| 1. |
- 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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| 2. |
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| 3. |
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| 4. |
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| 5. |
- 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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| 6. |
- 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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| 7. |
- Enckell, Merit
(författare)
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Structural health monitoring using modern sensor technology : long-term monitoring of the New Årsta Railway Bridge
- 2006
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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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| 8. |
- Gram, Annika
(författare)
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Numerical Modelling of Self-Compacting Concrete Flow : Discrete and Continuous Approach
- 2009
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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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| 9. |
- Johansson, Anders
(författare)
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Impregnation of concrete structures : transportation and fixation of moisture in water repellent treated concrete
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Water repellent agents, today mainly consisting of alkylalkoxysilanes, are often used on concrete to prolong the service life of the structure. This is accomplished by protecting the reinforcement bars from chlorides or by changing the moisture content inside. When the concrete is treated with a water repellent agent the properties of the surface layer turn from hydrophilic to hydrophobic and thereby water droplets are stopped from entering, still allowing water vapour to pass through. This property change can reduce chloride ingression and stop heavy rain from penetrating through the surface layer. This thesis presents results concerning how the moisture transport and fixation in the surface layer of the concrete is affected by a water repellent treatment. It also presents an investigation in which the effective penetration depth and the factors that influence it are studied. The methods used covers uni-dimensional transport of moisture using the so called cup method, measurements on moisture fixation using climate boxes with saturated salt solutions, penetration depth by cracking samples and spraying water on them, and field tests in a harsh tunnel environment. The moisture diffusion coefficient for a water repellent treated concrete is close to constant and not nearly as dependent on the relative humidity (RH) as for untreated concrete. Unlike untreated concrete, where capillary suction plays an important role for the moisture transport at high RH, the vapour transport is the dominant transport mechanism even at high RH for water repellent treated concrete. The moisture fixation is affected by a water repellent treatment and the effect is clearest at high moisture levels. There is, however, a certain amount of moisture present in a concrete treated with a water repellent agent. It can also be seen that the main reason for this is that the capillary porosity is affected by the treatment to a relatively high degree while the gel porosity to a large extent remains unaffected. The three most important factors for the penetration of any water repellent agent into concrete is time, porosity and degree of saturation. An empirical equation is derived that gives an idea on how much these factors affect the efficient penetration depth of the water repellent agent. Measures prolonging the service life of a concrete structure will lead to savings of natural resources and thus both economical and environmental savings for the community. The aim with the PhD-project is to develop explanation models to the promising results that have been obtained from the empirical research during the last decade and by doing this also create a better knowledge about when and how to apply a water repellent agent in order to benefit as much as possible from the product. The results presented in this Lisenciate thesis will be used as input in these models in the planned second phase of this project.
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| 10. |
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| 11. |
- Magnusson, Johan
(författare)
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Structural concrete elements subjected to air blast loading
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the design of structures to resist the effects of air blast loading or other severe dynamic loads it is vital to have large energy absorbing capabilities, and structural elements with large plastic deformation capacities are therefore desirable. Structures need to be designed for ductile response in order to prevent partial or total collapse due to locally failed elements. The research in this thesis considers experimental and theoretical studies on concrete beams of varying concrete strength. The nominal concrete compressive strength varied between 30 MPa and 200 MPa. A total of 89 beams were tested of which 49 beams were reinforced with varying amounts of tensile reinforcement. These beams were also reinforced with stirrups and steel fibres were added to a few beams. The remaining 40 beams were only reinforced with steel fibres with a fibre content of 1.0 percent by volume. Two different fibre lengths having constant length-to-diameter ratio were employed. The tests consisted of both static and air blast tests on simply supported beams. The blast tests were performed within a shock tube with a detonating explosive charge. All experimental research focused on deflection events, failure modes and loads transferred to the supports. The dynamic analyses involve single-degree-of-freedom (SDOF) modelling of the beam response and the use of iso-damage curves. Also, the dynamic support reactions were calculated and compared with test results. For beams with tensile reinforcement, the failure mode of some beam types was observed to change from a flexural failure in the static tests to a flexural shear failure in the dynamic tests. Beams with a high ratio of reinforcement and not containing steel fibres failed in shear, whereas beams with a lower ratio of reinforcement failed in flexure. The introduction of steel fibres prevented shear cracks to develop, thus increasing the shear strength of the beams. The presence of steel fibres also increased the ductility and the residual load capacity of the beams. Beams subjected to air blast loading obtained an increased load capacity when compared to the corresponding beams subjected to static loading. The SDOF analyses showed good agreement with the experimental results regardless of concrete strength and reinforcement amount. The results of using iso-damage curves indicate conservative results with larger load capacities of the beams than expected. The theoretical evaluations of the dynamic reactions were in agreement with the measured average reactions, both in amplitudes and in general shape. The experimental results with steel fibre reinforced concrete beams indicate that the dynamic strength was higher than the corresponding static strength and that the toughness was reduced when increasing the compressive strength. Beams of normal strength concrete failed by fibre pull-out while a few beams of high strength concrete partly failed by fibre ruptures. It may be favourable to use shorter fibres with smaller aspect ratios in structural elements of high strength concrete and subjected to large dynamic loads. Further research should involve studies on the size effect, on different boundary conditions, on different types of structural elements and on the combination of blast and fragment loads. The theoretical work should involve analyses both with the use of SDOF modelling and finite element analysis.
