| 1. |
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| 2. |
- Abbasiverki, Roghayeh
(författare)
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Analysis of underground concrete pipelines subjected to seismic high-frequency loads
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Buried pipelines are tubular structures that are used for transportation of important liquid materials and gas in order to provide safety for human life. During an earthquake, imposed loads from soil deformations on concrete pipelines may cause severe damages, possibly causing disturbance in vital systems, such as cooling of nuclear power facilities. The high level of safety has caused a demand for reliable seismic analyses, also for structures built in the regions that have not traditionally been considered as highly seismically active. The focus in this study is on areas with seismic and geological conditions corresponding to those in Sweden and Northern Europe. Earthquakes in Sweden for regions with hard rock dominated by high-frequency ground vibrations, Propagation of such high-frequency waves through the rock mass and soil medium affect underground structures such as pipelines.The aim of this project is investigating parameters that affect response of buried pipelines due to high-frequency seismic excitations. The main focus of the study is on reinforced concrete pipelines. Steel pipelines are also studied for comparison purposes. The effects of water mass, burial depth, soil layer thickness and non-uniform ground thickness caused by inclined bedrock are studied. The results are compared to those obtained for low-frequency earthquakes and the relationship between strong ground motion parameters and pipelines response is investigated. It is shown that, especially for high frequency earthquake excitations, non-uniform ground thickness due to inclined bedrock significantly increase stresses in the pipelines. For the conditions studied, it is clear that high-frequency seismic excitation is less likely to cause damage to buried concrete pipelines. However, the main conclusion is that seismic analysis is motivated also for pipelines in high-frequency earthquake areas since local variation in the ground conditions can have a significant effect on the safety.
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| 3. |
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| 4. |
- Ahmed, Lamis
(författare)
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Models for analysis of shotcrete on rock exposed to blasting
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In underground construction and tunnelling, the strive for a more time-efficient construction process naturally focuses on the possibilities of reducing the times of waiting between stages of construction. The ability to project shotcrete (sprayed concrete) on a rock surface at an early stage after blasting is vital to the safety during construction and function of e.g. a tunnel. A complication arises when the need for further blasting affects the hardening of newly applied shotcrete. If concrete, cast or sprayed, is exposed to vibrations at an early age while still in the process of hardening, damage that threatens the function of the hard concrete may occur. There is little, or no, established knowledge on the subject and there are no guidelines for practical use. It is concluded from previous investigations that shotcrete can withstand high particle velocity vibrations without being seriously damaged. Shotcrete without reinforcement can survive vibration levels as high as 0.5−1 m/s while sections with loss of bond and ejected rock will occur for vibration velocities higher than 1 m/s. The performance of young and hardened shotcrete exposed to high magnitudes of vibration is here investigated to identify safe distances and shotcrete ages for underground and tunnelling construction, using numerical analyses and comparison with measurements and observations. The work focuses on finding correlations between numerical results, measurement results and observations obtained during tunnelling. The outcome will be guidelines for practical use. The project involves development of sophisticated dynamic finite element models for which the collected information and data will be used as input, accomplished by using the finite element program Abaqus. The models were evaluated and refined through comparisons between calculated and measured data. First, existing simple engineering models were compared and evaluated through calculations and comparisons with existing data. The first model tested is a structural dynamic model that consists of masses and spring elements. The second is a model built up with finite beam elements interconnected with springs. The third is a one-dimensional elastic stress wave model. The stress response in the shotcrete closest to the rock when exposed to P-waves striking perpendicularly to the shotcrete-rock interface was simulated. Results from a non-destructive laboratory experiment were also used to provide test data for the models. The experiment studied P-wave propagation along a concrete bar, with properties similar to rock. Cement based mortar with properties that resembles shotcrete was applied on one end of the bar with a hammer impacting the other. The shape of the stress waves travelling towards the shotcrete was registered using accelerometers positioned along the bar. Due to the inhomogeneous nature of the rock, the stress waves from the blasting attenuate on the way from the point of explosion towards the shotcrete on the rock surface. Material damping for the rock mass is therefore accounted for, estimated from previous in-situ measurements. The vibration resistance of the shotcrete-rock support system depends on the material properties of the shotcrete and here were age-dependent properties varied to investigate the behaviour of young shotcrete subjected to blast loading. The numerical simulations require insertion of realistic material data for shotcrete and rock, such as density and modulus of elasticity. The calculated results were in good correspondence with observations and measurements in-situ, and with the previous numerical modelling results. Compared to the engineering models, using a sophisticated finite element program facilitate modelling of more complex geometries and also provide more detailed results. It was demonstrated that wave propagation through rock towards shotcrete can be modelled using two dimensional elastic finite elements in a dynamic analysis. The models must include the properties of the rock and the accuracy of the material parameters used will greatly affect the results. It will be possible to describe the propagation of the waves through the rock mass, from the centre of the explosion to the reflection at the shotcrete-rock interface. It is acceptable to use elastic material formulations until the material strengths are exceeded, i.e. until the strains are outside the elastic range, which thus indicates material failure. The higher complexity of this type of model, compared to the engineering models, will make it possible to model more sophisticated geometries. Examples of preliminary recommendations for practical use are given and it is demonstrated how the developed models and suggested analytical technique can be used to obtain further detailed limit values.
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| 5. |
- Ahmed, Lamis
(författare)
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Models for analysis of young cast and sprayed concrete subjected to impact-type loads
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The strive for a time-efficient construction process naturally put focus on the possibility of reducing the time of waiting between stages of construction, thereby minimizing the construction cost. If recently placed concrete, cast or sprayed, is exposed to impact vibrations at an early age while still in the process of hardening, damage that threatens the function of the hard concrete may occur. A waiting time when the concrete remains undisturbed, or a safe distance to the vibration source, is therefore needed. However, there is little, or no, fully proven knowledge of the length of this distance or time and there are no established guidelines for practical use. Therefore, conservative vibration limits are used for young and hardening concrete exposed to vibrations from e.g. blasting.As a first step in the dynamic analysis of a structure, the dynamic loads should always be identified and characterized. Here it is concluded that impact-type loads are the most dangerous of possible dynamic loads on young and hardening concrete. Shotcrete (sprayed concrete) on hard rock exposed to blasting and cast laboratory specimens subjected to direct mechanical impact loads have been investigated using finite element models based on the same analysis principles. Stress wave propagation is described in the same way whether it is through hard rock towards a shotcrete lining or through an element of young concrete. However, the failure modes differ for the two cases where shotcrete usually is damaged through loss of bond, partly or over larger sections that may result in shotcrete downfall. Cracking in shotcrete due to vibrations only is unusual and has not been observed during previous in situ tests. The study of shotcrete is included to demonstrate the need of specialized guidelines for cases other than for mass concrete, i.e. structural elements or concrete volumes with large dimensions in all directions.Within this project, work on evaluating and proposing analytical models are made in several steps, first with a focus on describing the behaviour of shotcrete on hard rock. It is demonstrated that wave propagation through rock towards shotcrete can be described using two-dimensional elastic finite element models in a dynamic analysis. The models must include the material properties of the rock and the accuracy of these parameters will greatly affect the results. It is possible to follow the propagation of stress waves through the rock mass, from the centre of blasting to the reflection at the shotcrete-rock interface. It is acceptable to use elastic material formulations until the strains are outside the elastic range, which thus indicates imminent material failure. The higher complexity of this type of model, compared with mechanical models using mass and spring elements, makes it possible to analyse more sophisticated geometries. Comparisons are made between numerical results and measurements from experiments in mining tunnels with ejected rock mass and shotcrete bond failure, and with measurements made during blasting for tunnel construction where rock and shotcrete remained intact. The calculated results are in good correspondence with the in situ observations and measurements, and with previous numerical modelling results. Examples of preliminary recommendations for practical use are given and it is demonstrated how the developed models and suggested analytical technique can be used for further detailed investigations.The modelling concept has also been used for analysis of impact loaded beams and concrete prisms modelled with 3D solid elements. As a first analysis step, an elastic material model was used to validate laboratory experiments with hammer-loaded concrete beams. The laboratory beam remained un-cracked during the experiments, and thus it was possible to achieve a good agreement using a linear elastic material model for fully hardened concrete. The model was further developed to enable modelling of cracked specimens. For verification of the numerical results, earlier laboratory experiments with hammer impacted smaller prisms of young concrete were chosen. A comparison between results showed that the laboratory tests can be reproduced numerically and those free vibration modes and natural frequencies of the test prisms contributed to the strain concentrations that gave cracking at high loads. Furthermore, it was investigated how a test prism modified with notches at the middle section would behave during laboratory testing. Calculated results showed that all cracking would be concentrated to one crack with a width equal to the sum of the multiple cracks that develop in un-notched prisms. In laboratory testing, the modified prism will provide a more reliable indication of when the critical load level is reached.This project has been interdisciplinary, combining structural dynamics, finite element modelling, concrete material technology, construction technology and rock support technology. It is a continuation from previous investigations of the effect on young shotcrete from blasting vibrations but this perspective has been widened to also include young, cast concrete. The outcome is a recommendation for how dynamic analysis of young concrete, cast and sprayed, can be carried out with an accurate description of the effect from impact-type loads. The type of numerical models presented and evaluated will provide an important tool for the work towards guidelines for practical use in civil engineering and concrete construction work. Some recommendations on safe distances and concrete ages are given, for newly cast concrete elements or mass concrete and for newly sprayed shotcrete on hard rock.
