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Investigation of cracking due to restraint forces in Swedish concrete slab frame bridges

Almen, Robin LU (2016) In TVBK-5252 VBK920 20161
Division of Structural Engingeering
Abstract
When concrete slab frame bridges are designed with modern linear 3D FE-models large tensile
restraint forces will arise in the transversal direction of the bridge from the temperature and shrinkage loads. These restraint forces are much larger than those that are accounted for in the older 2D models. This leads to that the amount of transversal reinforcement, calculated in the 3D FE-calculations, is much higher then what has been standard earlier. This thesis investigated whether or not cracking due to restraint forces is a problem for existing Swedish concrete frame bridges. This was done through modelling existing bridges with 3D FEM. Two different reinforcement models were applied and the calculated amount of reinforcement was compared... (More)
When concrete slab frame bridges are designed with modern linear 3D FE-models large tensile
restraint forces will arise in the transversal direction of the bridge from the temperature and shrinkage loads. These restraint forces are much larger than those that are accounted for in the older 2D models. This leads to that the amount of transversal reinforcement, calculated in the 3D FE-calculations, is much higher then what has been standard earlier. This thesis investigated whether or not cracking due to restraint forces is a problem for existing Swedish concrete frame bridges. This was done through modelling existing bridges with 3D FEM. Two different reinforcement models were applied and the calculated amount of reinforcement was compared to the existing reinforcement. Furthermore different types of concrete slab frame bridges were inspected. The different types were bridges with open or
closed bottom plate, bridges where the valve was skewed or not and bridges that either crossed a
pedestrian/bike path or a car road. Finally the bridges were investigated ocularly to help decide if restraint cracking is a real problem or a problem for the 3D FEM. The results of this investigation showed that cracking was common for bridges that crossed pedestrian/bike paths; however, the crack width was usually within the design limits. Furthermore the results of the comparisons between the two reinforcement models showed that there was a large difference depending on how the restraint forces are accounted for. The standard Eurocode method, where no special regards are taken to the
restraint forces, could give an overestimation up to 2000%. The other method, where special regard is taken to the restraint forces, only gave an overestimation up to a maximum of 100%. (Less)
Popular Abstract (Swedish)
När betongplattrambroar modelleras med moderna linjära 3D FE-modeller kommer stora dragkrafter
att uppstå i brons tvärriktning från temperatur- och krympningslasterna. Dessa tvångskrafter är då
mycket större än vad som har beaktats i de äldre 2D modellerna. Detta leder till att den tvärgående
armeringsmängden, som beräknas i 3D-modellerna, är mycket större än vad som har varit norm innan.
Denna avhandling har undersökt huruvida sprickbildning på grund av tvångskrafter är ett problem för befintliga svenska plattrambroar. Detta har gjorts genom att modellera befintliga broar med FEM med olika modeller för att bestämma armeringsbehovet. Därefter har de uträknade armeringsbehoven
jämförts med den befintliga inlagda armeringen. Vidare har... (More)
När betongplattrambroar modelleras med moderna linjära 3D FE-modeller kommer stora dragkrafter
att uppstå i brons tvärriktning från temperatur- och krympningslasterna. Dessa tvångskrafter är då
mycket större än vad som har beaktats i de äldre 2D modellerna. Detta leder till att den tvärgående
armeringsmängden, som beräknas i 3D-modellerna, är mycket större än vad som har varit norm innan.
Denna avhandling har undersökt huruvida sprickbildning på grund av tvångskrafter är ett problem för befintliga svenska plattrambroar. Detta har gjorts genom att modellera befintliga broar med FEM med olika modeller för att bestämma armeringsbehovet. Därefter har de uträknade armeringsbehoven
jämförts med den befintliga inlagda armeringen. Vidare har olika typer av plattrambroar inspekterats. De olika typerna var broar med antingen öppen eller sluten bottenplatta, broar där valvet antingen var skevt eller rak och broar som antingen korsade en gång- och cykelväg eller en bilväg. Slutligen
undersöktes broarna okulärt för att avgöra om sprickbildning orsakat av tvångskrafter är ett verkligt problem eller ett problem för 3D FEM. Resultaten av denna undersökning visade att sprickbildning
var vanligt för broar som korsade gång- och cykelvägar. Sprickvidderna var däremot vanligtvis inom de tillåtna gränsvärdena. Dessutom visade jämförelserna mellan de två armeringsmodeller att det blev en stor skillnad beroende på hur tvångskrafterna behandlas. Standard Eurokod metoden, där ingen
särskild hänsyn tas till de tvångskrafterna, kan ge en överskattning upp till 2000 %. Den andra
metoden, där särskild hänsyn tas till tvångskrafterna, gav endast en överskattning upp till max 100 %. (Less)
Please use this url to cite or link to this publication:
author
Almen, Robin LU
supervisor
organization
alternative title
Utredning om sprickor orsakade av tvångskrafter i svenska betongplattrambroar
course
VBK920 20161
year
type
H3 - Professional qualifications (4 Years - )
subject
keywords
slab frame bridges, concrete cracking, crack control, restraint, restraint forces, finite element
publication/series
TVBK-5252
report number
TVBK-5252
ISSN
0349-4969
language
English
additional info
Examinator: Roberto Crocetti
id
8886185
date added to LUP
2016-07-01 09:18:16
date last changed
2016-07-01 09:18:16
@misc{8886185,
  abstract     = {When concrete slab frame bridges are designed with modern linear 3D FE-models large tensile
restraint forces will arise in the transversal direction of the bridge from the temperature and shrinkage loads. These restraint forces are much larger than those that are accounted for in the older 2D models. This leads to that the amount of transversal reinforcement, calculated in the 3D FE-calculations, is much higher then what has been standard earlier. This thesis investigated whether or not cracking due to restraint forces is a problem for existing Swedish concrete frame bridges. This was done through modelling existing bridges with 3D FEM. Two different reinforcement models were applied and the calculated amount of reinforcement was compared to the existing reinforcement. Furthermore different types of concrete slab frame bridges were inspected. The different types were bridges with open or
closed bottom plate, bridges where the valve was skewed or not and bridges that either crossed a
pedestrian/bike path or a car road. Finally the bridges were investigated ocularly to help decide if restraint cracking is a real problem or a problem for the 3D FEM. The results of this investigation showed that cracking was common for bridges that crossed pedestrian/bike paths; however, the crack width was usually within the design limits. Furthermore the results of the comparisons between the two reinforcement models showed that there was a large difference depending on how the restraint forces are accounted for. The standard Eurocode method, where no special regards are taken to the
restraint forces, could give an overestimation up to 2000%. The other method, where special regard is taken to the restraint forces, only gave an overestimation up to a maximum of 100%.},
  author       = {Almen, Robin},
  issn         = {0349-4969},
  keyword      = {slab frame bridges,concrete cracking,crack control,restraint,restraint forces,finite element},
  language     = {eng},
  note         = {Student Paper},
  series       = {TVBK-5252},
  title        = {Investigation of cracking due to restraint forces in Swedish concrete slab frame bridges},
  year         = {2016},
}