Span Bridges Research Articles

Modeling Nonlinear Aeroelastic Forces for Bridge Decks with Various Leading Edges Using LSTM Networks

With the rapid increase in bridge spans, the mitigation of risk to flutter (aeroelastic instability) is of critical importance in the design of long-span bridges, especially considering the more frequent intense hurricanes under climate change. Although the strong nonlinearities of the aeroelastic (self-excited) forces in wind–bridge interactions can be well captured through either numerical simulations or experimental tests, both are expensive and time consuming. Hence, it is important to develop an efficient reduced-order model for the simulations of nonlinear aeroelastic forces on the bridge decks. This study proposes a reduced-order model based on the long short-term memory (LSTM) network to simulate the nonlinear aeroelastic forces on bridge decks with various leading edges, and thus rapidly predict the corresponding post-flutter behaviors of long-span bridges. To generate the training datasets, computational fluid dynamics (CFD) was employed to simulate the nonlinear aeroelasticities of bridge decks with a wide range of leading-edge configurations and wind speeds. Trained on the high-fidelity CFD datasets, the LSTM network takes the motion of a bridge deck, leading-edge angles and wind speeds as inputs and outputs the nonlinear aeroelastic forces on the bridge decks. A hybrid loss function utilizing the prediction errors of both aeroelastic forces simulated by the LSTM network and the bridge deck responses calculated by the Newmark-β algorithm was introduced into the training process to improve the network performance. The prediction results of the trained LSTM model were compared with the CFD simulations, which demonstrated that the nonlinear aeroelastic forces of the bridge deck with various leading edges can be accurately and efficiently acquired by the proposed LSTM model.

Dynamic Behavior of Metro Train–LSB (Long–Span Bridge) System Considering Nonlinearity of Resilient Wheel

To overall investigate the mechanical performance of resilient wheels to suppress the vehicle–bridge (especially LSB) coupled vibration, the coupled dynamic characteristics of metro train–LSB considering nonlinear resilient wheels are studied. Firstly, the mechanical property test of rubber of resilient wheel is designed and conducted, the mechanical characteristics of the nonlinear resilient wheel (NLRW) and linear resilient wheel (LRW) are discussed, and the dynamic model of LRW and NLRW are established. Then, based on train–track–bridge dynamic interaction theory, the coupled dynamic models of metro train–LSB considering LRW and NLRW are established, respectively. Adopting the established model, the dynamic influences of NLRW and LRW on the metro train–LSB coupled system are investigated by long-short wave irregularity excitation. The effects of damping characteristics of LRW and NLRW on the metro train–LSB system are discussed from the time–frequency domain. Results show that the wheel–rail vertical force of NLRW is smaller than that of LRW. The acceleration of the web, axle box, bogie, and car body of the NLRW is smaller than that of the LRW. The main frequency of wheel–rail vertical force under the action of NLRW and LRW is about 4 and 22[Formula: see text]Hz. The main frequencies of the rim and web of the NLRW are about 25[Formula: see text]Hz, while those of the LRW are about 50 and 25[Formula: see text]Hz, respectively. The acceleration of the web of the NLRW is significantly smaller than that of the LRW. The main frequency of acceleration of the LSB is about 10[Formula: see text]Hz, and the acceleration of the LSB under the action of NLRW is significantly less than that of the LRW when the frequency is in the range of 22–62[Formula: see text]Hz. Vibrations of the metro train and LSB increase with the increase of speed, and the dynamic response of the metro train–LSB system under the action of NLRW is smaller than that of LRW.

Buckling behavior of orthotropic steel deck stiffened by slender bulb flats for large span bridges

Slender bulb flat stiffeners with a large height-to-thickness ratio were proposed for the orthotropic steel decks (OSDs) in a large span suspension bridge. The buckling behavior of the panels stiffened with bulb stiffeners under pure compression was experimentally and numerically studied in this paper. Four specimens consisting of four longitudinal stiffeners and a top deck plate were fabricated and subjected to axial compression loading tests. Finite element models were established and validated by the result tests. A parametric analysis was conducted to study the effects of residual stresses and geometric imperfections on buckling behavior. A buckling failure of overall stiffener buckling before the yielding and ductile post-buckling behavior were observed in the tests. A buckling strength of 311∼337 MPa was obtained in the tests. The ratio of buckling stress to yield strength ranging from 0.80 to 0.86 was slightly lower than that of closed ribs, which shows a potential use of the slender bulb flat in large span suspension bridges. The numerical results showed that the residual stresses can decrease the load-bearing capacity by 10%. The residual stresses have a higher influence on the resistance than the regular geometrical imperfections. The standard vehicle load has negligible influence on the buckling resistance, but overload may cause a certain decrease.