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| 7. |
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| 8. |
- Albrektsson, Joakim, 1981-
(författare)
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Durability of fire exposed concrete : Experimental Studies Focusing on Sti„ffness & Transport Properties
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Road and rail tunnels are important parts of the modern infrastructure. High strength concrete (HSC) is commonly used for tunnels and other civil engineering structures, since it allows high load carrying capacity and long service life. In general, Swedish road and rail tunnels should be designed for a service life of 120 years. However, HSC has shown to be sensitive to severe fires in the moist tunnel environment, i.e., fire spalling may occur. Extensive research shows that addition of polypropylene (PP) fibres in the fresh concrete mix significantly reduces the risk of fire spalling. The durability of a concrete structure is mainly governed by the transport properties. Further, experimental studies aimed at understanding the protective mechanism of PP fibres indicate that fluid transport increases in connection with the melting temperature of such fibres. This might reduce the durability of fire exposed concrete with addition of PP fibres. This study aims to investigate whether the use of PP fibres has any significant effect on the durability of moderate fire exposed concrete structures.The experimental study focused on transport properties related to durability and stiffness reduction of fire exposed civil engineering concrete with and without addition of PP fibres. The study consists of three parts; (i) unilateral fire exposure in accordance with the standard time-temperature curve (Std) and a slow heating curve (SH), (ii) uniformly heating of non-restrained samples to 250oC, and (iii) moderate unilateral fire exposure, 350oC, of restrained samples. Changes in material properties caused by the fire exposure were studied by means of ultrasonic pulse velocity, full field-strain measurements during uniaxial compression core tests, polarization and fluorescence microscopy (PFM), water absorption and non-steady state chloride migration.The study shows that fire exposure influences different properties of importance for load carrying capacity and durability. To get a clear image of the fire damage one has to combine different test methods during damage assessments. Transport properties of concrete both with and without addition of PP fibres were considerably affected even at moderate fire exposure. Hence, the service life might be reduced. All series with addition of PP fibres exhibited higher water absorption compared to the series without PP fibres. The practical importance of this might, however, be small since also the water absorption of concrete without PP fibres was considerably affected for the fire scenarios considered in this study. Behind the fire exposed surface, i.e., between 30 and 60 mm, no change in water absorption was observed for concrete without PP fibres. However, higher water absorption of the series with addition of PP fibres was observed.Indicative fire tests aimed to evaluate the resistance to fire spalling during a subsequent severe fire was also conducted. The concretes with addition of PP fibres showed no signs of fire spalling, while progressive spalling was observed for the concrete without PP fibres.
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| 9. |
- Andersson, Andreas, 1980-
(författare)
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Capacity assessment of arch bridges with backfill : Case of the old Årsta railway bridge
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work presented in this thesis comprises the assessment of existing arch bridges with overlying backfill. The main objective is to estimate the load carrying capacity in ultimate limit state analysis. A case study of the old Årsta railway bridge is presented, serving as both the initiation and a direct application of the present research. The demand from the bridge owner is to extend the service life of the bridge by 50 years and increase the allowable axle load from 22.5 to 25 metric tonnes. The performed analyses show a great scatter in estimated load carrying capacity, depending on a large number of parameters. One of the factors of main impact is the backfill material, which may result a significant increase in load carrying capacity due to the interaction with the arch barrel. Based on theoretical analyses, extensive conditional assessments and the demand from the bridge owner, it was decided that the bridge needed to be strengthened. The author, in close collaboration with both the bridge owner and the persons performing the conditional assessment, performed the development of a suitable strengthening. The analyses showed a pronounced three-dimensional behaviour, calling for a design using non-linear finite element methods. Due to demands on full operability during strengthening, a scheme was developed to attenuate any decrease in load carrying capacity. The strengthening was accepted by the bridge owner and is currently under construction. It is planned to be finalised in 2012. The application of field measurements to determine the structural manner of action under serviceability loads are presented and have shown to be successful. Measured strain of the arch barrel due to passing train has been performed, both before, during and after strengthening. The results serve as input for model calibration and verification of the developed strengthening methods. The interaction of the backfill was not readily verified on the studied bridge and the strengthening was based on the assumption that both the backfill and the spandrel walls contributed as dead weight only. The finite element models are benchmarked using available experimental results in the literature, comprising masonry arch bridges with backfill loaded until failure. Good agreement is generally found if accounting for full interaction with the backfill. Similarly, accounting for the backfill as dead weight only, often results in a decrease in load carrying capacity by a factor 2 to 3. Still, several factors show a high impact on the estimated load carrying capacity, of which many are difficult to accurately assess. This suggests a conservative approach, although partial interaction of the backfill may still increase the load carrying capacity significantly.
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| 10. |
- Andersson, Andreas, 1980-
(författare)
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Utmattningsanalys av järnvägsbroar : En fallstudie av stålbroarna mellan Stockholm Central och Söder Mälarstrand, baserat på teoretiska analyser och töjningsmätningar
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Föreliggande avhandling omfattar en fallstudie av utmattningsrisken för järnvägsbroarna mellan Stockholm Central och Söder Mälarstrand. Ett stort antal utmattningssprickor i broarna över Söderström och Söder Mälarstrand har sedan länge varit kända. I samband med en bärighetsutredning av sträckan har ett stort antal anslutningspunkter i samtliga broar identifierats som kritiska avseende utmattningsrisk. Sträckan är den mest trafikerade i Sverige och de förenklade beräkningsmetoder som anges i Banverkets föreskrift för bärighetsberäkningar är i vissa fall inte tillämpliga. De formella bärighetsberäkningarna har visat på flerfaldiga överskridanden i utnyttjandegrad gällande utmattning. I de punkter som beräkningarna visar störst risk för utmattning har inga sprickor påträffats, trots omfattande förbandsbesiktningar. Beräkningarna baseras på typiserade spänningskollektiv och givet antal spänningsväxlingar, oberoende av den aktuella trafikmängden. Enligt bärighetsnormen ges möjlighet att beakta den verkliga trafikmängden baserat på historiskt bruttotonnage och typiserade trafiklaster. Dessa beräkningar har utförts och visar på ännu större risk för utmattning, jämfört med den förenklade metoden. I syfte att på ett ännu mer nyanserat sätt uppskatta utmattningsrisken har en metod använts, baserat på uppskattning av den faktiska trafikmängden och dess fördelningar. Beräkningarna baseras på trafikdata tillgänglig från Banverket. Metoden är tillämplig på andra järnvägsbroar på andra sträckor. Utöver teoretiska beräkningar har töjningsmätningar utförts. Under 2006 utförde dåvarande Carl Bro AB töjningsmätningar på bro över Söder Mälarstrand och viadukt söder om Söder Mälarstrand, avseende några enskilda tågöverfarter. Under 2008 utförde KTH Brobyggnad omfattande töjningsmätningar på bro över Söderström, avseende all trafik under en månads tid.
