| 1. |
- Khouri Chalouhi, Elisa, 1991-
(author)
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Optimal design solutions of road bridges considering embedded environmental impact and cost
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Continuous urbanization and population growth are increasing the demand for transportation infrastructure such as bridges. The construction of these structures represents a significant economic investment for public authorities; moreover, the construction sector accounts for a big portion of CO2 emissions. For countries across the world to deliver on their promises of keeping global warming limited, a change in the design philosophy is needed. Within the bridge engineering field, a common design approach can be identified as point-based design. While this approach delivers functional solutions, it often results in an expensive and not climate-friendly solution. Design based on structural optimization represents a good alternative as shown by many researchers in the last decades. However, it has not replaced the traditional design procedure yet. Among the reasons, there is the lack in literature of complete design of realistic structures and the complexity of the proposed optimal solutions. Moreover, a collection of recommendations for designers to assist them in the decision-making process is missing as well. The aim of this work is to cover the gap between theoretical studies and actual application by proposing optimal design solutions of road bridges that are feasible and simple to build. An automated design and optimization procedure is presented as an alternative to the traditional point-based design with the aim of reducing embedded environmental impact and cost. In the field of road bridges, the procedure is applied to three common structures: reinforced concrete beam bridges, reinforced concrete overhang bridge slabs and decks of composite beam bridges. The potential savings obtained by replacing traditional design with the proposed solution are shown through case studies. The use of commercial software commonly employed in design offices and the comparison with existing structures shows the feasibility of the optimal solutions obtained with this approach. Parametric studies are performed to help the potential user make appropriate decisions when performing optimization on these types of structures. As a support in the early design stages instead, recommendations on best solutions are given in the form of graphs and tables. Finally, the relationship between optimal solutions concerning cost and embedded environmental impact is studied for several materials. Material improvements or replacement to further reduce embedded emissions are proposed as well.
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| 2. |
- Avendaño, Juan Camilo
(author)
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Detection and quantification of cracks in concrete bridges using drone-image inspection
- 2024
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Licentiate thesis (other academic/artistic)abstract
- The assessment of civil infrastructure plays an important role in ensuring the safety of the general public and the durability of structures. Traditional inspection methods often involve manual labour and subjective evaluations, resulting in limitations in efficiency and accuracy. In recent years, there has been an increasing interest on using advanced technologies, such as unmanned aerial vehicles (UAVs), image analysis and machine learning techniques, to establish them as alternatives for the inspection process. These techniques provide different advantages compared with the manual method in terms of time, objectivity, and safety. The results of these techniques can allow the engineers in charge of the assessment and maintenance planning to obtain detailed results that can improve their efficiency but they are not without challenges. This research project aims to evaluate different methods used for damage detection and quantification and their integration with UAVs as an alternative to structural inspections. The proposed methodology combines image analysis techniques, Convolutional Neural Networks (CNNs) with drones to address the different aspects of inspections, from the data gathering to the damage detection and quantification. This methodology focuses on detecting and quantifying small cracks as narrow as 0.1 mm on concrete structures, aiming to achieve results comparable to those of traditional inspection. Furthermore, an application demonstrating the feasibility of the methodology in inside environments is also presented, focusing on the inspection of the internal section of a box girder bridge, including the creation of 3Dphotogrammetrical models to improve the inspection process. The results of the thesis highlight the methodology’s capabilities in detecting small cracks with a high probability and the possibility to use it for inside inspections without ideal conditions. This demonstrates the potential of integrating the different methods to transform structural inspections toward more efficient methodologies. Furthermore, the analysis of the results evaluates the drawbacks encountered and outlines future research directions aimed at advancing image-based inspections and their practical application.
