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  • 1.
    Aagah, Orod
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Aryannejad, Siavash
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Dynamic analysis of soil-steel composite railway bridges: FE-modeling in Plaxis2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    A soil-steel composite bridge is a structure comprised of corrugated steel plates, which are joined with bolted connections, enclosed in friction soil material on both sides and on the top. The surrounding friction soil material, or backfill, is applied in sequential steps, each step involving compaction of the soil, which is a necessity for the construction to accumulate the required bearing capacity. Soil-steel composite bridges are an attractive option as compared with other more customary bridge types, owing to the lower construction time and building cost involved. This is particularly true in cases where gaps in the form of minor watercourses, roads or railways must be bridged.

    The objective of this master thesis is the modelling of an existing soil-steel composite railway bridge in Märsta, Sweden with the finite element software Plaxis. A 3D model is created and calibrated for crown deflection against measurement data collected by the Division of Structural Engineering and Bridges of the Royal Institute of Technology (KTH) in Stockholm, Sweden.

    Once the 3D model is calibrated for deflection, two 2D models with different properties are created in much the same way. In model 1, the full axle load is used and the soil stiffness varied, and in model 2 the soil stiffness acquired in the 3D model is used and the external load varied. The results are compared to measurement data. In 2D model 1 an efficient width of 1,46 m for the soil stiffness is used in combination with the full axle load, and in 2D model 2 an efficient width of 2,85 m is used for the external load, in combination with the soil stiffness acquired in the 3D model.

    Aside from this, parametric studies are performed in order to analyse the effect of certain input parameters upon output results, and in order to analyse influence line lengths.

    Recreating the accelerations and stresses in the existing bridge using finite element models is complicated, and the results reflect this. Below are shown the discrepancies between model results and measurement data for the pipe crown. The scatter in the measurement data has not been taken into consideration for this; these specific numbers are valid only for one particular train passage.

    For crown deflection, the 3D model shows a discrepancy of 4%, 2D model 1 5% and 2D model 2 8% compared with measurement data. For crown acceleration, in the same order, the discrepancy with measurements is 1%, 71% and 21% for maximum acceleration, and 46%, 35% and 28% for minimum acceleration. For maximum crown tensile stress, the discrepancy is 95%, 263% and 13%. For maximum crown compressive stress, the discrepancy is 70%, 16% and 46%.

  • 2.
    Abbasiverki, Roghayeh
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Analysis of underground concrete pipelines subjected to seismic high-frequency loads2016Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Nedgrävda rörledningar (pipelines) är rörformiga strukturer som används för transport av viktiga flytande material och gas för att säkerhetsställa samhälleliga funktioner. Denna typ av infrastruktursystem korsar stora områden med olika geologiska förhållanden. Under en jordbävning kan markdeformationer påverka rörledningar av betong vilka kan få allvarliga skador som i sin tur kan leda till störningar i vitala system, såsom till exempel kylning av kärnkraftsanläggningar. Den höga säkerhetsnivå som eftersträvas ger upphov till ett behov av tillförlitliga seismiska analyser, även för strukturer som byggs i regioner som traditionellt inte har ansetts som seismiskt aktiva. Fokus i denna licentiatuppsats ligger på områden med seismiska och geologiska villkor som motsvarar de i Sverige och norra Europa. Jordbävningar i Sverige klassas som händelser inom en tektonisk platta som för regioner med hårt berg kan resultera i jordbävningar som domineras av högfrekventa markvibrationer. Sådana högfrekventa vågor propagerar genom bergmassa och jordmaterial och kan där påverka underjordiska strukturer såsom rörledningar.

    Syftet med detta projekt är att undersöka vilka parametrar som har stor påverkan på nedgrävda rörledningar som utsätts för högfrekventa seismiska vibrationer. Tyngdpunkten i studien är på rörledningar av armerad betong men stålledningar studeras också i jämförande syfte. Två-dimensionella finita elementmodeller används, utvecklade för dynamisk analys av rörledningar belastas av seismiska vågor som propagerar från berggrunden genom jorden. Modellerna beskriver båda längsgående och tvärgående snitt av rörledningar. Samspelet mellan rörledningar och omgivande jord beskrivs av en icke-linjär modell. De studerade rörledningarna antas vara omgivna av friktionsjord med stor, medel eller liten styvhet. Effekterna av vattenmassa i rören, grundläggningsdjup, jordlagrens tjocklek och varierande jordtjocklek på grund av lutande berggrund studeras. Det visas hur två-dimensionella modellerbaserade på plan töjning kan användas för seismisk analys av rörledningar med cirkulära tvärsnitt.

    Resultaten jämförs med de som erhållits för lågfrekventa jordbävningar och förhållandet mellan markrörelseparametrar och responsen hos rörledningar undersöks. Det visas att den naturliga frekvensen för modellerna beror av jordtyp, tjocklek och variation hos jordlagret. Det visas att, särskilt för högfrekventa jordbävningar, olikformigt varierande markdjup på grund av lutande berggrund avsevärt ökar spänningarna i rörledningarna. För de förhållanden som studerats är det klart att det är mindre sannolikt att högfrekvent seismisk belastning ska orsaka skador på nedgrävda rörledningar av betong. Dock är den viktigaste slutsatsen att seismisk analys ändå motiveras, även för rörledningar i områden där jordbävningar med högt frekvensinnehåll förekommer eftersom lokala variationer i markförhållanden kan ha en betydande inverkan på säkerheten.

  • 3.
    Abbasiverki, Roghayeh
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Analysis of buried reinforced concrete pipelines subjected to seismic waves2014Konferensbidrag (Refereegranskat)
  • 4.
    Abbasiverki, Roghayeh
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Larsson, Stefan
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Jord- och bergmekanik.
    Seismic response of buried concrete pipelines subjected to highfrequency earthquakesIngår i: Geotechnical and Geological Engineering, ISSN 0960-3182, E-ISSN 1573-1529Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Buried pipelines are tubular structures that cross large areas with different geological conditions. During an earthquake, imposed loads from soil deformations on concrete pipelines may cause severe damages. In this study, the use of two-dimensional finite element models of pipelines and surrounding soil for simulation of seismic waves that propagate from the bedrock through the soil are demonstrated. The models describe both longitudinal and transverse cross-sections of pipelines and the soil-pipe interaction is modelled as a nonlinear behaviour. The effects of uniform ground with different burial depths, soil layer thickness, soil stiffness and bedrock geometry on the seismic response of reinforced concrete pipelines is studied. Two earthquakes, with high and low frequency contents, are employed for the dynamic analysis. The results show that there is a much smaller risk of damage from high-frequency earthquakes, but that there is a significant effect on the response due to possible irregular ground with inclined bedrock.

  • 5.
    Abbasiverki, Roghayeh
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Malm, Richard
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Analysis of shallowly buried reinforced concrete pipelines subjected to earthquake loads2014Ingår i: Nordic Concrete Research, ISSN 0800-6377, nr 51, s. 111-130Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Buried reinforced concrete pipelines are widelyused in e.g. water and wastewater systems. Failure of these infrastructures mayresult in drastic effects and recently they have been brought into focus asvital components in safety systems for nuclear power installations. The highlevel of safety has here lead to a demand for reliable earthquake risk analyses.In this paper, methods are compared and the use of seismic design loadsdemonstrated. FE analysis in 2D of soil-pipe interaction under seismic wavepropagation is performed. The performance of concrete pipes subjected toseismic waves with different frequency content is evaluated with respect todifferent soil condition but also water mass effect.