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| 13. |
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| 14. |
- Arvidsson, Therese
(författare)
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Train–Bridge Interaction : Literature Review and Parameter Screening
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- New railway lines are continuously being constructed and existing lines are upgraded. Hence, there is a need for research directed towards efficient design of the supporting structures. Increasingly advanced calculation methods can be motivated, especially in projects where huge savings can be obtained from verifying that existing structures can safely support increased axle loads and higher speeds.This thesis treats the dynamic response of bridges under freight and passenger train loads. The main focus is the idealisation of the train load and its implications for the evaluation of the vertical bridge deck acceleration. To ensure the running safety of train traffic at high speeds the European design codes set a limit on the vertical bridge deck acceleration. By considering the train–bridge interaction, that is, to model the train as rigid bodies on suspension units instead of constant moving forces, a reduction in bridge response can be obtained. The amount of reduction in bridge deck acceleration is typically between 5 and 20% for bridges with a span up to 30 m. The reduction can be higher for certain train–bridge systems and can be important also for bridge spans over 30 m. This thesis aims at clarifying for which system parameter combinations the effect of train–bridge interaction is important.To this end, a thorough literature survey has been performed on studies in train–track–bridge dynamics. The governing parameters in 2D train–bridge systems have been further studied through a parameter screening procedure. The two-level factorial methodology was applied to study the effect of parameter variations as well as the joint effect from simultaneous changes in several parameters. The effect of the choice of load model was thus set in relation to the effect of other parameter variations.The results show that resonance can arise from freight train traffic within realistic speed ranges (< 150 km/h). At these resonance peaks, the reduction in bridge response from a train–bridge interaction model can be considerable.From the screening of key parameters it can furthermore be concluded that the amount of reduction obtained with a train–bridge interaction model depends on several system parameters, both for freight and passenger train loads. In line with the European design code’s guidelines for dynamic assessment of bridges under passenger trains an additional amount of damping can be introduced as a simplified way of taking into account the reduction from train–bridge interaction. The amount of additional damping is today given as function of solely the bridge span length, which is a rough simplification. The work presented in this thesis supports the need for a refined definition of the additional damping.
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| 15. |
- Ay, Lutfi, 1961-
(författare)
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Steel fibrous cement based composites: material and mechanical properties : behavior in the anchorage zones of prestressed bridges
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This PhD thesis is divided into two parts. Part one dealswith the development of the material and the mechanicalproperties of Steel Fibrous Cement Based Composites (SFCBC) forimproving bridge design and construction. It familiarizes thehydration mechanisms of the high performance concrete with thehelp of Powers´ and Jensen´s models. Concretes withdifferent water-cement ratio were compared with each other withrespect to degree of hydration and hydration products. Thisanalysis showed that high performance concrete has higherstrengths not because it has more gel solid, but due to ithaving less porosity and higher filler content compared toordinary concrete.A number of experiments were performed to achieve a mixdesign method for a SFCBC, which has good workability, highearly and long-term strength and good durabilitycharacteristics. A Self-compacting and self-leveling fibrouscomposite, which has ultra high strengths (Compressive strengthfc= 180 ~ 220MPa and flexural tensile strengthfföi= 14 ~ 32MPa depending on the volumefraction of fibers) was produced. This composite was alsotested under different curing conditions in order toinvestigate the effect of curing on hydration andself-desiccation shrinkage. These tests showed that SFCBCshould not be water-cured under a long period andself-desiccation influences the compressive strengthnegatively. Test of scaling at freezing showed that SFCBC hasvery good durability characteristics.Part two deals with the behavior of SFCBC in the anchoragezones of prestressed bridges. The prismatic composite specimenswere tested for different volume fractions of fibers underdifferent concentrations ratios of strip loading. The resultsof these tests showed that the ultimate strength of the SFCBCspecimens was approximately twice that of ordinary concretewith the same size (fc= 60MPa reinforced with stirrups). Therefore,SFCBC has good possibility to replace the traditional rebars inthe anchorage zones of prestressed bridges.This composite has different behavior than the traditionalconcrete e.g. crack formation, failure criteria, effectivestrength and angle of friction. A vertical crack on thecenterline was occurred while wedge developed under the loadingplate. In contrast to ordinary concrete, the cracks could notreach to the bottom of the blocks.The tests results gave the ideas of that this material actslike metals or plastics in the high fiber content. Thismaterial is neither very brittle as concrete nor very ductileas metals but it is somewhere between them.Upper-bound plasticity solutions were utilized for modelingthe bearing capacity of SFCBC. Predictions of this method aregood enough to estimate the bearing capacity of SFCBC in theanchorage zones of prestressed bridges.Keywords:Process improvement of bridges, Prestressedconcrete, High performance concrete, Ultra high performanceconcrete, Hydration, Cement based composites, Fibers,Self-compacting concrete, Bearing capacity, Anchorage zones,Tests
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| 19. |
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| 21. |
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| 22. |
- Billberg, Peter
(författare)
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Form pressure generated by self-compacting concrete : influence of thixotropy and structural behaviour at rest
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Self-compacting concrete (SCC) offers rational and fast casting process since it merely has to be poured, or pumped, into the formwork without any compaction work needed. But this can be at the cost of high form pressure. However, reported results show that SCC can act thixotropically, i.e., build up a structure at rest, and this can reduce the form pressure considerably. Thus, in order to utilise the favourable possibilities to increase effectiveness without risking form collapses, the need arises for deeper and broader understanding of the mechanisms behind this thixotropic behaviour. Methodologies have been developed for the characterisation and measurement of the structural build-up at rest, both for the fluid (micro mortar) phase and the concrete itself. Hypotheses state that thixotropic mechanisms originate within the colloidal domain and, thus, motivate studies on the fluid phase comprising this domain. The stress-strain methodology is based on the hypothesis stating that the magnitude of the structure is represented by the maximum elastic stress the fresh material can withstand before the structure breaks. An instrumented steel tube is used to simulate various casting heights and rates. Results show that both micro mortar and SCC are thixotropic and this behaviour is influenced by every measure taken influencing the interparticle colloidal forces. The time-dependent structural build-up of SCC is a function of an irreversible structure (slump-loss) and a reversible, thixotropic structure. There is apparently a threshold value of the structural build-up necessary to reach before obtaining any significant form pressure reduction. Housing SCC´s, with W/C = 0.58, show low degree of structural build-up and pressure decrease while civil engineering SCC´s can show the opposite, but this often at the cost of slump-loss. Recommendations are presented and for the nearest future, suggesting a conservatism regarding design of formwork systems when SCC is used. If the behaviour of a SCC is known it should be used to optimise the formwork. If not, calculating with hydrostatic pressure should be done or the knowledge missing should be gained by using this methodology. A third option is given and this is to monitor the form pressure in real time using sensors.
