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Railway owners manage geographically dispersed networks comprising major elements of ageing infrastructure that are very susceptible to natural hazards. Consequently, transport agencies must address maintenance issues to guarantee serviceability and safety. This includes increased inspections and investing into structural health monitoring (SHM) programs. Regular SHM of existing bridges are usually scheduled during their service life to evaluate their health and as part of proactive maintenance where future deterioration is anticipated. Typically, a routine inspection consists of field measurements and visual observations made by a bridge inspector. However, disruption to civil infrastructure services due to scheduled maintenance work, visual inspection, etc. is increasing.  The main purpose of SHM is to collect information such as geometry, previous and ongoing concrete deterioration, steel rebar corrosion, water seepage, concrete cover delamination, deflections, or settlements etc. The way such data are documented is through field inspection notes, freehand sketches, and photographs. Oftentimes, the data is stored in different systems and data collection and visualization still relies on paper-based record keeping processes. In addition, the procedure is highly dependent on the inspector’s experience [1], and knowledge of the structural behavior, together with the material properties of the system being investigated. The method has its limitations in the sense that only accessible parts are investigated due to time shortage, safety issues, or the difficult terrain in which the structure is sometimes located. This is especially true for large structures, such as bridges, where investigating the whole area would be highly time-consuming and potentially unsafe [2]. Honfi et al. [3] noted that the inspection’s duration is highly dependent on the bridge span (less than 10m can amount to 0.5 days and bigger than 100 m can amount to 20 days). In addition, defects can only be detected when their presence is visible to the naked eye, so they may already affect the life of the structure. Graybeal et al. [4] noted that routine inspections have relatively poor accuracy, with the following factors affecting the reliability of these results: inspector fear of traffic, near visual acuity, color vision, accessibility, and complexity. Furthermore, knowledge transfer from one inspection period to another becomes difficult when different inspectors carry out the investigation. Therefore, there is a strong need to identify new inspection and monitoring techniques for infrastructure that, in addition to being contactless and productive, reduce disruption, and improve the efficiency and reliability of the acquired data. With the expansion of the low-cost consumer cameras, photogrammetry could play an important role in supporting SHM on existing bridges. Vaghefi et al. [5] carried out a study of 12 remote sensing technologies and their potential to detect a series of common problems on US bridges. They concluded that 3D optical technologies have potential for documenting surface-related defects. Faster bridge inspection and visualization was described when aiming to quantify the defects over bridge deck surfaces with a low cost and easily deployable technology. Other studies reported on the use of photogrammetry as alternative to traditional measurement applied in laboratory environment; a review is done by Baqersad et al. [6]. The researchers themselves have a well-proven experience in applying photogrammetry for determination of failure mechanisms in concrete structures, defect detection, and monitoring full-field deformations. In an effort, by Popescu et al. [7], to develop new monitoring and inspection methods with a preliminary study, photogrammetry and terrestrial laser scanning utilized to generate the 3D model of six railway bridges located in northern Sweden. Results have shown an acceptable performance of 3D model of existed infrastructure generated by photogrammetry. Therefore, the current project will contribute with optical alternatives to traditional SHM approaches that are low-cost, suitable for field application, and easily deployable. The results indicate that bridge inspection on generated digital model is more reliable, productive, and accessible than traditional surveys. For 3D model generation we used photogrammetry technique, which is more efficient and cost-effective compared to the laser scanning, but improvements in accuracy and automation during the image acquisition phase are still required.  The approach of autonomous defect detection performed on two case studies. Two types of defects including cracks, and block opening in a hard-to-access area was successfully detected and measured by pixel-wise mapping to an orthophoto. The proposed method has considerable potential in automated infrastructure inspection but some problems due to background noise remain to be overcome. The existence of noisy patterns such as shadows, dirt, and snow or water spots on surfaces makes damage detection very challenging, especially for the fine cracks. Overall, while the automated inspection technique proposed herein performs well, it clearly still requires supervision by a human inspector.