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| 12. |
- Malm, Richard, 1980-
(författare)
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Analys av sprickbildning och sprickbredd vid plant spänningstillstånd i balkliv av armerad betong
- 2005
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- I denna förstudie har analys av spänningar, sprickinitiering och sprickpropagering studerats för stora betongkonstruktioner i brukgränstillstånd. Speciellt har sneda sprickor studeras som vanligtvis uppstår broars balkliv, som ett resultat av kombinerad belastning av normal- och tvärkrafter. Det har studerats hur dessa förhållanden avspeglas i dagens dimensioneringsnormer och standarder. För att tydligare belysa skillnaden mellan de metoder som finns i olika normer har ett beräkningsexempel på Gröndalsbron och Alviksbron använts. Beräkningsmetoder som används vid dimensionering i brukgränstillstånd antar att strukturen är sprucken och befinner sig i stabiliserat sprickmönster. Beräkningsmetoder som utvecklats i vetenskapliga artiklar, så som t.ex. Modifierade tryckfältsteorin, baseras generellt på laboratorieförsök där nytillverkade, ospruckna balkar belastas för att registrera de sprickbredder, töjningar och spänningar som uppstår. Eftersom betongkonstruktioner i princip alltid har sprickor kommer dessa metoder att underskatta sprickbredder och armeringsspänningar i brukgränstillstånd. Vid jämförelse med verkliga uppmätta sprickbredder på Gröndalsbron gav följande två metoder mycket god överensstämmelse; generella metoden i NS 3473 samt BBK’s fackverksmodell med spricklutningen som ger lika armeringsspänningar i de två riktningarna. Beräkningarna visar att metoden i Eurocode 2 och BBK’s fackverksmodell där spricklutningen antas motsvara huvudspänningsriktningen, tenderar att överskatta sprickbredden. Det finns ett flertal olika metoder för att beskriva uppsprickning och sprickpropagering i finita element (FE) formuleringar. I denna rapport har fördelar och nackdelar med dessa olika metoder beskrivits och dessutom har några vanliga konventionella finita element program studerats. Vid FE modellering av uppsprickning hos spröda material finns generellt två inriktningar smeared crack eller discrete crack. Skillnaden mellan dessa är att vid modellering med smeared crack-metoder krävs ingen förkunskap om var sprickorna kommer att uppträda, medan vid discrete crack-metoder kan strukturen endast spricka vid fördefinierade områden. Vid dimensionering av betongkonstruktioner är smeared crack-metoder mest lämpliga, eftersom kunskapen om var uppsprickningen kommer att ske oftast saknas.
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| 13. |
- Malm, Richard, 1980-
(författare)
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Predicting shear type crack initiation and growth in concrete with non-linear finite element method
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, the possibility to numerically describing the behaviour that signifies shear type cracking in concrete is studied. Different means for describing cracking are evaluated where both methods proposed in design codes based on experiments and advanced finite element analyses with a non-linear material description are evaluated. It is shown that there is a large difference in the estimation of the crack width based on the calculation methods in design codes. The large difference occurs due to several of these methods do not account for shear friction in the crack face. The finite element method is an important tool for analysing the non-linear behaviour caused by cracking. It is especially of importance when combined with experimental investigations for evaluating load bearing capacity or establishing the structural health. It is shown that non-linear continuum material models can successfully be used to accurately describe the shear type cracking in concrete. A method based on plasticity and damage theory was shown to provide accurate estimations of the behaviour. The methods based on fracture mechanics with or without inclusion of damage theory, overestimated the stiffness after crack initiation considerably. The rotated crack approach of these methods gave less accurate descriptions of the crack pattern and underestimated the crack widths. After verification of the material model, realistic finite element models based on plasticity and damage theory are developed to analyse the cause for cracking in two large concrete structures. The Storfinnforsen hydropower buttress dam is evaluated where the seasonal temperature variation in combination with the water pressure have resulted in cracking. With the numerical model the cause for cracking can be explained and the crack pattern found in-situ is accurately simulated. The model is verified against measurements of variation in crest displacement and crack width with close agreement. The construction process of a balanced cantilever bridge, Gröndal Bridge, is numerically simulated and a rational explanation of the cause for cracking is presented. It is shown that large stresses and micro-cracks develop in the webs during construction, especially after tensioning the continuing tendons in the bottom flange. Further loads from temperature variation cause cracking in the webs that is in close agreement with the cracking found in-situ. The effect of strengthening performed on this bridge is also evaluated where the vertical Dywidag tendons so far seem to have been successful in stopping further crack propagation.