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| 23. |
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| 24. |
- Broms, Carl Erik, 1937-
(författare)
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Concrete flat slabs and footings : Design method for punching and detailing for ductility
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Simple but still realistic physical models suitable for structural design of flat concrete plates and column footings with respect to punching are presented. Punching of a flat plate is assumed to occur when the concrete compression strain at the column edge due to the bending moment in the slab reaches a critical value that is considerably lower than the generally accepted ultimate compression strain 0.0035 for one-way structures loaded in bending. In compact slabs such as column footings the compression strength of the inclined strut from the load to the column is governing instead. Both the strain limit and the inclined stress limit display a size-effect, i.e. the limit values decrease with increasing depth of the compression zone in the slab. Due respect is also paid to increasing concrete brittleness with increasing compression strength. The influence of the bending moment means that flat plates with rectangular panels display a lower punching capacity than flat plates with square panels – a case that is not recognized by current design codes. As a consequence, punching shall be checked for each of the two reinforcement directions separately if the bending moments differ. Since the theory can predict the punching load as well as the ultimate deflection of test specimens with good precision, it can also treat the case where a bending moment, so called unbalanced moment, is transferred from the slab to the column. This opens up for a safer design than with the prevailing method. It is proposed that the column rotation in relation to the slab shall be checked instead of the unbalanced moment for both gravity loading and imposed story drift due to lateral loads. However, the risk for punching failure is a great disadvantage with flat plates. The failure is brittle and occurs without warning in the form of extensive concrete cracking and increased deflection. Punching at one column may even initiate punching at adjacent columns as well, which would cause progressive collapse of the total structure. A novel reinforcement concept is therefore presented that gives flat plates a very ductile behaviour, which eliminates the risk for punching failure. The performance is verified by tests with monotonic as well as cyclic loading.
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| 25. |
- Bryne, Lars Elof, 1969-
(författare)
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Time dependent material properties of shotcrete for hard rock tunnelling
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis different mechanical properties for shotcrete (sprayed concrete) such as compression strength, bond strength, bending tensile strength, elastic modulus, free and restrained shrinkage as a function of its age was investigated. One of the main issues was to investigate the difference between ordinary cast concrete and shotcrete. Reliable material data for young and hardening shotcrete is scarce which in the past have made such comparisons difficult. Also, less accurate data representative for cast concrete has often been used in numerical modelling and design analyses. The focus of the project has particularly been on the properties bond strength and restrained shrinkage for which two new testing methods has been developed and evaluated. Microstructural studies have also been performed as a complement to the bond strength testing.The bond to rock is one of the most important properties for shotcrete used as rock reinforcement. During the very first time after spraying the physical properties and the bond to the rock depend on the set accelerator and the micro structure that is formed. The investigation of early age bond strength of shotcrete is of great importance both from a production perspective and a safety perspective. The newly developed method was tested and evaluated and proved that it can be used for bond strength testing already from a couple of hours after shotcreting. The bond, or adhesion, depends on several factors such as texture of the rock, the type of accelerator, application technique, etc. In this work the development of the microstructure in the interfacial transition zone (ITZ) and strength of the bond was investigated. The results show that the bond strength is related to the hydration process, i.e. the strength gain of the shotcrete. The early development of the ITZ was here studied using a scanning electron microscope (SEM) making it possible to observe changes over time, before and after proper cement hydration.Restrained shrinkage cracking of shotcrete, especially in the case of shotcrete sprayed on soft drains that are parts of a tunnel lining not continuously bonded to the rock, can be detrimental for the sustainability of an infrastructure tunnel system. Maintenance and repair costs can be high over time. It is shown that the developed test method realistically captures the behaviour of shotcrete drains on hard rock in situ. The method can be used in the evaluation of different technical solutions for avoiding or minimizing shrinkage cracks in shotcreted soft drains. It can also be used to assess the performance of shotcrete fully bonded to a rock surface, with respect to the ability to prevent cracking or to distribute possible shrinkage damage into several fine cracks instead of one wide.
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| 26. |
- Chen, Feng, 1987-
(författare)
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Sustainable Implementation of Electrified Roads : Structural and Material Analyses
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Given the promise of the Inductive Power Transfer (IPT) technology for eRoad applications, the potential challenges for a successful integration of dynamic IPT technology into the physical road structure are explored extensively in this research work. The Finite Element Method (FEM) is selected for studying the structural performance of an eRoad under operational conditions. In this, an energy-based finite strain constitutive model for asphalt materials is developed and calibrated, to enable the detailed investigation of the structural response and optimization of the considered eRoad. In the context of enabling both dynamic charging and autonomous driving for future electric vehicles, the influences to the pavement (rutting) performance by the changed vehicle behaviour are investigated as well. Moreover, to study the effect on the IPT system by the integration, the potential power loss caused within eRoad pavement materials is further examined by a combined analytic and experimental analysis. The direct research goal of this Thesis is therefore to enhance the possibility of a sustainable implementation of the eRoad solutions into the real society. At the same time, it aims to demonstrate that the road structure itself is an important part of smart infrastructure systems that can either become a bottleneck or a vessel of opportunities, supporting the successful integration of these complex systems.
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| 27. |
- Chen, Feng, 1987-
(författare)
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The Future of Smart Road Infrastructure : A Case Study for the eRoad
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the future, physical roads will not only serve for the mobility of the vehicles but also have the capability of enabling different smart functionalities, such as car2road communication, energy harvesting or dynamic charging of electrical vehicles. To ensure the sustainability of these advances, the environmental, economic and social costs for the road infrastructure itself should not offset its possible advances. Additionally, the road infrastructure itself may also need to be modified to ensure the long-term performance of the new functionalities.This licentiate mainly focused on the electrified road (called ‘eRoad’) infrastructure, which can be a representative case of the future smart road. Specifically, a historical overview of the technology development towards the electrification of road transportation sector is presented, along with an overview of prospective technologies for implementing an eRoad’s charging infrastructure. Of these, the Inductive Power Transfer (IPT) charging technology is examined in further details.The potential knowledge gaps for a successful integration of IPT charging technology within actual road infrastructure are discussed. Some general recommendations are given throughout the licentiate thesis, regarding such as the appropriate design of eRoad structure and right selection of road materials, the cost-effective maintenance operations in the long term, and the eRoad’s role in the overall life cycle environmental impacts in the electrification of road transportation sector. This licentiate provides the basis for further focus in this field and outlines the potential research areas that need further investigation to ensure the future of systemically optimized smart road infrastructure.
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| 28. |
- Du, Guangli, 1985-
(författare)
-
Life cycle assessment of bridges, model development and case studies
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent decades, the environmental issues from the construction sector have attracted increasing attention from both the public and authorities. Notably, the bridge construction is responsible for considerable amount of energy and raw material consumptions. However, the current bridges are still mainly designed from the economic, technical, and safety perspective, while considerations of their environmental performance are rarely integrated into the decision making process. Life Cycle Assessment (LCA) is a comprehensive, standardized and internationally recognized approach for quantifying all emissions, resource consumption and related environmental and health impacts linked to a service, asset or product. LCA has the potential to provide reliable environmental profiles of the bridges, and thus help the decision-makers to select the most environmentally optimal designs. However, due to the complexity of the environmental problems and the diversity of bridge structures, robust environmental evaluation of bridges is far from straightforward. The LCA has rarely been studied on bridges till now.The overall aim of this research is to implement LCA on bridge, thus eventually integrate it into the decision-making process to mitigate the environmental burden at an early stage. Specific objectives are to: i) provide up-to-date knowledge to practitioners; ii) identify associated obstacles and clarify key operational issues; iii) establish a holistic framework and develop computational tool for bridge LCA; and iv) explore the feasibility of combining LCA with life cycle cost (LCC). The developed tool (called GreenBridge) enables the simultaneous comparison and analysis of 10 feasible bridges at any detail level, and the framework has been utilized on real cases in Sweden. The studied bridge types include: railway bridge with ballast or fix-slab track, road bridges of steel box-girder composite bridge, steel I-girder composite bridge, post tensioned concrete box-girder bridge, balanced cantilever concrete box-girder bridge, steel-soil composite bridge and concrete slab-frame bridge. The assessments are detailed from cradle to grave phases, covering thousands of types of substances in the output, diverse mid-point environmental indicators, the Cumulative Energy Demand (CED) and monetary value weighting. Some analyses also investigated the impact from on-site construction scenarios, which have been overlooked in the current state-of-the-art.The study identifies the major structural and life-cycle scenario contributors to the selected impact categories, and reveals the effects of varying the monetary weighting system, the steel recycling rate and the material types. The result shows that the environmental performance can be highly influenced by the choice of bridge design. The optimal solution is found to be governed by several variables. The analyses also imply that the selected indicators, structural components and life-cycle scenarios must be clearly specified to be applicable in a transparent procurement. This work may provide important references for evaluating similar bridge cases, and identification of the main sources of environmental burden. The outcome of this research may serve as recommendation for decision-makers to select the most LCA-feasible proposal and minimize environmental burdens.
