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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.

In response to the extensive damage of coastal bridges sustained in recent tsunamis, this paper describes an investigation into tsunami-induced effects on two common bridge types, an open-girder deck with cross-frames and one with solid diaphragms. To this end, large-scale (1:5) physical models with realistic structural members and elastomeric bearings were constructed and tested under a range of unbroken solitary waves and more realistic tsunami-like transient bores. The flexible bearings allowed the superstructure to rotate and translate vertically, thus simulating the wave–structure interaction during the tsunami inundation. Detailed analysis of the experimental data revealed that for both bridge types the resistance mechanism and transient structural response is characterized by a short-duration phase that introduces the maximum overturning moment, upward movement, and rotation of the deck, and a longer-duration phase that introduces significant uplift forces but small moment and rotation due to the fact that the wave is approaching the point of rotation. In the former phase the uplift is resisted mainly by the elastomeric bearings and columns offshore of the center of gravity of the superstructure (C.G.), maximizing their uplift demand. In the latter phase the total uplift is distributed more equally to all the bearings, which tends to maximize the uplift demand in the structural members close to the C.G. The air-entrapment in the chambers of the bridge with diaphragms modifies the wave–structure interaction, introducing (a) a different pattern and magnitude of wave pressures on the superstructure due to the cushioning effect; (b) a 39% average and 148% maximum increase in the total uplift forces; and (c) a 32% average increase of the overturning moment, which has not been discussed in previous studies. Deciphering the exact effect of the trapped air on the total uplift forces is challenging because, although the air consistently increases the quasi-static component of the force, it has an inconsistent and complex effect on the slamming component, which can either increase or decrease. Interestingly, the air also has a complex effect on the uplift demand in the offshore bearings and columns, which can decrease or increase even more than the total deck uplift, and an inconsistent effect on the uplift force of different structural components introduced by the same wave. These are major findings because they demonstrate that the current approach of investigating the effect of trapped air only on the total uplift is insufficient. Last but not least, the study reveals the existence of significant differences in the effects introduced by solitary waves and transient bores, especially when air is trapped beneath the deck; it also provides practical guidance to engineers, who are advised to design the elastomeric bearings offshore of the C.G. for at least 60% and 50% of the total induced uplift force, respectively, for a bridge with cross-frames and one with diaphragms, instead of distributing the total uplift equally to all bearings.

Field surveys in recent tsunami events document the catastrophic effects of large waterborne debris on coastal infrastructure. Despite the availability of experimental studies, numerical studies investigating these effects are very limited due to the need to simulate different domains (fluid, solid), complex turbulent flows and multi-physics interactions. This study presents a coupled SPH–FEM modeling approach that simulates the fluid with particles, and the flume, the debris and the structure with mesh-based finite elements. The interaction between the fluid and solid bodies is captured via node-to-solid contacts, while the interaction of the debris with the flume and the structure is defined via a two-way segment-based contact. The modeling approach is validated using available large-scale experiments in the literature, in which a restrained shipping container is transported by a tsunami bore inland until it impacts a vertical column. Comparison of the experimental data with the two-dimensional numerical simulations reveals that the SPH–FEM models can predict (i) the non-linear transformation of the tsunami wave as it propagates towards the coast, (ii) the debris–fluid interaction and (iii) the impact on a coastal structure, with reasonable accuracy. Following the validation of the models, a limited investigation was conducted, which demonstrated the generation of significant debris pitching that led to a non-normal impact on the column with a reduced contact area and impact force. While the exact level of debris pitching is highly dependent on the tsunami characteristics and the initial water depth, it could potentially result in a non-linear force–velocity trend that has not been considered to date, highlighting the need for further investigation preferably with three-dimensional models.