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| 14. |
- Malm, Richard, 1980-
(författare)
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Shear cracks in concrete structures subjected to in-plane stresses
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- After only two years of service, extensive cracking was found in the webs of two light-rail commuter line bridges in Stockholm, the Gröndal and Alvik bridges. Due to this incident it was found necessary to study the means available for analysing shear cracking in concrete structures subjected to in-plane stresses. The aim of this PhD project is to study shear cracking with these two bridges as reference. In this thesis, the first part aims to study the possibility of using finite element analysis as a tool for predicting shear cracking for plane state stresses. The second part is concerning how the shear cracks are treated in the concrete design standards. Shear cracking in reinforced beams has been studied with non-linear finite element analyses. In these analyses the shear cracking behaviour was compared to experiments conducted to analyse the shear failure behaviour. Finite element analyses were performed with two different FE programs Abaqus and Atena. The material model used in Atena is a smeared crack model based on damage and fracture theory with either fixed or rotated crack direction. The material model used in Abaqus is based on plasticity and damage theory. The fixed crack model in Atena and the model in Abaqus gave good results for all studied beams. For the two studied deep beams with flanges the results from the rotated crack model were almost the same as obtained with the fixed crack model. The rotated crack model in Atena gave though for some beams a rather poor estimation of the behaviour. The calculation of crack widths of shear cracks has been studied for the long-term load case in the serviceability state for the Gröndal and Alvik bridges, with the means available in the design standards. The methods based on the crack direction corresponding to the principal stress and do not include the effect of aggregate interlocking seems to be too conservative. Two of the studied methods included the effect of aggregate interlocking, it was made either by introducing stresses in the crack plane or implicitly by changing the direction of the crack so that it no longer coincide with the direction of principal stress. For calculations based on probable load conditions, these methods gave estimations of the crack widths that were close to the ones observed at the bridges. Continuous measurements of cracks at the Gröndal and the Alvik bridges have also been included. Monitoring revealed that the strengthening work with post-tensioned tendons has, so far, been successful. It also revealed that the crack width variations after strengthening are mainly temperature dependent where the daily temperature variation creates movements ten times greater than those from a passing light-rail vehicle. Monitoring a crack between the top flange and the webs on the Gröndal Bridge showed that the top flange was moving in a longitudinal direction relative to the web until the strengthening was completed. The crack widths in the sections strengthened solely by carbon fibre laminates seem to increase due to long-term effects.
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| 15. |
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| 16. |
- Mattsson, Hans-Åke, 1959-
(författare)
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Funktionsentreprenad Brounderhåll : en pilotstudie i Uppsala län
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Before 1992 the Swedish Road Administration (SRA) carried out all bridge maintenance and minor repair for all bridges in Sweden by themselves. The bridge maintenance crew in a county consisted typically of 3-6 workers and a bridge-engineer. SRA and some contractors suggest that it could be a good idea for SRA to procure bridge maintenance in one or two counties for a long-time, e. g., seven to ten years. The bridge maintenance crew could be a model for this. The aim of the research project is to present an updated model for procurement of bridge maintenance based on functional requirements. The base for this updated model will be the findings and conclusions that could be drawn from a real project – a case study. The research project shall continuously follow-up the performed maintenance and document how the contractor is planning and performing the work. The research will specially focus on measurable verifying methods for the performed maintenance. The results from the research project will be evaluated and compared with standard maintenance methods and the results will hopefully be used to update current regulations. The hope is also that the contractor will develop new and effective maintenance methods with the larger freedom a functional contract enables. At the end the final goal is to reduce the cost for the society for bridge maintenance in the future. The basic idea behind performance contract is that the client makes measurable functional demands with regard to the finished product, instead of presenting technical solutions. As an example the client could demand a certain friction and smoothness for the road surface. These functional demands should be formulated so that they have a direct relevance for the safety and flow of traffic. It is important that these functional requirements are divided into a target level and an absolutely lowest possible level (acute level). A contractor should maintain the target level both as an average functional level during the contract period and when the contract is completed. For the acute level there should be stipulated a maximum allowable time before corrective action needs to be taken. The methods that have been used in the research project are interviews, meetings, literature studies, reports, follow-up, statistics, participating in seminars, the authors own inspections, annual reports and so on. Since the author didn’t find anything published about bridge management on performance contract, to the author’s best knowledge, the literature studies have been concentrated on nearby topics, e. g., highways on performance contract and bridge maintenance in general et cetera. The research project has so far consisted mostly of a pilot study. From the beginning the idea behind the project was: • To procure bridge maintenance for the small and mid-sized bridges, • in one or two counties, • for a longer time, e. g., seven to ten years. • The value of a maintenance contract could be in the range of about 100 MSEK for the whole time. Since this is the first project of its kind in Sweden the owner (SRA) did not dare to let this pilot project be too voluminous. What will be tested and followed by this research project is to use contracting for maintenance based on functional requirements for all 400 bridges in Uppsala County in Sweden and for a period of three years and with an option for three more years. Uppsala County is situated some 20 km to 200 km north of Stockholm. To summarise the actual contract: • A contractor should perform bridge maintenance for all 400 bridges in Uppsala County. • The contract was three years (1 Sept. 2004 – 31 Aug. 2007) with an option for three more years (1 Sept. 2007 – 31 Aug. 2010). • The bridges were deemed to be in satisfactory condition if the contractor verified that they met the functional requirements in SRA’s regulations once a year. • Repair of 25 bridges during the contract’s first three years. • If the option for three more years will be used, then there will be some additional bridge repairs. • The contractor was expected to contribute in the research project. There were six contractors that requested the tender documents, but only three of them submitted an offer to SRA, see table below. Contractor Submitted offer Vägverket Produktion 20 387 943 SEK DAB-Domiflex AB 23 728 040 SEK NCC Construction 28 620 000 SEK (Advance 2 000 000 SEK) All of the three contractors deemed to have met the standards of a contractor set by SRA. Vägverket Produktion (VP) was the lowest bidder and therefore it was contracted by SRA for this project. Interviews