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| 29. |
- Du, Guangli, 1985-
(författare)
-
Towards Sustainable Construction: Life Cycle Assessment of Railway Bridges
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since last few decades, the increased pressure from the environmental issues of natural resource depletion, global warming and air pollution have posed a great challenge worldwide. Among all the industrial fields, bridge infrastructures and their belonged construction sector contribute to a wide range of energy and raw materials consumptions, which is responsible for the most significant pollutions. However, current bridges are mainly designed by the criterion of economic, technique, and safety standards, while their correlated environmental burdens have unfortunately rarely been considered. The life cycle assessment (LCA) method has been verified as a systematic tool, which enables the fully assessment and complete comparison for the environmental impact among different bridge options through a life cycle manner. The study presented in this thesis is focused on railway bridges, as the LCA implementation is under great expectations to set a new design criterion, to optimize the structural design towards the environmental sustainability, and to assist the decision-making among design proposals. This thesis consists of two parts: an extended summary and three appended papers. Part one gives an overview introduction that serves as a supplementary description for this research work. It outlines the background theory, current development status, the LCA implementation into the railway bridges, as well as the developed excel-based LCA tool. Part two, includes three appended papers which provides a more detailed theoretical review of the current literatures and knowledge associated with bridge LCA, by highlighting the great challenging issues. A systematic flowchart is presented both in Paper I and Paper II for how to model and assess the bridge life cycle, together by coping with the structural components and associated emissions. This flowchart is further illustrated on a case study of the Banafjäl Bridge in Sweden, which has been extensively analyzed by two LCA methods: CML 2001 method and streamlined quantitative approach. The obtained results can be contributed as an analytical reference for other similar bridges. Based on the theoretical review and analytical results from case studies, it has been found that the environmental profile of a bridge is dominated by the selected structural type, which affects the life cycle scenarios holistically and thus further influences the environmental performance. However, the environmental profile of the structure is though very case specific; one cannot draw a general conclusion for a certain type of bridge without performing the LCA study. The case study has found that the impact of material manufacture phase is mostly identified significant among the whole life cycle. The availability of the inventory data and project information are appeared as the major problem in the bridge LCA study. Moreover, lack of standardized guideline, criteria and input information is another key issue. A criterion is needed to illustrate what are the qualified limits of a bridge to fulfill the environmental requirements. Therefore, the development of LCA for railway bridges still needs further collaborative efforts from government, industry and research institutes.
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| 30. |
- Döse, Magnus, 1970-
(författare)
-
Ionizing Radiation in Concrete and Concrete Buildings : Empirical Assessments
- 2016
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One of the major issues with radiation from the natural isotopes 40K, 226Ra (238U) and 232Th and their decay products is the forthcoming legislation from the European Commission in relation to its Basic Safety Directive (2014). The European legislation is mandatory and could not be overthrown by national legislation. Hence, even though the BSS is still a directive it is foreseen as becoming a regulation in due time.The reference value of the natural isotopes, from a radiation point of view, set for building materials is 1 mSv per year (EC, 2014). Earlier recommendations (The Radiation Protection Authorities in Denmark, Finland, Iceland, Norway and Sweden, 2000) within the Nordic countries set an upper limit at 2 mSv per year of radiation from building materials.The main objective within the frame of the thesis was to investigate gamma radiation in relation to Swedish aggregates and their use as final construction products and the applicability and use of a model (EC, 1999) for building materials to calculate the effective dose within a pre-defined room. Part of the thesis also investigates different methodologies that can be used to assess the radiation in a construction material made up of several constituents (building materials) and aims to show that for some purposes as for the construction industries (precast concrete), that a hand-held spectrometer can be used with good accuracy, even though the object is limited in thickness and size. Secondly, the author proposes a simplified way of assessing the radiation in a construction material by use of correlation coefficient of a specified recipe by use of a hand-held spectrometer. Moreover, an understanding of the different building materials´ contribution to the finalized construction product, e.g. concrete is demonstrated, and how to achieve a good control of the radiation levels in the concrete building.
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| 31. |
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| 32. |
- Edlund, Stefan
(författare)
-
Buckling of T-section beam-columns in aluminium with or without transverse welds
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with buckling of T-section beam-columns inaluminium with or without transverse welds. Totally 26 unweldedand 39 transversely welded T-section beam-columns were tested.Five of the welded beams were clamped. All unwelded and therest of the welded beams were simply supported for bending. Thewelding affects the load-carrying capacity of the beam-columns,because it introduces a heat-affected zone with reducedstrength. All beam-columns had the same theoreticalcross-section dimensions. The thickness of the flange and theweb was 6 mm. The depth and the width were 60 mm. Thetheoretical beam lengths were 500, 1020 and 1540 mm,respectively. Tensile tests of both the parent and theheat-affected material were made in order to determine thematerial properties.Comparisons were made between the buckling tests and threecodes, the European aluminium code Eurocode 9, the Britishaluminium code BS 8118 and the Swedish steel code BSK. Someinterpretations of the codes had to be made, because the codesare not totally clear when applied on T-sections. Most problemsare related to the fact that the section modulus is not thesame for the two edges. In the interaction formulas, only theedge in compression was considered when the bending momentcapacity was calculated. The chosen interpretation of the codeswas often very conservative when compared with the bucklingtests.The general-purpose finite element program Abaqus was usedto develop numerical models of the tested beam-columns. Shellelements were used. The models were calibrated with the resultsfrom the buckling tests. The stress-strain curves used in thefinite element calculations were obtained from the tensiletests. The results of the finite element calculations weresatisfactory. The numerical models could predict the loadcarrying capacity accurate enough. A similar deformed shape ofthe tested and calculated beam-columns was also obtained.Different modifications of Eurocode 9 were analysed in orderto improve the results. One modification was that the ultimatestrength of the heat-affected zone was used instead of theyield strength of the parent material whenthe bucklingreduction factors of a welded section were calculated. Thecalculation of the bending moment capacity in the interactionformulas was also modified. The plastic section modulus wasused to calculate the bending moment capacity when the tip ofthe web was in tension. When the bending moment acted in theopposite direction, the calculation of the bending momentcapacity was based on a modified classification of the webelement. The investigation in this thesis indicates thatEurocode 9 is too severe in the classification of thecross-section. The way the bending moment capacity iscalculated for unsymmetric cross-sections in the interactionformulas needs to be further analysed. Tensile failure at thetip of the web was also discussed. This thesis shows that thecodes need to be improved when it concerns unsymmetriccross-sections. Some information how Eurocode 9 can be improvedis given.Keywords: Buckling, buckling tests, Eurocode 9, aluminiumbeam-columns, beam-columns, T-sections, finite elementanalysis, transverse welds, codes, unsymmetriccross-sections.