The Research on Obtaining the Geometric Dimension of Cable-Stayed Bridges Based on 3D Laser Scanning

The traditional manual measurement methods are time-consuming and error-prone when they are used for cable-stayed bridges’ geometric dimensions acquisition. They are always limited by various adverse conditions such as large bridge spans, the high height of bridge towers, more risk of manual operation, and many other unpredictable factors. In contrast, three-dimensional (3D) laser scanning technology is extremely useful for solving the above problems. After obtaining plenty of point cloud data and point cloud models, precise and accurate geometric dimensions of cable-stayed bridges can be obtained accurately and conveniently. Taking a cable-stayed bridge named XingLinBao as an example, the accuracy and convenience of 3D laser scanning are verified.

Aerodynamic Interference and Dynamic Influence of Wind Barrier on Train-bridge Coupling Vibration System

Wind barrier is an important wind-resistant measure for the running performance of trains on long-span bridges. This study aims to clarify how the aerodynamic interference of wind barrier to the train-bridge system affects the dynamic response of the system. The aerodynamic interference and dynamic influence of wind barriers on the train-bridge system are studied by wind tunnel test and coupling vibration analysis. Wind barriers with different ventilation rates are selected to study their wind-resistant performance on trains travelling in four lanes on the bridge. The results show that installing wind barriers can increase the side and lift coefficients of bridge and decrease the side and lift coefficients of train. The maximum difference is that installing a wind barrier with ventilation of 0 can increase the side coefficient of the bridge by 0.6, while reducing the side coefficient of train in Lane 1 from 1.25 to −0.25. Although the wind barrier has changed the aerodynamic coefficient of the bridge, the maximum dynamic response of train-bridge system depends more on its influence on the aerodynamic coefficient of train. Installing a wind barrier with 0% ventilation rate can reduce the maximum lateral displacement at mid span of bridge by 10 mm, the maximum reduction rate of the wheel from 0.38 to 0.1, and the lateral car body acceleration from 1.1 m/s2 to 0.45 m/s2. The vertical dynamic response of train-bridge system is insensitive to wind barrier. The key effect of optimizing train side coefficient on wind-resistant performance of wind barrier is pointed out.

Evaluasi Struktur Jembatan Gantung Pejalan Kaki Dumpoh, Magelang Jawa Tengah

The bridge analyzed is a suspension type with a function as a pedestrian bridge. The bridge has a total span of 53.75 m and a width of 1.8 m, steel construction with wooden deck. The service life factor, damage to the bridge frame, and overload are certainly a problem for this bridge structure. Evaluation of the structure using survey data from existing measurements at the bridge location, then analyzed using the SAP2000 program. The result is that all tower frames, girders, main cables, hangers, and bridge decks, the nominal capacity is still able to withstand the ultimate load. However, the deflection in the middle of the bridge span is 0.72 m and has exceeded the allowable deflection (L/200). So based on the results of the evaluation of the Dumpoh suspension bridge structure, the cross-sectional strength of the frame is still safe, but the stiffness of the deflection value does not meet.

Longitudinal Multiple Presence of Trucks on Continuous Bridge Spans

In designing and evaluating roadway bridges in the surface transportation infrastructure, truck load is a major variable to account for. For daily operation, truck load also is a primary factor. Trucks on continuous spans were studied, with a focus on their behavior of longitudinal multiple presence in the same lane(s). Current US specifications include provisions for how to account for such multiple presence, and these provisions have evolved over the years. However, the basis for the provisions and their changes have not been well documented. An unprecedentedly large number of high-quality in-motion truck weight data were gathered in eight states across the US and used to investigate trucks’ longitudinal multiple presence behavior. A new approach to analyzing each platoon of trucks recorded in traffic was developed for this purpose. Each random platoon’s total load effect was identified, covering every truck in the platoon, to obtain reliable statistics of the maximum load effects. Results show that longitudinal multiple presence increases with truck volume and span length. Relevant current AASHTO provisions therefore were found to be conservative or overconservative. Accordingly, it was concluded that lower longitudinal multiple presence factor values for evaluation and design are more justifiable. These results may be used by bridge owners and engineers for realistic load rating and design, for more-uniform structural safety and cost effectiveness. This is consistent with the top two goals of the AASHTO Committee on Bridges and Structures’ strategic plan for extending bridge service life and assessing bridge condition.