were carried out with all six contractors that had requested tender documents. All of them thought that a multiyear bridge maintenance contract was an interesting idea. Large companies tend to want large contracts and small companies tend to settle for smaller contracts. All of the contractors thought that it was easy to calculate the 25 bridge repairs compared to bridge maintenance on functional demands. According to the contract VP should repair 25 bridges during a three year period. VP divided these repairs in three equal parts: nine bridges 2005, eight bridges 2006 and eight bridges 2007. The functional requirements for the bridges should be verified once a year according to the contract. Both representatives for SRA and VP carried out bridge inspections during the first year and it was noted that the representatives had a different view on some of the discovered defects on the bridges. The representatives had a different view mainly on the bridges’ structural members’ slope and embankment end, edge beam and surfacing. It is important to specify how to measure and interpret the results from inspections regarding defects in functional requirements. Defects in functional requirements should be divided into acute defects and non-acute defects. Acute defects needs to be more precisely defined but could be surfacing against bridge, settling in slope and embankment end and flushing. These defects should be rectified as soon as possible. Non-acute defects could be rectified when there is enough work for the contractor to carry out but not later then October 31st every year. The research project will continue to follow-up and evaluate the first three years of the pilot study. The research project will also follow-up and evaluate if the option for extending the contract three more years will be used. According to the contract, if the option will be used, there need to be a meeting between the client and the contractor not later than 31 Aug. 2006 and a settlement need to be reached not later than 30 Sep. 2006. It is of interest to study the possibility to use, in future tender documents, the indicator Lack of Capital Value and/or the average permissible level of defects in functional requirements for the bridge stock. Further research should also be focused on how defects on different members of the bridge evolve and the cost associated to rectify them. It is of interest to know how many defects that are evolved during a normal year for the 400 bridges in the study. If one knew the number of defects one can estimate the costs to rectify these. The estimated cost can then be included as information for the potential contractor in future tender documents. So far SRA’s representatives are satisfied with the project and with the good relationship that evolved between SRA and the contractor. SRA is also satisfied with the increased focus on the bridge functional requirements. If this project will continue to show good results then SRA will consider procure bridge maintenance on similar contracts for more counties.
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| 17. |
- Mattsson, Hans-Åke, 1959-
(författare)
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Integrated Bridge Maintenance : Evaluation of a pilot project and future perspectives
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The trend in many countries is to outsource maintenance with competitive tendering. The design of the tender is then a crucial issue. A new type of tendering contract, called "Integrated Bridge Maintenance", was introduced in one experimental area in Sweden. In this case the preventive bridge maintenance is separated from the standard road maintenance contract. The ideas behind these changes are that the new approach can increase efficiency through a combination of increased specialization, economies of scale and through giving the private contractor a greater degree of freedom concerning exactly what to do and exactly when to do it. A pilot project has been running since 2004 for all bridges in Uppsala County with about 400 bridges and since 2007 for all bridges in Örebro County with about 700 bridges. The experiences and lessons from this pilot project are presented in this thesis together with guidelines on how to procure Integrated Bridge Maintenance in the future. An important feature of the contract was that it contained a combination of specific measures that the contractor should carry out and properties of the bridges that the contractor was responsible to maintain. This created a balance between predictability and flexibility for the contractor. The contractor could make long term planning for the work. The client was satisfied because of increased competence and a low price. The latter can partly be explained by the possibility for the specialised bridge crew to receive additional work from other clients. As information about old bridges always is incomplete a partnering structure needs to be built into the contract. Experience has also shown that a conscious policy to maintain long run competition is important. The general conclusion is that the project was seen as successful and as creating more "value for money". To manage a bridge stock optimally from a life cycle perspective is a very complex task, since the conditions for the individual bridge can vary greatly from place to place which the answers from the research questions indicate. Besides following-up and evaluating the Integrated Bridge Maintenance projects a number of research questions have been studied. Is Integrated Bridge Maintenance a successful method to increase the effectiveness and to increase the standard in bridge maintenance alternatively increasing the service life for the bridge stock at an optimal cost, i.e., will IBM lead to lower LCC? It is difficult to answer this question with exact numbers after so short time, but so far the opinion is that the effectiveness has increased. How can a bridge stock develop over a long time e.g. 15 years? Based on historical data one can calculate, for instance, new construction rate, demolition rate and average age for the bridge stock. This information could together with different future scenarios be a basis for different bridge management strategies for the actual bridge stock. What is the real service life for a bridge? Survival analysis for the different types of bridges in the actual bridge stock will give a good estimate of the different expected service life. Why and at which age are bridges demolished? Two main reasons were found in this study: deterioration process of the bridge had gone too far and/or load bearing capacity was too low, and road were rerouted. What is the real service life for a bridge edge beam, one of the most often repaired element of Swedish bridges? Survival analysis of edge beams located on different types of roads will give a good estimate of the different expected service life. How should a long-term contract for bridge maintenance and specially Integrated Bridge Maintenance be procured? The bridge manager should have a good understanding of the answers on the research questions above when the tender documents are to be prepared for the actual bridge stock. Thereafter the area that the contract should cover could be chosen, a good balance between properties and measures, defining the working cycle for properties, a flexible partnering structure in the contract and a suitable length of the contract (x years) inclusive an option (+ y years) and finally good incentives in the contract. To sum up, the main purpose with the doctoral project has been reached. A model for procurement of bridge maintenance has been developed; see the projects in Uppsala and Örebro. The contractor has developed more effective methods for bridge maintenance. The doctoral project has been a step closer to the end goal of reducing the society’s costs for bridge maintenance in the future. The bridges should be functional to the lowest possible cost during its expected service life (LCC). The doctoral project has also contributed with new knowledge in the area of bridge maintenance, the actual development of a bridge stock over time, real service life for road bridges in Sweden and survival analysis.
