| 1. |
- Adam, Abderisak, 1988
(författare)
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Managing construction challenges: Viability of a dynamic capabilities approach for the public client
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Construction clients in the public sector face a large number of challenges in designing, procuring and managing construction projects in a manner that is conducive to the organization’s overall goals. In particular, clients have faced challenges in delivering projects that satisfied the projects’ goals with respect to cost overruns, delays and sustainable construction. The role of the client in managing these challenges has more recently been emphasized with a growing number of studies and governmental reports calling for the development of the client’s capabilities.This thesis examines the capabilities of the construction client through a dynamic capabilities framework, particularly with respect to the activities of sensing, seizing and transforming. Furthermore, the thesis explores whether the concept of dynamic capabilities is a viable approach for understanding how to manage the clients’ capabilities in a way that ensures that construction-related challenges are addressed. The thesis is based primarily on a case study of a large public construction client located in Sweden.Findings are presented in three appended papers. The thesis concludes with a discussion on the viability of using a dynamic capabilities framework in the specific case described in this thesis. It is argued that the concept of dynamic capabilities is inadequate for capturing the specific context in which public client organizations operate. Suggestions for alternative approaches to understanding the management and development of capabilities are then discussed.
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| 2. |
- Nasrollahi, Kourosh, 1991
(författare)
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Differential railway track settlement in a transition zone – Field measurements and numerical simulations
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In a transition zone between two different railway track forms, there is a discontinuity in track structure leading to a gradient in track stiffness. Examples include transitions between different superstructures, e.g., slab track to ballasted track, and/or between different substructures, e.g., embankment to a bridge or tunnel structure. Differences in loading and support conditions at the interfaces between track superstructure and substructure on either side of the transition may lead to differential track settlement and an irregularity in longitudinal rail level soon after construction because of densification of ballast and consolidation in the subsoil. This results in an amplification of the dynamic traffic loading along the transition. To ensure the safety of railway operation and reduce maintenance costs, it is necessary to monitor the condition of the transition zone and detect any operational change at an early stage. A methodology for the simulation of long-term differential track settlement, the development of voided sleepers leading to a redistribution of rail seat loads, and the evolving irregularity in vertical track geometry at a transition between two track forms, is presented. For a prescribed traffic load, the accumulated settlement is predicted using an iterative approach. It is based on a time-domain model of vertical dynamic vehicle–track interaction to calculate the contact forces between sleepers and ballast in the short term. These are used in an empirical model to determine the long-term settlement of the ballast and subgrade below each sleeper. Gravity loads and state-dependent track conditions are accounted for. The methodology is applied to a transition zone between a ballasted track and a slab track that is subjected to heavy haul traffic. The influence of higher axle loads and the implementation of under sleeper pads on sleeper settlement is assessed. Based on fibre Bragg grating sensors, a setup for in-situ long-term condition monitoring of track bed degradation in a transition zone has been developed and implemented to provide data for verification and calibration of the simulation model. The system is designed for measurements in an operational railway track in harsh conditions in the north of Sweden. The instrumentation along the transition comprises four clusters, each with an optical strain gauge array on the rail web in one sleeper bay, and an accelerometer and a displacement transducer on the sleeper end. Two additional accelerometers are installed far from the transition zone to measure a reference state. Combined, the data should not only provide details on long-term settlements, but also the change in dynamic response it underpins.
