Committee:
     PRESIDENT: GALLEGO MEDINA, JUAN
     SECRETARI: MARTINEZ REGUERO, ADRIANA HAYDEE
     VOCAL: SKAF REVENGA, MARTA
Thesis abstract: This doctoral thesis focuses on the study of steel slag from electric arc furnaces as a technically and environmentally viable substitute for natural aggregates in asphalt mixtures. While the primary objective was to evaluate its thermo-mechanical behaviour and potential for urban heat island (UHI) mitigation, other fundamental aspects were also addressed to validate its real-world application in sustainable urban pavements, such as moisture resistance, fatigue performance and cracking behaviour.Through a series of experimental investigations, structured as independent yet complementary chapters, the influence of steel slag on the physico-chemical, mechanical, and thermal properties of asphalt mixtures was analysed, along with its integration into embedded solar collector systems (ASC).Initially, the physical, morphological, and chemical properties of steel slag were characterised to understand its effect on aggregate–bitumen adhesion and moisture resistance (ITSR). Through bitumen affinity tests, digital image analysis, and ITSR testing, it was demonstrated that steel slag improves resistance to moisture damage—even under total replacement—due to its high surface roughness and its composition rich in metallic oxides.In a second stage, partial replacement of natural aggregates by steel slag in the fine fractions was evaluated. Similar benefits were observed in terms of moisture resistance, with density remaining within conventional ranges. This result suggests that the use of steel slag in fine fractions may overcome previous limitations related to increased total mix weight.Subsequently, the mechanical behaviour was addressed through indirect tensile strength, stiffness, and fatigue tests. Mixtures with different levels of slag replacement and bitumen film thicknesses (TF) were designed and evaluated using four-point bending and strain sweep (EBADE) tests. The results showed that increasing the slag content raises mixture stiffness but reduces fatigue resistance, an effect attributed to the material's hardness and its tendency to decrease the effective bitumen film thickness. However, a well-optimised mixture—such as HMA_SL* with a corrected TF—achieved performance similar to the control mixture, even under critical temperature conditions.Furthermore, crack resistance was assessed using the Fénix test, which showed that although slag-containing mixtures require more energy to initiate cracking, their post-failure behaviour tends to be more brittle. Nevertheless, the mixture optimised in terms of bitumen film thickness showed significant improvements in toughness (IT) and fracture energy (GF), highlighting that adjusting the binder content is essential to mitigate this limitation.In parallel, the thermal properties of the mixtures were investigated through both experimental tests and numerical simulations (FEM). It was observed that steel slag reduces the thermal conductivity of the mixture, slowing down its cooling rate and thus extending the compaction window. While this also lengthens the required cooling time prior to traffic opening, the simulations accurately predicted thermal evolution, facilitating better design and process control.Finally, the application of steel slag in asphalt pavements with embedded solar collectors (ASC) was explored, aimed at UHI mitigation and thermal energy recovery. Dense mixtures containing steel slag (AC16D + AC22D) exhibited favourable thermal balance, reducing surface temperature by up to 16.3 °C and improving heat collection efficiency compared to gap-graded mixtures with the same material (BBTM11-B + AC22D). This performance confirms its potential as a functional material for sustainable urban applications.Altogether, the findings of this thesis validate steel slag as a technically sound, functional, and environmentally competitive material for the development of both structural and functional asphalt mixtures, contributing to more sustainable urban paving practices.