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| 18. |
- Ngoma, Athuman M. K.
(författare)
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Characterisation and Consolidation of Historical Lime Mortars in Cultural Heritage Buildings and Associated Structures in East Africa
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For the period of several centuries, the influence of several distinct cultures produced rich and diverse cultural heritage that we see today in East Africa countries. The most tangible remains of these heritages are stone built buildings and structures including, palaces, mosques, residential houses and tombs. At present, these heritages are in different physical state, some are in relatively good condition while many are in an appalling condition. The presence of these historical monuments has benefited these countries economically and culturally therefore, it is essential to ensure that these monuments continue to exist. Material characterisation of the historical buildings and associated structures was used to develop a suitable method of intervention that is sympathetic to the original materials. Mortar is the most damaged material therefore, historical mortar from Stone Town historical buildings and associated structures has been characterised by visual examination, optical microscopy, x-ray diffraction and hydrostatic weighing and the results have been compared. The historical mortar is mainly comprised of calcite, quartz and feldspar. The mortar condition has been divided into hard mortar, soft mortar and, soft and friable mortar. The deteriorated mortar that required consolidation is soft mortar and, soft and friable mortar with a porosity of approximately 27%. Calcium hydroxide solution (limewater) has been selected as consolidant and the consolidation procedure involves two steps. Firstly a limewater impregnation procedure has been developed and secondly, the effect of limewater treatment has been determined. For the application procedure it has been observed that, when limewater comes into contact with calcium carbonate a precipitation reaction occurs and that is the cause of poor penetration ability of calcium hydroxide solution. Major influencing factors on the penetration ability of calcium hydroxide solution have been established as, application method and absorption capacity of the treated material during the impregnation process. Optimization of the penetration ability of calcium hydroxide solution has been achieved by impregnating from the middle of the impregnated specimen. Sugar has been used to study the influence of additive on enhancing calcium hydroxide solubility. It has been verified that solubility of calcium hydroxide in a solution of sugar is proportional to the amount of sugar in the solution. Porosity and strength tests have been used to study the effectiveness of calcium hydroxide treatment. Under the conditions studied no appreciable change of porosity has been detected. It is postulated that the calcium hydroxide was deposited at the binder/aggregate interface and at the secondary pores. In terms of strength, evidence has been found to suggest the strength increment varies quantitively with the amount of calcite crystals deposited.
