Bridge Section Research Articles

Unsteady RANS simulations of flow around a bridge section

This paper presents the results of unsteady Reynolds-averaged Navier–Stokes (URANS) simulations of flow around a common bridge deck geometry. Computations are performed with a noncommercial unstructured flow solver using two-dimensional hybrid meshes with fine near-wall resolution. The influence of different simulation parameters (grid refinement, time-step size, turbulence modelling) is analyzed, in particular in order to obtain flow solutions independent of spatial and temporal discretization. Results given by a one-equation eddy-viscosity turbulence model and a two-equation explicit algebraic Reynolds stress model are compared. Despite the limits imposed by the URANS approach and the relatively inexpensive two-dimensional computations, satisfactory agreement is found with the experimentally measured forces and pressures. These simulations help to explain the discrepancy between the results of two wind-tunnel test campaigns and show the dramatic influence of non-perfectly sharp edges on the global flow field development. The capability of the numerical approach to capture complex Reynolds number effects is also discussed.

Numerical study on suppression of vortex-induced vibrations of box girder bridge section by aerodynamic countermeasures

This paper investigates the mechanism of reduction in the amplitude of vortex-induced vibrations for a box girder bridge section in the presence of aerodynamic countermeasures using 3D LES turbulence model. Being the basic configuration for the bridge section, the aeroelastic instability of rectangular section with an aspect ratio of 4 is investigated in heaving mode under smooth flow conditions and the wake characteristics are examined. Thereafter flow around box girder section having width to depth ratio of 3.81 in the presence of aerodynamic countermeasures is analyzed and the effect of these countermeasures on the unsteady lift forces is evaluated using forced oscillation simulations. Then response of the box girder section in the presence of such aerodynamic countermeasures is investigated by conducting the free oscillation simulations, and the predicted amplitudes of vibration are compared with the experimental results. Flow visualization is employed to clarify and understand the modified flow characteristics around bridge section in the presence of aerodynamic countermeasures resulting in a reduced amplitude of vibration. Further a method based on forced oscillations to identify the reduced velocity corresponding to the maximum amplitude of vibration is proposed.

New estimation methodology of six complex aerodynamic admittance functions

This paper describes a new method for the estimation of six complex aerodynamic admittance functions. The aerodynamic admittance functions relate buffeting forces to the incoming wind turbulent components, of which the estimation accuracy affects the prediction accuracy of the buffeting response of long-span bridges. There should be two aerodynamic admittance functions corresponding to the longitudinal and vertical turbulent components, respectively, for each gust buffeting force. Therefore, there are six aerodynamic admittance functions in all for the three buffeting forces. Sears function is a complex theoretical expression for the aerodynamic admittance function for a thin airfoil. Similarly, the aerodynamic admittance functions for a bridge deck should also be complex functions. This paper presents a separated frequency-by-frequency method for estimating the six complex aerodynamic admittance functions. A new experimental methodology using an active turbulence generator is developed to measure simultaneously all the six complex aerodynamic admittance functions. Wind tunnel tests of a thin plate model and a streamlined bridge section model are conducted in turbulent flow. The six complex aerodynamic admittance functions, determined by the developed methodology are compared with the Sears functions and Davenport`s formula.

An experimental study of train-induced structural and environmental vibrations of a rail transit elevated bridge with ladder tracks

The ladder track is a new type of elastically supported vibration-reduction track system that has been applied to several urban railways in China. A field experiment was carried out at the trial section of an elevated bridge on Beijing Metro Line 5 where the ladder track is installed. The vibration responses of rails, sleepers, bridge deck, and the surrounding ground surface were measured when the train traversed on the ladder track and on the common non-ballasted slab track. The data were analysed in the time domain and the frequency domain. The experimental results show that as compared to the common non-ballasted track, the ladder track has special vibration reduction characteristics.

