and a Bayesian-optimized XGBoost (BO-XGBoost) model was developed to establish a nonlinear mapping between temperature peaks and thermal parameters. Validated against field monitoring data from a prestressed concrete continuous rigid-frame bridge, the method demonstrated high accuracy: the inversiontemperature curves closely matched measured data, with a maximum peak temperature error of only 1.40 °C (relative error 2.5%). Compared to conventional machine learning models (DT, SVR, BP and LSTM), BO-XGBoost showed superior predictive performance and convergence efficiency. The proposed approach provides a scientific basis for real-time temperature control and crack prevention in concrete box girders and is applicable to temperature field analysis in mass concrete structures. Full article

Ultra-high-performance concrete (UHPC) exhibits significantly superior compressive and tensile properties compared to conventional concrete, demonstrating substantial application potential in bridge engineering. This study conducted full-scale bending tests on a 30 m prestressed UHPC-NC composite box girder within an actual engineering context. The testing flexural capacity $M_t=\mathrm{34,469.2} \mathrm{k}\mathrm{N}·\mathrm{m}$ exceeded the design requirement $M_d=\mathrm{18,138.0} \mathrm{k}\mathrm{N}·\mathrm{m}$, with $M_t/M_d=1.90$. Finite element modeling (FEM) was employed to analyze and predict experimental outcomes, revealing a simulated flexural capacity of approximately 37,597.1 $\mathrm{k}\mathrm{N}·\mathrm{m}$. The finite element models further explored failure mode transitions governed by the loading position while the concentrated load-to-support distance exceeds 9.62 m (shear span to effective depth ratio λ = 6.3), and the box girder fails in flexure; while less than 9.62 m, the box girder fails in shear. The flexural capacity of the test girder was also estimated using Response-2000 software and the recommended formulas from the Chinese code T/CCES 27-2021 (Technical specification for ultra-high-performance concrete girder bridge). The Response-2000 software yielded a flexural capacity estimate of $M_r=\mathrm{30,816.1} \mathrm{k}\mathrm{N}·\mathrm{m}$. The technical specification provided two estimating results: (with safety factors) $M_{u1}=\mathrm{25,414.4} \mathrm{k}\mathrm{N}·\mathrm{m}$ and (without safety factors) $M_{u2}=\mathrm{33,810.9} \mathrm{k}\mathrm{N}·\mathrm{m}$. All estimated values of Response-2000 and Chinese code were rationally conservative ($M_r,{ M}_{u1}, M_{u2}<M_t$). Comparative analysis demonstrates that Abaqus FEM accurately simulates the flexural behavior of the prestressed UHPC-NC composite box girders. Both Response-2000 calculations and the Chinese code T/CCES 27-2021 provide critical references for similar applications of prestressed UHPC-NC composite box girders. Full article

Asynchronous-pouring construction (APC) technology employs a suspended hanging basket directly supported by corrugated steel webs (CSWs) with high shear strength, significantly enhancing construction efficiency. To further elucidate the characteristics of APC and promote its application in prestressed concrete (PC) composite box girder bridges with CSWs, this study analyzes the sustainable development of APC from two aspects, including environmental impact and economic performance. Finite element models of APC and traditional balanced cantilever construction (TBCC) were established for the case bridge with a main span of 105 m. The stress distribution and deflection of the main girder in the cantilever construction state are compared with field measurements, and the variations in stress and deflection in typical sections during construction are analyzed. Additionally, a simplified theoretical method is proposed for calculating stress and deflection in PC composite girder bridges during the cantilever construction stage using APC. Results demonstrate that APC demonstrates significant advantages in reducing economic costs and minimizing long-term environmental impacts. Furthermore, this method ensures acceptable stress and deflection throughout construction. The proposed simplified formula for CSW deflection in the maximum segment agrees well with both measured data and finite element results, providing a valuable reference for deflection calculation in APC applications. Full article

Traditional damage detection methods of prestressed concrete box girder bridges have low efficiency and cannot quantify the structure’s internal damage. We used an inversion method and a falling weight deflectometer to estimate the mechanical parameters of prestressed box girder bridges. A finite element model of the bridge dynamics under impact loading was established. A perturbation-based update was conducted, and a multi-parameter inversion algorithm was constructed. The measured data were used for the efficient identification of the bridge’s elasticity modulus and the prestressing tensile force. The theoretical validation indicated a high modeling accuracy and inversion efficiency, with a convergence accuracy within 1%. The initial value had a minimal influence on the inversion results. The engineering application showed that the maximum error of the elastic modulus between the inversion and the rebound methods was 1.55%. The loss rates of the deck slab’s elastic modulus and the prestressing force obtained from the inversion were 4.39% and 7.64%, respectively. The proposed method provides a new strategy for evaluating damage to prestressed box girder bridges. Full article

Shear lag stresses increase significantly in cracked concrete box girders; however, most existing models assume intact sections and are, therefore, unsuitable for rapid field diagnosis. This study integrates a stepped stiffness model with deflection influence lines to accurately capture the mechanical response of damaged, simply supported box girders. Regions containing flexural cracks are assigned a reduced bending stiffness ${EI}^{\prime }$, whereas intact zones retain the original stiffness $EI$. A closed-form stiffness-reduction coefficient $\phi ={EI}^{\prime }/EI$ is obtained from crack geometry and, independently, from the second derivative of the deflection influence line. Embedding $\phi$ in a variational shear lag formulation yields explicit expressions for flange displacement and normal stress without numerical iteration. This approach is validated by finite element simulations of a plexiglass scale model with four preset damage levels and by a load test on a 30 m prestressed concrete box girder bridge. Field measurements show that midspan stiffness decreased to 81% of the as-built value; the proposed method reproduces this value with a deviation of 3%. Predicted upper-flange stresses differ from measured values by 5.7–13.6% and from finite element results by less than 10% for damage ratios up to 40%. The second derivative of the influence line difference exhibits a distinct peak at the cracked region, accurately localizing the damage. Compared with classical formulas, the proposed model (i) is fully closed-form, (ii) links global deflection data to local shear lag stresses, and (iii) delivers conservative estimates suitable for routine bridge assessment. Full article