Assessment of Extreme Wave Impact on Coastal Decks with Different Geometries via the Arbitrary Lagrangian-Eulerian Method

Given the documented wave-induced damage of elevated coastal decks during extreme natural hazards (e.g., hurricanes) in the last two decades, it is of utmost significance to decipher the wave-structure-interaction of complex deck geometries and quantify the associated loads. Therefore, this study focuses on the assessment of solitary wave impact on open-girder decks that allow the air to escape from the sides. To this end, an arbitrary Lagrangian-Eulerian (ALE) numerical method with a multi-phase compressible formulation is used for the development of three-dimensional hydrodynamic models, which are validated against a large-scale experimental dataset of a coastal deck. Using the validated model as a baseline, a parametric investigation of different deck geometries with a varying number of girders Ng and three different widths, was conducted. The results reveal that the Ng of a superstructure has a complex role and that for small wave heights the horizontal and uplift forces increase with the Ng, while for large waves the opposite happens. If the Ng is small the wave particles accelerate after the initial impact on the offshore girder leading to a more violent slamming on the onshore part of the deck and larger pressures and forces, however, if Ng is large then unsynchronized eddies are formed in each chamber, which dissipate energy and apply out-of-phase pressures that result in multiple but weaker impacts on the deck. The decomposition of the total loads into slamming and quasi-static components, reveals surprisingly consistent trends for all the simulated waves, which facilitates the development of predictive load equations. These new equations, which are a function of Ng and are limited by the ratio of the wavelength to the deck width, provide more accurate predictions than existing empirical methods, and are expected to be useful to both engineers and researchers working towards the development of resilient coastal infrastructure.

Assessment of Extreme Wave Impact on Coastal Decks with Different Geometries via the Arbitrary Lagrangian-Eulerian Method

Given the documented wave-induced damage of elevated coastal decks during extreme natural hazards (e.g. hurricanes) in the last two decades, it is of utmost significance to decipher the wave-structure-interaction of complex deck geometries and quantify the associated loads. Therefore, this study focuses on the assessment of solitary wave impact on open-girder decks that allow the air to escape from the sides. To this end, an arbitrary Lagrangian-Eulerian (ALE) numerical method with a multi-phase compressible formulation is used for the development of three-dimensional hydrodynamic models, which are validated against a large-scale experimental dataset of a coastal deck. Using the validated model as a baseline, a parametric investigation of different deck geometries with a varying number of girders Ng and three different widths, was conducted. The results reveal that the Ng of a superstructure has a complex role and that for small wave heights the horizontal and uplift forces increase with the Ng, while for large waves the opposite happens. If the Ng is small the wave particles accelerate after the initial impact on the offshore girder leading to a more violent slamming on the onshore part of the deck and larger pressures and forces, however, if Ng is large then unsynchronized eddies are formed in each chamber, which dissipate energy and apply out-of-phase pressures that result in multiple but weaker impacts on the deck. The decomposition of the total loads into slamming and quasi-static components, reveals surprisingly consistent trends for all the simulated waves, which facilitates the development of predictive load equations. These new equations, which are a function of Ng and are limited by the ratio of the wavelength to the deck width, provide more accurate predictions than existing empirical methods, and are expected to be useful to both engineers and researchers working towards the development of resilient coastal infrastructure.

Numerical simulation and optimization of aerodynamic uplift force of a high-speed pantograph

Aiming at the problem that aerodynamic uplift forces of the pantograph running in the knuckle-downstream and knuckle-upstream conditions are inconsistent, and their magnitudes do not satisfy the corresponding standard, the aerodynamic uplift forces of pantographs with baffles are numerically investigated, and an optimization method to determine the baffle angle is proposed. First, the error between the aerodynamic resistances of the pantograph obtained by numerical simulation and wind tunnel test is less than 5%, which indicates the accuracy of the numerical simulation method. Second, the original pantograph and pantographs equipped with three different baffles are numerically simulated to obtain the aerodynamic forces and moments of the pantograph components. Three different angles for the baffles are −17°, 0° and 17°. Then the multibody simulation is used to calculate the aerodynamic uplift force of the pantograph, and the optimal range for the baffle angle is determined. Results show that the lift force of the baffle increases with the increment of the angle in the knuckle-downstream condition, whereas the lift force of the baffle decreases with the increment of the angle in the knuckle-upstream condition. According to the results of the aerodynamic uplift force, the optimal angle of the baffle is determined to be 4.75° when the running speed is 350 km/h, and pantograph–catenary contact forces are 128.89 N and 129.15 N under the knuckle-downstream and knuckle-upstream operating conditions, respectively, which are almost equal and both meet the requirements of the standard EN50367:2012.