중간지점부의 캠버 조정에 따른 강합성교의 모멘트저감 효과

본 연구에서는 구조해석 모델링의 적합성을 평가하기 위하여, 고속철도상의 2주형 거더교에서 KTX 시험 활 하중에 의한 동적 거동에 대한 계측과 3D 모델링을 통한 시간이력해석이 수행된다. 이를 바탕으로 중앙지점부 캠버 조정을 통한 프리스트레스가 도입된 대상 교량에서 지점부의 모멘트저감 효과의 검토를 위하여, 시공단계 해석이 수 행되며, 장기거동에 대한 응력손실까지 고려된다. 적정수준의 초기 도입력을 산정하여 경제적인 교량단면을 위한 모 멘트 저감 방법이 연구된다. 최종적으로 교량 단면을 보다 효율적으로 사용할 수 있는 경제적인 교량 설계방법을 제 시한다.

Force generated by actomyosin contraction builds bridges between adhesive contacts

Extracellular matrices in vivo are heterogeneous structures containing gaps that cells bridge with an actomyosin network. To understand the basis of bridging, we plated cells on surfaces patterned with fibronectin (FN)-coated stripes separated by non-adhesive regions. Bridges developed large tensions where concave cell edges were anchored to FN by adhesion sites. Actomyosin complexes assembled near those sites (both actin and myosin filaments) and moved towards the centre of the non-adhesive regions in a treadmilling network. Inhibition of myosin-II (MII) or Rho-kinase collapsed bridges, whereas extension continued over adhesive areas. Inhibition of actin polymerization (latrunculin-A, jasplakinolide) also collapsed the actomyosin network. We suggest that MII has distinct functions at different bridge regions: (1) at the concave edges of bridges, MIIA force stimulates actin filament assembly at adhesions and (2) in the body of bridges, myosin cross-links actin filaments and stimulates actomyosin network healing when breaks occur. Both activities ensure turnover of actin networks needed to maintain stable bridges from one adhesive region to another.

Identification of aerodynamic parameters for eccentric bridge section model

The equations of motion for bridge deck section model elastically suspended in wind tunnel are formulated about mass center of the system using the Lagrangian approach, accommodating both the elasticity and damping eccentricities in the formulation. The Subsection Extended-Order Iterative Least Square (SEO-ILS) algorithm is developed in the state space for direct identification of system matrices from free vibration data of section model obtained from wind tunnel testing. The flutter derivatives can be extracted straightforwardly from the difference in the system matrices identified at zero wind velocity and at a specific wind velocity, respectively. By making use of complex modal decomposition technique, a procedure is employed to correct the system matrix at zero wind velocity considering both eccentricities. The proposed method is applied to identify the flutter derivatives of a thin plate section model and the section model of a suspension bridge. The results show a favorable agreement between the flutter derivatives of a thin plate obtained with the proposed method and those derived from the analytic formulae. The identified direct flutter derivatives of the suspension bridge section model also are in good agreements with those obtained using Scanlan's method. It is shown that the use of the corrected system matrix at zero wind velocity leads to better accuracy in identifying the flutter derivatives especially at high reduced wind velocity than using the original system matrix, and the eccentricity is found to have more influence on the cross flutter derivatives than on the direct flutter derivatives.

Comparisons of bridges flutter derivatives and generalized ones

The causes of the nonlinearity of self-excited aerodynamic force of bridge are interpreted from such two aspects as amplitude and wind velocity. The concept of “generalized flutter derivative” is proposed, and its physical meaning is illustrated. The graphs of the generalized flutter derivatives of plate and Sutong Bridge section model are plotted. The characteristics of all generalized flutter derivatives are compared and analyzed, and their superiorities are verified. The results indicate that the physical meaning of generalized flutter derivatives are more explicit compared to the traditional ones. It is more convenient to understand the nonlinearity properties of self-excited aerodynamic force of bridge according to the generalized flutter derivatives graphs with the wind velocity as the horizontal coordinate.

Die Resektion der talokalkanearen Coalitio im Kindesund Adoleszentenalter ohne und mit Stellungskorrektur

