Coupled CFD-FEM Simulation of Steel Box Bridge Exposed to Fire

Increasing fire-induced bridge failures are demanding more precise behavior prediction for the bridges subjected to fires. However, current numerical methods are limited to temperature curves prescribed for building structures, which can misestimate the fire impact significantly. This paper developed a framework coupling the computational dynamics (CFD) method and finite element method (FEM) to predict the performance of fire-exposed bridges. The fire combustion was simulated in CFD software, Fire Dynamic Simulator, to calculate the thermal boundary required by the thermomechanical simulation. Then, the adiabatic surface temperatures and heat transfer coefficient were applied to the FEM model of the entire bridge girder. A sequential coupled thermomechanical FEM simulation was then carried out to evaluate the performance of the fire-exposed bridge, thermally and structurally. The methodology was then validated through a real fire experiment on a steel beam. The fire performance of a simply supported steel box bridge was simulated using the proposed coupled CFD-FEM methodology. Numerical results show that the presented method was able to replicate the inhomogeneous thermomechanical response of box bridges exposed to real fires. The girder failed due to the buckling of a central diaphragm after the ignition of the investigated tanker fire in no more than 10 min. The framework presented in this study is programmatic and friendly to researchers and can be applied for the estimation of bridges in different fire conditions.

Numerical Analysis on the Crosswind Influence Around a Generic Train Moving on Different Bridge Configurations

In this article, a numerical approach is applied to study the flow regimes surround a generic train model travelling on different bridge configurations under the influence of crosswind. The bridge is varies based on the different geometry of the bridge girder. The crosswind flow angle (Ψ) is varied from 0° to 90°. The incompressible flow around the train was resolved by utilizing the Reynolds-averaged Navier-Stokes (RANS) equations combined with the SST k-ω turbulence model. The Reynolds number used, based on the height of the train and the freestream velocity, is 3.7 × 105. In the results, it was found that variations of the crosswind flow angles produced different flow regimes. Two unique flow regimes appear, representing (i) slender body flow behaviour at a smaller range of Ψ (i.e. Ψ ≤ 45°) and (ii) bluff body flow behaviour at a higher range of Ψ (i.e. Ψ ≥ 60°). As the geometries of the bridge girder were varied, the bridge with the wedge girder showed the worst aerodynamic properties with both important aerodynamic loads (i.e. side force and rolling moment), followed by the triangular girder and the rectangular girder. This was due to the flow separation on the windward side and flow structure formation on the leeward side, both of which are majorly influenced by the flow that moved from the top and below of the bridge structures.

Performance of Pier-to-Pier Cap Connections of Integral Bridges under Thermal and Seismic Loads

In general, most highway bridges are constructed using prestressed concrete or steel girders. Mechanical joints are provided at the end of each span, to allow for the expansion of the bridge deck due to shrinkage of concrete, thermal effects, and deflections, among others. Smooth riding ability, low noise, wear resistance, and water tightness should be provided by expansion joints. In recent times, the increased traffic volume, along with heavier vehicle movements, adversely affects the performance of expansion joints in the bridge girder, causing a possible failure in one of the above-mentioned mechanisms. The deterioration of the expansion joint may result in leakage of water, concrete cracking, and potential problems in the underlying substructure. In this paper, we study the pier-pier cap connections in integral bridges subjected to thermal and seismic loads using analytical methods and experimental tests.

Aerodynamic Performance Evaluation of a Skydio UAV via CFD As a Platform for Bridge Girder Inspection: Phase 1 Study

The goal of the proposed work was to analyze the aerodynamic performance of a Skydio 6 unmanned aerial vehicle (UAV) as a supplementary tool for bridge girder inspections. The use of UAVs has become more attractive due to their ability to gather critical information in less time and at a lower cost when compared to traditional bridge girder inspection techniques. In pursuit of this goal, the present work presents aerodynamic performance evaluation results via computational fluid dynamics (CFD) of a Skydio 2 UAV for bridge girder inspection. The study is implemented using the commercially available CFD solver, ANSYS FLUENT (v. 19). The evaluation study utilized an unstructured tetrahedron meshing technique throughout the numerical analysis, with a standard k-epsilon turbulence model. The Multiple Reference Frame (MRF) model was also used to model the rotation of the propellers toward their local reference frame at 6000 revolutions per minute (RPM). This paper presents the numerical modeling methodology as well as a discussion of parametric results. The parametric results presented show reliable moment coefficient and thrust making the Skydio 2 UAV suitable for bridge inspection.