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| 33. |
- Elgazzar, Hesham
(författare)
-
End-Shield Bridges for High-Speed Railway : Full scale dynamic testing and numerical simulations
- 2017
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increasing need for High-Speed Railway (HSR) to reduce the travelling time requires increasing research within this field. Bridges are main components of any railway network, including HSR networks, and the optimization of their design for this purpose would contribute to a faster and more cost effective development of the HSR network. The initial investment, the running and maintenance costs of the bridges can be decreased through better understanding of the their dynamic behaviour.This thesis studies the dynamic behaviour of end-shield railway bridges under HSR operation. 2D beam analysis is used to study the effect of the distribution of the train’s axle load. Relatively accurate 3D FE-models are developed to study the effect of Soil-Structure Interaction (SSI) and the dynamic response of the bridges. Modelling alternatives are studied to develop an accurate model. A full scale test of a simply supported Bridge with end-shields using load-controlled forced excitation was performed and the results were used to verify the theoretical models.A manual model updating process of the material properties of the 3D FE-model is performed using FRFs from the field measurements. A Simple 2D model is also developed, where a spring/dashpot system is implemented to simplify SSI, and updated to reproduce the field measured responses.The conclusions of the project emphasize the importance of SSI effects in the dynamic analysis of end-shield bridges for predicting their dynamic behaviour.The conclusions also show that the modelling of the surrounding soil and the assumption of the soil material parameters have significant effect on the dynamic response. Even the boundary conditions, bedrock level and the ballast on the railway track affects the response. The results also show that the bridge’s concrete section behaves as uncracked section under the studied dynamic loading.
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| 34. |
- Enckell, Merit
(författare)
-
Structural health monitoring using modern sensor technology : long-term monitoring of the New Årsta Railway Bridge
- 2006
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Structural Health Monitoring (SHM) is a helpful tool for engineers in order to control and verify the structural behaviour. SHM also guides the engineers and owners of structures in decision making concerning the maintenance, economy and safety of structures. Sweden has not a very sever tradition in monitoring, as countries with strong seismic and/or aerodynamic activities. Anyway, several large scale monitoring projects have taken place in recent years and SHM is slowly making entrance as an essential implement in managing structures by engineers as well as owners. This licentiate thesis presents a state-of-the art-review of health monitoring activities and over sensory technologies for monitoring infrastructure constructions like bridges, dams, off-shore platforms, historical monuments etc. related to civil engineering. The fibre optic equipment is presented with special consideration. The permanent monitoring system of the New Årsta Bridge consists of 40 fibre optic sensors, 20 strain transducers, 9 thermocouples, 6 accelerometers and one LVDT. The aims of the static study are: to control the maximal strains and stresses; to detect cracking in the structure; to report strain changes under construction, testing period and in the coming 10 years; and to compare conventional system with fibre optic system. The system installation started in January 2003 and was completed October 2003. The measurements took place from the very beginning and are suppose to continue for at least 10 years of operation. At the construction phase the measurements were performed manually and later on automatically through broad band connection between the office and central data acquisition systems located inside the bridge. The monitoring project of the New Årsta Railway Bridge is described from the construction phase to the testing phase of the finished bridge. Results of the recorded statistical data, crack detection and loading test are presented and a comparison between traditional techniques like strain transducers and fibre optic sensors is done. Various subjects around monitoring and sensor technologies that were found under the project are brought up in order to give the reader a good understanding, as well of the topics, techniques and of the bridge. Example of few applications is given with the aim of a deeper insight into monitoring related issues.
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| 35. |
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| 36. |
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| 37. |
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| 38. |
- Gasch, Tobias
(författare)
-
Concrete as a multi-physical material with applications to hydro power facilities
- 2016
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During its lifetime, a concrete structure is subjected to many different actions, ranging from mechanical loads to environmental actions. To accurately predict its integrity from casting and throughout its service life, a modelling strategy is required that considers mechanical loading but also implicitly accounts for physical effects such as temperature and moisture variations. This is especially true for large concrete structures found in many infrastructure applications such as bridges, nuclear power plants and dams. Modelling concrete as a multi-physical material is becoming an increasingly used approach for which large research efforts are being made, including the development of more refined mathematical and numerical methods as well as considering more physical and chemical variables in the coupled model.The research project, of which this licentiate thesis is the first phase, aims at investigating aging concrete structures at hydro power facilities, with focus on the internal structures of the power plants. This thesis presents a review of advanced mathematical methods and concepts for modelling aging concrete found in the literature which can later be applied to study such structures. The focus is on models that describe the deformational behaviour of concrete where aspects such as aging, cracking, creep and shrinkage are investigated. However, in order to accurately describe such phenomena, a multi-physical approach is adopted where moisture and temperature variations in the concrete are studied. Also, models that describe the chemical behaviour related to hydration and thus in extension aging, are also reviewed and introduced in the multi-physical framework. The use of such models are discussed in the context of the finite element method (FEM), in which coupled models are implemented, verified and applied in the appended papers using two different FE codes.Several verification examples are presented covering different aspects of the implemented models, both in isolation and coupled in a multi-physical setting. By comparing the numerical results with experimental data from the literature it can be shown that it is possible to predict most aspects of aging concrete that have been of interest here. While these examples are all on a laboratory scale, numerical examples and case studies are also provided that exemplify how the models can be applied on a structural scale. By using the developed analysis tools, valuable information and insights can be gained on aging concrete structures and these tools will in the next phase of the research project be applied to large concrete structures at hydro power facilities.
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| 39. |
- Getachew, Abraham, 1970-
(författare)
-
Traffic Load Effects on Bridges, Statistical Analysis of Collected and Monte Carlo Simulated Vehicle Data
- 2003
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Research in the area of bridge design has been and still isconcentrated on the study of the strength of materials andrelatively few studies have been performed on traffic loads andtheir effects. Traffic loads have usually been assumed to begiven in codes. This is mainly because it is very difficult tomodel traffic loads in an accurate manner because of theirrandomness.In this work, statistical evaluations of traffic loadeffects, obtained from real as well as Monte Carlo (MC)simulated vehicle data, are presented. As the dynamiccontribution of the vehicle load was filtered by the systemused for measuring vehicle weight, no attention was paid in thepresent study to the dynamic effects or the impact factor. Thedynamic contribution of the traffic load models from codes wasdeducted wherever they were compared with the result from theevaluation of the real data. First, the accuracy of thecollected data was investigated. This was done to examine theinfluence of what was most probably unreasonable data on thefinal evaluated results. Subsequently, the MC simulationtechnique, using a limited amount of the collected data, wasused to generate fictitious vehicle data that could representresults from field measurements which would otherwise have tobe recorded under a long period. Afterwards, the characteristictotal traffic loads for bridges with large spans weredetermined by probabilistic analysis. This was done using realas well as simulated data and the two were compared. Theseresults were also compared with the corresponding valuescalculated using the traffic load model from the Swedish bridgedesign code.Furthermore, using traffic data, different load effects onbridges (girder distribution factor of slab-on-girder bridgesand the mid-span deflection as well as the longitudinal stressat critical locations on box-girder bridges) were investigated.The main task was to obtain a more accurate knowledge oftraffic load distributions on bridges as well as their effectsfor infrastructure design. The results showed that the trafficload models from codes gave considerably higher load effectscompared to the current actual traffic load effects. Theseinvestigations were based on the available data for the actualposition of the vehicles on a single bridge and might not coverall possible traffic scenarios. The results showed only how thereal traffic loads, under”normal”conditions andtheir transverse positions relate to the load model accordingto the codes.KEYWORDS:bridge, traffic load, load effect, transversedistribution, characteristic value,weigh in motion, MonteCarlo simulation, Rice’s formula, level crossinghistogram, vehicle queue.