Committee:
     PRESIDENT: GÓRECKI, JAROSLAW
     SECRETARI: KOMARIZADEHASL, SEYEDMILAD
     VOCAL: ATENCIO CASTILLO, EDISON PATRICIO
Thesis abstract: The BIM digitization has generated a growing automation of traditional AECO project development processes. However, this automation has mainly benefited building projects, which has generated a critical gap in infrastructure projects, such as (1) bridges, (2) roads, and (3) tunnels. This gap is explained by infrastructure projects' lack of standardization compared with building projects. Recently, the BIM industry has incorporated conventional computer programming as a tool capable of partially reducing this lack of automation, developing code-line algorithms. However, both the work interface and the high technical skills required to produce these scripts have been unfriendly to AECO industry professionals. To resolve this gap, BIM software development companies generated an alternative algorithm creation technique called Visual Programming (VP). This technique creates their scripts through visual expressions, represented as process charts instead of the code lines of conventional programming, optimizing the working interface of different human resources from AECO projects. However, the development of VP algorithms for infrastructure projects is still limited.To fill these gaps, the objective of this thesis will be to study the potential automation of infrastructure project processes, developing an integrated platform between VP algorithms and BIM models.At a general level, the platform proposed by this thesis has the following 2 elements: (1) VP algorithms; These custom scripts have the specific function of processing information from external databases and deliver specific data as outputs, and (2) BIM models; These information models will digitally collect the outputs of the VP algorithms and associate them with specific BIM families of the infrastructure projects under study. This thesis focuses on studying transversal problems of Civil Engineering using VP-BIM tools through the development of the following applications:Firstly, this thesis develops a calculation module to estimate (1) greenhouse (GHG) emissions; these pollutants contribute to global warming and climate change by trapping heat in the Earth's atmosphere [1–3] and (2) carbon footprint for vehicle traffic on specific roads in any country with the appropriate traffic and vehicle fleet data. The main novelty of this module is the automated integration of the GHG emission factors recommended by the European Environmental Agency (EEA) TIER 1 level with specific fleet data through a customized VP script. This proposed module was applied on a road in Barcelona (Spain), and the results were compared with a similar study made by the Barcelona transport agency. In addition, specific calculation modules were developed to measure the impact of emission reduction strategies.The second application developed by this thesis aims to use visual programming as an educational tool. A parametric programming workflow is employed to replicate the structural behavior of a beam within a BIM Model. This approach enables students to visualize and analyze structural performance, fostering a deeper connection between classroom theory and hands-on experimentation. This system aims to improve the visualization and understanding of structural data for AEC industry professionals by generating dynamic 3D and 2D models. The educational impact of this tool was assessed through a survey conducted in a structural analysis course at the University of La Serena (Chile), demonstrating its effectiveness in enhancing student comprehension and engagement with modern engineering practices.

Committee:
     PRESIDENT: D\'AYALA, DINA
     SECRETARI: MOLINS BORRELL, CLIMENT
     VOCAL: DE FALCO, ANNA
Thesis abstract: This research was developed in response to the increasing need for coherent and integrated methodologies to assess the complex and multifaceted risks threatening cultural heritage. Three critical issues were identified at the outset. The inconsistency in terminology and the absence of standardised definitions across risk analysis frameworks, hindering both comparability between studies and the development of actionable strategies. The scarcity of methodologies capable of addressing a large number of heritage architectures, resulting in time and cost-intensive risk assessments that are tailored to specific architectural contexts and difficult to apply elsewhere. The prevailing preference for methodologies that focus on single hazardous events often overlooks the potential for cascading or compound events, despite current risk management guidelines advocating for the integration of multi-event information in planning and preparedness strategies. To address these gaps, the research proposes a quantitative methodology for regional-scale physical vulnerability estimation, specifically targeting seismic and landslide vulnerabilities in historical churches. The adopted methodology is based on a multilayer single-hazard framework, aiming to harmonise and standardise risk analysis procedures. Physical vulnerability is expressed through an index-based approach that combines event intensity indicators with churches physical resistance indicators. While seismic and landslide phenomena are analysed independently, both are evaluated within a shared conceptual approach, which enables direct comparison and prioritisation across hazardous events. Three main phases can be identified. First, the risk context is defined by identifying the objectives, study area characteristics, and hazardous event types. A consistent and scalable data collection process is designed, including the creation of a survey form tailored to masonry churches. The survey form draws on literature-based indicators and existing vulnerability analysis methodologies to support systematic and standardised data gathering for a large building sample. Second, event-specific physical vulnerability indices are developed and validated. The seismic vulnerability index draws on a regression-based model informed by nonlinear static analyses performed on archetypes derived from a typological classification. Generalised Linear Models (GLMs) are employed to relate the probability of failure to churches main geometric attributes. The resulting seismic physical vulnerability index represents the expected tendency of vulnerability over a properly selected range of intensities. The landslide vulnerability index is adapted from an existing method and recalibrated using resistance indicators specifically selected for historical churches. Both indices range into a 0–1 scale and allow for comparability within prioritisation and disaster risk reduction frameworks. Finally, the methodology is extended to estimate scenario-based risk for earthquake-triggered landslides, combining the landslide vulnerability index with susceptibility data and uniform exposure. This scenario-based approach enables the estimation of risk without requiring information on the frequency of the triggering events. The full methodology is applied to a case study in northern Tuscany, a region characterised by high seismicity and widespread slope instability, encompassing 71 surveyed masonry churches. Results reinforce the value of an integrated yet adaptable vulnerability analysis strategy.