Numerical Simulation of Characteristics of Wind Field at Bridge Sites in Flat and Gorge Terrains under the Thunderstorm Downburst

To investigate the effects of thunderstorm downburst on the characteristics of wind field at bridge sites in flat and gorge terrains, firstly, numerical simulation of wind fields in the flat terrain under the thunderstorm downburst was conducted through the SST k-ω turbulence model, combined with the impinging jet technology. After verification of the reliability of the numerical model, settings, and methods, the characteristics of wind field over a long-span bridge site in a gorge terrain under the thunderstorm downburst were investigated and the distributions of wind speed and wind attack angle in the flat and gorge terrains were compared. The results show that, under the effects of the thunderstorm downburst, the wind speeds are relatively maximum at the midspan point of the girder in the flat terrain. Besides, the farther away from the midspan point, the smaller the wind speeds, which is opposite to the case in the gorge terrain. The wind speeds at each typical monitoring point are basically the same in the two terrains, before the thunderstorm downburst hits the bridge girder. Later the wind speeds at each point in the gorge terrain are much higher than those in the flat terrain. Most wind attack angles are negative at the monitoring points in the flat terrain, but the farther away they are from the midspan point, the greater the wind attack angles will be. However, the wind attack angles at the monitoring points in the gorge terrain are generally larger than those in the flat terrain, and they gradually turn to be positive farther away from the midspan point. In the flat terrain, both wind speeds and wind attack angles (or their absolute values) at the girder are large within about t = 75∼130 s, indicating that the thunderstorm downburst may exert significant effects on the bridge. However, in the gorge terrain, due to the large wind speeds and wind attack angles (or their absolute values) at the girder after t = 75 s, full attention needs to be paid to the effects of the thunderstorm downburst during this period.

Performance Evaluation of a Prestressed Belitic Calcium Sulfoaluminate Cement (BCSA) Concrete Bridge Girder

Belitic calcium sulfoaluminate (BCSA) cement is a sustainable alternative to Portland cement that offers rapid setting characteristics that could accelerate throughput in precast concrete operations. BCSA cements have lower carbon footprint, embodied energy, and natural resource consumption than Portland cement. However, these benefits are not often utilized in structural members due to lack of specifications and perceived logistical challenges. This paper evaluates the performance of a full-scale precast, prestressed voided deck slab bridge girder made with BCSA cement concrete. The rapid-set properties of BCSA cement allowed the initial concrete compressive strength to reach the required 4300 psi release strength at 6.5 h after casting. Prestress losses were monitored long-term using vibrating wire strain gages cast into the concrete at the level of the prestressing strands and the data were compared to the American Association of State Highway and Transportation Officials Load and Resistance Factor Design (AASHTO LRFD) predicted prestress losses. AASHTO methods for prestress loss calculation were overestimated compared to the vibrating wire strain gage data. Material testing was performed to quantify material properties including compressive strength, tensile strength, static and dynamic elastic modulus, creep, and drying and autogenous shrinkage. The material testing results were compared to AASHTO predictions for creep and shrinkage losses. The bridge girder was tested at mid-span and at a distance of 1.25 times the depth of the beam (1.25d) from the face of the support until failure. Mid-span testing consisted of a crack reopening test to solve for the effective prestress in the girder and a flexural test until failure. The crack reopen effective prestress was compared to the AASHTO prediction and AASHTO appeared to be effective in predicting losses based on the crack reopen data. The mid-span failure was a shear failure, well predicted by AASHTO LRFD. The 1.25d test resulted in a bond failure, but nearly developed based on a moment curvature estimate indicating the AASHTO bond model was conservative.

Seismic behavior of the main girder of a bridge with viscoelastic dampers

Introduction. The seismic stability of bearing structures is one of the main objectives of design and construction of structures in earthquake areas. The co-authors have analyzed the effect of a damper, located at the intersection of structural elements, on the seismic response of the main girder of a steel-concrete bridge exposed to the seismic impact. The purpose of this study is to select optimal values of viscous and elastic elements to ensure the seismic resistance of the bridge. Materials and methods. The finite element method was used to simulate the geometric characteristics of the bridge. The model of the bridge has rod elements to simulate girders and viscous elastic elements to simulate dampers. In the study, different values of elastic and viscous characteristics of the damper were used in pairs. The nonlinear problem statement helped to analyze the bridge structure using the direct dynamic method. Results. As a result, we obtained a graphic chart describing the relationship between horizontal displacements and the time for each pair of values of elastic and viscous characteristics of the damper for Maxwell and Kelvin – Voigt models. The effect of changes in the values of stiffness and damping parameters on the values of the period and eigenfrequencies of this superstructure was also investigated. Conclusions. The co-authors chose the damper parameters to minimize seismic displacements of the bridge girder and optimally suppress the dynamic interaction between the bridge elements. Viscoelastic elements of the Kelvin – Voigt type provide more regular values of horizontal displacements of the girder when the direction of the seismic effect changes. We also recommend to select the pair of values equal to 20 000 kN/m, 800 kN s/m, and to use the Kelvin – Voigt model in the design of a viscoelastic damper.