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| 19. |
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| 20. |
- Skoglund, Pål
(författare)
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Chloride transport and reinforcement corrosion in the vicinity of the transition zone between substrate and repair concrete
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One of the major degradation problems in concrete structures is chloride initiated reinforcement corrosion resulting in cracked, spalled and delaminated concrete. Thesedamages are repaired for large amounts of money and because of high repair costs it is important to perform durable repairs. This thesis work has included interviews, laboratory and field studies in the area of concrete repairs. The interviews were held mainly with bridge engineers at the Swedish Road Administration and Banverket (the Swedish Railway Administration). The questions asked tothese people were about their experience in the field of concrete repairs. The objective withthe interview study was to collect knowledge and experience about concrete repair at these two governmental authorities. The main objective of the laboratory study was to investigate chloride transport in the transition zone between a chloride contaminated substrate concrete and an initially chloride free repair concrete by establishing chloride profiles. The second objective was to detect any reinforcement corrosion in relation to the transition zone. The reinforced laboratory specimens with premixed chlorides (1 or 4 wt % per cement) in the substrate concrete have been exposed during 13 years either outdoors or in a climate chamber with relative humidity of 80 %. The main results show that reinforcement corrosion occurred in and near the transition zone in local active areas with passive areas between, macrocell corrosion, and that the chlorides are transported from the contaminated substrate concrete into the repair concrete. Three different repaired concrete structures, one road bridge, one pedestrian bridge and one parking structure, were investigated in the field study. All three structures are treated with deicing agents in the winter time. The objective with the field study was to investigate if the same phenomenon can be observed as in the laboratory study. The main conclusions, from the investigation on drilled cores from each structure, are that chlorides in contaminated substrate concrete can be transported into a repair concrete and reinforcement corrosion may occur in the transition zone between the two different materials. The results are in accordance with the results in the laboratory study. It was also seen that a repair concrete with relative low w/cratio may reduce the ingress of external chlorides. Finally, the results in this thesis indicate that there is a risk for reinforcement corrosion in the vicinity of the transition zone between repair concrete and a substrate concrete which must be considered in concrete repair work. For example the chloride content around a repair must not exceed a certain level when a repair is performed. The chloride transport into the repair concrete can be useful to transport chlorides and reduce the content of chlorides in the substrate concrete. The advantages with this are that the amount of removed contaminated substrate concrete can be minimized and the risk for corrosion in the substrate concrete is lower. If the repair concrete is reinforced with conventional black steel there may on the other hand be a risk for corrosion in the repair concrete instead if high levels of chlorides are transported. Also external exposure of chlorides must be considered for the risk of corrosion in the repair material. Further research is needed about when different corrosion mechanisms and chloride diffusion mechanisms occur in reinforced concrete repairs. The experience from the used analyzing methods in the laboratory investigations are possible to use in coming research projects in the field of concrete repair. The next step after this thesis work should be in order to increase the understanding of the repaired concrete system including the important compatibility issues, the author believes that the most fruitful way consists of further laboratory investigations, field studies and optimisation of the repair material.
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| 21. |
- Stenbeck, Torbjörn, 1965-
(författare)
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Promoting Innovation in Transportation Infrastructure Maintenance : Incentives Contracting and Performance Based Specifications
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Knowledge of what action that is needed to drive innovation at a desired speed is in demand in civil engineering and its related maintenance. 1. What measures to stimulate innovation have been tested? 2. How much innovation has been achieved by contracting? 3. How much innovation was achieved by performance-based specifications? 4. How can cost models contribute to innovation? Methods include qualitative and quantitative methods that have been timed and mixed to optimize their merits. Sweden, France, USA and Canada have used as research ground. Technology transfer, multi-criteria evaluation, variant bidding, idea mailbox, weatherregulated payment, contests and earmarked funds for innovative projects were some of the method beside and within contracting and performance-based specifications that have been tested. Contracting as such has cut costs in Sweden but not in North America. Neither Sweden nor North America has noticed any increase of innovation, rather the contrary. The savings have primarily been achieved by cuts on staff and by using standardized, less expensive and less advanced machinery. Contracted highway maintenance provinces in Canada and Sweden on average had about 50 % higher costs than inhouse provinces and Washington State. The difference is reduced to 26 %, when corrected by weather and the higher traffic in the contracted provinces. Prestige, politics and competitivity made it difficult to extract economic data from private contractors, and even from the public owners and may explain the contradictory results in previous studies. The internally driven innovation appears small and incentives to innovation weak in inhouse systems, but contrary to expectation even less in contracted systems. Performance-based specifications (PBS), such as Design-Build (DB), have reduced delivery times and kept the budget better than traditional contracts, but quality, lifecycle cost and technical progress was rarely analyzed and even less confirmed in the literature, why a multiple case study was carried out. The result was that three out of four PBS cases delivered lower quality in the long run or showed higher costs already on the opening day, when compared to a traditional contract alternative. Cost models contribute to innovation by making regions with different conditions comparable and provide tools for rational planning and decision making. One model for how highway maintenance costs depend on snow, bridges and traffic and one model for how bridge maintenance costs depend on size and age were elaborated. Models included in contracts, e.g. to allow a contractor to reduce the weather risk, appear to have contributed to a more successful contracting rollout in Sweden than in Canada. France provides experience of how inhouse innovation contests and industry-own patent-like routines can promote innovation. After the first two years with an incentive contract, Banverket received 10 % better quality measured as train delay and 20 % better quality measured as the number of technical errors at no cost. A lesson learnt is that the success of performance-based specifications depends on how well the owner can describe and define the contracts, how compliance is measured and how deviations are handled, i.e. how the contractor is penalized for non-fulfillment or awarded for excess delivery