Effect of structural repairs on the load rating and reliability of a prestressed concrete bridge

Prestressed girders often deteriorate over time due to environmental and man-made stressors, lowering the strength and serviceability of bridge structures. Although structural repairs are implemented to improve the load carrying capacity of the structure, the presence of numerous unknowns leads to high uncertainty in estimating the adequacy of repairs. For instance, the cross-section of the remaining strands, material properties, applied external loads, and workmanship assumptions made throughout the repair process introduce ambiguities when estimating the adequacy of the repairs. This study evaluates the efficiency of re-tensioning repairs of prestressed concrete bridge span girders. The repairs include field splicing, re-tensioning, of deteriorated or damaged strands by torquing a splicing coupler. The evaluation in this study considers component, system reliability, and load ratings while accounting for several uncertainties, such as structural repair, material properties, and external loads. This paper introduces an approach to account for prestressing strands damage and repair uncertainties while also accounting for other uncertainties. In this regard, five cases are studied: as-built, repaired, and three varying degrees of damage cases. First, the distribution for structural demand and capacity accounting for uncertainty in loads, material properties, and repair process is defined for each girder in the prestressed concrete bridge span. In doing so, Monte-Carlo simulation is employed to determine the distributions. Accordingly, the limit state function of the girders is defined from the obtained distributions. Then, the component reliability of each AASHTO (American Association of State Highway and Transportation Officials) Type II girder is calculated from the obtained reliability indices based on the determined limit state functions. Finally, a system reliability model of the span is developed from the component reliability of each girder. Some advantages and disadvantages of using component and system reliability index versus load rating in damaged and repaired prestressed concrete bridge girders are also discussed. Several critical conclusions are made regarding the uncertainties in structural repair, material properties and external loads, and their impact on the load rating and the component and system reliability of the prestressed concrete bridge structure girders.

Modeling and Testing of a Composite Steel-Concrete Joint for Hybrid Girder Bridges.

A hybrid girder bridge adopts a steel segment at the mid-span of the main span of a continuous concrete girder bridge. The critical point of the hybrid solution is the transition zone, connecting the steel and concrete segments of the beam. Although many girder tests revealing the structural behavior of hybrid girders have been conducted by previous studies, few specimens took the full section of a steel-concrete joint due to the large size of prototype hybrid bridges. In this study, a static load test on a composite segment to bridge the joint between the concrete and steel parts of a hybrid bridge with full section was conducted. A finite element model replicating the tested specimen results was established through Abaqus, while parametric studies were also conducted. The test and numerical results revealed that the concrete filling in the composite solution prevented the steel flange from extensive buckling, which significantly improved the load-carrying capacity of the steel-concrete joint. Meanwhile, strengthening the interaction between the steel and concrete helps to prevent the interlayer slip and simultaneously contributes to a higher flexural stiffness. These results are an important basis for establishing a rational design scheme for the steel-concrete joint of hybrid girder bridges.

Optimal design of cable-stayed bridge and its approach spans under spatially varying ground motions

The out-of-phase vibration between neighboring structures owing to their different vibration characteristics and spatially varying seismic excitations may result in strong impact between the adjacent structural components, which might result in detrimental damage to the structures. To preclude such damage, the gap size of the expansion joint and the vibration period ratio between the adjacent structures should be carefully selected. Herein, the framework of performance-based seismic design (PBSD) is extended to optimize the gap size and period ratio between the cable-stayed bridge and its approach spans under the spatially varying ground motions. Considering the computational burden, an equivalent cable-stayed bridge model is proposed and verified, and then adopted in the optimization process. Based on the multi-stripe analysis (MSA) method, the component fragility curves (pylons, bearings, and local damage) for the typical cable-stayed bridge are derived, and then the corresponding structural fragility functions, namely, repair cost ratios (RCRs) are derived. The optimal gap size and period ratio between main bridge and approach spans could be identified by the proposed optimization framework under both uniform and spatially varying excitations. The analytical results demonstrated that the optimal gap size and period ratio depend on the earthquake characteristics and the excitation methods. The optimized RCR values of the bridge subjected to the spatial varying ground motions are much larger than those of bridge under the uniform excitation.