Resection of the painful medial talocalcaneal fibrocartilaginous or bony bridge, thereby restoration of mobility of the peritalar joint complex; in case of flatfoot deformity realignment of the hindfoot and midfoot by medial sliding calcaneal osteotomy and in some cases correction of equinus contracture by intramuscular lengthening of the gastrocnemius muscle. Before growth arrest: --Bony or fibrocartilaginous bridge at the medial or dorsomedial talocalcaneal region with or without pain. --Rigid flatfoot deformity caused by talocalcaneal coalition. After growth arrest: --Resection is indicated only in case of local pain or hindfoot deformity. Resection is not indicated in cases without local pain or deformity after growth arrest or in cases with marked osteoarthritis of the talonavicular or talocalcaneal joint. If the cross section of the bony bridge exceeds 20 x 30 mm, resection is not recommended. Longitudinal incision at the medial facet of the subtalar joint. Exposure of the bony bridge. Subsequent resection until the talocalcaneal joint line is clearly visible. Gentle mobilization of the contracted subtalar joint to regain inversion. After resection of the coalition the distance between the corresponding bone areas should measure at least 10 mm. Bone wax is used to prevent bleeding and the gap is filled with fatty tissue. Additionally, in some cases an intramuscular lengthening of the contracted gastrocnemius muscle is necessary. In case of flatfoot deformity alignment should be restored by calcaneal lengthening and/or medializing sliding calcaneal osteotomy. The lower leg is immobilized in a cast for at least 2 weeks postoperatively; additional procedures require an extended period of immobilization. Afterwards, range of motion exercises are useful to regain motion of the peritalar joint complex. 24 resections of a talocalcaneal coalition in 22 pediatric or adolescent patients were carried out. The coalition was located at the medial joint facet in 18 cases and in the dorsomedial talocalcaneal region in seven cases (in one patient combination of both). Three patients presented with an additional calcaneonavicular coalition. A talocalcaneal bone bridge of the entire joint was found in five cases. In seven patients an intramuscular lengthening of the gastrocnemius muscle was necessary. In nine patients a calcaneal lengthening procedure, and in five patients a calcaneal sliding osteotomy were added. A lengthening in the region of a calcaneocuboid synostosis was untertaken in one case. After a mean follow-up of 21.2 months 17 patients are completely or nearly pain-free. Five patients still complain of pain, but are improved. Two patients were lost to follow-up.

Aerodynamic Flutter Control for Typical Girder Sections of Long-Span Cable-Supported Bridges

Aerodynamic flutter control for long-span cable-supported bridges was investigated based on three basic girder sections, i.e. streamlined box girder section, box girder section with cantilevered slabs and two-isolated-girder section. Totally four kinds of aerodynamic flutter control measures (adding fairings, central-slotting, adding central stabilizers and adjusting the position of inspection rail) were included in this research. Their flutter control effects on different basic girder sections were evaluated by sectional model or aeroelastic model wind tunnel tests. It is found that all basic girder sections can get aerodynamically more stabled with appropriate aerodynamic flutter control measures, while the control effects are influenced by the details of control measures and girder section configurations. The control effects of the combinations of these four kinds of aerodynamic flutter control measures, such as central-slotting plus central-stabilizer, were also investigated through sectional model wind tunnel tests, summarized and compared to the flutter control effect of single measure respectively.

Study on the Bridge Surface Deicing System in Yuebei Section of Jingzhu Highway

The bad snowy weather in early 2008 induced large scale damages of the transportation system in Southern provinces of China, and seriously influence the normal running of society and economy. The establishment of highway deicing and snow-melting system has been the urgent task. Because of the structure characters and the particularity of construction technology of bridge system, its system design and construction become in to the key problems. In this article, combining the characters of bridge section in Yuebei section of Jingzhu Highway, we compared present highway and bridge snow-melting deicing technologies, and selected proper technologies to establish the corresponding deicing program to enhance the traffic quality and reduce the quantity of accident.

Evaluation of Prestressed Concrete I-Girder Bridge Design Software with NCHRP Process 12-50

NCHRP Process 12-50 was used to evaluate and verify prestressed concrete bridge design software commonly used in Indiana. A test bed of 40 bridge structures was developed with input from practicing engineers and Indiana Department of Transportation (INDOT) specialists. The test bed included 20 simple-span and 20 multispan bridges. The primary parameters were bridge span, girder spacing, section type, strand pattern (straight or draped), and concrete strength. The remaining parameters were held constant with practical or consensus values provided by engineers or the INDOT bridge design manual. The section types included were AASHTO Types II, III, and IV and Indiana modified Bulb-Tee beams (54–78 in. deep). An indigenous computer program, PURDUE PSBD, was developed to implement the bridge design calculations specified in the AASHTO LRFD Bridge Design Specifications, which are currently endorsed by the INDOT bridge design manual. Both CONSPAN (the most common bridge design software in Indiana) and PURDUE PSBD generated calculation results for the complete test bed of bridges. The output from both computer programs was compared to identify assumptions and discrepancies from the AASHTO LRFD specifications. These comparisons indicated excellent agreement between the results from both programs for ( a) concrete stresses and deflections at service-level loads, ( b) nominal flexural strength, ( c) nominal shear strength, and ( d) initial camber and deflections. The test bed of bridge structures and the PURDUE PSBD program developed in this research are recommended for evaluating and verifying other bridge design software.