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Sommaren 2006 så upptäcktes ett flertal sprickor på bron över Vårby fjärden i närheten av Stockholm. Samtliga sprickor syntes ha uppstått i svetsar som förbinder vertikala livavstyvningar med huvudbalkarnas överflänsar. På uppdrag av Trafikverket så har en utredning genomförts med syftet att klarlägga orsaken till sprickornas uppkomst. Utredningen omfattande bl.a.-Töjningsmätningar på bron. -Delskadeberäkningar enligt Palmgren-Miner och utförda på basis av långtidsmätningarna-Finita element analyser-Mikroskopanalyser av bit av en svets med en sprickyta-Tester utförda på en mindre samverkansbro vid Luleå Tekniska Universitet (LTU)Resultatet av utredningen påvisar entydigt att orsaken till sprickorna är utmattning. De för utmattning relevanta spänningarna tros vara resultatet av påtvingade rotationer på styva livavstyvningar och tvärförband. Rotationerna uppstår då betongfarbanan böjer sig för tunga fordon. Med all rimlig visshet så förbisågs denna sekundära effekt när bron konstruerades.Tester på en mindre samverkansbro har utförts vid Luleå tekniska Universitet. Två olika typer av tvärförband testades. Testerna och resultatet av dessa beskrivs i uppsatsen.På basis av resultatet av Vårby-utredningen samt av utförda tester vid LTU, och med ett syfte att minska sannolikheten för liknande sprickbildningar, så har ett antal detaljutformningar utvärderats. Vidare så föreslås en enkel metod för utvärdering av kritisk spänningsvidd i livavstyvningar.

The assumptions encountered during the analysis and design of civil engineering structures lead to a difference in the structural behavior between calculations based models and real structures. Moreover, the recent approach in civil engineering nowadays is to rely on the performance-based design approaches, which give more importance for durability, serviceability limit states, and maintenance.Structural identification (St-Id) approach was utilized to bridge the gap between the real structure and the model. The St-Id procedure can be utilized to evaluate the structures health, damage detection, and efficiency. Despite the enormous developments in parametric time-domain identification methods, their relative merits and performance as correlated to the vibrating structures are still incomplete due to the lack of comparative studies under various test conditions and the lack of extended applications and verification of these methods with real-life data.This licentiate thesis focuses on the applications of the parametric models and non-parametric models of the System Identification approach to assist in a better understanding of their potentials, while proposing a novel strategy by combining this approach with the utilization of the Singular Value Decomposition (SVD) and the Complex Mode Indicator Function (CMIF) curves based techniques in the damage detection of structures.In this work, the problems of identification of the vertical frequencies of the top storey in a multi-storey¸ building prefabricated from reinforced concrete in Stockholm, and the existence of damage and damage locations for a bench mark steel frame are investigated. Moreover, the non-parametric structural identification approach to investigate the amount of variations in the modal characteristics (frequency, damping, and modes shapes) for a railway steel bridge will be presented.

Improving productivity is a central challenge in most industries and so also in construction. In many countries, such as Great Britain and US (Egan, 1998; Huang et al., 2009; Teichholz, 2001), governmental reports and research publications have highlighted the slow growth of productivity in the construction industry. In Sweden the urgency of improving productivity and client satisfaction in the construction industry have initiated a number of government investigations (SOU, 2002; SOU, 2009; SOU, 2012).A recent investigation of government clients' actions to improve productivity and innovation in infrastructure projects have recommended better planning regarding the procurements of projects, increased amount of turnkey contracts and that the sector must become more industrialized. As a response, the Swedish Transportation Administration has launched a research and innovation program where an increased industrial mindset and standardization of products is on the agenda. With the exception of the process-based housing sector, increased industrialization has however been difficult to achieve in the project-based construction industry.The aim of the research is to find the most important parts and processes that can be industrialized to make bridge construction projects more efficient. Empirical data has been collected through questionnaire surveys, workshop and case studies. The data has resulted in four appended papers with focus on mapping the concept of industrialization. Each paper contributes to the aim, but focuses on different aspects of the concept.An interesting aspect of the empirical results from the research is the multi-facetted view practitioners and industry experts have on industrialization, a concept involving elements like prefabrication, standardization and processes. Many of the identified core elements of industrialization focus on processes (long-term) rather than projects (short-term). Some major barriers for industrialization are identified involving: lack of repetition possibilities, strict norms and rules, Design-bid-build contracts, government regulations, and the existing conservatism in the infrastructure sector. Interesting is that out of the five largest barriers, three could be traced back to the client role. As such, the clients (i.e. STA in Sweden) must address these barriers in order to enhance increased industrialization. Launch of the long-term research and innovation program by STA, where increased industrialization throughout the value chain and standardization of products are on the agenda, is a first step toward breaking down barriers, hence possibilities for increased productivity. Standardization of parts and products is shown to be a possible way of decreasing complexity related to on-site construction. Case studies have shown that massive saving in terms of time can be achieved utilizing prefabrication instead of traditional on-site construction. But standardization and prefabrication will not be more common as long as identified barriers like aesthetics issues and assumptions that quality is decreasing are available among practitioners. Also the small chances for large-scale production and repetitiveness are hindering standardized parts and products to be more commonly used.The general conclusion of this research is that massive savings in terms of time can be achieved when utilizing more industrialized methods and techniques during construction of concrete bridges, but barriers have to be dealt with before long-term productivity increases can be achieved.