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| 3. |
- Colmenares, Daniel
(author)
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Human-structure interaction effect on the dynamic response of footbridges : An analytical and experimental study
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Lightweight, slender and lightly damped footbridges are often susceptible to HumanInduced Loads (HILs) when pedestrian step frequencies coincide with the naturalfrequencies of the structure. For vertical vibrations, this can compromise the serviceabilitylimit state of the system. The Human-Structure Interaction (HSI) effectoccurs due to the presence of pedestrians that modify the dynamic behaviour ofthe coupled pedestrian-bridge system. Typically, the dynamic analysis of such footbridgesemploys the Finite Element Method (FEM) with stationary harmonic loadingscenarios to assess the dynamic performance of such structures. This researchproject aims to develop a general closed-form solution for the moving harmonic loadproblem (Paper I) using 2D Bernoulli–Euler beam theory for continuous beams onelastic supports. Additionally, it seeks to formulate closed-form solutions for thedynamic amplification factor of the coupled pedestrian-bridge system (Paper II),along with equivalent damping and force models (Paper III) based on response amplitudes.Furthermore, an experimental study of the HSI-effect was conducted onthe Folke Bernadotte Bridge in Stockholm (Paper IV), quantifying the changes ofthe dynamic properties ofthe system and validating the analytical Frequency ResponseFunction (FRF) found in previous studies (Paper II). Finally, the HSI-effectwas studied within the framework of random vibration theory (Paper V) to understandthe expected value of the response of the coupled system using a crowd loadPower Spectral Density (PSD).
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| 4. |
- Colmenares, Daniel
(author)
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On the dynamics of footbridges : A theoretical approach and a comparison between running and walking loads
- 2021
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Licentiate thesis (other academic/artistic)abstract
- The dynamic behaviour of lightweight footbridges is often susceptible to HumanInduced Loads (HILs). Generally HILs are taken into account as moving harmonicfunctions in which the loading frequency represents the step frequency of the pedestrians.In this way, there may be resonance if the loading frequencies fall within therange of the natural frequencies of the bridge, potentially compromising the serviceabilitylimit state of the structure. Therefore, it is important to understand how toaddress and model HILs in the context of lightweight and slender structures. Furthermore,interesting effects can be considered in the field of footbridge dynamics,such as the Human Structure Interaction (HSI) effect. The HSI effect can be understoodwithin a framework in which pedestrians behave as Tuned Mass Dampers(TMDs), possibly modifying the dynamic behaviour of the footbridge. In addition,the evaluation of the dynamic response of a footbridge is usually made through atime consuming dynamic analysis using the Finite Element Method (FEM). Mostof the analysis of this type of slender structures rely on a prescribed stationary harmonicloading scenario, and this is usually done in the context of a walking crowdevent and not much attention is given to running load events.The aims of this research project are to study the influence of running and walkingloads on the dynamic response of footbridges as well as to investigate and developa closed-form method in order to simulate the dynamic behaviour of footbridgessubjected to HILs. This has been achieved by comparing different approachesin order to simulate running load events for a small number of pedestrians withrespect to experimental results (Paper I). In addition, the simply supported beamand the clamped-clamped beam (Paper II) are studied when subjected to a movingharmonic load in a closed-form framework. Then, a comparison between normalwalking and normal running conditions is made. Finally, a general closed-formsolution for the moving harmonic load problem (Paper III) is developed using the2D Bernoulli–Euler beam theory for a continuous beam system on elastic supports.The results from the study indicate that running is more critical than walking fora single pedestrian crossing, despite the fact that it is easier to achieve a steadystate condition in a normal walking event than in a normal running event. Finally,the general solution of the moving harmonic load problem is found and it can beused to solve any load spectra in the time domain, with its static component, for ageneral multi-span beam system.
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| 5. |
- Neves, Ana C.