Committee:
     PRESIDENT: GETTU, RAVINDRA
     SECRETARI: TURMO CODERQUE, JOSE
     VOCAL: GIL BERROCAL, CARLOS
Thesis abstract: The application of fiber-reinforced concrete (FRC) in bridge structures presents a significant advancement in structural performance, reinforcement optimization, and serviceability enhancement. This study examines the impact of FRC on bridge design, focusing on its ability to reduce reinforcement demands, improve crack control, and enable internal force redistribution. Despite these advantages, challenges related to fiber distribution, orientation, and potential brittle failure necessitate careful consideration in both design and construction.The integration of FRC in U-shaped light-train viaducts, as demonstrated in the Metrorrey Line 2 viaduct, highlights its potential to replace conventional reinforcement partially or entirely in sections with low reinforcement ratios. In particular, FRC enhances shear strength in bottom slabs and webs, leading to a reduction in transverse reinforcement requirements and simplifying reinforcement layouts. While FRC alone sustains ultimate limit state (ULS) loads in sections with low internal forces, in heavily loaded sections, its primary contribution lies in improving serviceability limit state (SLS) performance through better crack control and reduced reinforcement needs. Transversally posttensioned viaducts further amplify the benefits of FRC, as reduced internal force demands facilitate significant reinforcement reductions. However, despite theoretical possibilities for eliminating reinforcement, rebar bands remain necessary to ensure robustness, ease tendon placement, and enhance constructability.Following on the previous findings, the replacement of skin reinforcement in the webs by FRC is assessed in a road bridge. Several numerical models are prepared, from which it can be observed that such reinforcement can be eliminated. However, the elimination of the skin reinforcement produced a failure with a reduced deformation capacity. Depending on the structural case, allowing fibers to undergo strains beyond ultimate crack width can allow to attain redistribution and higher deformation capacities. Nonetheless, the risk of brittle failure in continuous elements with large cross-sections poses a challenge. Addressing these risks requires further research to experimentally validate redistribution mechanisms and establish calibrated design methodologies that account for fiber failure.Two experimental campaigns highlight the variability in fiber distribution and its implications for mechanical performance. Standard construction practices resulted in significant variations in fiber concentration, particularly in self-compacting concrete (SCC), where segregation was more pronounced. In addition, poor fiber alignment in precast elements led to substantial strength reductions, necessitating a revaluation of quasi-isotropic fiber orientation assumptions in design codes. These findings emphasize the importance of controlled casting methods to ensure stable fiber distributions and orientations, ensuring reliable material behavior in bridge applications.Overall, while FRC offers notable advantages in reducing reinforcement requirements, enhancing crack control, and enabling redistribution, its successful implementation in bridge structures depends on rigorous construction methodologies and refined design considerations.

Committee:
     PRESIDENT: RAMOS SCHNEIDER, GONZALO
     SECRETARI: LOZANO GALANT, JOSE ANTONIO
     VOCAL: MIRARCHI, CLAUDIO
Thesis abstract: The construction industry in Saudi Arabia is experiencing rapid growth driven by the ambitious Vision 2030, but challenges related to inefficiencies, cost overruns, and delays persist. This research presents a comprehensive framework designed to optimize the construction process in Saudi Arabia by integrating Lean Construction, Building Information Modeling (BIM), and Emerging Technologies. Through an extensive review of 64 academic papers, this research identifies key tools and methodologies within Lean, BIM, and Emerging Technologies, that have been successfully applied in construction management. However, it also highlights the absence of a comprehensive framework that effectively integrates these domains in a structured manner.The research was developed through the Design Science Research Method (DSRM) and proposes a novel framework that categorizes these elements across the four phases of construction: Plan, Design, Construct, and Operate. This integration seeks to align functionality, optimize processes, and enhance lifecycle efficiency, while addressing the limitations of current approaches. The framework initially evaluated through expert consensus using the Delphi Method and subsequently tested in a real-world case study of a confidential mega-scale project in Saudi Arabia during the Design phase. Using pre-defined Key Performance Indicators (KPIs) such as cost efficiency, time efficiency, productivity, waste reduction, quality and safety, stakeholder satisfaction, and process automation, the study provides insights into the practical impact of the framework in improving project outcomes.The findings demonstrate the potential of the integrated framework to reduce waste, improve collaboration, and optimize overall project performance. This research contributes to the advancement of construction project management in Saudi Arabia by proposing a transformative approach that integrates Lean, BIM, and Emerging Technologies, offering practical recommendations for stakeholders seeking to enhance their construction processes. This framework aims to guide the Saudi construction industry in overcoming existing challenges and achieving more efficient, cost-effective, and high-quality project outcomes.Expert evaluations and practical applications validate the effectiveness and relevance of the framework, highlighting its potential to revolutionize construction management in Saudi Arabia and offering a robust model for other regions encountering similar challenges.