In view of the widespread damage to coastal bridges during recent tsunamis (2004 Indian Ocean and 2011 in Japan) large-scale hydrodynamic experiments of tsunami wave impact on a bridge with open girders were conducted in the Large Wave Flume at Oregon State University. The main objective was to decipher the tsunami overtopping process and associated demand on the bridge and its structural components. As described in this paper, a comprehensive analysis of the experimental data revealed that: (a) tsunami bores introduce significant slamming forces, both horizontal (Fh) and uplift (Fv), during impact on the offshore girder and overhang; these can govern the uplift demand in connections; (b) maxFh and maxFv do not always occur at the same time and contrary to recommended practice the simultaneous application of maxFh and maxFv at the center of gravity of the deck does not yield conservative estimates of the uplift demand in individual connections; (c) the offshore connections have to withstand the largest percentage of the total induced deck uplift among all connections; this can reach 91% and 124% of maxFv for bearings and columns respectively, a finding that could explain the damage sustained by these connections and one that has not been recognized to date; (e) the generation of a significant overturning moment (OTM) at the initial impact when the slamming forces are maximized, which is the main reason for the increased uplift in the offshore connections; and (f) neither maxFv nor maxOTM coincide always with the maximum demand in each connection, suggesting the need to consider multiple combinations of forces with corresponding moments or with corresponding locations of application in order to identify the governing scenario for each structural component. In addition the paper presents “tsunami demand diagrams”, which are 2D envelopes of (Fh, Fv) and (OTM, Fv) and 3D envelopes of (Fh, Fv, OTM), as visual representations of the complex variation of the tsunami loading. Furthermore, the paper reveals the existence of a complex bridge inundation mechanism that consists of three uplift phases and one downward phase, with each phase maximizing the demand in different structural components. It then develops a new physics-based methodology consisting of three load cases, which can be used by practicing engineers for the tsunami design of bridge connections, steel bearings and columns. The findings in this paper suggest the need for a paradigm shift in the assessment of tsunami risk to coastal bridges to include not just the estimation of total tsunami load on a bridge but also the distribution of this load to individual structural components that are necessary for the survival of the bridge.

Protection of coastal cultural heritage is among the most urgent global priorities, as these sites face increasing threats from climate change, sea level rise, and human activity. This study emphasises the value of innovative geospatial tools and data ecosystems for timely risk assessment. The role of land administration systems, geospatial documentation of coastal cultural heritage sites, and the adoption of innovative techniques that combine various methodologies is crucial for timely action. The coastal management infrastructure in Greece is presented, outlining the key public authorities and national legislation, as well as the land administration and geospatial ecosystems and the various available geospatial ecosystems. We profile the Hellenic Cadastre and the Hellenic Archaeological Cadastre along with open geospatial resources, and introduce TRIQUETRA Decision Support System (DSS), produced through the EU’s Horizon project, and a Digital Twin methodology for hazard identification, quantification, and mitigation. Particular emphasis is given to the role of Digital Twin technology, which acts as a continuously updated virtual replica of coastal cultural heritage sites, integrating heterogeneous geospatial datasets such as cadastral information, photogrammetric 3D models, climate projections, and hazard simulations, allowing for stakeholders to test future scenarios of sea level rise, flooding, and erosion, offering an advanced tool for resilience planning. The approach is validated at the coastal archaeological site of Aegina Kolona, where a UAV-based SfM-MVS survey produced using high-resolution photogrammetric outputs, including a dense point cloud exceeding 60 million points, a 5 cm resolution Digital Surface Model, high-resolution orthomosaics with a ground sampling distance of 1 cm and 2.5 cm, and a textured 3D model using more than 6000 nadir and oblique images. These products provided a geospatial infrastructure for flood risk assessment under extreme rainfall events, following a multi-scale hydrologic–hydraulic modelling framework. Island-scale simulations using a 5 m Digital Elevation Model (DEM) were coupled with site-scale modelling based on the high-resolution UAV-derived DEM, allowing for the nested evaluation of water flow, inundation extents, and velocity patterns. This approach revealed spatially variable flood impacts on individual structures, highlighted the sensitivity of the results to watershed delineation and model resolution, and identified critical intervention windows for temporary protection measures. We conclude that integrating land administration systems, open geospatial data, and Digital Twin technology provides a practical pathway to proactive and efficient management, increasing resilience for coastal heritage against climate change threats.