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| 3. |
- Hlal, Fatima, 1989
(författare)
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Stainless Steel Corrugated Web Girders for Composite Road Bridges: Concept Evaluation and Flange Buckling Resistance
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Achieving a sustainable bridge design requires careful consideration of economic viability and environmental impact over the entire lifespan of the structure. While stainless steel is recognized for its excellent life cycle performance, its high cost prevents it from being used to a larger extent in bridges. In this thesis work, a new solution is investigated to mitigate this issue. The new solution comprises the use of corrugated webs in stainless steel girders which is expected to result in reduced material consumption and cost. The work in this thesis focuses on two problem areas in this field. First, a study is performed to examine the competitiveness of the new concept in relation to conventional designs of steel-concrete composite road bridges. The second part of the work focuses on the problem of flange buckling in girders with corrugated webs. Previous research has shown that the design models developed for flange buckling resistance, including the one in EN 1993-1-5, frequently result in unsafe design. Furthermore, these models were developed for carbon steel and have not been updated for stainless steel. To explore the economic and environmental benefits of the new concept, two studies have been conducted. Firstly, three design solutions are examined on a case study bridge with three continuous spans. These design solutions include carbon steel flat web, stainless steel flat web, and stainless steel corrugated web girder bridges. A genetic algorithm is used to optimize each design solution in terms of weight. The three optimal solutions are then assessed in terms of investment costs, life cycle costs (LCC), and environmental life cycle impact. Secondly, two of the considered design solutions, namely carbon steel flat web and stainless-steel corrugated web girders, are employed to conduct multiple parametric studies using a simply supported reference bridge. For both design solutions, the effects of optimization targets on weight, investment cost, life cycle cost, and environmental life cycle impact are initially investigated. Following that, the focus is put on the life cycle cost (LCC) as an optimization target, and the impact of various design input parameters is investigated. These parameters include span length, girder depth, average daily traffic (ADT) with the associated number of heavy vehicles per slow lane (Nobs), and time intervals and expenses for maintenance activities. Furthermore, a sensitivity analysis is conducted to study the influence of the inflation rate and discount rate. The results indicate that the new concept offers considerable potential saving in weight, life cycle costs, and life cycle impacts for both simply supported and continuous bridges. The saving is more apparent with deeper girders, higher ADT, and more intense maintenance activities. Saving is also larger when inflation is high and discount rate is low. After studying the potential of corrugated web girders to reduce costs and environmental impacts in the case of employing stainless steel, a study of the flange buckling behaviour in duplex stainless-steel girders is conducted in this work. A parametric finite element model is developed and validated with tests conducted on beams made of carbon steel. The material is then changed to EN1.4162, and linear buckling analysis (LBA) and geometrically and materially nonlinear analysis with imperfections (GMNIA) are carried out on 410 girders with typical bridge girder dimensions. The results are compared to previously developed models for carbon steel, and a new buckling curve and flange local buckling design procedure for duplex stainless-steel girders with corrugated webs are proposed. The study shows that the new proposed design model generates more accurate estimates of flange buckling resistance than previous proposed models.
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| 4. |
- Mangold, Mikael, 1982
(författare)
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The effect of resource sustainability interventions on social sustainable development in the built environment
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There are several sustainable development targets for the Swedish housing market. The sector as a whole is expected to contribute to the reduction of greenhouse gases. Housing prices should increase and not inflate. Meanwhile, the development of the built environment should contribute to well being and decrease segregation. Prioritization amongst these targets is often done through policy and by actors in the housing market. This thesis focuses on the trade-offs between environmental and social sustainable development targets. The thesis builds on two studies of development in the built environment. The main study describes an environmental upgrade of housing in a disadvantaged area of Gothenburg, and the second investigates a redevelopment area with high environmental ambitions. Environmental targets, such as CO2 reduction, have in some cases been profitably achieved in housing projects in Sweden. The principal study of this thesis describes the implementation of volumetric billing of water at Bredfjällsgatan which successfully reduced water usage and was profitable for the implementing real estate company. However, the system’s change also increased the average monthly costs for the households, and the average monthly costs increased even more in households where the inhabitants were unemployed. The lock-in effect of welfare dependency is increased by rising monthly expenses. This group lacks economic incentive to save water since welfare pays for water usage. The analyses of water consumption data show that while economic incentives account for some reduction of water consumption, other parameters such as household size, crowdedness of apartments, and household level of education are also important factors. Households receiving welfare are not economically affected by the implementation of volumetric billing of water but are further socially excluded from society when trapped in welfare dependence. The real estate owner states economic and environmental aspects as motivators for the system’s change. Social sustainable development targets on a societal level are not an outspoken priority to the same extent. The real estate owners in disadvantaged housing areas should be recognized as important actors in the development to tackle segregation of the housing market.The second study presents empirical insights from a housing area that is being built with high environmental ambitions. Perspectives of sustainable development amongst developers in the area differ, but it is apparent that social dimensions of sustainable development receive less attention. The complexity of social dimensions is not fully addressed. Social sustainable development is for example thought of as comfortable outdoor environments in the area, while the larger societal impacts of the housing project were not considered to the same extent. Integration, affordability, and equity were given direct focus; instead these targets are often assumed to be reached by varying apartment sizes and mixing tenure in the area.