Committee:
     PRESIDENT: YUAN, SUN
     SECRETARI: RAMOS SCHNEIDER, GONZALO
     VOCAL: CARRILLO ALONSO, LUIS
Thesis abstract: This work presents a study on the construction analysis of cable-stayed bridges built by the cantilever method, with a particular focus on the effects of time-dependent phenomena such as creep and shrinkage. In the design of these structures, construction analysis is essential, as the highest stresses and deflections typically occur during the erection process, rather than in service. Therefore, accurately simulating the construction sequence is necessary to ensure structural safety and reliability. However, many existing analysis tools have limitations, such as difficulties in isolating and evaluating individual construction stages, high computational time and storage requirements, and the dependence on global iterative procedures to reach the final target state. These challenges make the construction simulation process both time-consuming and restrictive.To address these limitations, this research proposes and develops efficient computational methods for simulating the construction process of cable-stayed bridges. A first method, referred to as the Direct Algorithm, is presented for use in cases where time-dependent effects are neglected. This algorithm allows for the independent simulation of each construction stage without relying on the superposition principle or on information from previous or subsequent stages.When time-dependent effects such as creep and shrinkage must be considered, the Forward-Direct Algorithm is proposed. This method enables the simulation of the construction process while accounting for long-term concrete behavior, and does so without requiring iterative procedures to adjust the tensioning forces.One of the main contributions of this work is the definition of new criteria for the Objective Service Stage, understood as the target geometry and stress state of the bridge at a specific time. These criteria consider both the cantilever construction process and the influence of time-dependent phenomena. The aim is to establish a tensioning strategy that requires only a single prestressing operation for each stay cable, thereby avoiding costly and complex tuning operations either at the end of construction or during the service life of the structure.The proposed algorithms and criteria are validated through a case study based on the geometry of a real bridge design, analyzed under different construction scenarios. The results confirm the accuracy and reliability of the Direct Algorithm and the Forward-Direct Algorithm in predicting structural behavior during both construction and service. Comparisons with traditional analysis methods from the literature highlight the advantages of the proposed approaches in terms of both precision and computational efficiency. This research offers practical tools and strategies for improving the design and construction of cable-stayed bridges, particularly those built with cast-in-place concrete and erected using the cantilever method, where time-dependent effects play a significant role.

Committee:
     PRESIDENT: ZHOU, GUANG DONG
     SECRETARI: CHEN, YUZI
     VOCAL: CLADERA BOHIGAS, ANTONI
Thesis abstract: The Yangtze River shipping industry is becoming increasingly developed. To ensure the navigability of the Yangtze River, regular channel maintenance is required, which generates a large amount of dredged sand. Utilizing dredged sand concrete (DSC) in new prefabricated building structures is an important way to achieve resource utilization of dredged sand. The shear performance of concrete components in prefabricated structures is not only a critical part of the structural load-bearing calculations but also a significantly variable factor in the application of DSC structures. Based on that, this thesis focuses on the application of dredged sand in new prefabricated concrete components as the main research objective, conducting studies on the performance of dredged sand mortar and concrete as well as the shear performance of components through a combination of experimental and theoretical analysis. The research work developed includes:The changes in the performance of composite materials by replacing fine aggregate with dredged sand (DS) in dredged sand mortar was studied. The effects of DS on dredged sand mortar under two different cementitious systems, rich in mineral powder and rich in fly ash, were analyzed separately. The compressive and flexural strengths of the dredged sand mortar composites were evaluated, and the mechanical properties of the mortar were studied. The durability of the mortar was investigated by measuring its drying shrinkage and water absorption. Additionally, the microstructure of DS mortar was examined to explore the effects of DS on the microstructure of dredged sand mortar.The influence of steam curing systems on the mechanical properties and microstructure of dredged sand concrete was investigated. DSC was produced using different steam curing regimes and DS content. The results show that steam curing has a significant effect on improving the strength of DSC. Under reasonable steam curing, the 1-day strength of DSC can be increased from 2.1 MPa to 27 MPa, with a 7.8% increase in 28-day strength. Furthermore, the study found that the improvement in compressive strength is not directly correlated with the energy consumption of steam curing. Although the energy consumption at 40°C steam curing is 67% higher than at 60°C, the 1-day strength at 40°C is 7.5% lower than at 60°C. However, low-temperature steam curing leaves more room for further strength increase. These results indicate that a reasonable steam curing regime is crucial for the strength of DSC.As a possible field of application of the