  • 6. Abd-Alla, E. S. M .
    et al.
    Moriyoshi, A.
    Partl, Manfred
    EMPA, Swiss Federal Laboratories for Materials Testing and Research.
    Takahashi, K.
    Kondo, T.
    Tomoto, T.
    New wheel tracking test to analyze movements of aggregates in multi-layered asphalt specimens2006Ingår i: Journal of the Japan Petroleum Institute, ISSN 1346-8804, E-ISSN 1349-273X, Vol. 49, nr 5, s. 274-279Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper describes a new wheel tracking test for analyzing movements of aggregates in mixtures. The test device is conducted using as examples four-layered specimens taken from two Swiss national motorways, where severe rutting (G section) and longitudinal cracking (H section) were observed. This test method was developed by Moriyoshi. Tests can be carried out under temperature distributions similar to field situation. Two-dimensional movements and strains between aggregates for four-layered specimens due to the moving wheel loads were analyzed by right angle for direction of wheel pass. For this purpose, the cross section of the slabs with a width of 30 cm was divided optically into 5 vertical subsections. The transverse permanent surface deformations, the area changes in the transversal subsections as well as the maximum deformation of the surface and layer-interface through the centerline of the applied wheel load were determined. Strain distributions between aggregates in mixtures at high temperature (45 degrees C) under 600 passes were also measured by photo analysis. Test results show consolidation of the asphalt mixtures and material flow on the surface near the wheel load. The results also demonstrate that the aggregates (size of aggregate: 2 mm or larger) in each mixture move mainly in vertical direction. Large strains (40% or larger) between aggregates at summer condition were measured in the surface mixture near wheel track after 600 passes.

  • 7.
    Abdi, Adel
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap.
    Lind, Hans
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Fastigheter och byggande.
    Birgisson, Björn
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap.
    Designing appropriate contracts for achieving efficient winter road and railway maintenance with high performance quality: A survey of the state of practice in Sweden2014Ingår i: International Journal of Quality and Service Sciences, ISSN 1756-669X, E-ISSN 1756-6703, Vol. 6, nr 4, s. 399-415Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Purpose - For a long time, the winter maintenance of the Swedish road and railway network had been performed in-house by Swedish Transport Administration, Swedish local authorities i.e. municipalities and Stockholm public transport. During the last 15 years the winter operation and maintenance of these state infrastructures have been performed by public procurement and contracting from independent contractors, where in practice the lowest price is the dominating selection criteria. The aim of this paper is to investigate and identify how these contracts are designed and how satisfied the parties are with the contract and the quality of the performed work during the winter and point our directions for improvement. Design/methodology/approach - The study was conducted by a literature review and followed by semi-structured interviews and electronic questionnaire. Findings - The results of the study which are based on the interviews and the online questionnaire show that there is widespread dissatisfaction with the contracts among both clients and contractors. Practical implications - The article prepares a basis showing how a contract affects the quality of the performed winter road and railway maintenance services. Originality/value - The findings lead to a number of suggestions about how to improve the contracts, e.g. having a separate winter maintenance contract to increase the quality of performed winter maintenance measures, a more partnering-like structure where consultations and adjustment can be made during the contract period. A partnering structure also makes it less important to get all the details right in the contract.

  • 8.
    Abdi Yussuf, Yusuf
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggteknik och design.
    Jalal Ibrahim, Zand
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggteknik och design.
    FRP:s användning inom brokonstruktioner2019Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    I dagsläget är de flesta broar i Sverige tillverkade med betong eller stål. Dessa broar är många gånger förknippade med stora kostnader som ofta beror på underhåll och reparation. FRP, som står för Fiber Reinforced Polymer, är ett relativt nytt material i bärande stommar men är ett väl etablerat material i förstärkningssammanhang. I Europa och i synnerhet Nederländerna finns det flertal broar byggda i FRP. Men på grund av brist på normer och regelverk att luta sig emot sker det sällan någon form av brokonstruktion med FRP i Sverige. Detta examensarbete syftar till att undersöka befintliga normer och studera hur materialet FRP används vid förstärkning och konstruktion av broar. Vidare syftar även arbetet till att undersöka egenskaperna hos FRP som byggmaterial och jämföra det med konventionella material som stål och betong. FRP, också benämnd fiberkomposit, är ett kompositmaterial som kan sammanställas på flera olika sätt. Genom olika material som kombineras och olika tillverkningsprocesser som används kan man på så sätt ge individuell utformning till materialet för dess användning. Fördelarna med FRP är många, men i allmänhet har det god styrka, god beständighet samtidigt som det har en låg vikt. Detta resulterar i att inom brokonstruktion så ger det strukturen en minskad egenvikt, vilket i sin tur underlättar en mängd olika saker. Detta arbete visar på att FRP-material har fördelaktiga egenskaper och kan i vissa situationer vara mer gynnsamt att använda än stål eller betong. Dock som tidigare påpekat saknas det specifika Eurokoder för detta material. Däremot är vi säkra på att introduktionen av en ny Eurokod samt med uppmuntran från myndigheter kommer användningen av FRP inom brokonstruktion utan tvekan öka. 

  • 9.
    Abdulrahman, Keiwan
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Potrus, Fadi
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Numerical analysis and model updating of a steel-concrete composite bridge: Parametric study & Statistical evaluation2015Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In the year 2006, only 10 years after the steel- concrete composite bridge, Vårby bridge was built, fatigue cracks were found during an inspection. To further investigate the reasons and the potential danger of the cracks, an investigation under the commission of the Swedish Transport Administration was issued in 2009. After the detection of fatigue cracks, several measurements were carried out in order to monitor the static behavior by the use of strain gauges at selected positions along the bridge. The measurements from the strain gauges monitoring the global behavior were then used to calibrate an finite element model.

     

    The present report is part of the research of understanding the behavior of steel-concrete composite bridges. Numerical analysis and model updating have been used in order to understand and determine how different parameters affects the strain range and the global behavior. The numerical analysis and parameter study were performed in the Finite Element software Abaqus and programming language Python. The outcome of the parameter study was then used to perform the model updating by the method of falsification in MATLAB.

     

    The results from the parameter study and the model updating showed that the measured strains could be reached with a wide range of parameter combinations. Even with unreasonable parameter values, the measured strains were obtained. To investigate the reason for this, a multiple linear regression analysis was performed which showed that the strain range is strongly correlated to the Young’s modulus of steel and concrete and also to the connector elasticity, which resembles the studs in the real bridge.

     

    Two different finite element models, with two completely different input parameter values, obtain the same strain range for the global behavior. It is therefore not certain to assume that a model is accurate and valid based on the fact that the predicted strain range from the finite element model is close to the measured strain range since the global behavior of a steel- concrete composite bridge can be modeled by many different sets of parameters.

  • 10.
    Acar, Yalda
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Jingstål, Pontus
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Influence of the Non-linear Effects in the Design of Viscous Dampers for Bridge Cables2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In this master thesis the performance of external viscous dampers attached to cables in cable-stayed bridges have been studied. A comparison has been performed between a linear and a non-linear cable model. The comparison was carried out for two bridge cables, one from the Dubrovnik Bridge and the other from the Normandie Bridge. The performance of the dampers have been measured in terms of maximum achieved damping ratio and minimum amplitude of vibration.

    The analysis was performed using the finite element method. The damping ratio was measured using both the half-power bandwidth method and by calculating the loss factor. The half-power bandwidth method can only be applied to a linear system. Therefore, the loss factor was evaluated for the linear model and compared to the results obtained using the half-power bandwidth method. From the comparison, it was concluded that the damping ratio evaluated using the loss factor was similar to the results obtained when using the half-power bandwidth method. However, when calculating the loss factor, it was of great importance that the resonance frequency of the system was accurately determined. The loss factor was then calculated for the non-linear model and compared to the results obtained for the linear model. Since the loss factor measures the energy dissipated in a system, it could be utilised for the non-linear model. When computing the strain energy for the non-linear model an approximate method was used to take into consideration the strain energy caused by the static deformation of the cable.