Flutter characteristics of bridges under non-uniform wind speed

Increasing the bridge span reduces the aerodynamic stability of a bridge’s structure, and the complex wind environment in mountainous areas makes wind-resistant designs of bridges more difficult. The flutter response of bridges under a uniform flow field has been extensively studied. However, there are still various blind areas regarding the impact of non-uniform inflow on the aerodynamic stability of structures. Because of the increasing complexity of wind fields at bridge sites in mountainous areas, further investigation of the wind resistance characteristics of bridges under inhomogeneous wind fields is required. The non-uniform wind speed distribution model is first summarized in this paper, and the research conditions are set based on it. Considering a simply supported beam bridge and suspension bridge as the research objects, the flutter responses of the two bridges under the set conditions were explored, and their likenesses were compared. The analysis results demonstrate that the flutter stability of the bridge is reduced under non-uniform wind speed; therefore, the non-uniformity of wind speed cannot be completely ignored in the wind resistance design. The degree of influence of wind velocity non-uniformity on structural flutter stability hardly changes with the change in angle of attack (AOA), which can be used to simplify the bridges wind resistance design under a nonuniform inflow.

Mechanical deformation properties of Continuous Welded Rail on kilometer-span suspension bridge for high-speed railway

The complex bridge-track interaction between kilometer-span bridges and continuous Welded Rail (CWR) brings great challenges to CWR designing. Taking a suspension bridge with laying CWR as a case, the mechanical properties of CWR on the bridge are analyzed to reveal the sensitive areas of the track, and the design method of CWR and track structures on the beam ends are proposed. The results show that the unidirectional Rail Expansion Joints(REJ) need to be installed on the beam end of the kilometer-span bridge to reduce rail longitudinal force. Due to the bridge characteristics, there is no CWR fixed area on the kilometer-span bridge, and rail longitudinal force on the main span caused by bending loads needs to be concerned. The deformation of track on the beam end is complex, which is the weak area on the kilometer bridge, the large relative displacement between the stock rail of REJ and the main beam can cause poor stability of ballast bed on beam end, small resistance fasteners need to be laid on the sides of stock rail on the main beam to increase the stability of ballast and fasteners on the beam end. To improve the driving safety and comfort of beam end, the Sleeper-Supporting Apparatus (SSA) should be specially designed to ensure the uniform transition of track on beam ends. Temperature and wind loads have a significant impact on track regularity on the kilometer span bridge, the dynamic response of trains and bridges under those loads needs to be attended to.

RETHINKING THE 10% RULE: PATIENT-SPECIFIC MODELLING OF STRAIN IN DISTAL FEMUR FRACTURES

The objective of this study was to use patient-specific finite element modeling to measure the 3D interfragmentary strain environment in clinically realistic fractures. The hypothesis was that in the early post-operative period, the tissues in and around the fracture gap can tolerate a state of strain in excess of 10%, the classical limit proposed in the Perren strain theory.Eight patients (6 males, 2 females; ages 22–95 years) with distal femur fractures (OTA/AO 33-A/B/C) treated in a Level I trauma center were retrospectively identified. All were treated with lateral bridge plating. Preoperative computed tomography scans and post-operative X-rays were used to create the reduced fracture models. Patient-specific materials properties and loading conditions (20%, 60%, and 100% body weight (BW)) were applied following our published method.[1]Elements with von Mises strains >10% are shown in the 100% BW loading condition. For all three loading scenarios, as the bridge span increased, so did the maximum von Mises strain within the strain visualization region. The average gap closing (Perren) strain (mean ± SD) for all patient-specific models at each body weight (20%, 60%, and 100%) was 8.6% ± 3.9%, 25.8% ± 33.9%, and 39.3% ± 33.9%, while the corresponding max von Mises strains were 42.0% ± 29%, 110.7% ± 32.7%, and 168.4% ± 31.9%. Strains in and around the fracture gap stayed in the 2–10% range only for the lowest load application level (20% BW).Moderate loading of 60% BW and above caused gap strains that far exceeded the upper limit of the classical strain rule (<10% strain for bone healing). Since all of the included patients achieved successful unions, these findings suggest that healing of distal femur fractures may be robust to localized strains greater than 10%.