dredged sand concrete, the shear behavior and load-bearing capacity of large shear key dredged sand concrete dry joints used in precast construction were studied. The studied parameters include the height of the key base, the number of keys, and the concrete strength. The research found that the height of the key base significantly affects the failure mode and shear load-bearing capacity. When the key base height increased by 100%, the shear load-bearing capacity of the joint increased by 156%. Digital Image Correlation (DIC) and Distributed Fiber Optic Sensing (DFOS) technologies revealed the load transfer characteristics in large shear keys, validated the inclined strut principle, and observed changes in the inclined strut angle with the increase in shear key size. Simultaneously, a separation trend was observed at the lower contact surface of the joint due to shear transfer at the large key teeth. Based on these findings, an improved shear strength calculation method for large shear key dry joints was established. The calculation results show that this method is more accurate in predicting the shear strength of large shear key dry joints compared to existing methods for smaller key dry joints.

Committee:
     PRESIDENT: BLANCO ÁLVAREZ, ANA
     SECRETARI: MONSERRAT LOPEZ, ANDREA
     VOCAL: JOSA I CULLERÉ, IRENE
Thesis abstract: In recent decades, fibre-reinforced concrete (FRC) has played a significant role in construction due to its enhanced residual flexural tensile strength in comparison to plain concrete. However, with the increasing use of FRC, the dismantling of FRC structures is becoming an important challenge. Unlike plain and reinforced concrete, the recycling of FRC produces two primary by-products: recycled fibres and recycled aggregates with embedded fibres. Despite its significance, limited research has been conducted on the reuse of these by-products in new concrete. To address this research gap, this thesis focuses on polypropylene fibre-reinforced concrete (PPFRC) as a case study and examines its recycling process and the reuse of the resulting recycled materials.Initially, PPFRC was produced (parent concrete) and recycled by analysing the quantity and morphology of the recovered fibres and recycled aggregates. These recycled materials were used to produce new concrete (with recycled aggregates and recycled fibres) that was characterized, and the results were compared with the mechanical properties of the parent concrete. The findings revealed that the properties of concrete using recycled materials were reduced to different extends compared with the parent concrete.However, when different ratios of recycled fibres were incorporated into concrete, the mechanical properties showed significant improvement compared to using 100% recovered fibres, particularly at a fibre content of 3 kg/m³. Moreover, hybrid -virgin and recycled- fibre concretes outperformed those made entirely with virgin fibres. Thus, under certain conditions, it is feasible to replace virgin fibres with recovered fibres while maintaining or even enhancing mechanical performance.Furthermore, this thesis compares the mechanical properties and microstructure of new FRC made with recycled FRC aggregates to concretes made with natural aggregates and conventional recycled concrete aggregates. Concrete incorporating recycled FRC aggregates demonstrated advantages in fibre distribution at lower fibre contents. However, at higher fibre contents, the embedded fibres were found to have a detrimental effect. Micrographs and chemical dot plots revealed unique characteristics at the interface between the recycled aggregates and the fresh cement paste, highlighting changes in hydration and porosity compared to samples made with natural aggregates and conventional recycled aggregates.Future work on recycled FRC could include exploring the durability and long-term stability of the material, as well as investigating the potential application of recycled fine aggregates in concretes. 

Committee:
     PRESIDENT: ALMEIDA, RICARDO
     SECRETARI: PUJADAS ÁLVAREZ, PABLO
     VOCAL: FUERTES CASALS, ALBA
Thesis abstract: Indoor air quality and thermal comfort in educational buildings have significant impacts on students’ health, well-being, productivity, and learning performance. Schools, where students spend most of their day, are often challenged to maintain good indoor air quality due to high occupancy density and long occupancy duration. Students have different thermal sensations than adults, and they tend to passively adapt to the indoor environment without complaining. This creates challenges in maintaining a comfortable thermal environment in classrooms. Moreover, indoor air quality and thermal comfort often have complex interactions with ventilation, leading to difficulties in balancing the two aspects. Therefore, the assessment of indoor air quality, thermal comfort, and ventilation of educational buildings has always been the focus of the educational and scientific community.This doctoral research aims to assess indoor air quality, thermal comfort, and ventilation in educational buildings in the Mediterranean climate, contributing to a number of identified important research gaps on the topic. The main results include: the comprehensive assessment of indoor air quality and thermal comfort in educational buildings, the development of a data-driven predictive model for indoor air quality and thermal comfort in educational buildings, the modeling of students' thermal comfort, and the enhancement of field thermal comfort survey data in schools.This doctoral thesis presents the core of this doctoral research. These results contribute to the topic from both scientific and practical perspectives and provide useful references for relevant research.