    From the comparison between the linear and non-linear cable models, it was concluded that the optimal damper coefficients obtained by both models are not significantly different. However, there is an uncertainty in the results due to the fact that an approximate method was used when calculating the strain energy for the nonlinear model. It was also observed that a very accurate evaluation of the system’s resonance frequency was needed to calculate the loss factor. It was also observed that the variation in amplitude of vibration for varying damper coefficient was small for all modes of vibration for the Dubrovnik Bridge Cable as well as for the first mode of vibration for the Normandie Bridge Cable. The difference in the results between the two bridge cables needs to be investigated further in order to get a better understanding of the results.

  • 11. Adler, J
    et al.
    Bergholm, Fredrik
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Väg- och banteknik (stängd 20110301).
    Pagakis, S
    Parmryd, I
    Noise and colocalization in fluorescence microscopy: solving a problem2008Ingår i: Microscopy and Microanalysis, ISSN 1431-9276, E-ISSN 1435-8115, Vol. 22, nr 5Artikel i tidskrift (Refereegranskat)
  • 12.
    Adolphson, Marcus
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö, Urbana och regionala studier.
    Fröidh, Oskar
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Transportplanering.
    Impact on urban form by the localization of railway stations: Evidence from Sweden2019Ingår i: Cities, ISSN 0264-2751, E-ISSN 1873-6084, Vol. 95, artikel-id 102362Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Since the 1990s a number of new railway stations have been established in Sweden on new or rerouted lines, while other stations have been reconstructed at their original locations. Some stations were located in urban surroundings, others in semi-urban or peripheral locations depending on the trade of between regional speed, and local urban circumstances. The urban form consequences depending on station localisation of these transport infrastructure investments are nonetheless unknown. In order to provide a basis for future planning, this research aims to provide knowledge on urban form consequences of relocating railway stations. 13 stations were selected in a case study. Changes in urban densities from 1993 to 2013 were analysed by a combination of kernel techniques and estimation of monocentric density models. Stations within an urban and semi-urban environments show strong agglomeration tendencies. Within peripheral environments, the urban development was unclear or even negative. In an urban environment, the location of the station still attracted more urban resources compared to the location of the urban density centre. These findings should be understood in the light of a market-oriented socio-economic context since 1990th influencing the planning system and the development of urban form.

  • 13.
    Ahmed, Abubeker Worake
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Mechanistic-Empirical Modelling of Flexible Pavement Performance: Verifications Using APT Measurements2014Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Mechanistic-Empirical  (M-E)  pavement  design  procedures  are  composed  of  a  reliable  response model to estimate the state of stress in the pavement and distress models in order to predict the different types of pavement distresses due to the prevailing traffic and environmental conditions. One of the main objectives of this study was to develop a response model based on multilayer elastic  theory   (MLET)  with  improved  computational  performance  by   optimizing  the   time consuming parts of the MLET processes. A comprehensive comparison of the developed program with  two  widely  used  programs  demonstrated  excellent  agreement  and  improved  computational performance.  Moreover,  the  program  was  extended  to  incorporate  the  viscoelastic  behaviour  of bituminous materials through elastic-viscoelastic correspondence principle. A procedure based on collocation of linear viscoelastic (LVE) solutions at selected key time durations was also proposed that improved the computational performance for LVE analysis of stationary and moving loads. A comparison  of  the  LVE  responses  with  measurements  from  accelerated  pavement  testing  (APT) revealed a good agreement. Furthermore the developed response model was employed to evaluate permanent deformation models  for  bound  and  unbound  granular  materials  (UGMs)  using  full  scale  APTs.  The  M-E Pavement  Design  Guide  (MEPDG)  model  for  UGMs  and  two  relatively  new  models  were evaluated  to  model  the  permanent  deformation  in  UGMs.  Moreover,  for  bound  materials,  the simplified  form  of  the  MEPDG  model  for  bituminous  bound  layers  was  also  evaluated.  The measured  and  predicted  permanent  deformations  were  in  general  in  good  agreement,  with  only small discrepancies between the models. Finally, as heavy traffic loading is one of the main factors affecting the performance of flexible pavement, three types of characterizations for heavy traffic axle load spectrum for M-E analysis and design of pavement structures were evaluated. The study recommended an improved approach that enhanced the accuracy and computational performance. 

  • 14.
    Ahmed, Lamis
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap.
    Impact-type vibration effects on young concrete for tunnelling2016Rapport (Övrigt vetenskapligt)
    Abstract [en]

    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.

    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. 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.

  • 15.
    Ahmed, Lamis
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Laboratorieprovningar av stötbelastade betongprismor vid tidig ålder2015Ingår i: Tidskriften Betong, ISSN 1101-9190, nr 5, s. 51-54Artikel i tidskrift (Övrigt vetenskapligt)
  • 16.
    Ahmed, Lamis
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Models for analysis of shotcrete on rock exposed to blasting2012Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Inom undermarks- och tunnelbyggande leder strävan efter en mer tidseffektiv byggprocess till fokus på möjligheten att reducera väntetiderna mellan byggetapper. Möjligheten att projicera sprutbetong på bergytor i ett tidigt skede efter sprängning är avgörande för säkerheten under konstruktionen av t.ex. en tunnel. En komplikation uppstår när behovet av ytterligare sprängning kan påverka härdningen av nysprutad betong. Om betong, gjuten eller sprutad, utsätts för vibrationer i ett tidigt skede under härdningsprocessen kan skador som hotar funktionen hos den hårdnade betongen uppstå. Kunskapen i ämnet är knapphändig, eller obefintlig, och det finns inga etablerade riktlinjer för praktisk användning.

    Slutsatsen från tidigare undersökningar visar att sprutbetong kan tåla höga vibrationer (partikelhastigheter) utan att allvarliga skador uppstår. Oarmerad sprutbetong kan vara oskadd efter att ha utsatts för så höga vibrationsnivåer som 0,5–1 m/s medan partier med förlorad vidhäftning till berget kan uppträda vid vibrationshastigheter högre än 1 m/s. Funktionen hos ung och hårdnande sprutbetong som utsätts för höga vibrationsnivåer undersöks här för att identifiera säkra avstånd och sprutbetongåldrar för undermarks- och tunnelbyggande, med hjälp av numeriska analyser och jämförelser med mätningar och observationer. Arbetet fokuserar på att finna samband mellan numeriska resultat, mätresultat och observationer från tunnelbyggande. Det slutliga resultatet kommer att vara riktlinjer för praktisk användning.

    Projektet omfattar utveckling av sofistikerade dynamiska finita elementmodeller för vilka insamlad information och data kommer att användas som indata för det finita elementprogrammet Abaqus. Modellerna utvärderades och förfinats genom jämförelser mellan beräknade och uppmätta resultat. Först jämfördes befintliga enkla mekaniska, ingenjörsmässiga modeller vilka utvärderades genom beräkningar och jämförelser med befintliga data. Den första modellen är en strukturdynamisk modell bestående av massor och fjäderelement. Den andra är en modell uppbyggd av finita balkelementet sammankopplade med fjädrar. Den tredje är en endimensionell elastisk spänningsvågsmodell. Spänningstillståndet i sprutbetongen närmast berget, utsatt för vinkelrätt inkommande P-vågor simulerades. Resultat från icke-förstörande laborationsprovningar användes också som testdata för modellerna. Experimentellt studerades P-vågsutbredning i en betongbalk med egenskaper likvärdiga med berg. Cementbruk med egenskaper liknande sprutbetong applicerades på balkens ena ände medan en hammare användes i den andra. Formen hos den genererade spänningsvågen som propagerade mot sprutbetongänden registrerades med accelerometrar utplacerade längs balken.