(author)
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Structural Health Monitoring of Bridges : Data-based damage detection method using Machine Learning
- 2020
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Doctoral thesis (other academic/artistic)abstract
- Civil engineering structures built according to modern codes are designed for a service life of normally more than 100 years. At the same time, there is a growing pressure to keep existing aged structures in service despite the fact that they have reached the original designed lifetime, with bridges being a good example of this. Naturally, in order to meet these goals, one must ensure the safety of these vulnerable structures by improving their reliability, as well as safeguarding their users. While doing so, infrastructure owners and managers have the desire to maintain the costs as low as possible. One of the key objectives is to identify damage in the structure at its earliest possible stage so that, if deemed appropriate, intervention can take place promptly. For the exposed reasons, there is an upsurge in the demand for clever strategies that can support maintenance and decision-making concerning structures. These are based on cost-effective and reliable inspection and monitoring solutions defined through a process commonly referred to as Structural Health Monitoring. This thesis consists of an extended summary and four appended papers. The author proposes an approach to Structural Health Monitoring of bridges with focus on damage detection, by means of applying data-based methods and techniques for statistical analysis. The research work starts with the development of the method in Paper I, validated with data generated from a simple numerical model of a railway bridge. In this and subsequent papers with respective case studies, data is collected during train passages, in healthy and damaged states of the structure. Part of the data collected under the healthy state is used for training Artificial Neural Networks, as the primary algorithm of the proposed method. Afterwards, new data collected under healthy or damaged states can be directly compared with the correspondent predictions by the networks. The research work then follows logically into assessing the cost of implementing SHM in Paper II. More specifically, the expected cost associated with possible alternatives regarding maintenance decision-making is assessed in light of a case study and its variants. Then, in Paper III, the influence of the frequency content of the collected data on the performance of the networks is investigated. It mainly deals with revealing that the information contained in the higher frequencies of the measured response is not only non-negligible for the purpose of damage detection but actually more useful than the information extracted from the lower frequencies. This conclusion is verified in light of both numerical and experimental field data. Finally, in Paper IV, the proper use of Artificial Neural Networks for the assessment of structural condition is given more attention. This is put into effect by investigating which adjustments in the hyperparameters, features and data structure end up enhancing the performance of the algorithm. The results presented in this thesis demonstrate the potential benefits of integrating the proposed approach into current Structural Health Monitoring practices. This research work intends to contribute with recommendations for proactive maintenance by which data is continuously collected and analyzed in almost real-time, providing the grounds for well-informed decision-making.
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| 6. |
- Tell, Sarah, 1990-
(author)
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Vibration mitigation of high-speed railway bridges : Application of damping devices in theory and practice
- 2021
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Doctoral thesis (other academic/artistic)abstract
- The dynamic response of railway bridges is an important aspect to consider, as the repetitive loading from passing trains may result in excessive vibrations of the bridge deck. Several design criteria are developed in order to assure the structural safety and passenger comfort during train crossings of a bridge. However, bridges are usually not designed to be adaptable to future requirements or changes in the design codes, due to e.g. cost issues.Prospectively, higher speeds of trains and an increased passenger capacity could potentially mean that bridges designed according to prevailing design requirements turn obsolete. This could be particularly problematic, as the planned interconnecting routes within the European Union increases the possibility that faster and longer trains will cross the Swedish railway lines. Hence, an increased demand for innovative design solutions for new bridges and efficient upgrading methods for existing lines has emerged.The aim of the present thesis is to propose a vibration mitigation strategy that is insensitive to changes in the structural geometry or train composition. The main focus is a retrofit method with damping devices installed between the bridge superstructure and the supports, which will reduce the dynamic response of bridges subjected to passing trains. Theoretical studies, numerical simulations and experimental tests are performed and analysed to examine if the proposed retrofit systemis suitable for the present case. A proof-of-concept and a reliability study are conducted, to ensure the applicability and robustness of the proposed method. Finally, real-time hybrid simulations, laboratory tests and full-scale field experiments are conducted in order to validate the proposed vibration mitigation strategy.In theory, it is found that the damping devices efficiently reduced the response of the bridge below permitted limits. From a practical point of view, the experimental test indicates that the equivalent damping ratio of the system is increased due to the damper retrofit. However, the actual measured effect of the damping devices on the bridge deck response turns out to be lower than expected from numerical simulations. The reason for this is likely due to malfunction of the dampers, which was verified in additional laboratory tests after the field measurements. Hence, adequate damper forces were not provided at low amplitudes of vibration. Conclusively, further studies are necessary in order to validate the proposed method, but the applicability of the system still shows great potential based on the results from this research work.