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| 5. |
- Sciegaj, Adam, 1990
(författare)
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Multiscale Modelling of Reinforced Concrete
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since concrete cracks at relatively low tensile stresses, the durability of reinforced concrete structures is highly influenced by its brittle nature. Cracks open up for ingress of harmful substances, e.g. chlorides, which in turn cause corrosion of the reinforcement. Crack widths are thus limited in the design codes, and accurate prediction methods are needed. For structures of more complex shapes, current computational methods for crack width predictions lack precision. Hence, the development of new simulation tools is of interest. In order to properly describe the crack growth in detail, cracking of concrete, constitutive behaviour of steel, and the bond between them must be accounted for. These physical phenomena take place at length scales smaller than the dimensions of large reinforced concrete structures. Thus, multiscale modelling methods can be employed to reinforced concrete. This thesis concerns multiscale modelling of reinforced concrete. More specifically, a two-scale model, based on Variationally Consistent Homogenisation (VCH), is developed. At the large-scale, homogenised (effective) reinforced concrete is considered, whereas the underlying subscale comprises plain concrete, resolved reinforcement bars, and the bond between the two. Each point at the large-scale is associated with a Representative Volume Element (RVE) defining the effective response through a pertinent boundary value problem. In a numerical framework, the procedure pertains to a so-called FE 2 (Finite Element squared) algorithm, where each integration point in the discretised large-scale problem inherits its response from an underlying RVE problem. In order to properly account for the concrete–reinforcement bond action, the large-scale problem is formulated in terms of a novel effective reinforcement slip variable in addition to homogenised displacements. In a series of FE 2 analyses of a plane problem pertaining to a reinforced concrete deep beam with distributed reinforcement layout, the influence of boundary conditions on the RVE, as well as the sizes of the RVE and the large-scale mesh, are studied. The results of the two-scale analyses with and without incorporation of the effective reinforcement slip are compared to fully-resolved (single-scale) analysis. A good agreement with the single-scale results in terms of structural behaviour, in particular load-deflection relation and average strain, is observed. Depending on the sub-scale boundary conditions, approximate upper and lower bounds on structural stiffness are obtained. The effective strain field gains a localised character upon incorporation of the effective reinforcement slip in the model, and the predictions of crack widths are improved. The two-scale model can thus describe the structural behaviour well, and shows potential in saving computational time in comparison to single-scale analyses.
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| 6. |
- Hörteborn, Axel, 1986
(författare)
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Ship Behaviour and Ship Bridge Allision Analysis
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The demand for maritime transport has increased with the growing demand for worldwide trade. This has led to a major increase in maritime traffic and ship sizes over the last decades, which raises the probability of accidents. The methods used in maritime risk assessments today are based on old hypotheses that do not include all data available today. The main objective of this thesis is to develop numerical models and methods for the analysis of what is considered as normal navigation behaviour at sea today and improve the analysis of probability for ship-bridge allisions. The first part of the thesis describes what is considered as normal meeting distance at sea today. This information is later used while identifying failure events to ensure that the event behaviour was not caused by other ships. These few cases are excluded from the methodology since the communication and situational awareness in the situations are not known. However, while studying the probability of ship-bridge accidents, it is also important to understand how waterway restrictions may affect the probability of ship-ship collisions. Therefore, this thesis also includes a study of how the improved knowledge concerning meeting distance could be used in a near ship-ship collision identification model. One of the main findings considering normal meeting distance is that small and large ships meet each other at a similar distance at sea. In the second part of the thesis, a methodology is proposed to estimate the probability of ship-bridge allision. The presented methodology uses Automatic Identification System (AIS) data and a ship manoeuvring simulator to simulate and analyse marine traffic with regards to risks for accidents, such as ship-bridge allisions. A failure event identification method is also presented, which is needed to determine the frequency, duration and behaviour for the accident scenarios. The three events that were modelled and simulated in the simulator were: drifting ship, sharp turning ship and missing turning point. The probability of the different failure events corresponded to previous statistics confirming the AIS-based methodology. This means the methods to obtain the probability and duration of the failure events could be utilised in other areas. The simulation methodology was confirmed with the probability of grounding in the Great Belt VTS area. This thesis firstly contributes to a better understanding of the modelling of probability for ship-bridge allisions. This will support bridge-building engineers who need to take into account accidental loads from ship-bridge allision while designing bridges. Secondly, this thesis also contributes to a better representation of normal behaviour at sea, which is used both in fairway designs and in estimations of ship-ship collisions.