Fatigue Characteristics of Long-Span Bridge-Double Block Ballastless Track System

The key issues in designing ballastless track for high-speed railway bridges are to reduce maintenance and improve track smoothness by understanding fatigue damage characteristics. This paper is based on the principle of bridge-rail interaction and train-track-bridge coupling dynamics, the refined simulation model of bridge-CRTS I Bi-block ballastless track system is established by using the finite element method. The longitudinal force distribution law of CWR (Continuously Welded Rail) and the dynamic response characteristics of coupling systems are studied, based on the Miner rule and S-N curve. The fatigue characteristics of ballastless track system laying on long-span bridge under the dynamic train load and the effect of ballastless track system design parameters changes on fatigue characteristics are discussed. The results show that the extreme values of longitudinal force of CWR all appear in the middle of the bridge span or near the bridge bearing, and attention should be paid to the strength checking of CRW laying on long-span bridge. Under the dynamic train load, the fatigue life curve of rail on the bridge is relatively smooth and the minimum life of rail which is laying on continuous bridge decreases from 27.1 years to 17 years that which is laying on cable-stayed bridge. The life curve of track plate laying on continuous bridge is relatively smooth, and the life curve of track plate laying on cable-stayed bridge is related to the stiffness of elastic cushion, which decreases in a stepped manner, and there will be no fatigue failure on the track plate during service. The life curve of the baseplate is related to the type of bridge, the minimum life value of the baseplate appears near the bridge bearing, and there will be no fatigue failure on the baseplate during service. Increasing the stiffness of elastic cushion can effectively improve the fatigue life of track plate, and increasing the vertical stiffness of fasteners can enhance the connection between rail and track plate and improve the fatigue life of rail. The increase in train speed will increase the dynamic stress amplitude of track structure and reduce the fatigue life of the rail.

Superstructure bridge selection based on Life-Cycle cost analysis for short and medium span bridges

Bridge life cycle cost analysis (BLCCA) is a method that evaluates the total cost of a structure. Historically, deterministic approaches of the method have been used for the cost-effective selection of maintenance/preventive alternatives for different projects. However, decision makers are inherently risk averse and deterministic approaches are not strong enough to do a comprehensive informed based selection. Therefore, implementation of stochastic methods could be beneficial for decision makers and structural engineers in the superstructure selection process. Based upon common practice in Indiana, three different span length ranges were selected and eight different superstructure types both in steel and concrete were evaluated. Substructures were neglected in the analysis. The analysis was conducted for span configurations that included simple spans, two and three span continuous girders, for each span range. Cost-effective life-cycle profiles for each superstructure type were used based on Indiana Department of Transportation experience. Both deterministic and stochastic analyses were performed. In general, the inclusion of long term-costs using BLCCA reduces the differences in cost-effectiveness between alternatives for the same span length. Galvanized steel options were found to be cost-effective for different span lengths, especially for shorter spans, while prestressed bulb tees were generally the best option for longer spans.

Dynamic Responses of Spread Slab Beam Bridges Considering Inconsistent Road Roughness Conditions

In order to deeply study the dynamic response of a new type of low section short span bridge system, the numerical analysis of the extended plate girder bridge under the action of moving vehicles was carried out. In the study, the inconsistent road roughness conditions are considered, and the influence of vehicle speed on the influencing factors is discussed. The analysis results show that under various load conditions, the structural response of the outer plate beam is more critical. In addition, the amplification effect of external plate beam caused by consistent pavement roughness is greater than that caused by inconsistent pavement roughness. The torsional mode of the vehicle can be activated by the input excitation of inconsistent pavement roughness conditions, which should be handled carefully in the design.