    På grund av bergets inhomogena karaktär kommer spänningsvågorna från sprängningen att dämpas ut på vägen från detonationspunkten till sprutbetongen på bergytan. Materialdämpningen hos bergmassan måste därför beaktas och kan uppskattas utifrån resultat från fältmätningar. Vibrationståligheten hos förstärkningssystem av sprutbetong och berg beror av materialegenskaperna hos sprutbetongen och i den här studien varierades de åldersberoende egenskaperna för att undersöka beteendet hos nysprutad och hårdnande sprutbetong utsatt för sprängbelastning. De numeriska simuleringarna kräver realistiska materialdata för sprutbetong och berg, som t.ex. densitet och elasticitetsmodul.

    De beräknade resultaten var i god överensstämmelse med observationer och mätningar i fält plats, och med de tidigare numeriska resultaten. Jämfört med de mekaniska modellerna kan ett sofistikerat finit elementprogram underlätta modellering av mer komplexa geometrier och också ge mer detaljerade resultat. Det visades att vågutbredning genom berg och fram emot sprutbetong kan beskrivas med tvådimensionella elastiska finita element i en dynamisk analys. Modellerna måste beskriva bergets egenskaper och noggrannheten i dessa parametrar kommer att ha stor inverkan på resultaten. Det kommer att vara möjligt att beskriva vågutbredningen genom bergmassan, från detonationspunkten till reflektionen vid bergytan, det vill säga gränssnittet mellan sprutbetong och berg. Det är acceptabelt att använda elastiska materialformuleringar tills materialet elasticitetsgräns överskrids tills töjningar utanför det elastiska området nås, vilket därmed indikerar materialbrott.

    Den högre komplexiteten hos den här typen av modell, jämfört med de mekaniska modellerna, kommer att göra det möjligt att analysera mer komplexa tunnelgeometrier. Exempel på preliminära rekommendationer för praktiskt bruk ges och det visas hur de utvecklade modellerna och den föreslagna analysmetodiken kan användas för att fastställa ytterligare detaljerade gränsvärden.

  • 17.
    Ahmed, Lamis
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Vulnerability of shotcrete on tunnel walls during construction blasting2018Konferensbidrag (Refereegranskat)
  • 18.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    A comparison of models for shotcrete in dynamically loaded rock tunnels2010Ingår i: Shotcrete: Elements of a system / [ed] E. Stefan Bernard, Taylor & Francis Group, 2010, s. 1-10Konferensbidrag (Refereegranskat)
    Abstract [en]

    During blasting in tunnels and mines, the shotcrete-rock interaction is influenced by propagating stress waves. Shotcrete support in hard rock tunnels is here studied through numerical analysis and comparisons with previous numerical results, measurements and observations in situ. The stress response in the shotcrete closest to the rock when exposed to P-waves striking perpendicularly to the shotcrete-rock interface is simulated. The first model tested is an elastic stress wave model, which is onedimensional with the shotcrete assumed linearly elastic. The second is a structural dynamic model that consists of masses and spring elements. The third model is a finite element model implemented using the Abaqus/Explicit program. Two methods are used for the application of incident disturbing stress waves: as boundary conditions and as inertia loads. Results from these three types of models are compared and evaluated as a first step before a future extension to more detailed analyses using 3D models.

  • 19.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Behaviour of sprayed concrete on hard rock exposed to vibration from blasting operations2014Konferensbidrag (Refereegranskat)
  • 20.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Direct shear strength of high-strength fibre concrete2010Ingår i: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 62, nr 5, s. 379-390Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An experimental and theoretical study of the shear behaviour of steel-fibre-reinforced concrete is presented. Twenty-seven direct shear push-off tests were carried out on high-strength concrete, with and without steel fibre reinforcement. The test series contained uncracked and precracked specimens for the study of the slipping response and the shear stress that can be transferred across an open crack. The test variables were the fibre content and the reinforcement ratio. The test results were compared with information provided by the available codes and other, previous results. The test results indicated that incorporation of steel fibres and bars in concrete members subjected to shear leads to an improved mechanical behaviour before failure. Based on the presented experimental results, an equation governing the direct shear strength is proposed and verified against test results from other test series.

  • 21.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Dynamic measurements for determination of Poisson’sratio of young concrete2017Konferensbidrag (Refereegranskat)
  • 22.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Experimental and numerical investigation of stress wave propagation in shotcrete2011Ingår i: Nordic concrete research: Research projects 2011 / [ed] D.H. Bager, 2011, s. 59-62Konferensbidrag (Refereegranskat)
  • 23.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Laboratory investigation of stress waves in young shotcrete on rock2012Ingår i: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 64, nr 10, s. 899-908Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To study the behaviour of shotcrete under dynamic load, a non-destructive laboratory experiment was set up with P-wave propagation along a concrete bar, with properties similar to rock. Cement-based mortar with properties that resemble shotcrete was applied to 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. Finite-element modelling was used to verify the test results, which showed that the laboratory model with an impacting hammer could be used to initiate the same type of stress waves that result from blasting in good-quality rock. Previously recommended maximum allowed peak particle vibration velocities were verified.

  • 24.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Structural dynamic and stress wave models for analysis of shotcrete on rock exposed to blasting2012Ingår i: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 35, nr 1, s. 11-17Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During blasting in tunnels and mines, the interaction between shotcrete (sprayed concrete) and rock is influenced by propagating stress waves. Shotcrete support in hard rock tunnels is studied here through numerical analysis using three different modelling approaches. The stress response in the shotcrete closest to the rock when exposed to P-waves striking perpendicularly to the shotcrete–rock interface is simulated. 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 element beam elements interconnected with springs. The third is a one-dimensional elastic stress wave model. The models give comparable results, although the definition of the dynamic loads is different. The analysis results can be used to estimate whether the shotcrete will fail or not for a prescribed distance to detonating explosives inside the rock.

  • 25.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Malm, Richard
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Ansell, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Finite element simulation of shotcrete exposed to underground explosions2012Ingår i: Nordic Concrete Research, ISSN 0800-6377, nr 45, s. 59-74Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An elastic finite element model is used tosimulate theinducedstress waves from blasting, propagating in rock towards shotcrete on a tunnel wall. Due to the inhomogeneous nature of the rock, the stress wavesattenuate onitsway from the point of explosiontowardsthe shotcrete on the rock surface. Material damping for the rock-mass is estimated from in-situ measurements. The vibration resistance of the shotcrete-rock support system depends on the material properties of the shotcrete. Age-dependent material properties are varied to investigate the behaviour of young shotcrete subjected to blast loading. Finally, finite element analysis results are presented and verified through comparison with other numerical models, measurements and observations.

  • 26.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Silfwerbrand, Johan
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap.
    Dynamic Measurements for Determining Poisson’s Ratio of Young Concrete2018Ingår i: Nordic Concrete Research, ISSN 0800-6377, nr 58, s. 95-105Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Knowledge of the elastic properties of concrete at early age is often a pre-requisite for numerical calculations. This paper discusses the use of a laboratory technique for determining Poisson’s ratio at early concrete age. A non-destructive test set-up using the impact resonance method has been tested and evaluated. With the method, it has been possible to obtain results already at 7 hours of concrete age. Poisson's ratio is found to decrease sharply during the first 24 hours to reach a value of 0.08 and then increase to approximately 0.15 after seven days.

  • 27.
    Ahmed, Lamis
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Sjölander, AndreasKTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.Ansell, AndersKTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Evaluation and analysis of laboratory tests of bolts-anchored, steel-fiber-reinforced shotcrete linings2017Proceedings (redaktörskap) (Refereegranskat)
  • 28. Akulich, A
    et al.
    Isacsson, Ulf
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Laboratorieundersökningar av åldringsegenskaper hos dränerande asfaltbetong1992Rapport (Övrigt vetenskapligt)
  • 29.
    Albrecht, Martin
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik, Miljöstrategisk analys (fms).
    Enabling socio-technical transitions – electric vehicles and high voltage electricity grids as focal points of low emission futures2017Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Today humankind is facing numerous sustainability challenges that require us to question CO2 intensive practices like those present in the transport and energy sector. To meet those challenges, many countries have adopted ambitious climate targets. Achieving such targets requires an understanding of the wider socio-technical context of transitions. The aim of this licentiate thesis is therefore to analyse such socio-technical transitions towards low-emission futures enabled by the electrification of passenger cars and high voltage grid development.