Committee:
     PRESIDENT: BARRIS PEÑA, CRISTINA
     SECRETARI: MURCIA DELSO, JUAN
     VOCAL: HERRADOR BARRIOS, MANUEL
Thesis abstract: The effect of corrosion on reinforcement and its impact on the service life reduction of existing reinforced and prestressed concrete infrastructures has led to the search for alternatives to conventional steel with enhanced durability. In this context, fiber-reinforced polymer (FRP) reinforcements are a promising alternative, as they are not susceptible to corrosion. However, their implementation as active reinforcement in the construction sector is still scarce, due to the limited research conducted and the fact that their use is not included in most current design guidelines, which restrict their application to passive reinforcement.The main objective of this thesis is to study the structural behavior of prestressed concrete elements with active FRP reinforcement, with the aim of contributing to the development of future design recommendations that ensure their functionality, safety, and durability. To this end, an experimental campaign was conducted on 20 simply supported beams with a span of 4.50 m, consisting of 10 flexural tests with a 3-point bending configuration and 18 shear tests (on 9 beams) subjected to a single-point load applied at a distance of three times the effective depth from one of the supports. Additionally, tests were carried out to characterize the mechanical properties of the materials, evaluate the bond performance of the prestressed FRP tendons, and verify the effectiveness of the anchorage systems used for each material.The study considered glass fiber-reinforced polymer bars with thermosetting resin (GFRP), glass fiber-reinforced polymer bars with thermoplastic resin (TP-GFRP), carbon fiber-reinforced polymer bars (CFRP), and carbon fiber composite cables (CFCC), as well as steel strands (control), prestressed at different levels. The exhaustive instrumentation allowed for the recording of the applied load, displacements at multiple points, rotations at the support, strains at different sections in both active and passive reinforcement, and the slip of the active reinforcement with respect to the concrete during the tests. The use of the digital image correlation (DIC) system enabled the capture of crack formation and propagation during each test.The beams tested in a 3-point bending configuration failed when the active longitudinal reinforcement reached its ultimate strength, leading to a decrease in the prestressing force and to the formation of a diagonal crack. In the beams tested in shear, the failure mode was as expected but more brittle compared to that of the prestressed steel beams. In some cases, the shear failure was accompanied by a tensile failure of the reinforcement in the section where the critical shear crack opened, due to the increase in tension produced by the shear force. The analytical formulations were able to predict the ultimate load values and the numerical modelling (using the ABAQUS programme) reproduced the performance of the beams in service but in some cases, they were not able to predict the failure load.