Investigation on influence factors of buffeting response of bridges and its aeroelastic model verification for Xiaoguan Bridge

A time-domain procedure for analyzing buffeting responses of bridges is presented and implemented in ANSYS, formulated taking into account the self-excited forces, aerodynamic admittance functions (AAFs) and the coherence of buffeting forces. The buffeting forces simulated based on the span-wise coherence of buffeting forces and also considering the aerodynamic admittance functions, together with the steady aerodynamic forces are applied as external loads to the structural model to analyze the buffeting responses in time domain. In order to account for self-excited forces, elemental aeroelastic stiffness and aeroelastic damping matrices for spatial beam elements are derived following the quasi-steady theory and are incorporated in buffeting analysis through the user-defined Matrix27 element in ANSYS. The procedure is applied to the Xiaoguan Bridge, China, during the longest double cantilever stage of construction. The wind tunnel tests of four typical bridge section models are performed to measure the aerodynamic parameters of the bridge including the steady aerodynamic coefficients and aerodynamic admittance functions. The bridge aeroelastic model testing is also carried out, and coherence functions of buffeting forces are derived from the measured buffeting forces. The measurement results of the displacements and internal forces are compared with those obtained from the analytical predictions. The influence factors, including aeroelastic effect, aerodynamic admittance functions and coherence of buffeting forces, are studied in some detail. It is shown the present method inclusive of above factors gives much closer predictions of buffeting responses to the experimental results.

An archaeo-seismological study of the Nîmes Roman aqueduct, France: indirect evidence for an M > 6 seismic event?

This paper presents a synthesis of a multidisciplinary study carried out along the Nimes Roman aqueduct, located in the southeast part of France. The study was motivated by archaeologists attempting to explain the partial destructions of only one aerial bridge of the aqueduct (Pont de la Lone). Given its close proximity to the Nimes seismically active fault, a possible seismic origin for the destructions was invoked. Seismologists and structural engineers thus carried out a variety of field and numerical investigations to test the seismic hypothesis. Supporting field evidence was found first along the aerial bridge section of the aqueduct: broken stalactites, arch warping, cracks and destruction of the bridge just above a breast wall shortly after its construction. Secondly, the underground part of the canal was analysed: irregularity in the thickness of calcite deposits of the canal walls, presence of numerous cracks, horizontal shift of the otherwise linear structure of the canal and presence of calcite twins in the deposits, found only where the canal crosses the Nimes fault system. Numerical modelling and experimental results show that (1) only the Pont de la Lone would have suffered serious damage under seismic solicitation (assuming an M6 earthquake at 10 km distance). The second aerial bridge, the three levels arches Pont du Gard, an historical monument still standing today, would have suffered less damage, due to its very different fundamental frequency of around 0.4 Hz, far from the amplified seismic near-field spectrum; (2) the numerical models also show that a fall of the canal wall would require a higher magnitude event (M > 6); (3) the presence of calcite twinning requires a differential static stress of 4 MPa or greater, which can only be achieved very close to the fault rupture of a M > 6 earthquake; (4) finally, local surface rupturing of such a fault would also corroborate the hypothesis that the observed offset of the canal may be partly seismically induced. Although other possible origins for each individual evidence may not be excluded, the observed spatiotemporal concentration of architectural/geological anomalies together with the numerical results allow us to support a possible co-seismic origin for these disorders, indirectly attesting to the potential seismic activity (M > 6) of the nearby Nimes fault. Furthermore, following the conclusions of archaeological studies, the disorders occurred between 250 and 350 year AD, thus providing timing for this possible seismic event, an essential parameter in seismic hazard analysis. These results validate the archaeo-seismological approach as a tool that may help improve the knowledge of major infrequent earthquakes in areas of moderate seismic activity.