    A combination of different transitions theories (for ex. Multi-level perspective and Technological innovation systems) and institutional theory has been used. To reach the aim paper I analyses the climate impacts of electric vehicles (EVs) and policy measures to achieve a breakthrough scenario for EVs. The results show that a mixture of short and long term policies are needed that take into account the technology development stage and behavioural aspects of EV adopters. Paper II addresses the need to include the high voltage transmission grid and its planning procedures as a central part of debates on transitions. Therefore the opportunities, challenges and reasons for conflict in the established regime are studied. The results show that in order to achieve a sustainable grid development regime, it is necessary to spend time on achieving legitimacy and social sustainability. The third paper uses semi-structured expert interviews and focuses on innovation dynamics for EV adoption. By focusing on dynamics instead of single policy measures, it is possible to grasp interactions within a niche, but also in between a niche, regime and landscape. The results show that strong initial technology legitimacy was needed to start substantial innovation dynamics. This could be further strengthened with a strong and broad coalition of actors. Both those factors led, if present, to an improved variety and match of policy instruments.

    As such this thesis has shown that transitions are not just about technology or policy instruments as such but about the dynamics and processes needed to enable them. This can be relevant in other transitions that otherwise may underestimate the importance of these components.

  • 30.
    Albrecht, Martin
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik, Miljöstrategisk analys (fms).
    System innovation dynamics around electric vehicles. The cases of Norway, Denmark and Sweden.Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    This paper focuses on the comparison of electric car innovation patterns in Norway, Sweden and Denmark. Doing so, it takes a closer look at what the most essential dynamics in the systems were over time and what enabled those dynamics. The main research aim is to contribute to a wider understanding of why Norway is so much ahead of Sweden and Denmark in electric car adoption. The purpose is also to adopt a perspective that goes beyond a mere focus on economic policy instruments. In order to do so different theory elements are combined in a framework. These elements stem from the transition theory literature field, especially the technological innovation system (TIS) and the multi-level perspective (MLP). This combination allows analysing the development behind a dynamic, not just when it comes to an innovation itself but also with regards to the established regime. The data is gathered through analysis of existing documents and data as well as a series of 27 expert interviews conducted in the three case countries. The findings suggest that there are important differences in transition patterns that can account for the electric vehicle (EV) diffusion situation we can find nowadays in the three Nordic countries. An important stepping stone was the need for a very strong legitimacy of the original EV vision that is also anchored in a coordinated, sector overarching coalition of actors that thinks strategically and long term. Moreover some general beneficial dynamics could be identified across the countries in question. In Norway these beneficial dynamics can be summarised as a systems motor, in Denmark as a failed entrepreneurial motor that shifted towards a constrained municipal motor and in Sweden as a loosely, coordinated and weaker version of a systems motor.

  • 31.
    Aldenlov, Jens
    et al.
    Lulea Univ Technol, Dept Business Adm Technol & Social Sci, S-97187 Lulea, Sweden..
    Bergquist, Bjarne
    Lulea Univ Technol, Dept Business Adm Technol & Social Sci, S-97187 Lulea, Sweden..
    Eriksson, Per-Erik
    Lulea Univ Technol, Dept Business Adm Technol & Social Sci, S-97187 Lulea, Sweden..
    Soderholm, Peter
    Lulea Univ Technol, Dept Business Adm Technol & Social Sci, S-97187 Lulea, Sweden..
    Karrbom Gustavsson, Tina
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Fastigheter och byggande.
    Public procurement of railway infrastructure maintenance - a literature review2017Ingår i: PROCEEDINGS OF THE 9TH NORDIC CONFERENCE ON CONSTRUCTION ECONOMICS AND ORGANIZATION / [ed] Buser, M Lindahl, G Raisanen, C, POLYTEKNISK FORLAG , 2017, s. 10-21Konferensbidrag (Refereegranskat)
    Abstract [en]

    The maintenance of railway infrastructure has in several instances been changed from government-based to being based on public procurement, with varying degrees of flexibility for the contractor to design their maintenance work. The purpose of-giving contractors a larger freedom of choice of how to perform maintenance is to stimulate them to innovate and develop their maintenance processes. Since the contracts differ in between and there are changes in government policies over time that affects both existing and new contracts, a comparison between different contracts becomes challenging. A literature review has been conducted to understand the change in procurement strategy and how to encourage contractors to innovate. The research questions include: What procurement strategies are there? How is maintenance evaluated? How does procurement affect the innovation opportunities for entrepreneurs? The literature review focuses on railway maintenance and contract design between client and contractor. In total, 17 articles matched the search criteria and were selected for the review. To have successful maintenance service, five articles suggested partnering as a strategy with common goals in combination with good communication during the entirety of the contract. When selecting incentive plan, four articles mentions that a focus on performance-based incentives in combination with risk management is better rather than actual payment schemes. The reason being that payment is often the main cause of conflicts between client and contractor. The scientific literature suggests that improvement in incentives improves quality of maintenance, decreases delays and technical failures. The conclusion from the literature review is that partnering in railway maintenance is considered successful. With accurate knowledge about railway assets the incentive plan becomes accurate which reduces costs. The literature review is a part of a research project with an overall goal to develop a model to guide the selection of appropriate type of procurement strategy, contract and control of maintenance for a more sustainable railway system.

  • 32. Alemu, Belachew Yirsaw
    Expropriation, valuation and compensation practice in Ethiopia: The case of Bahir Dar city and surrounding2013Ingår i: Property Management, ISSN 0263-7472, E-ISSN 1758-731X, Vol. 31, nr 2, s. 132-158Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Purpose: The aim of this paper is to examine the expropriation, valuation and compensation practice. This paper tries to investigate how the expropriation and compensation laws are implemented when privately held land and attached real properties are taken for public purpose development in Bahir Dar city and surrounding. However, further research should be undertaken nation-wide to explore the problems throughout the country. Design/methodology/approach: The paper reports the findings of a survey of expropriatees from main practices throughout Bahir Dar city and its surroundings. Findings: There is a big gap between the actual practice of expropriation, valuation and compensation and the Laws. Lack of application of standardized methods and procedures created situations of unfair valuation and compensation. Practical implications: The practical implication is that the living status of affected people before and after expropriation could be useful. Originality/value: The value of the paper for government officials, real property valuers and investors is that transparency, consistency and fair compensation are useful.

  • 33.
    Amer, Wadi
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Soil Steel Composite Bridges: A comparison between the Pettersson-Sundquist design method and the Klöppel & Glock design method including finite element modelling2012Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 34.
    Amer, Wadi
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Lars, Pettersson
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Structural response of a high profile arch flexible culvert in sloping terrain using finite element modeling2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    Flexible culverts are generally considered cost-effective structures for their simplicity in construction and the short time involved in the erection process. This has constantly motivated practitioners to explore the different areas of application including their performance in sloping environment. Yet, the complex nature of the interaction between the soil and steel materials marks a challenge, where the performance of these structures is fundamentally influenced by the quality of the backfill soil and its configuration around the conduit/arch. Surface slopes may affect the structural response by inducing an asymmetrical soil support and an unbalanced earth loading.

    The use of numerical simulation is utilized to provide insights about the performance of flexible culvert in sloping environment, where a case study of a high profile arch is investigated under different construction schemes. The paper focuses mainly on predicting the structural behavior of soil loading effects. The study includes the influence of different slopes in combination with various depths of soil cover.