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| 40. |
- Getachew, Abraham
(författare)
-
Trafiklaster på broar : Analys av insamlade och Monte Carlo genererade fordonsdata
- 2000
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis begins with the description of background ,aims and goals of the project. Afterwards, a brief explanation of the probability theory and some probabilistic distribution functions that are used in this work are given.Then the concept of structural reliability is explained. Subsequently the meaning of Monte-Carlo simulation technique in relation to this workis described. Traffic load models given indifferent codes cannot be used directly for the design of long-span bridges, i.e.bridges with span lengths larger than 200 meters. For the determination of the characteristic load values for such bridges, the Swedish National Road Administration (Vli.gverket) conducted traffic load measurements in five different locations in Sweden. All measurement data of course contain errors. Therefore, the collected data from one of the measurement series are investigated in this work. The investigation shows that among the collected data there are vehicles that are registered with unreasonable lengths or/and weights. Totally about 10% of the whole collected data are considered to be inaccurate and should be excluded before further analyses of the vehicle data. About 10%,of the whole collected data, are vehicle dataregistered with one axle. Because of the limited information, these vehicles could not be identified and therefore are not excluded. The characteristic and design traffic load values for different queue lengths are calculated using vehicle data both before and after filtration of inaccurate data. The results hows that the influence of inaccurate data is insignificant. The largest difference between characteristic load values calculated before and after filtration of inaccurate data is 3,5%. Comparing the characteristic as well as the design traffic load values with corresponding values according to BRO 94 shows that the code values are considerably higher than the actual values. In this work, the Monte-Carlo simulation technique is also used to generate vehicle data. The simulated vehicle data show good agreement with the collected data. Afterwards, the probability distribution functions from the simulated as well as the collected vehicle data are calculated and compared. The result shows that the probability distribution functions agree well specially for grater queue weight values.
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| 41. |
- Gonzalez, Ignacio
(författare)
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Application of monitoring to dynamic characterization and damage detection in bridges
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The field of bridge monitoring is one of rapid development. Advances in sensor technologies, in data communication and processing algorithms all affect the possibilities of Structural Monitoring in Bridges. Bridges are a very critical part of a country’s infrastructure, they are expensive to build and maintain, and many uncertainties surround important factors determining their serviceability and deterioration state. As such, bridges are good candidates for monitoring. Monitoring can extend the service life and avoid or postpone replacement, repair or strengthening works. The amount of resources saved, both to the owner and the users, by reducing the amount of non-operational time can easily justify the extra investment in monitoring.This thesis consists of an extended summary and five appended papers. The thesis presents advances in sensor technology, damage identification algorithms, Bridge Weigh-In-Motion systems, and other techniques used in bridge monitoring. Four case studies are presented. In the first paper, a fully operational Bridge Weigh-In-Motion system is developed and deployed in a steel railway bridge. The gathered data was studied to obtain a characterization of the site specific traffic. In the second paper, the seasonal variability of a ballasted railway bridge is studied and characterized in its natural variability. In the third, the non-linear characteristic of a ballasted railway bridge is studied and described stochastically. In the fourth, a novel damage detection algorithm based in Bridge Weigh-In-Motion data and machine learning algorithms is presented and tested on a numerical experiment. In the fifth, a bridge and traffic monitoring system is implemented in a suspension bridge to study the cause of unexpected wear in the bridge bearings.Some of the major scientific contributions of this work are: 1) the development of a B-WIM for railway traffic capable of estimating the load on individual axles; 2) the characterization of in-situ measured railway traffic in Stockholm, with axle weights and train configuration; 3) the quantification of a hitherto unreported environmental behaviour in ballasted bridges and possible mechanisms for its explanation (this behaviour was shown to be of great importance for monitoring of bridges located in colder climate) 4) the statistical quantification of the nonlinearities of a railway bridge and its yearly variations and 5) the integration of B-WIM data into damage detection techniques.
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| 42. |
- González, Ignacio, 1985-
(författare)
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Study and Application of Modern Bridge Monitoring Techniques
- 2011
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The field of monitoring is one of rapid development. Advances in sensor technologies, in data communication paradigms and data processing algorithms all influence the possibilities of Structural Health Monitoring, damage detection, traffic monitoring and other implementations of monitoring systems. Bridges are a very critical part of a country’s infrastructure, they are expensive to build and maintain, and many uncertainties surround important factors determining the serviceability and deterioration of bridges. As such, bridges are good candidates for monitoring. Monitoring can extend the service life and avoid or postpone replacement, repair or strengthening work. Many bridges constitute a bottleneck in the transport network they serve with few or no alternative routes. The amount of resources saved, both to the owner and the users, by reducing the amount of non-operational time can easily justify the extra investment in monitoring. This thesis consists of an extended summary and three appended papers. The thesis presents advances in sensor technology, damage identification algorithms and Bridge Weigh-In-Motion techniques. Two case studies are carried out. In the first a bridge and traffic monitoring system is implemented in a highway suspension bridge to study the cause of unexpected wear in the bridge bearings. In the second a fully operational Bridge Weigh-In-Motion system is developed and deployed in a steel railway bridge. The gathered data was studied to obtain a characterization of the site specific traffic.
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| 43. |
- Gram, Annika, 1971-
(författare)
-
Modelling of Bingham Suspensional Flow : Influence of Viscosity and Particle Properties Applicable to Cementitious Materials
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Simulation of fresh concrete flow has spurged with the advent of Self-Compacting Concrete, SCC. The fresh concrete rheology must be compatible with the reinforced formwork geometry to ensure complete and reliable form filling with smooth concrete surfaces. Predicting flow behavior in the formwork and linking the required rheological parameters to flow tests performed on the site will ensure an optimization of the casting process.In this thesis, numerical simulation of concrete flow and particle behaviour is investigated, using both discrete as well as a continuous approach. Good correspondence was achieved with a Bingham material model used to simulate concrete laboratory tests (e.g. slump flow).It is known that aggregate properties such as size, shape and surface roughness as well as its grading curve affect fresh concrete properties. An increased share of non-spherical particles in concrete increases the level of yield stress, τ0, and plastic viscosity, µpl. The yield stress level may be decreased by adding superplasticizers, however, the plastic viscosity may not. An explanation for the behaviour of particles is sought after experimentally, analytically and numerically. Bingham parameter plastic viscosity is experimentally linked to particle shape. It was found that large particles orient themselves aligning their major axis with the fluid flow, whereas small particles in the colloidal range may rotate between larger particles. The rotation of crushed, non-spherical fine particles as well as particles of a few microns that agglomorate leads to an increased viscosity of the fluid.Generally, numerical simulation of large scale quantitative analyses are performed rather smoothly with the continuous approach. Smaller scale details and phenomena are better captured qualitatively with the discrete particle approach. As computer speed and capacity constantly evolves, simulation detail and sample volume will be allowed to increase.A future merging of the homogeneous fluid model with the particle approach to form particles in the fluid will feature the flow of concrete as the physical suspension that it represents. One single ellipsoidal particle in fluid was studied as a first step.
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| 44. |
- Gram, Annika
(författare)
-
Numerical Modelling of Self-Compacting Concrete Flow : Discrete and Continuous Approach
- 2009
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the advent of Self-Compacting Concrete (SCC) that flows freely, under the soleinfluence of gravity, the wish for hassle-free and predictable castings even in complexcases, spurged the simulation of concrete flow as a means to model and predictconcrete workability. To achieve complete and reliable form filling with smoothsurfaces of the concrete, the reinforced formwork geometry must be compatible withthe rheology of the fresh SCC. Predicting flow behavior in the formwork and linkingthe required rheological parameters to flow tests performed on the site will ensurean optimization of the casting process.In this thesis, numerical simulation of concrete flow is investigated, using both discreteas well as continuous approaches.The discrete particle model here serves as a means to simulate details and phenomenaconcerning aggregates modeled as individual objects. The here presented cases aresimulated with spherical particles. However, it is possible to make use of nonsphericalparticles as well. Aggregate surface roughness, size and aspect ratio maybe modeles by particle friction, size and clumping several spheres into forming thedesired particle shape.The continuous approach has been used to simulate large volumes of concrete. Theconcrete is modeled as a homogeneous material, particular effects of aggregates,such as blocking or segregation are not accounted for. Good correspondence wasachieved with a Bingham material model used to simulate concrete laboratory tests(e.g. slump flow, L-box) and form filling. Flow of concrete in a particularly congestedsection of a double-tee slab as well as two lifts of a multi-layered full scale wall castingwere simulated sucessfully.A large scale quantitative analysis is performed rather smoothly with the continuousapproach. Smaller scale details and phenomena are better captured qualitativelywith the discrete particle approach. As computer speed and capacity constantlyevolves, simulation detail and sample volume will be allowed to increase.A future merging of the homogeneous fluid model with the particle approach to formparticles in the fluid will feature the flow of concrete as the physical suspension thatit represents. One single ellipsoidal particle falling in a Newtonian fluid was studiedas a first step.