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| 7. |
- Veganzones Muñoz, José Javier, 1989-
(author)
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Bridge Overhang Slabs with Edge Beams : LCCA and Structural Analysis for the Development of New Concepts
- 2020
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Doctoral thesis (other academic/artistic)abstract
- Bridge edge beams are associated with high life-cycle costs because of the need of maintenance, which also causes traffic disturbances. For this reason, the Swedish Transport Administration started a project to find better solutions. One of the proposals was a design without edge beam. However, the edge beam contributesto the load distribution and its removal would imply a loss of robustness, especially in bridges with overhang slabs. The efficiency of this effect depends onthe width of the overhang slab. Moreover, the width of the slab in itself, even inthe absence of an edge beam, may influence the load capacity of the structure. These aspects are paramount for the performance of tests that study the shear capacity of overhang slabs and assess design methods.The aim of this thesis is to contribute to the development of functional edge beam solutions in terms of cost and investigate the structural behavior of bridge overhang slabs with edge beams. A life-cycle cost analysis was the method to evaluate and identify edge beam alternatives that could qualify for further studies, including the use of stainless steel. Non-linear FE-analyses validated from experimental tests were used to investigate the influence of this member and the width of the overhang slab on the structural behavior under concentrated loads. Recommendations for minimal widths that ensure full load capacity of experimental specimens and an assessment of the existing calculation methods with special emphasis on the effective width were also studied.The outcome led to the implementation of new edge beam solutions. The results showed that the influence of the edge beam is not only quantitative due to its load-carrying function but also qualitative as it may affect the failure mode. The load capacity increased with the width until a threshold was reached. The mechanisms behind were the increase of shear capacity and the distribution of the forces sideways, with an eventual redistribution. Recommendations for minimal widths that ensure full capacity were presented for its consideration in the design of experimental tests, with or without edge beams. Effective widths are practical for a preliminary design but may lead to unreliable estimates. Modified approaches given the control section and the presence of an edge beam were proposed.
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| 8. |
- Zangeneh Kamali, Abbas, 1980-
(author)
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Dynamic Soil-Structure Interaction Analysis of Railway Bridges : Numerical and Experimental Results
- 2018
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Licentiate thesis (other academic/artistic)abstract
- The work reported in this thesis presents a general overview of the dynamic response of short-span railway bridges considering soil-structure interaction. The study aims to identify the effect of the surrounding and underlying soil on the global stiffness and damping of the structural system. This may lead to better assumptions and more efficient numerical models for design.A simple discrete model for calculating the dynamic characteristics of the fundamental bending mode of single span beam bridges on viscoelastic supports was proposed. This model was used to study the effect of the dynamic stiffness of the foundation on the modal parameters (e.g. natural frequency and damping ratio) of railway beam bridges. It was shown that the variation in the underlying soil profiles leads to a different dynamic response of the system. This effect depends on the ratio between the flexural stiffness of the bridge and the dynamic stiffness of the foundation-soil system but also on the ratio between the resonant frequency of the soil layer and the fundamental frequency of the bridge.The effect of the surrounding soil conditions on the vertical dynamic response of portal frame bridges was also investigated both numerically and experimentally. To this end, different numerical models (i.e. full FE models and coupled FE-BE models) have been developed. Controlled vibration tests have been performed on two full-scale portal frame bridges to determine the modal properties of the bridge-soil system and calibrate the numerical models. Both experimental and numerical results identified the substantial contribution of the surrounding soil on the global damping of short-span portal frame bridges. A simplified model for the surrounding soil was also proposed in order to define a less complicated model appropriate for practical design purposes.