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| 22. |
- Söderqvist, Johan
(författare)
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Design of concrete pavements : design criteria for plain and lean concrete
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- New road infrastructure projects are important and constitute of large investments that have to serve the society for a long time. The investments have to be durable at the lowest life cycle cost and the pavements have to sustain loads from increasing traffic intensity and heavy traffic loads. In Sweden less than 1 ‰ of the national road network consists of concrete pavements. In parts of Europe and in the U.S., on the other hand, concrete roads are used to a large extent for highways as well as rural roads. To encourage the competition between different road materials in Sweden, the tools for designing robust concrete pavements have to be brought forward. In order to emphasize plain concrete pavements as an alternative in road construction, the design must also be competitive. The current Swedish design method for concrete pavements is straightforward but offers no flexibility when designing roads with, for instance higher traffic loads. The method calculates concrete thicknesses on the conservative side since only a limited number of parameters are treated. Modern methods that take into account many more parameters in the design are being developed internationally. For a new Swedish design method, these parameters have to be established for actual conditions in Sweden. Also, the design has to be flexible and meet the demands from contractors and clients for a wider use. The aim of this project is to develop a new design method for plain concrete pavements that is more flexible than today. A new design method is also intended for the Swedish Road Administrations’ (SRA) computer based public design guide, PMS Objekt. Information for a new design method has been assembled mainly by investigating two newly developed design methods, VENCON2.0 in the Netherlands, and the Mechanistic-Empirical Pavement Design Guide (MEPDG) in the USA. Comparative calculations between the Swedish design method and the MEPDG are presented. The comparison is made on the level of input parameters and highlights the advantageous aspects of a semi-mechanistic design procedure where the functional properties of a concrete pavement are calculated incrementally over the design period. Plain and lean concrete, separately, but also the in composite beams, have been studied in flexural fatigue testing. The results show that Tepfers’ fatigue criterion is valid for both plain and lean concrete when subjected to flexural fatigue loading. The results also show that the fatigue strength of composite beams of plain and lean concrete is mainly dependent on the strength of the lean concrete but that Tepfers’ fatigue criterion is applicable. The bond between plain in lean concrete is found to be strong and fatigue resistant, making the composite section able to accommodate higher stresses. The bond nevertheless contributes to the risk for reflection cracks in the plain concrete wear layer and a recommendation to focus on stresses in the bottom of the lean concrete is formulated. Also, well distributed expansion joints in the lean concrete are necessary. A new project for measuring temperature gradients for use in concrete pavement design is also presented. This is done with means of concrete prisms placed in the pavement and are done in order to establish actual temperature gradients for various locations in Sweden. Also, the nonlinear gradients that act in the pavement as well as the negative temperature gradients will be analysed for the use in the design. Finally, the thesis outlines a new design method for Swedish conditions. The method is possible to develop gradually and is based on FE-analysis for fast computations. In the design, stresses from traffic and temperature loads are calculated simultaneously in a number of critical locations in the concrete slab. The method will also make it possible to alter design features as slab lengths and widths, with various connections between the slabs.
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| 23. |
- Ülker-Kaustell, Mahir, 1975-
(författare)
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Some aspects of the dynamic soil-structure interaction of a portal frame bridge
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For certain bridge types, the influence of soil-structure interaction (SSI) may have an important contribution to the stiffness and damping of the structural system. From a design point of view, this influence may be both conservative and non-conservative and therefore, an increased knowledge within this field could lead to better design assumptions. In terms of maintenance, assessment and upgrading of existing structures, an increased knowledge of the phenomena and parameters which govern the soil-structure interaction, may lead to more realistic models and thereby, to more precise information for the decision makers and railway system owners and administrators. SSI appears to be most important for short and relatively stiff structures such as portal frame bridges. Dynamic analyzes of this bridge type have shown a large sensitivity in the choice of boundary conditions, where applying elastic constraints on the vertical degree of freedom at the support, compared to fixing this degree of freedom, may increase the maximum vertical bridge deck acceleration by as much as a factor of three. In this thesis, numerical analysis procedures for the computation of dynamic stiffness functions describing the frequency dependency of the foundation-soil interface have been explored under the assumption that the analysis can be performed using linear theories alone. The numerical solution of the equations of motion of structural systems, including such frequency dependent parameters, is performed using an integration scheme based on the discrete Fourier transform. Furthermore, preliminary experimental work on a newly built portal frame bridge is described. This portal frame bridge is subject to a case study in which the the computational techniques mentioned above are applied on a two dimensional model of the bridge. Theoretically, the damping of the SSI is shown to give a large contribution to those modes of vibration which excite the foundations much. These structural modal damping ratios may be much larger than those prescribed by the design codes. Those modes of vibration which do not excite the foundations much are similar to those obtained using clamped or constant elastic boundary conditions and in these cases, the contribution to the modal damping ratio of the structure is only a fraction of that prescribed by the design codes. A very rough analysis of measurements taken from the bridge indicate a similar behavior, but the amplitudes of vibration in many of the estimated modes are quite small (in the order of the quantization error of the measurement system) and therefore, the errors in the damping ratio estimates may be substantial. The work with this thesis have raised many questions, the answers to which are believed to substantially improve our understanding of resonance phenomena and also our possibilities to update numerical models of existing railway bridges using dynamic measurements. From the simplified analysis of a portal frame bridge performed within this project, it has been concluded that when the elastic modulus of the soil is increased, the total structural damping ratio when dynamic SSI is included decreases. Furthermore, with respect to vertical bridge deck accelerations, clamped boundary conditions are certainly not conservative as compared with static and dynamic SSI.