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| 45. |
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| 46. |
- Hansson, Håkan, 1969-
(författare)
-
Warhead penetration in concrete protective structures
- 2011
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The analysis of penetration of warheads in concrete protective structures is an important part of the study of weapon effects on protective structures. This type of analysis requires that the design load in the form of a warhead is determined, and its characteristic and performance within a protective structure is known. Constitutive equations for concrete subjected to weapon effects have been a major area of interest for a long time, and several material models for concrete behaviour are developed. However, it is not until recent years that it has been possible to use finite element (FE) analyses to simulate the behaviour of concrete targets during projectile penetration with acceptable results. The reason for this is a combination of several factors, e.g. development of suitable material models for concrete, enhancement of numerical methodology and affordable high capacity computer systems. Furthermore, warhead penetration has primary been of interest for the armed forces and military industry, with a large part of the conducted research being classified during considerable time. The theoretical bases for concrete material behaviour and modelling with respect to FE analyses of projectile penetration are treated in the thesis. The development of weapons and fortifications are briefly discussed in the thesis. Warheads may be delivered onto a protective structure by several means, e.g. artillery, missiles or aerial bombing, and two typical warhead types were used within the study. These warhead types were artillery shells and unitary penetration bombs for the use against hardened targets, with penetration data for the later warhead type almost non-existing in the literature. The penetration of warheads in concrete protective structures was therefore studied through a combination of experimental work, empirical penetration modelling and FE analyses to enhance the understanding of the penetration phenomenon. The experimental data was used for evaluation of empirical equations for concrete penetration and FE analyses of concrete penetration, and the use of these methods to predict warhead penetration in protective structures are discussed within the thesis. The use of high performance concrete increased the penetration resistance of concrete targets, and the formation of front and back face craters were prevented with the use of heavily reinforced normal strength concrete (NSC) for the targets. In addition, the penetration depths were reduced in the heavily reinforced NSC. The evaluated existing empirical penetration models did not predict the behaviour of the model scaled hardened buried target penetrators in concrete structures with acceptable accuracy. One of the empirical penetration models was modified to better describe the performance of these penetrators in concrete protective structures. The FE analyses of NSC gave reasonable results for all simulation cases, with the best results obtained for normal impact conditions of the penetrators.
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| 47. |
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| 48. |
- Hedebratt, Jerry
(författare)
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Industrial Fibre Concrete Floors : Experiences and Tests on Pile-Supported Slab
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Pile supported floor slabs have often been designed solely in ultimate limit state ULS and then foremost with uniformly distributed loadings UDL. The investigation of serviceability limit state SLS has been of simpler nature, even according to the governing codes of practice.Often it has been minimum‑reinforced with the presumption that full friction to the supporting ground is present, whit‑out any inspection, which by the Swedish code of practice even more reduced the addition of crack reinforcement. The cracks have not been controlled, before they in fact have occurred. For pile supported floor slabs the ground support will be there still, at least for a time, after the casting. As the ground settles, as dehydration always will occur, and drainage and the covering roof the precipitation to reach the ground, the slab will often be completely free bearing between the piles. The minimum reinforcement is based on the assumption that only the upper layer is needed to reinforce due to dehydration shrinkage – despite that the whole floor section in time will obtain the same moisture profile and also shrinkage magnitude. One often excludes the influence of creep and temperature and the affect from external loading and local variance of restraints in calculations in the SLS. Research on behaviour in SLS has been modest; in spite of that the contractors and the client and finally the end‑user of the floors often suffer from these problems.It has by this thesis been established that the shrinkage of the concrete used for industrial floors is large 0.9‑1.1 ‰, and that the problem foremost arise from cracking and problems with joints and unevenness in the floor. The integrated method for design and production of industrial floors is a way to the solution, but requires that all involved assign to co‑operate to 100 %. Furthermore it is required that one selects the proper materials to the proper design and the proper production method. If one will save cost this will often be on materials; which will lead to reduced reinforcement content and reduced concrete thickness. This way is wrong and will in end make the client suffer economically. A way to solve this has been to cast the floors with steel fibre concrete SFC; from the beginning often a little bit thicker and with moderate steel fibre content and complementary reinforcement, compared to present execution. The competition from abroad has nevertheless shaped solutions that with thinner slabs and less traditional reinforcement and invalid design calculations compete on faulty grounds. This work demonstrates how this make the floor suffer in ULS and SLS.Trough full‑scale testing (half of a normally loaded industrial floor in matter of geometry) where a pile supported floor slab has been simulated by a flat‑slab floor cast in steel fibre concrete, it has been shown that the solution with steel fibre concrete performs well in slabs for industrial floors. On one hand it gives the opportunity to production wise superior methods for placing concrete which potentially could gain the environment with reduced reinforcement content, and on the other hand SFC brings a ductile failure behaviour for loadings with much larger magnitudes than in normal ULS design, and further SFC provides with a stiffer response and with possibility to construct slabs with small creep deformation.Finally it has been established that, when it comes to short‑term point loadings (ULS) and with long-term point loadings (SLS) one can rely on the bearing capacity and the tough behaviour of SFC. And that one may exert an influence on both limit states, through variation of the SFC and the reinforcement content. This is shown for a real bearing structure, the pile supported industrial floor, and that in a safe way.
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- Heng, Piseth
(författare)
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Simplified mechanical models for the nonlinear dynamic analysis of elasto-plastic steel structures impacted by a rigid body
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Buildings subjected to impact and explosion are usually studied using large scale and highly nonlinear finite element model which are time-consuming. The first part of the thesis deals with the development of simple and accurate models for evaluating the nonlinear inelastic behaviour of steel frame structures subjected to impact. The research work in this part has produced four simplified models. The first model concerns with a 4DOF model that reproduces the behaviour of the impacted column. The restraining effect from the rest of the structure is modelled by an elastic spring, a head mass and a static load applied at the top of the column. In the second model, the impacted column is then further simplified using a SDOF model. The behaviour of the SDOF model is governed by an analytical force-displacement expressions of the column loaded by a located force. The maximum displacement of the impacted column can also be determined explicitly by adopting an energy-equivalent approach. Afterwards, in an effort to model the whole structure, two finite element models are developed. For these models, a co-rotational super-element that consists of a beam element and two generalized elasto-plastic hinges is obtained by performing a static condensation. An elastic flexible beam element is used in the first finite element model, whereas a rigid beam element is considered in the second one.In these models, inelasticity is concentrated at generalized elasto-plastic hinges which are modelled by combined axial-rotational springs. The behaviour of the hinges is uncoupled in the elastic range while an axial-bending interaction is considered in the plastic range making it possible to reproduce a wide range of cross-sections and joints. In addition, unilateral contact between rigid point masses is considered and the energy loss during impact is accounted by means of a restitution coefficient following Newton’s impact law. Energy-momentum scheme is used to solve the equations of motion produced by these models.The second part of the thesis concerns with the performance of the connectors in composite steel-concrete slabs under explosion. The purpose is to determine residual capacities of the shear connectors after being damaged by explosion using large-scale pull-out and push-out experimental tests and finite element simulations.
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