Urban flooding increasingly disrupts public transportation, critical for vulnerable populations including elderly and low-income groups. Most research on flood resilience in transportation focuses on private vehicles, overlooking vulnerable users’ reliance on public transport. This study addresses that gap by assessing flood-related disruption across the surface public-transport network of a large municipality in Athens, Greece. Using a two-dimensional coupled hydrological–hydraulic model, we simulate a 100-year flood and estimate water depths across the road network. Public transport and road infrastructure data are integrated in a Geographical Information System to identify segments where depths exceed 0.3 m, an operational safety threshold used for conservative detour screening. Critical links, affected bus stops and disrupted routes are systematically mapped, while the affected population is estimated through isochrone curves that delineate 15- and 30-minute accessibility. This approach pinpoints vulnerable areas, nodes and corridors in the network, supporting disaster preparedness and operational planning. The findings facilitate flood-risk maps tailored to public transport, enabling transit operators and municipal authorities to pre-emptively design alternative service plans.

Cultural heritage (CH) sites are frequently exposed to natural elements, and their exposure becomes particularly precarious with the onset of climate change. This increased vulnerability places these sites at risk of deterioration or complete destruction. Risks such as land deformation, floods, acid rain, and erosion significantly threaten historic monuments, while water-related hazards, significantly influenced by both climate change and human activities, present a particularly grave risk to these invaluable sites. Considerable research efforts have focused on safeguarding CH sites. However, there remains a deficiency in systemic approaches towards identifying and mitigating risks for CH sites. The TRIQUETRA project proposes a technological toolbox and a methodological framework for tackling climate change risks and natural hazards threatening CH in the most efficient way possible. It aims at creating an evidence-based assessment platform allowing precise risk stratification as well as a database of available mitigation measures and strategies, acting as a Decision Support System (DSS) towards efficient risk mitigation and site remediation. TRIQUETRA is a European project that brings together a diverse group of researchers with varied expertise, encompassing university research groups, research institutes, public entities, as well as small and medium-sized enterprises. In this article, TRIQUETRAs overall methodology is presented, and preliminary results concerning risk identification, TRIQUETRAs knowledge base, as well as novel sensors and coatings, are discussed.

Floods are devastating phenomena that occur almost all around the world and are responsible for significant losses, in terms of both human lives and economic damages. When floods occur, one of the challenges that emergency response agencies face is the identification of the flooded area so that access points and safe routes can be determined quickly. This study presents a flood detection methodology that combines transfer learning with vision transformers and satellite images from open datasets. Transformers are powerful models that have been successfully applied in Natural Language Processing (NLP). A variation of this model is the vision transformer (ViT), which can be applied to image classification tasks. The methodology is applied and evaluated for two types of satellite images: Synthetic Aperture Radar (SAR) images from Sentinel-1 and Multispectral Instrument (MSI) images from Sentinel-2. By using a pre-trained vision transformer and transfer learning, the model is fine-tuned on these two datasets to train the models to determine whether the images contain floods. It is found that the proposed methodology achieves an accuracy of 84.84% on the Sentinel-1 dataset and 83.14% on the Sentinel-2 dataset, revealing its insensitivity to the image type and applicability to a wide range of available visual data for flood detection. Moreover, this study shows that the proposed approach outperforms state-of-the-art CNN models by up to 15% on the SAR images and 9% on the MSI images. Overall, it is shown that the combination of transfer learning, vision transformers, and satellite images is a promising tool for flood risk management experts and emergency response agencies.