Externally bonded fibre-reinforced polymer (FRP) systems have shown to be a robust and durable way to repair, or strengthen concrete structures. Epoxy, as the most common bonding agent, provides excellent force transfer, and bonds well to the base substrate to the as well as to the strengthening material. However, the epoxy-bonded systems exhibit certain inherent weaknesses, such as low compatibility with the concrete substrate, degradation in strength and stiffness around 85 °C, and toxicity both during application and when subjected to fire. Epoxies also require a minimum application temperature often above 10 °C, and create sealed surfaces, potentially resulting in moisture and freeze/thaw problems.In recent years, alternative, inorganic bonding agents have been in the focus of research. Cementitious bonding agents, when combined with the FRP, have the potential to become a high-performance strengthening system, without the drawbacks of the epoxy-bonded systems. Inorganic binders provide excellent protection to the FRP against UV-degradation, fire, or vandalism. Contrary to epoxy, they can be applied in colder temperatures or climates. They show a better compatibility with the base concrete in terms of chemical or thermal compatibility, shrinkage properties, and they do not create diffusion-closed surfaces.In this thesis, the mineral-based composite (MBC) strengthening system has been investigated, with focus on the tensile behaviour of the material. The MBC comprises of a carbon fibre polymer (CFRP) grid and an inorganic, mineral-based binder. Additionally, MBC has been placed in a wider context within the field of externally bonded, mineral-based strengthening systems. On the material side, MBC has been modified and enhanced by involving strain-hardening mortars. The experimental work presented in the thesis consists of two test series aiming to investigate the tensile behaviour. First, uniaxial tensile tests were carried out on dogbone-shaped specimens, to characterize the tensile properties of the bare composite strengthening material. Then, wedge-splitting tests were conducted to investigate the post-cracking behaviour, toughness, and ductility of the MBC, and the interaction between the MBC and the base concrete.The chosen test methods have proven to be suitable to characterize the tensile behaviour of the MBC. In all cases, the specimens failed with CFRP rupture, indicating good bond, both on the base concrete-mortar, and the mortar-CFRP interface. The MBC strengthening system performed excellent in terms of load-carrying capacity. Furthermore, the strain-hardening mortar has been found to enhance both the load bearing and in particular, the deformation capacity. It has also been shown that the pseudo-ductile mortar is capable to shift the overall behaviour from brittle towards a more ductile failure.The potential in such improved mineral-based strengthening systems is enormous. The ductility provided by the strain-hardening mortars together with the stiffness and strength from the FRP component could result in a high-performance strengthening material applicable in a range of different situations, from shear-sensitive structures through mining applications, such as tunnel linings.

One of the widespread issues in concrete structures is cracks occurring at early age. Cracks that appear in the young concrete may cause early start of corrosion of rebars or early penetration of harmful liquids or gases into the concrete body. These situations could result in reduced service life and in significantly increased maintenance cost of structures. Therefore it is important for construction companies to avoid these cracks. Restraint represents one of the main sources of thermal and shrinkage stresses at early age concrete. Paper I, deals with both the compensation plane method, CPM, and local restraint method, LRM, as alternative methods studying crack risks for early age concrete. It is shown that CPM can be used both for cooling and heating, but basic LRM cannot be applied to heating. This paper presents an improved equivalent restraint method, ERM, which easily can be applied both for usage of heating and cooling for general structures. Restraint curves are given for two different infrastructures, one founded on frictional materials and another on rock. Such curves might be directly applied in design using LRM and ERM.In Paper II, existing restraint curves have been applied to the method of artificial neural networks (ANN) to model restraint in the wall for the typical structure wall-on-slab. It has been proven that ANN is capable of modeling the restraint with good accuracy. The usage of the neural network has been demonstrated to give a clear picture of the relative importance of the input parameters. Further, it is shown that the results from the neural network can be represented by a series of basic weight and response functions. Thus, the results can easily be made available to any engineer without use of complicated software.Paper III, discusses the influence of five casting sequences for the typical structure slab-on-ground. The aim is to map restraints from adjacent structures for a number of possible casting sequences, and to identify the sequence with the lowest restraint. The paper covers both continuous and jumped casting sequences, which include one, two and three contact edges. The result shows that the best casting sequence is the continuous technique with one contact edge.