New drawbead tester and numerical analysis of drawbead closure force

Currently, a great deal of controversy exists regarding the real forces generated in drawbeads during sheet metal forming processes. The present work focuses on the analysis of the uplift force. First, a detailed literature review is carried out to analyse previous experimental procedures used to measure uplift forces. It is found that previous setups do not perfectly replicate the real geometry of industrial drawbeads. In order to obtain reliable forces, an experimental drawbead tester capable of adequately replicating industrial drawbeads is developed. Later, a variety of steels ranging from mild steels to 3rd-generation ultra-high-strength steels are tested and reliable uplift and also restraining force values are obtained. The main purpose of the work is to share with the research community reliable experimental data that allows precise evaluation of the accuracy of current drawbead models and that supports the generation of new numerical and equivalent drawbead models. In parallel to the experimental procedure, a step forward in the understanding of the drawbead closing phenomena is also achieved through a 2D numerical model. The main purpose of the model is to identify the variables that greatly affect uplift force. Going beyond previous studies, in which some variables were analysed, the present work covers, in a holistic manner, the impact that material properties, the geometry of drawbeads and contact behaviour between sheet and drawbead have on the uplift force. It is determined that surprisingly minor geometrical deviations in the drawbead nominal geometry have a large impact on the uplift force.

Design and analysis of plate anchors in sand

Plate anchors, as an efficient and reliable anchorage system, have been widely used to resist uplift forces produced by structures, such as transmission towers, offshore platforms, submerged pipelines, and tunnels. In order to design a plate anchor it is important to know the factors which influence the design and uplift behavior of anchors embedded in sand. In this report a number of model uplift tests and numerical investigations made by different authors are described and based on these readings the uplift behavior of anchors in sand is explored and anchor's design procedure is described. In addition, basic anchor types, failure modes in anchors, and design codes are mentioned. Based on this study, it is found that the failure plane and uplift capacity is significantly influenced by the soil density and embedment depth. Therefore, it is concluded that the influence of sand density and embedment depth should be considered in anchor design.

Design and analysis of plate anchors in sand

Plate anchors, as an efficient and reliable anchorage system, have been widely used to resist uplift forces produced by structures, such as transmission towers, offshore platforms, submerged pipelines, and tunnels. In order to design a plate anchor it is important to know the factors which influence the design and uplift behavior of anchors embedded in sand. In this report a number of model uplift tests and numerical investigations made by different authors are described and based on these readings the uplift behavior of anchors in sand is explored and anchor's design procedure is described. In addition, basic anchor types, failure modes in anchors, and design codes are mentioned. Based on this study, it is found that the failure plane and uplift capacity is significantly influenced by the soil density and embedment depth. Therefore, it is concluded that the influence of sand density and embedment depth should be considered in anchor design.

Bearing systems for light rail bridges

<p>Light Railways are very frequently utilized for Mass Transit Systems to reduce the traffic impact in congested urban areas. Bridges for the Light Railways, even if their static scheme is often very simple, are peculiar structures where the interactions between vehicles, rail and bearings play a fundamental role. An important aspect of the bearings for Light Rail bridges, frequently requiring special solutions, is also the very high train frequency and the relatively high deformation of the structures under load, implying extremely high performance requirements and fatigue resistance of the bearings . In some cases, as for instance in monorail lines, also uplift forces shall be considered. The authors, currently involved in the design and supply of the structural bearings for several Light Rail projects in the world (Thailand, Egypt, Indonesia and others), describe the different solutions of the bearing systems currently utilized, putting in evidence the fatigue and wear resistance problems.</p><p><br clear="none"/></p>

Strengthening strategies of highway viaducts in Germany

<p>An entire generation of reinforced concrete highway bridges built in the post-war period in Germany meanwhile is approaching the end of their service life. The federal government and regional highway administrations have realized the need to repair, strengthen or to replace these structures and engage in extensive infrastructural investments to meet this challenge. It is not possible to replace those bridges in a short period, so that a guideline for reassessment of bridges has been developed to enable to prioritize the structures. Besides the replacement of the bridges, measures need to be taken in order to extend the lifespan of the decaying bridges until such replacement becomes available. Using the examples of four major highway viaducts near Frankfurt/Main and Hamburg efficient strategies to strengthen existing structures will be presented.</p><p>In the first example the efficient usage of external tendons to reduce the danger of a fatigue induced failure of a 50 years old prestressed concrete bridge will be presented.</p><p>A bridge of five spans with a total length of approximately 300 m showing inadequate shear resistance has been enhanced by installing inclined steel struts at the pillars. The struts are activated with a predefined force by built-in hydraulic jacks, while special spring elements used as supports reduce the effect of imposed deformations. Furthermore in critical areas of the webs additional shear reinforcement is mounted and subsequently covered by a concrete layer.</p><p>Another large viaduct was showing signs of fatigue at the coupling joints. A detailed analysis of the structure revealed, that the lifespan could be sufficiently prolonged by supporting the critical coupling joints with a predetermined force. The magnitude of the force is maintained constant by a balanced beam resembling a seesaw, which is mounted on a steel tower and fitted at its opposite end with counterweights.</p><p>The final example shows how to apply controlled uplift forces using an elastic bedded supporting beam construction.</p><p>These realized examples demonstrate, how with smart and intelligent measures critical bridges can be strengthened and an essential increase in lifespan can be achieved.</p>