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| 9. |
- Arvidsson, Therese
(author)
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Train–Track–Bridge Interaction for the Analysis of Railway Bridges and Train Running Safety
- 2018
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Doctoral thesis (other academic/artistic)abstract
- In this thesis, train–track–bridge interaction (TTBI) models are used to study the dynamic response of railway bridges. A TTBI model considers the dynamics of the train in addition to that of the track–bridge system. The TTBI model enables the assessment of train running safety and passenger comfort. In the bridge design stage, a moving force model is instead typically used for the train load. The main aim of this thesis is to use results from TTBI models to assess the validity of some of the Eurocode design criteria for dynamic analysis of bridges.A 2D rigid contact TTBI model was implemented in ABAQUS (Paper II) and in MATLAB (Paper III). In Paper V, the model was further developed to account for wheel–rail contact loss. The models were applied to study various aspects of the TTBI system, including track irregularities. The 2D analysis is motivated by the assumption that the vertical bridge vibration, which is of main interest, is primarily dependent on the vertical vehicle response and vertical wheel–rail force.The reduction in bridge response from train–bridge interaction was studied in Papers I–II with additional results in Part A of the thesis. Eurocode EN 1991-2 accounts for this reduction by an additional damping Δζ. The results show that Δζ is non-conservative for many train–bridge systems since the effect of train–bridge interaction varies with various train–bridge relations. Hence, the use of Δζ is not appropriate in the bridge design stage.Eurocode EN 1990-A2 specifies a deck acceleration criterion for the running safety at bridges. The limit for non-ballasted bridges (5 m/s2) is related to the assumed loss of contact between the wheel and the rail at the gravitational acceleration 1 g. This assumption is studied in Paper V based on running safety indices from the wheel–rail force for bridges at the design limit for acceleration and deflection. The conclusion is that the EN 1990-A2 deck acceleration limit for non-ballasted bridges is overly conservative and that there is a potential in improving the design criterion.
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| 10. |
- Wadi, Amer, Tekn. Lic. 1984-
(author)
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Soil-Steel Composite Bridges : Research advances and application
- 2019
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Doctoral thesis (other academic/artistic)abstract
- Soil-steel composite bridges are considered competitive structures being an economical alternative to similar span concrete bridges. This frequently stimulates practitioners to push their design limits and expand the different areas of application including their performance in sloping terrain. This also implies that most design methods are continuously being developed to address new market challenges and at the same time to seek for better design and construction.This thesis compiles the recent research efforts to advance the knowledge on the structural performance of soil-steel composite bridges (SSCB). The first part of the thesis investigates the performance of SSCB in sloping terrain, where numerical simulations are used to predict the behaviour of three case studies. This includes structural response under sloped soils and also avalanche loads (Paper I and Paper II). The research enabled to realize the importance of soil configuration around the wall conduit and its influence on the structural response. While the presence of surface slopes emphasizes the susceptibility of SSCB with low depths of soil cover, higher covers may help in reducing the influence of steep slopes and avalanche loads. It was also found that the downhill soil configuration has substantial effects on the flexural response. The findings of the study were also used to provide methods for preliminary estimates of normal forces under sloped soils and avalanches.To better understand the load bearing capacity of SSCB, the second part of this thesis deals with the behaviour of large-span structures. It includes the use of finite element method simulations (FEM) for the analysis and the prediction of a previous full-scale loading-to-failure test (Paper III). The study also presents response predictions on the ultimate capacity of a large-span structure pertaining to its ongoing preparation for a full-scale field test (Paper IV). The thesis also includes discussions and possible refinements on current design equations concerning buckling calculations and live load effects. The results of the study have allowed to realize the major role of the soil load effects on the subsequent formation of yield areas and failure loads. It is found that the load position has a direct influence on the ultimate capacity especially for large-span structures. The study also highlighted the variations in the distribution of the live load sectional forces in both the circumferential and the transverse directions of the corrugations. Furthermore, possible refinements are proposed on current design equations of which are believed closely relevant on the path for the design development of large-span structures.
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