Committee:
     PRESIDENT: BORRMANN BORRMANN, ANDRÉ
     SECRETARI: CASAS RIUS, JUAN RAMON
     VOCAL: BOSCHÉ, FRÉDERIC
Thesis abstract: Bridges are vital components of transport infrastructure networks which are facing a widespread lack of resilience due to aging and changing environmental conditions. Finding more efficient methods for monitoring bridge networks and effectively planning their maintenance is crucial for maintaining reasonable serviceability levels. Simultaneously, digital twins are emerging across industries as dynamic digital replicas of physical assets. These are continuously updated with information from their physical counterparts and serve as the foundation for digital tools that enhance workflows in decision-making processes throughout the lifecycle of any product.This dissertation translates the concept of digital twins to the bridge maintenance domain and presents a framework for developing graph-driven digital twin systems to assist bridge managers in tracking the state of their asset portfolio.For this purpose, two different proof-of-concept systems are presented: System A and System B. Both systems are cloud-based, modular, and use graphs to integrate multiple data sources describing the bridges, their context, and relevant maintenance information. The systems are tested with real data corresponding to two demonstration cases of road and railway bridges in the Spanish infrastructure network. Through these demonstrators, the digital twin systems are developed to integrate BIM, GIS, sensor time-series data, and data related to the results of monitoring processes that is structured according to regional standards.System A focuses on hosting digital twins of individual bridges. It uses a labelled property graph (LPG) to interconnect IFC data with IoT sensor data and the results from visual inspections and load tests. Data integration is achieved by matching GUIDs of data contained the graph with data stored in the different databases and systems connected. The implementation of the system is demonstrated through a web-based digital twin platform, containing applications that allow visualizing and interacting with contextualized inspection and load test data.System B focuses on interconnecting multiple bridge digital twins within the same network. It employs a knowledge graph built from Resource Description Framework (RDF)-based graphs and a set of ontologies. The system integrates geographical data according to INSPIRE data models, IFC models, and data from visual inspections. The system presents a data management approach based on strata, which manage and compartmentalize information subsets, and implements the information containers for linked document delivery (ICDD) standard for exchanging graph data with linked documents. The system is demonstrated through a set of fictitious scenarios that simulate interactions between bridge administrators and third parties.Through these systems, this dissertation demonstrates the usefulness of graph technologies in developing digital twins of bridges that are aligned with current industry standards and practices. It emphasizes the advantages of the Knowledge Graph-based approach for simplifying interactions with connected applications, enabling decoupled application development, and enhancing the system scalability and expandability with new datasets. Notwithstanding, real implementation of these systems requires further validation and use cases, as well as collaboration among system developers, administrators, academia, and industry stakeholders to generate a coherent digital ecosystem that enhances the efficiency and productivity of bridge maintenance practices.

Committee:
     PRESIDENT: PELLICER ARMIÑANA, EUGENIO
     SECRETARI: GASPAR FÀBREGAS, KÀTIA
     VOCAL: ALAVI, HAMIDREZA
Thesis abstract: The construction industry's significant environmental footprint necessitates innovative approaches to promote sustainability and integration of Circular Economy (CE) principles. This thesis develops and evaluates "DecideCircular", an advanced framework that integrates Building Information Modeling (BIM) and Virtual Reality (VR) to enhance circular economy processes in construction projects. By leveraging the immersive capabilities of VR in conjunction with the detailed information management of BIM, the framework allows project teams to visualize complex project details and engage in informed decision-making from the early design stages.Employing Design Science Research methodology, this thesis constructs a conceptual model that actively supports the selection of construction products and materials under a circular approach. The model facilitates the evaluation of materials and designs through a comprehensive set of sustainability metrics, including environmental impact, social implications, economic viability, and adherence to circularity principles. These indicators are crucial for assessing the sustainability profile of building materials and overall project designs, aiming to reduce waste and extend the lifecycle of materials through improved resource efficiency.The DecideCircular framework is implemented within existing software environments, enhancing the conventional BIM functionalities with VR's dynamic visualization capabilities. This integration is demonstrated through a case study, where the framework's application is showcased in a real-world setting. Within the immersive VR environment, stakeholders are equipped to evaluate and optimize various sustainability metrics of building products and the construction process itself, aligning project outputs with both project objectives and broader sustainability goals.The results of this thesis indicate that digitalization, particularly the synergy between BIM and VR, can significantly advance CE in the construction industry by enhancing the understanding of material impacts, promoting resource efficiency, and reducing waste. The results of this study not only bridges the gap between theoretical research and practical application but also sets the groundwork for future innovations in sustainable construction.