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| 24. |
- Westerberg, Bo, 1942-
(författare)
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Time-dependent effects in the analysis and design of slender concrete compression members
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The report deals with the effect of time-dependent concrete properties in the analysis and design of slender compression members. The main focus is on how to take these effects into account in nonlinear analysis, not on the properties as such in a materials science perspective.Simplified methods for practical design have earlier been calibrated against accurate calculations based on nonlinear analysis. Creep was then taken into account in a simplified way, using an effective creep ratio and an extended concrete stress-strain curve; shrinkage and strength increase were disregarded. The significance of these simplifications is studied here by comparisons with a more rigorous analysis, including a complete creep function plus the effects of shrinkage and strength increase.A good reason for not taking into account strength increase in normal design is that high loads can occur early in the service life. For slender compression members, however, this means that strength at the beginning of the service life is combined with second order effects at the end of it (including the full effect of creep). This is conservative but in principle not logical. Therefore, the effect of strength increase has been studied here. (Whether it should be allowed to take it into account in design is another question, to be considered by code writers.) The reduction of concrete strength due to high sustained stress is studied from different angles. The conclusion is that there is no need to take this into account in design. There are several independent reasons for this, each sufficient on its own: load factors, lower stress levels in case of second order effects, strength increase.The realism of the models for creep, shrinkage and strength increase given in Eurocode 2 (2004), when used in an accurate nonlinear analysis, has been examined by comparisons with tests of slender columns reported in the literature. Good agreement is found in most cases. The comparisons also confirm that high sustained stress has no effect in slender columns.
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| 25. |
- Wiberg, Johan, 1977-
(författare)
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Bridge Monitoring to Allow for Reliable Dynamic FE Modelling : A Case Study of the New Årsta Railway Bridge
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Today’s bridge design work in many cases demands a trustworthy dynamic analysis instead of using the traditional dynamic amplification factors. In this thesis a reliable 3D Bernoulli-Euler beam finite element model of the New Årsta Railway Bridge was prepared for thorough dynamic analysis using in situ bridge monitoring for correlation. The bridge is of the concrete box girder type with a heavily reinforced and prestressed bridge deck. The monitoring system was designed for long term monitoring with strain transducers embedded in the concrete and accelerometers mounted inside the edge beams and at the lower edge of the track slab. The global finite element model used the exact bridge geometry but was simplified regarding prestressing cables and the two railway tracks. The prestressing cables and the tracks were consequently not included and an equivalent pure concrete model was identified. A static macadam train load was eccentrically placed on one of the bridge’s two tracks. By using Vlasov’s torsional theory and thereby including constrained warping a realistic modulus of elasticity for the concrete without prestressing cables and stiffness contribution from the railway tracks was found. This was allowed by comparing measured strain from strain transducers with the linear elastic finite element model’s axial stresses. Mainly three monitoring bridge sections were used, each of which was modelled with plane strain finite elements subjected to sectional forces/moments from a static macadam train load and a separately calculated torsional curvature. From the identified modulus of elasticity the global finite element model was updated for Poisson’s ratio and material density (mass) to correspond with natural frequencies from the performed signal analysis of accelerometer signals. The influence of warping on the natural frequencies of the global finite element model was assumed small and the bridge’s torsional behaviour was modelled to follow Saint-Venant’s torsional theory. A first preliminary estimation of modal damping ratios was included. The results indicated that natural frequencies were in accordance between modelling and signal analysis results, especially concerning high energy modes. Estimated damping ratios for the first vibration modes far exceeded the lower limit value specified in bridge design codes and railway bridge dynamic analysis recommendations.
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| 26. |
- Wiberg, Johan, 1977-
(författare)
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Railway bridge response to passing trains : Measurements and FE model updating
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Today’s railway bridges are analysed in more detail for moving loads due to the increase in speeds and axle loads. However, these numerical analyses are very time consuming as they often involve many simulations using different train configurations passing at different speeds and many considerations to take into account. Thus, simplified bridge, track and train models are often chosen for practical and time efficient simulations.The New Årsta Railway Bridge in Stockholm was successfully instrumented during construction. A simplified 3D Bernoulli-Euler beam element FE model of the bridge was prepared. The FE model was first manually tuned based on static load testing. The most extensive work was performed in a statistical identification of significantly influencing modelling parameters. Consequently, parameters to be included in an optimised FE model updating, with consideration also to synergy effects, could be identified. The amount of parameters included in the optimisation was in this way kept at an optimally low level. For verification, measurements from several static and dynamic field tests with a fully loaded macadam train and Swedish Rc6 locomotives were used. The implemented algorithms were shown to operate efficiently and the accuracy in static and dynamic load effect predictions was shown to be considerably improved.It was concluded that the complex bridge can be simplified by means of beam theory and an equivalent modulus of elasticity, and still produce reliable results for simplified global analyses. The typical value of an equivalent modulus of elasticity was in this case approximately 25% larger than the specified mean value for the concrete grade in question.The optimised FE model was used in moving load simulations with high speed train loads according to the design codes. Typically, the calculated vertical acceleration of the bridge deck was much lower than the specified allowable code value. This indicates that multispan continuous concrete bridges are not so sensitive to train induced vibrations and therefore may be suitable for high speed train traffic.Finally, the relevant area of introducing the proposed FE model updating procedure in the early bridge design phase is outlined.
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