    The results enabled to realize the importance of soil configuration around the steel arch and its influence on the structural response. While the presence of surface slopes emphasizes the susceptibility of flexible culverts with low depths of soil cover, higher covers may help in reducing the effect of steep slopes. Sectional forces were found to increase with the increase of surface slopes. The study also highlighted recent research efforts on the topic and briefly discussed some design implications when building flexible culverts in sloping terrain.

  • 35.
    Andersson, Andreas
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Adaptive and semi-active vibration control of railway bridge dynamics2012Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Long Life Bridges is a Marie Curie 7th Framework Project funded under the Industry and Academia Partnerships and Pathways call, Grant Agreement No. 286276. The Project commenced in September 2011 and is continuing for 4 years until August 2015. The project vision is to extend the service lives of bridges through development of advanced assessment methods. The author wishes to acknowledge the financial contribution by the European Commission in supporting the project and funding this research.

    The work presented in this report has been conducted at Roughan & O’Donovan Innovative Solutions, Dublin, Ireland, during the period of January to December 2012, under supervision of Associate Professor Alan O’Connor. The author has been seconded from the Royal Institute of Technology (KTH), Division of Structural Engineering and Bridges.

    Within the project, experimental work to develop a prototype damper has been carried out at Trinity College Dublin (TCD), Department of Civil, Structural and Environmental Engineering. A special thank goes to Dr. Kevin Ryan and the laboratory staff at the Department for the help in manufacturing and testing the prototype damper.

    Full-scale testing has been performed on a railway bridge in Sweden. The tests were funded directly by the Swedish Transport Administration (Trafikverket). The instrumentation and field measurements were performed by KTH in collaboration with the author.

    The work presented, denoted secondment 1.1b, deals with development of adaptive and semi-active damping systems for railway bridges. The aim of the project is to develop methods for structural vibration control with applications for railway bridge dynamics. Much of the work has been related to a case study bridge.

    There is constant demand on rail authorities to increase both the allowable axle loads and the allowable speed on existing railway lines. As an example, the Swedish Transport Administration has recently investigated the possibility of upgrading part of the main lines to allow for future high-speed trains. Some lines are also being investigated with the aim of allowing ore transports with higher axle loads and longer trains. A large portion of the bridge stock was designed for significantly lower axle loads and only very few have been designed to account for dynamic effects. Increased dynamic effects may result in exceedance of dynamic design criteria, reduced service life due to fatigue, or even failure. Through better quantification of risk, it is often possible to prove that speeds can be increased with no adverse effect. However, for bridges where the level of risk is too high, a cost-effective means of reducing dynamic effects on bridges are active and semi-active control system. Semi-active control is well established in other fields and could prove to be a beneficial technique to allow train speeds to be increased.

    The concept of structural vibration control is to attenuate the dynamic response of a structure by means of an external damping device. Due to changes in either loading or structural behaviour, the properties of the damper device may need to be changed to efficiently mitigate vibrations. Two main principles of damper devices are commonly used; tuned mass dampers and shock absorbers. Tuned mass dampers consist of a suspended mass mounted on the main structure. Due to a phase-shift, the vibration of the suspended mass partly counteracts the corresponding motion of the main structure. Changing the stiffness of the suspended mass results in a variable adaptive tuned mass damper. Shock absorbers rely on producing the counteracting force by means of increased viscous damping. Devices with variable viscous damping are often categorised as semi-active. Fully active systems rely on producing the counteracting force by means of a load actuator. Adaptive and semi-active systems generally require much less energy to operate compared to fully active systems.

  • 36.
    Andersson, Andreas
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Dynamic analysis of simply supported slab bridges2019Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This report present results from simulations of simply supported concrete slab bridges for railway traffic. The geometry follows the Swedish standard deck models according to design drawing B2447-2 and B2447-8, with span lengths ranging from 2-8 m. For each bridge four different configurations are studied; straight or skewed bridge deck and short or long edge beams. In addition, a case of higher mass due to increased ballast depth is studied. In total 78 different bridge configurations are included.

    According to the numerical models the first natural frequency range from about 15-80 Hz depending on span length and configuration. In all simulations the first three modes of vibration are included. The limit criteria is a peak deck acceleration of 3.5 m/s2 when loaded by the HSLM-A train model. Including a speed safety factor 1.2 according to EN 1991-2 results in an allowable speed that range from 175-350 km/h depending on the bridge configuration. The allowable speed is somewhat higher for the skewed bridges compared to straight bridges. Increased mass results in lower acceleration but also lower resonance speed. An increase in ballast depth from 0.6 to 1.2 m generally results in lower allowable speed, except for the shortestbridges in the study.

    It should be noted that the above conclusions are based only on simulations. Before upgrading these bridges to speeds higher than 200 km/h experimental validation is recommended. On the other hand, most existing real trains are likely to result insignificantly lower dynamic response compared to the HSLM-A trains.

  • 37.
    Andersson, Andreas
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Impact loading on concrete slabs: Experimental tests and numerical simulations2014Rapport (Övrigt vetenskapligt)
    Abstract [en]

    In this report, the load capacity of concrete slabs subjected to concentrated loads is studied, considering both the static load capacity and the response due to impact of a falling mass. The purpose of the study is to gain more knowledge on the static and dynamic behaviour of the slabs and to use that knowledge in the assessment of the load capacity of inner lining systems in tunnels. The methodology involves experimental testing of a series of slabs, validation of numerical models and simulating the response of the inner lining system.

    A total of 18 slabs were manufactured, consisting of shotcrete and reinforcement mesh. Some of the slabs also included steel fibre reinforced concrete (SRFC). The size of the slabs were 1.75×1.75×0.12 m, suspended in four hangers #1.2 m and loaded centric on an area of 0.2×0.2 m. In addition, a series of core samples and beams were cut from two of the slabs for material testing and verification of numerical models.

    From the static load tests of the slabs, the load at cracking was obtained at 50 – 60 kN with a vertical midpoint displacement of 0.6 – 1.0 mm. The ultimate load ranged from 60 – 80 kN. The slabs showed significant ductility with a peak displacement of about 70 – 80 mm at post-failure. All slabs showed a two-way flexural failure. The concrete cover was in average 30 mm, measured from the compressive side, resulting in little difference between the crack load and the ultimate load. A vertical displacement of about 1 – 2 mm was required to obtain a crack width of 0.2 mm. Three slabs with only SRFC were tested until static failure, the ultimate load ranged from 85 – 90 kN but with less ductility compared to the slabs with rebar mesh.

    Impact load tests were performed using a steel mass of 600 kg. The free fall height was varied from 1 – 2 m. The peak impact load varied from 200 – 250 kN, without any clear correlation with the height. The corresponding impulse load varied from 4.0 – 5.5 kNs with a clear correlation to the height. All slabs subjected to impact load showed a one-way flexural failure, the residual strength after impact was sufficient to carry the static load of the steel weight. Several of the slabs showed significant fallout of concrete during impact, in one extreme case a total of 16 kg. Three slabs were tested with an outer layer of 30 mm of SRFC, none of these slabs showed any significant fallout.

    The static and dynamic response of the slabs have been simulated using nonlinear FE-models. The models generally show good agreement, both for static load, crack widths and response during impact. Similar models were used to simulate the response of the inner lining system. The results indicate a significant load capacity, both due to static and impact loading. The models are however not able to account for potential punching failure.

  • 38.
    Andersson, Andreas
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Load capacity assessment and strengthening of a railway arch bridge with backfill2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, a load capacity assessment and strengthening measures of a multi-span railway arch bridge with backfill are presented. The bridge is located in Stockholm, Sweden, and constitute a vital link for the national railway network. The bridge consists of 20 concrete arches with overlying backfill, each with a span of 20 m. After more than 80 years of service, severe deterioration of the concrete was found during conditional assessments. A load capacity assessment was performed and the theoretical ultimate load was found to be highly dependent on the development of soil pressures along the arch barrel. The demands from the railway authority are to increase the allowable axle load from 22,5 to 25 tonnes and extend the service life by 50 years. Due to the uncertainties in structural behaviour and progressing degradation, extensive strengthening measures for the arch barrels were decided. To allow for full traffic at all times, the strengthening was performed in stages, to minimize any temporary reduction in load capacity due to removal of existing material. The strengthening was designed using non-linear finite element analysis and each stage of strengthening has been verified using in-situ field measurements.