The main aim of this thesis is to refine models for strength and heat development of the young concrete, and evaluate if developed models at Luleå University of Technology (LTU) for creep, autogenous shrinkage and thermal dilation needs refinement. These are of importance in hardening control and in crack control of a concrete structure.Strength development is one of the most important properties in concrete to consider when analysing concrete structures. The need of actions on site is different at various stages of hardening, from the fresh concrete to the hardened concrete. This thesis defines a model analysing maturity and associated strength growth within three important time periods. The model can be applied separately within each of these periods depending on test data available. Known is that the temperature plays an important role on the strength development of concrete structures. Not so well known is that, if the concrete temperature remains high, strength reduction at later ages often occurs compared to hardening at lower temperature. Both these phenomena have been implemented in the model for strength growth and the functionality of the model is demonstrated by evaluation of laboratory tests for five concrete mixes and two types of cement.As heat of hydration affects the temperature levels and several other properties of concrete structures it is important to document the parameters accurately. In the traditional semi-adiabat (TSA) the measured heat energy originates from the reaction between cement and water. This energy warms up the concrete sample and all the ambient materials of the equipment. In order to model these energies, the TSA setup is transformed into an associated sphere. A refined model using a correction factor is introduced, which accounts for energies lost to the TSA setup materials. Results show that the effect of this factor cannot be disregarded. An increased insulation amount gives a decreased cooling factor but an increased need for correction.Creep at constant temperature, both for moist sealed specimens and drying out conditions, are evaluated. The Linear Logarithmic creep Model (LLM) is shown to work well for basic creep, i.e. creep at moist sealed conditions. But, for creep during simultaneous moist drying, there is a need to adjust the current model or develop a new model to account for the increase of creep due to ongoing drying.Autogenous shrinkage and thermal dilation (free deformation) are evaluated from tests. For the free deformation of young concrete at variable temperature the existing models are satisfactory in modelling the thermal dilation, but in some cases the autogenous shrinkage cannot be adequately described. A new or refined model is needed that works for autogeneous shrinkage even at more complex temperature variations.

The thesis deals with the axial strength of axially and eccentrically loaded concrete walls with cut-out openings strengthened by fiber-reinforced polymers (FRPs).Background: Functional modifications of concrete structures are common because existing structures must often be adapted to comply with current living standards. Such modifications may include the addition of new windows or doors and paths for ventilation and heating systems, all of which require openings to be cut into structural walls. These openings are a source of weakness and can size dependently reduce the structures’ stiffness and load-bearing capacity, thus, requiring the element to be repaired.Aim and objectives: The main aim of this project was to develop a toolbox containing solutions for strengthening concrete walls with existing or newly created openings using FRP materials. The two immediate objectives sought are: (1) An assessment of the research level on concrete walls with and without openings; (2) An experimental and numerical investigation of the structural behavior of the FRP strengthened walls with openings.Methods of investigation: The experimental program was defined by reviewing therelevant tests performed to date. The literature review revealed research gaps that the current study aims to fill. Moreover, preliminary nonlinear finite element analyses were performed prior to the experimental program in order to gain insight into the structural behavior of these elements. Nine specimens designed to represent typical wall panels in residential buildings, at half-scale, were constructed for testing to failure. The two types of openings examined comprised symmetric halfscaled single door-type openings, and symmetric half scaled double door-type openings. The test matrix was divided into three stages, namely: (1) Reference specimens, (2) Pre-cracked specimens strengthened by FRP and (3) Un-cracked specimens strengthened by FRP. The strengthening method used was FRP confinement with the aid of mechanical anchorages.Results: The results indicate that the 25% and 50% reductions in cross-sectional area of the solid wall caused by introducing the small opening and large opening reduced its load carrying capacity by nearly 36% and 50%, respectively. The application of the FRP confinement increases the capacity and the stiffness of the specimens with cut-out openings. The axial strengths were between 85 94.8% and 56.5-63.4% for specimens having a small and large opening, respectively, of that of a solid wall.Conclusion: The FRP-confinement together with the mechanical anchorages was able to partly restore the capacity of a solid wall. Better results might have been possible if longitudinal FRP strips or bi-directional fibers were used. The effects of steel anchorages were not investigated and it is believed that they might have had positive influences. However, the optimal distance between the anchors should be further investigated. Moreover, the influence of the prestressing force of the anchorages may also be an important parameter that has led to an increase in capacity. Keywords: Strengthening, Fiber-reinforced polymers, Concrete walls, Openings, Axial load, Eccentricity, Out-of-plane behavior, Two-Way