Correlation model of deflection and rotation on pci girder bridge

A bridge is an infrastructure that experiences dynamic and repetitive loading for a long period, so it is necessary to monitor the condition of the bridge structure to ensure that the bridge is always in proper condition. Deflection is the vertical displacement that can occur in the bridge. This study aims to obtain an correlation model in the form of regression equation with multiple regression analysis methods between the deflection value and the rotation value of the PCI Girder bridge. The analysis was carried out using Finite Element Method software, by modeling the PCI Girder bridge with several vehicle load cases, and the rotation and deflection values of the bridge will be obtained. Several schemes were made regarding the number and location of rotation sensors to determine the level of accuracy. To get the relationship between rotation value and deflection value, a multiple linear regression analysis was carried out. It can be generated a multiple linear regression equation with the dependent variable being the deflection value and the independent variable being the rotation value on the bridge placement. This equation can be used to predict the deflection value in the middle of the bridge span with the percentage difference shows value smaller than 5%. In the analysis, it is able to provide results with the smallest percentage difference between numerical comparison values and linear regression equations.

Numerical Study on the Evolution Law of Explosion Response of Extra-wide Self-anchored Suspension Bridge under the Influence of Concrete Shrinkage and Creep

In order to deeply reveal the evolution law of explosion response of super wide self anchored suspension bridge under the influence of concrete shrinkage and creep, the evolution law of explosion response of extra-wide self-anchored suspension bridge under the influence of concrete shrinkage and creep is studied by simulation experiment. Based on a real bridge, the dynamic response of vertical displacement of the bottom plate of the bridge under explosion load at different ages is analyzed by numerical simulation. Firstly, the refined finite element model of the whole bridge is established by using SolidWorks software and Hypermesh software; Secondly, the explosion load is applied by ANSYS/LS-DYNA software and *LOAD_BLAST_ENHANCED (LBE) method, and the reliability of the calculation method is verified by combining the explosion test results of concrete members in the literature; Finally, the dynamic response of the bridge at different ages is analyzed by modifying the elastic modulus of the material to make the main girder reach the linearity predicted in the literature. The results show that under the action of explosion shock wave, the stress of the concrete element on the top plate of the main girder reaches the limit value and fails, forming an elliptical breach. With the increase of the age of the bridge, the vertical displacement of the bottom plate in the middle of the bridge span increases continuously, and the growth rate is “fast in front and slow in back”, which is consistent with the impact of concrete shrinkage and creep on the bridge. The results of this paper can provide an important basis for the anti-explosion protection and reinforcement of concrete extra-wide self-anchored suspension bridge.

Failure analysis of the impact of a falling object on a bridge deck

Even if not explicitly considered in most structural design codes, nor studied in-depth in past literature, reports from all over the world seem to indicate that accidental dropping of large heavy objects from transportation trucks can occur. The impact of such heavy objects onto the deck of a bridge can potentially give rise to the development of internal forces higher than those for which the bridge was designed to. To this end, the assessment of the response of bridges subjected to potential impacts from falling objects should be undertaken through idoneous numerical modelling. In recent years, the Applied Element Method (AEM) has been extensively employed to explicitly model complete structural response from the initial elastic stage all the way up to collapse and ensuing debris distribution. The present study, therefore, explores the capability of the AEM to model impact scenarios on bridge decks. It starts with a validation against experimental data available in the literature, and then passes onto the modelling of a case-study, the Morandi bridge, which at the time of its collapse, in August 2018, was being crossed by a truck carrying a heavy steel coil. However, initially use is also made of simplified analytical expressions available in the literature to estimate the forces generated by an impact of this type, with a view to gain additional confidence and reassurance on the obtained numerical results. A local model of the bridge span that the steel coil could have impacted is first developed to preliminarily assess different potential impact scenarios, followed by the analysis of a full model of the collapsed viaduct, including the estimation of debris distribution.

Road bridge monitoring using digital image correlation

The paper considers problems, defects and methods of bridge span diagnostics. It is proposed to use the promising digital image correlation method based on laser speckle imaging and high-speed video recording during bridge testing. The analysis is given to test results of the bridge over the Burunduk River in the Tomsk region and its dynamic characteristics using the Faza-1T measuring system. Relative displacements of railway beam surface are determined under live loads when using digital image correlation. According to the analysis the experimental data, the digital image correlation method and described equipment are efficient for using them in sites.