  • 39.
    Andersson, Andreas
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Simplified approach to dynamic analysis of railway bridges for high-speed trains2018Rapport (Övrigt vetenskapligt)
    Abstract [en]

    In this report the analysis of 278 existing railway bridges is presented. The aim is to investigate how many of these bridges that potentially can be upgraded to higher speeds, with a target of 250 km/h. Due to the vast amount of bridges and the limited resources, the analyses are performed using simplified 2D models. The analysis is afflicted with several uncertainties, both regarding input parameters as well as model uncertainties. The results should therefore be interpreted carefully and primarily serve as an indicator for which bridges that may or may not meet the requirements. Large uncertainties are especially expected for portal frame bridges due to its inherently large interaction with the surrounding embankment and 3D behaviour.

    The results from the analysis show that a total of 22 bridges theoretically fail to meet the dynamic requirements. A combination of refined analysis and experimental validation is recommended to better assess the dynamic response for these bridges. Among the most critical cases are several steel-concrete composite bridges, that due to a combination of low mass and low natural frequency may be prone to resonant loading. Retrofitting with external dampers may for some bridges be a viable solution.

  • 40.
    Andersson, Andreas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Arvidsson, Therese
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Train-Track-Bridge Interaction for non-ballasted Railway Bridges on High-Speed Lines2017Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This report contains a comprehensive parametric study on the coupled dynamic train–track–bridge interaction (TTBI) system for non-ballasted railway bridges. The existing design limits in Eurocode EN 1990 A2 regarding vertical deck acceleration and vertical deck displacement is compared with the wheel–rail forces and car body acceleration from simulations.

    The simulations are based on a 2D TTBI model with linear Hertzian contact that allows for loss of contact. The model has been verified against both other numerical simulations as well as experiments, all with good agreement. The parametric study consists of a large number of theoretical bridges, all optimized to reach the limit of either vertical deck acceleration or vertical deck displacement. The study comprises both single- and double track bridges.

    The track irregularities are found to be of paramount importance. Two different levels are therefore studied; “higher track quality” corresponding to a well-maintained track for high-speed railways and “lower track quality” corresponding to the Alert Limit in EN 13848-5. The final conclusions are based on the “lower track quality” in order not to underestimate the risk of running safety and passenger comfort. Simulations with the bridge excluded show that the additional contribution from the bridge is low, especially for the lower track quality.

    The existing limit for vertical deck acceleration is set to 5 m/s2 in EN 1990 A2 and is based on a very simple assumption of the gravity acceleration reduced by a factor 2. The results in this report show that this likely is a too conservative measure of the running safety. Based on the wheel–rail forces from the simulations, the resulting wheel unloading factor and duration of contact loss does not reach critical values before the deck acceleration is beyond 30 m/s2.

    In EN 1990 A2, a vertical car body acceleration of 1 m/s2 is stipulated as “very good level of comfort” and is indirectly limited by the vertical deck displacement. Good agreement is generally found in the simulations between deck displacement and expected car body acceleration. In the simulations, the limit for car body acceleration is always exceeded before the running safety is compromised.

  • 41.
    Andersson, Andreas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Arvidsson, Therese
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Train-Track-Bridge Interaction for non-ballasted Railway Bridges on High-Speed Lines2018Ingår i: Railways 2018, 2018Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    This paper presents the result from a parametric study of the dynamic response of railway bridges during train passage. A 2D coupled train-track-bridge interaction (TTBI) model is used to calculate the response from both the bridge and the vehicle.

    To assure traffic safety and riding comfort, Eurocode EN 1990/A2 gives a set of design limits for railway bridges on high-speed lines. The vertical bridge deck acceleration and displacement are often of main interest. For bridges with non-ballasted tracks the vertical deck acceleration is limited to 5 m/s2, simply obtained as the gravity divided by a safety factor 2, under the assumption that loss of wheel-rail contact will occur at 1g. The vertical bridge deck displacement is an implicit measure to assure riding comfort, based on a limited set of simulations carried out in the 1980ies and 1990ies.

    The main aim of this paper is to study the relation between the vertical bridge deck acceleration and the risk of derailment as well as the relation between the vertical deck displacement to the riding comfort. The risk of derailment is estimated both as a wheel-unloading factor based on the filtered wheel-rail contact forces or as the duration of contact loss based on the unfiltered wheel-rail contact forces.

    A large set of theoretical bridges are studied, all optimised to reach the design limits according to EN 1990/A2 for either vertical bridge deck acceleration or displacement. The results show that there is no risk of derailment until the deck acceleration exceeds 30 m/s2. Based on the present parametric study, it appears that the current limit for vertical deck acceleration of non-ballasted railway bridges is very conservative but that the limits for vertical deck displacement is in the correct order of magnitude. It is further concluded that the magnitude of rail irregularities is of great importance, often causing larger dynamic response in the vehicle than due to the vibration of the bridge.

  • 42.
    Andersson, Andreas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Christoffer, Svedholm
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Dynamisk kontroll av järnvägsbroar, inverkan av 3D-effekter2016Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    I föreliggande rapport redovisas dynamiska analyser av järnvägsbroar för höghastighetståg. En jämförelse i dynamisk respons mellan 2D- och 3D-modeller har utförts för ett mindre urval av plattbroar, balkbroar och lådbroar. Varje tvärsnitt har först optimerats att precis klara de dynamiska kraven avseende 2D-dynamik, utan beaktande av den statiska dimensioneringen. I många fall skulle tvärsnitten troligen behöva ökas för att klara den statiska bärförmågan.

    Plattbroar med spännvidder från 10 – 25 m och 1 – 4 fack har analyserats. I flertalet fall, främst vid kortare spännvidder, är egenfrekvensen för böjning lägre i 3D-modellen jämfört med 2D-modellen. Detta beror på mindre medverkande tvärsnitt i böjning i 3D (shear-lag). Detta resulterar i en lägre resonanshastighet och därmed ofta en större dynamisk respons för samma hastighetsintervall. I övrigt överensstämmer det dynamiska verkningssättet väl mellan 2D och 3D. Inverkan av vridning synes inte vara styrande för de studerade fallen.

    På motsvarande sätt har balkbroar med spännvidder från 20 – 40 m och 1 – 4 fack analyserats. På samma sätt som för plattbroar ger balkbroar lägre böjfrekvens i 3D jämfört med 2D. För dubbelspårsbroar är skillnaden i respons mellan 2D och 3D liknande som för plattbroar. För enkelspåriga balkbroar visar 3D-modellen i några fall en avsevärt lägre respons utan utpräglade resonanstoppar inom samma hastighets­intervall som 2D-modellen. Orsaken tros vara en kombination av upplagens excentricitet och brons massa, vilket vid vertikal böjning bidrar till en horisontell masströghet. Detta visas i de flesta fall kunna beskrivas med en modifierad 2D-modell.

    Lådbroar med spännvidd 40 – 70 m i 1 – 3 fack har analyserats. P.g.a. hög vridstyvhet är egenfrekvensen för vridning mycket högre än första böjmoden och p.g.a. mindre shear-lag är egenfrekvensen för böjning likvärdig i 2D och 3D. Detta ger små skillnader i dynamisk respons mellan 2D och 3D-modellerna.

    I de fall dynamiska kontroller utförs med förenklade metoder enligt (Svedholm & Andersson, 2016) föreslås att följande beaktas:

    • Första böjfrekvensen n0 bör beakta inverkan av shear-lag och upplagens excentricitet baserat på en 3D-modell, vilket används som indata i design­diagrammen.