Bridge health monitoring system based on vibration measurements

A bridge health monitoring system is presented based on vibration measurements collected from a network of acceleration sensors. Sophisticated structural identification methods, combining information from the sensor network with the theoretical information built into a finite element model for simulating bridge behavior, are incorporated into the system in order to monitor structural condition, track structural changes and identify the location, type and extent of damage. This work starts with a brief overview of the modal and model identification algorithms and software incorporated into the monitoring system and then presents details on a Bayesian inference framework for the identification of the location and the severity of damage using measured modal characteristics. The methodology for damage detection combines the information contained in a set of measurement modal data with the information provided by a family of competitive, parameterized, finite element model classes simulating plausible damage scenarios in the structure. The effectiveness of the damage detection algorithm is demonstrated and validated using simulated modal data from an instrumented R/C bridge of the Egnatia Odos motorway, as well as using experimental vibration data from a laboratory small-scaled bridge section.

Prediction of aerodynamic characteristics of a box girder bridge section using the LES turbulence model

In this study, aerodynamic characteristics of a box girder bridge section are investigated by three-dimensional computational fluid dynamics using the LES turbulence model. Flow around the streamline box girder section is analyzed, and the effect of section details on the aerodynamic characteristics of bridge section is evaluated. In addition, forced vibration cases are simulated to investigate the aeroelastic behavior of rectangular sections with a high aspect ratio. The flutter characteristics of a box girder bridge section ( B/ D=11.6) are investigated and compared with experimental results of the generic rectangular cross-sections. Finally, influence of the geometrical modifications on the aeroelastic instability of the bridge section is pursued.

Prediction of flutter derivatives by artificial neural networks

This study presents an approach using artificial neural networks (ANN) algorithm for predicting the flutter derivatives of rectangular section models without wind tunnel tests. Firstly, a database of flutter derivatives is identified from a back-propagation (BP) ANN model that is built using experimental dynamic responses of rectangular section models in smooth flow as the input/output data. Then, these limited sets of database are employed as input/output data to establish a prediction ANN frame model to further predict the flutter derivatives for other rectangular section models without conducting wind tunnel tests. The results presented indicate that this ANN prediction scheme works reasonably well. Therefore, instead of going through wind tunnel tests, this ANN approach provides a convenient and feasible option for expanding the flutter derivative database that can help to determine an appropriate basic shape of the bridge section in the preliminary design.

The Piston-Stayed Bridge: A Novel Typology for a Mobile Bridge at Tervate, Belgium

Click to increase image sizeClick to decrease image sizeKey words:: typologypistonstaymobilemulti-functional

Enhancement of Flexural Design of Horizontally Curved Prestressed Bridges

In this paper, flexural behavior of horizontally curved prestressed (posttensioned) box bridges is studied by using three-dimensional and refined finite-element modeling and analysis. Bridge length, section geometry, and material properties are the same in all the models, while angle of curvature varies from 0 to 90° . The results of analysis show that in curved bridges, stress distribution is significantly different in comparison to straight bridges. Also, the level of stresses at some locations of section width is considerably high. It is proposed to vary the distribution of the prestressing tendons across section width in order to optimize the bridge capacity. Results show that by proper redistribution of prestressing in section width, significant reduction in resultant stress is possible.

Investigation of vortex response of a twin box bridge section at high and low Reynolds numbers

The vortex shedding response of a twin box bridge girder deck with and without guide vanes has been investigated at three different Reynolds numbers with the objective of identifying the mode of vortex excitation and suitable conditions for testing that will allow faithful evaluation of guide vane mitigation efficiency. It has been established that the displacement thickness must be at the order of 10% of the guide vane offset in order to allow sufficient flow rate to render the guide vane efficient. Conventional section model scales ranging from 1:50 to 1:100 are not likely to be capable of fulfilling such conditions. Measurement of the fluctuating pressure field around the twin girder deck indicates that vortices shed from the upwind box will impinge on the downwind box resulting in higher fluctuating pressures here than on the upwind box from where the vortices are shed. This process is likely to render the twin deck more susceptible to vortex shedding excitation than the mono box deck.