Recent major earthquake events that occurred in the Indian Ocean (2004), Chile (2010) and Japan (2011) generated tsunami waves of significant heights, which inundated nearby coastal cities causing extreme destruction and loss of human lives. Many coastal bridges were inundated by the tsunami and although they were able to withstand the earthquake, they were damaged by the subsequent waves. In particular, the tsunami inundation damaged 81 bridges on the coast of Sumatra in 2004 and 252 bridges in Japan in 2011 according to on-site investigations (Unjoh 2007 and Maruyama 2013a respectively). The main damage occurred in the connections of the superstructure to the substructure causing the bridge deck to be unseated and washed away. This damage pattern was observed for different types of bridges including steel-truss bridges, I-girder composite bridges, PC-girder bridges and box-girder bridges. These unforeseen events demonstrated the vulnerability of bridges to tsunami inundation. The main objectives of this study were to (a) understand the tsunami inundation mechanism of coastal bridges, (b) evaluate the accuracy of existing simplified predictive equations for tsunami loads, (c) identify the difference in the bridge response when subjected to unbroken solitary waves and more realistic turbulent bores, (d) investigate not only the total waves forces but also the distribution of these forces in each bearing and connection in order to determine the max force that each connection has to withstand, (e) shed light on the physics of the dynamic wave-structure interaction and how it is affected by the dynamic characteristics of the bridge, (f) gain an insight into the role of air-entrapment and nonlinear wave-air interaction for bridges with diaphragms, (g) examine the tsunami forces for different types of bridges including I-girder bridges with cross-frames and diaphragms as well as box-girder bridges, (h) investigate possible mitigation strategies, such as air-vents in the deck, and (i) develop a high quality database that can be used for validation of CFD and FSI models, and development of recommendations and design guidelines for establishing tsunami-resilient bridges. To this end, advanced fluid-structure interaction (FSI) analyses, which considered both the hydrodynamics and structural dynamics, were conducted in LS-DYNA using High-Processing Computing (HPC). Three different wave types and four different bridge configurations were simulated in the analyses and interesting results were obtained. To complement these analyses and advance the state-of-the-art large-scale hydrodynamic experiments were conducted in the Large Wave Flume of the O.H. Hinsdale Wave Research Laboratory at Oregon State University. Twelve configurations of a 1:5 scale I-girder composite bridge, several wave heights between 0.36m and 1.40m, two water depths and a total of 270 runs were tested in the LWF in order to meet the objectives of the project. The results of the study demonstrate (a) the complexity of the tsunami inundation mechanism with the existence of four different phases, among which a phase with a large overturning moment and a distinct rotational bridge mode at the time of the first impact of the tsunami wave on the bridge where the impulsive horizontal and uplift tsunami loads are maximized, introducing the largest tension in the offshore bearings for most of the waves (Phase 1), a phase with a pure uplift of the bridge and a governing translational bridge mode as all the chambers of the bridge become inundated and the quasi-static component of the uplift force is maximized (Phase 3), introducing the maximum tension in many bearings, and a phase with a downward force when the wave hits the top side of the deck, introducing significant compression especially in the onshore bearings (Phase 4), (b) the dependence of the tsunami forces on the wave type with the bores introducing larger horizontal forces than vertical ones and the solitary waves the opposite, (c) the insufficiency of the current research approach of examining the tsunami effects on bridges via the calculation of the total tsunami forces on the deck and the need to examine the forces in each connection and bridge member in order to really understand the effects of the complex wave-structure interaction, (d) the significance of the inertial forces and the bridge dynamic characteristics on the fluid-structure interaction and the forces introduced in the connections, shear keys and substructure, with the very stiff bridge configurations witnessing larger connection forces than the applied load for many bore heights due to dynamic amplification, (e) the increase of the total uplift forces in bridges with diaphragms due to the air-entrapment and the complex effect on the bridge connections due to the nonlinear wave-air interaction, which is also different for solitary waves and bores, (f) the variation of the tsunami loads for different types of bridges, with the box-girder bridge witnessing uplift forces up to 5 times larger than the ones applied on an I-girder bridge with cross-frames, and (g) the effectiveness of air-vents in the bridge deck as a mitigation measure against tsunamis as well as their limitations, the importance of the distance of the vents from the diaphragms and the girders forming the chambers, and the existence of significant 3D effects even in the case of 2D wave propagation with impact of the waves normal to the bridge span.