Committee:
     PRESIDENT: SHI -, ZHONGQI
     SECRETARI: ZHOU, ZHIGUANG
     VOCAL: ZHOU, HONGYUAN
Thesis abstract: The evolution mechanism of structural performance remains a critical research topic in structural mechanics. Cracks, serving as indicators of performance deterioration, manifest physically at the meso-scale as processes of crack initiation and propagation, while at the macro-scale, they correspond to the global responses of structural stiffness degradation and load-bearing capacity attenuation. Traditional manual inspection methods are time-consuming and labor-intensive, and the acquired data are often unsuitable for direct application in structural evolution analysis. Consequently, this study focuses on developing performance evolution methodologies for crack-damaged buildings, aiming to enhance assessment efficiency and provide robust support for the lifecycle safety management of large-scale urban building structures.This research primarily addresses crack evolution prediction, crack-embedded finite element modeling techniques, rapid finite element modeling methods, and automated crack embedding approaches. Firstly, based on the curvature characteristics of reinforced concrete (RC) members, a method for predicting crack locations according to curvature variations is proposed and validated for accuracy through four-point bending tests. Secondly, to further improve prediction precision, an initial-condition-free crack prediction method is introduced. This approach, grounded in nonlinear bond-slip theory, is capable of describing extreme scenarios of reinforcement-concrete debonding, and its feasibility is experimentally verified.Regarding crack embedding within finite element models, this study presents a method for calculating the flexibility matrix of cracked elements based on strain energy release rate theory, along with modification techniques adaptable to diverse boundary conditions. Simultaneously, a novel simulation method utilizing nonlinear spring elements is proposed for unreinforced masonry structures, and its effectiveness is experimentally validated. Building upon this, a method for embedding cracks into masonry structures is further developed. This method simulates the alterations in tensile-compressive and shear behavior of post-cracking elements by adjusting the mechanical properties of planar elements and spring elements.Finally, a computer vision data-driven geometric adaptive modular finite element modeling method is proposed. This technique enables rapid acquisition of geometric information for frame structures, facilitating swift modeling and condition assessment. Additionally, to address the challenge of automated crack embedding in finite elements, a labeled crack embedding method is introduced. By assigning labels containing information on crack position, orientation, and boundary conditions, rapid integration of crack data is achieved.In summary, this study yields significant advancements in performance analysis methods for damaged buildings. It establishes theoretical formulations for crack location prediction and develops modeling approaches for damaged beams, columns, and walls, thereby laying a scientific foundation for constructing a structural performance evolution analysis framework.

Committee:
     PRESIDENT: MEDINA MARTÍNEZ, CÉSAR
     SECRETARI: COROMINAS GONZÀLEZ, ANDREU
     VOCAL: SKAF REVENGA, MARTA
Thesis abstract: Currently, the construction industry faces the challenge of adopting more sustainable practices, with the use of recycled aggregates in structural concrete production emerging as a key strategy. This doctoral research evaluates the viability and efficacy of structural concrete incorporating high volumes of fine and coarse recycled aggregates, specifically recycled concrete aggregates (RCA-type A) and mixed recycled aggregates (MRA-type B). The recycled aggregate concretes were subjected to exposure conditions ranging from XC1 to XC4 classes, extending to more severe environmental conditions such as XS1. The study was conducted in several experimental phases. In the first phase, the physical, chemical, and mechanical characteristics of recycled aggregates were evaluated. All concrete mixtures were designed with a compressive strength of 30/37 MPa and a cement, CEM II A/L 42.5R, content of 300 kg/m³. The second phase involved a comprehensive analysis of the physical, mechanical, and durability properties of concrete mixtures with varying proportions of RCA-type A and MRA-type B, using effective water–cement ratios of 0.48 and 0.52. This phase aimed to determine the maximum replacement percentage of recycled aggregates that could be incorporated without compromising the mechanical performance of the concrete. Results confirmed the feasibility of integrating up to 60% coarse RCA (CRCA) and 20% fine RCA (FRCA) in structural concrete mixtures, achieving mechanical properties comparable to natural aggregate concrete (NAC). The analysis was extended to the use of MRA-type B, validating good mechanical performance with up to 40% coarse MRA (CMRA) and 15% fine MRA (FMRA) without compromising structural performance.The third and fourth phases expanded the study, focusing on the effects on concrete durability using the limits established in previous phases. Recycled aggregate concrete (RAC) and NAC mixtures were produced with similar compressive strengths using effective water–cement ratios of 0.47 and 0.51, respectively. These phases utilized different cement types, such as CEM II A/L 42.5 R, CEM II A/S 42.5 N/SRC, and CEM III/B 42.5 N-LH/SR, to evaluate drying shrinkage, chloride permeability, and accelerated carbonation of the various mixtures and the influence of cement type. After validating those mixtures with up to 50% CRCA and 20% FRCA maintain their structural integrity under conditions susceptible to carbonation and chloride-induced corrosion, in the final phase, with additional studies on natural carbonation and chloride profiles, the concrete produced up to 60% CRCA and 20% FRCA was validated. The findings of this research indicate that concrete mixtures with high percentages of recycled aggregates, RCA and MRA, not only meet current regulatory standards but, in some cases, exhibit enhanced properties compared to those of NAC. These results support their application in structures with extended service life expectations. Furthermore, it is concluded that recycled concrete exhibits properties similar to NAC when working with the same compressive strengths. This doctoral work underscores the sustainability of recycled concrete as a viable alternative, promoting environmentally responsible construction practices without compromising structural integrity in demanding environments.