    • Då första vridmoden nT < 1.2n0 bör en fullständig dynamisk kontroll utföras i 3D.

    • I de fall en 3D-modell visar flera närliggande egenmoder för böjning med samma form bör en fullständig dynamisk kontroll utföras i 3D.

  • 43.
    Andersson, Andreas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Karoumi, Raid
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG. KTH, Tidigare Institutioner (före 2005), Byggkonstruktion.
    A soil-steel bridge under high-speed railways2017Ingår i: Archives of Institute of Civil Engineering / [ed] Arkadiusz Madaj, Iwona Jankowiak, Poznan, 2017, Vol. 23, s. 45-52Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents some recent research on railway bridge dynamics with application to buried flexible structures. Based on a combination of simulations and full-scale testing, current research indicates that a rather comprehensive numerical model is required to accurately describe the response from passing trains.

  • 44.
    Andersson, Andreas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Karoumi, Raid
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Attenuating resonant behavior of a tied arch railway bridge using increased hanger damping2012Ingår i: Bridge Maintenance, Safety, Management, Resilience and Sustainability - Proceedings of the Sixth International Conference on Bridge Maintenance, Safety and Management, Taylor & Francis Group, 2012, s. 2572-2577Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, dynamic analyses and field measurements of a tied arch railway bridge is presented. Excessive vibrations of the hangers were obtained, caused by resonance during train passages. The resulting increase of the stress level and number of stress cycles were shown to decrease the fatigue service life significantly. The most critical section is a threaded turnbuckle connection of the hangers. Due to low damping of the hangers, more than 50 % of the cumulative fatigue damage was related to free vibrations after train passage. Passive dampers were installed to attenuate the vibrations by means of increased damping. A combination of field measurements and numerical models are used to investigate the behavior of the bridge and the impact of increased hanger damping.

  • 45.
    Andersson, Andreas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Karoumi, Raid
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Dynamics of railway bridges, analysis and verification by field tests2015Ingår i: EVACES'15, 6th International Conference On Experimental Vibration Analysis For Civil Engineering Structures / [ed] Glauco Feltrin, EDP Sciences, 2015, Vol. 24Konferensbidrag (Refereegranskat)
    Abstract [en]

    The following paper discusses different aspects of railway bridge dynamics, comprising analysis, modelling procedures and experimental testing. The importance of realistic models is discussed, especially regarding boundary conditions, load distribution and soil-structure interaction. Two theoretical case studies are presented, involving both deterministic and probabilistic assessment of a large number of railway bridges using simplified and computationally efficient models. A total of four experimental case studies are also introduced, illustrating different aspects and phenomena in bridge dynamics. The excitation consists of both ambient vibrations, train induced vibrations, free vibrations after train passages and controlled forced excitation.

  • 46.
    Andersson, Andreas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Karoumi, Raid
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    O'Connor, Alan
    Trinity College Dublin.
    Development of a multi-passive tuned mass damper, theory and experiments2014Ingår i: Proceedings of the 9th International Conference on Structural Dynamics, EURODYN 2014, Porto, 2014, s. 1551-1556Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, a bi-directional multi-passive tuned mass damper is presented. The applicationfor the damper is on vertical hangers of an existing steel arch railway bridge.The hangers have been found susceptible to resonance and the resulting stressesresults in a reduced service life due to fatigue. Due to different boundaryconditions, the natural frequencies of the hangers are different in thelongitudinal and the transverse direction. In addition, the natural frequenciesincrease during train passage, due to increased tensile force in the hangers. Aprototype of the damper has been developed, consisting of two suspended massescoupled in series. Different lateral suspensions are used to obtain differentnatural frequencies in the longitudinal and the transverse direction. One massis tuned to the conditions of the fully loaded bridge and the other mass to theunloaded bridge. The performance of the damper is verified using controlledloading under laboratory conditions and the results are compared with a finiteelement model. The damper is shown to perform as expected and the motion of thetwo masses is near uncoupled. Finally, the performance of the damper isverified by in-situ testing on the case study bridge.

  • 47.
    Andersson, Andreas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Karoumi, Raid
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    O'Connor, Alan
    External damping of stay cables using adaptive and semi-active vibration control2013Ingår i: Proceedings of the 8th International Cable Supported Bridge Operators Conference, Edinburgh, Scotland, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, the performances of different external damping systems for stay cables are studied based on numerical simulations. Two types of dampers have been analysed; a near anchorage viscous damper and a tuned mass damper (TMD) mounted near the midspan of the stay cable. For the passive case, both dampers are tuned to the fundamental mode of vibration of the cable. The optimal viscous damping for the near anchorage damper is determined based on well-known equations for a taut string. For the TMD, parametrical studies have been performed to determine the optimal damping ratio as function of the damper mass. The resulting vibration mitigation from the two systems are also studied for higher modes of vibration and the potential increase in performance using an adaptive or semi-active vibration control system is studied.

  • 48.
    Andersson, Andreas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Karoumi, Raid
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    O'Connor, Alan
    Semi-active damping systems for railway bridges2012Ingår i: / [ed] Colin Caprani, Alan O'Connor, Dublin, 2012, s. 177-182Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, a semi-active control system for vibration mitigation of railway bridges is presented. The real time frequency response is estimated using a short-time Fourier transform, employing curve fitting to relevant peaks for increased accuracy. A control algorithm developed in Matlab® is linked to a commercial FE-software, facilitating application on arbitrary structures. A numerical study of an existing tied arch railway bridge is presented. From earlier field measurements and numerical analysis, resonance of several hangers during train passage was observed. This was shown to significantly reduce the fatigue service life of the hangers and for the most critical section about 50% of the cumulative damage was related to free vibrations. A system of passive dampers was later installed and the increase in resulting damping was measured. Within the present study, the previous results are reanalysed and compared with a semi-active approach. The natural frequencies of the hangers vary as a result of the variation in axial force. A semi-active control system has the potential to improve the vibration response of the structure when compared to the installed passive system.

  • 49.
    Andersson, Andreas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Karoumi, Raid
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    O'Connor, Alan
    Vibration mitigation of railway bridges using adaptive damping control2013Ingår i: Assessment, Upgrading and Refurbishment of Infrastructures, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, the advantage of an adaptive damping system is presented. A damper with variable stiffness is tuned based on estimates of the real-time frequency response, facilitating optimal vibration mitigation. The performance of the developed routines is investigated on an existing tied arch railway bridge. Based on previous field measurements, resonant behaviour of several hangers was found. In combination with low structural damping, the induced stresses resulted in a reduced fatigue service life. Passive dampers are currently installed on the longer hangers, each tuned to the fundamental natural frequency of the individual hanger. However, increased axial force during train passage results in a significant variation in natural frequency, with an apparent risk of detuning the passive dampers. The predicted performance of an adaptive damping system to account for this variation in dynamic behaviour is presented and its potential application is discussed.

  • 50.
    Andersson, Andreas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Leander, John
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Karoumi, Raid
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Extending the fatigue service life of a railway bridge by local approaches2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, fatigue assessment of a steel railway bridge is presented. The bridge is located in central Stockholm, Sweden, and is one of the most vital links for the railway network. The bridge services both freight trains and commuter trains with more than 500 passages per day. The main load bearing structure is designed as a steel grillage of welded I-beams. Fatigue critical sections have been identified at locations where secondary bracing systems are welded to the flanges of the I-beams. Both numerical simulations and extensive field measurements have shown a significant exceedance of the theoretical fatigue service life. Based on analysis of local stress concentrations, improvement of fatigue critical details have been suggested. The decrease in stress concentration is demonstrated both by numerical simulations and in-situ field measurements and shows a significant improvement when estimating the remaining fatigue service life.

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