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| 7. |
- Alhede, Andreas, 1996
(författare)
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Novel approaches for monitoring effects of steel corrosion in reinforced concrete
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Corrosion of steel reinforcement is a common deterioration mechanism in reinforced concrete structures. This deterioration impacts the safety of the structure and may require extensive repair and maintenance work. There is currently no method available for accurately measuring internal corrosion damage non-destructively. Therefore, establishing correlations between outer signs of corrosion, such as crack pattern and width, and the corresponding internal corrosion morphology and level is of significant interest. However, prior research has shown that relying solely on crack width as a performance indicator for corrosion damage is inadequate. Hence, further research is needed to study the corrosion and cracking processes in reinforced concrete to be able to identify and quantify underlying physical processes and factors. To contribute to knowledge in the field, this thesis focuses on novel approaches for non-destructive monitoring of the effects of steel corrosion in small-scale reinforced concrete samples. In this work, time-resolved neutron and X-ray Computed Tomography were applied to link the evolution of material phases to kinematics. Further, two independent studies, one using neutron and the other using X-ray Computed Tomography, were used to quantify corrosion-induced deformations within concrete. These deformations were successfully quantified, and the identified locations of concrete cracking correlated well with the observed strain localisation. Interestingly, the kinematics quantified allowed for the detection of strain localisation in areas where concrete cracks were too small to be visually identified from the image data, indicating the potential for early-stage concrete crack detection. Additionally, an expression for the average volumetric strain in the compressed corrosion layer was derived based on the evolution of material phases within the sample. Further, an experimental setup was designed to monitor corrosion-induced deformations adjacent to the steel-concrete interface using an open-ended steel tube instrumented with an optical fibre for distributed strain sensing. X-ray Computed Tomography allowed for quantitative and qualitative assessment of corrosion level and concrete cracking. The corrosion-induced deformations in the steel tube were found to be non-uniform, indicating a non-uniform distribution of radial stress around the steel. This non-uniformity correlated well with the location of the corrosion-induced cracks, with extension hoop strains observed in the steel tube at the location of these cracks, and contraction hoop strains observed in between them. Corrosion was more severe in bands along the steel, coinciding with the position of the longitudinal cracks. The research conducted in this work demonstrated the potential of non-destructive monitoring of steel corrosion in reinforced concrete. For future research aiming at increasing the fundamental understanding of corrosion-induced concrete cracking, it is essential to integrate advanced experimental techniques with numerical modelling.
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| 8. |
- Lozano Mendoza, Fabio José, 1991
(författare)
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Explosions in urban environments: Modelling of gas explosions and risk of premature shear failure in reinforced concrete structures
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The risk for accidental gas explosions in urban environments has increased in Sweden in recent years. This is due to densification of existing urban centres and the rise of vehicles powered by alternative fuels. Because of this, blast-resistant design of reinforced concrete (RC) structures may eventually become a common aspect of urban development and structural engineering. This thesis aims at expanding the knowledge concerning explosion and blast loads in urban environments and the response of RC structures subjected to it. Two key research areas were identified. The first one deals with the strength of vapour cloud explosions (VCEs) on urban roads. The strength of the blast source is a necessary input to predict the blast load generated by VCEs. However, there is much subjectivity and inconsistency today in the determination of the explosion strength, particularly for the conditions on urban roads. This work used computational fluid dynamics (CFD) calculations in combination with the principles of factorial design to determine the expected strength for several explosion scenarios on urban roads and identify the most significant parameters affecting the resulting strength. For the studied scenarios, the explosion strength varied approximately from 2 kPa to 100 kPa. Moreover, the number of vehicles in the transversal direction (i.e., vehicles standing side by side) was found to have the most significant effect on the explosion pressure. The other area is concerned with the uncertainties related to the failure modes of blast-loaded RC one-way slabs. The motivation behind this research area is the need to prevent brittle shear failure in blast-loaded RC elements. The Monte Carlo method was used to determine the probability of premature shear failure of the blast-loaded slabs considering the uncertainties associated with the materials, geometry, and resistance models. The slabs were initially designed to have a balanced failure (i.e., the resistance to shear and bending failure are theoretically equal). Bending failure was found to be the expected failure mode for the studied cases. However, the likelihood of shear failure (particularly for slabs without stirrups) may still be considered relatively high, depending on the risk tolerability of a given design. Thus, an additional partial factor to enhance the confidence level regarding the preferred failure mode was put forward.
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| 9. |
- Neves, Cláudia, 1991-
(författare)
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Structural Health Monitoring of Bridges : Model-free damage detection method using Machine Learning
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This is probably the most appropriate time for the development of robust and reliable structural damage detection systems as aging civil engineering structures, such as bridges, are being used past their life expectancy and beyond their original design loads. Often, when a significant damage to the structure is discovered, the deterioration has already progressed far and required repair is substantial. This is both expensive and has negative impact on the environment and traffic during replacement. For the exposed reasons the demand for efficient Structural Health Monitoring techniques is currently extremely high. This licentiate thesis presents a two-stage model-free damage detection approach based on Machine Learning. The method is applied to data gathered in a numerical experiment using a three-dimensional finite element model of a railway bridge. The initial step in this study consists in collecting the structural dynamic response that is simulated during the passage of a train, considering the bridge in both healthy and damaged conditions. The first stage of the proposed algorithm consists in the design and unsupervised training of Artificial Neural Networks that, provided with input composed of measured accelerations in previous instants, are capable of predicting future output acceleration. In the second stage the prediction errors are used to fit a Gaussian Process that enables to perform a statistical analysis of the distribution of errors. Subsequently, the concept of Damage Index is introduced and the probabilities associated with false diagnosis are studied. Following the former steps Receiver Operating Characteristic curves are generated and the threshold of the detection system can be adjusted according to the trade-off between errors. Lastly, using the Bayes’ Theorem, a simplified method for the calculation of the expected cost of the strategy is proposed and exemplified.
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| 10. |
- Allahvirdizadeh, Reza
(författare)
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Reliability-Based Assessment and Optimization of High-Speed Railway Bridges
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing the operational speed of trains has attracted a lot of interest in the last decades and has brought new challenges, especially in terms of infrastructure design methodology, as it may induce excessive vibrations. Such demands can damage bridges, which in turn increases maintenance costs, endangers the safety of passing trains and disrupts passenger comfort. Conventional design provisions should therefore be evaluated in the light of modern concerns; nevertheless, several previous studies have highlighted some of their shortcomings. It should be emphasized that most of these studies have neglected the uncertainties involved, which preventsthe reported results from representing a complete picture of the problem. In this respect, the present thesis is dedicated to evaluating the performance of conventional design methods, especially those related to running safety and passenger comfort, using probabilistic approaches. To achieve this objective, a preliminary study was carried out using the first-order reliability method for short/medium span bridges passed by trains at a wide range of operating speeds. Comparison of these results with the corresponding deterministic responses showed that applying a constant safety factor to the running safety threshold does not guarantee that the safety index will be identical for all bridges. It also shows that the conventional design approaches result in failure probabilities that are higher than the target values. This conclusion highlights the need to update the design methodology for running safety. However, it would be essential to determine whether running safety is the predominant design criterion before conducting further analysis. Therefore, a stochastic comparison between this criterion and passenger comfort was performed. Due to the significant computational cost of such investigations, subset simulation and crude Monte-Carlo (MC) simulation using meta-models based on polynomial chaos expansion were employed. Both methods were found to perform well, with running safety almost always dominating the passenger comfort limit state. Subsequently, classification-based meta-models, e.g. support vector machines, k-nearest neighbours and decision trees, were combined using ensemble techniques to investigate the influence of soil-structure interaction on the evaluated reliability of running safety. The obtained results showed a significant influence, highlighting the need for detailed investigations in further studies. Finally, a reliability-based design optimization was conducted to update the conventional design method of running safety by proposing minimum requirements for the mass per length and moment of inertia of bridges. It is worth mentioning that the inner loop of the method was solved by a crude MC simulation using adaptively trained Kriging meta-models.
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