Modellering av temperaturbelastade plattrambroar - utvärdering av tvångslaster och armeringsbehov
(2026) In TVSM-5000 VSMM01 20261Structural Mechanics
Department of Construction Sciences
- Abstract
- Portal frame bridges are common in Sweden and are continuously subjected to temperature variations. These variations give rise to restraint forces when the structure is prevented from moving freely during thermal expansion or contraction. Previous studies indicate that the amount of reinforcement in portal frame bridges has increased substantially over the past 50 years, which can partly be attributed to stricter requirements for three-dimensional modelling as well as changes in design standards. At the same time, clear guidelines are lacking in both the Eurocodes and the Swedish Transport Administration regarding how temperature actions should be modelled and which temperature distributions ought to be considered in three-dimensional... (More)
- Portal frame bridges are common in Sweden and are continuously subjected to temperature variations. These variations give rise to restraint forces when the structure is prevented from moving freely during thermal expansion or contraction. Previous studies indicate that the amount of reinforcement in portal frame bridges has increased substantially over the past 50 years, which can partly be attributed to stricter requirements for three-dimensional modelling as well as changes in design standards. At the same time, clear guidelines are lacking in both the Eurocodes and the Swedish Transport Administration regarding how temperature actions should be modelled and which temperature distributions ought to be considered in three-dimensional analyses.
This study aims to analyse how temperature actions influence the reinforcement demand in portal frame bridges and to examine the effects of different temperature load cases, creep, and boundary conditions.
The investigation was carried out using finite element analysis, where geometric dimensions and material properties were implemented in a model of a reference bridge located in Falkenberg. The portal frame bridge was modelled in BRIGADE Plus with load cases both including and excluding temperature actions. Minimum reinforcement and reinforcement required for crack-width control were subsequently calculated based on the results extracted from the deck slab.
A comparison between reinforcement demand with and without temperature actions indicates that the additional reinforcement required due to thermal effects is significantly larger in the transverse direction than in the longitudinal direction. For the studied reference case, the minimum reinforcement calculated in the serviceability limit state also results in a greater transverse reinforcement demand than that obtained in the ultimate limit state. Revised guidelines regarding minimum reinforcement may therefore be perceived as one of the reasons behind the increased amount of reinforcement placed in modern bridges, particularly when this reinforcement is governed by pure tension. Minimum reinforcement under pure tension implies that, in some cases, no crack-width calculation is required for the existing bridge.
To reduce the reinforcement demand, especially in cases where temperature differences between bridge components are governing, a temperature difference of 10 °C between the deck slab and the frame legs, instead of 15 °C, can lead to a noticeable reduction. At a temperature difference of 5 °C, this reduction becomes even more pronounced. (Less) - Abstract (Swedish)
- Plattrambroar är vanligt förekommande i Sverige och utsätts kontinuerligt för temperaturvariationer. Dessa variationer ger upphov till tvångslaster när konstruktionen hindras från att röra sig fritt vid termisk expansion eller kontraktion. Tidigare studier indikerar att armeringsmängden i plattrambroar har ökat betydligt under de senaste 50 åren, vilket bland annat kan kopplas till ökade krav på tredimensionell modellering samt ändringar av dimensioneringsnormer. Samtidigt saknas tydliga riktlinjer i Eurokoderna och Trafikverket för hur temperaturlaster ska modelleras och vilka temperaturfördelningar som bör beaktas vid tredimensionell analys.
Detta arbete syftar till att analysera hur temperaturlaster påverkar armeringsbehovet i... (More) - Plattrambroar är vanligt förekommande i Sverige och utsätts kontinuerligt för temperaturvariationer. Dessa variationer ger upphov till tvångslaster när konstruktionen hindras från att röra sig fritt vid termisk expansion eller kontraktion. Tidigare studier indikerar att armeringsmängden i plattrambroar har ökat betydligt under de senaste 50 åren, vilket bland annat kan kopplas till ökade krav på tredimensionell modellering samt ändringar av dimensioneringsnormer. Samtidigt saknas tydliga riktlinjer i Eurokoderna och Trafikverket för hur temperaturlaster ska modelleras och vilka temperaturfördelningar som bör beaktas vid tredimensionell analys.
Detta arbete syftar till att analysera hur temperaturlaster påverkar armeringsbehovet i plattrambroar och att undersöka inverkan av olika temperaturfall, krypning samt randvillkor.
Studien har genomförts med hjälp av finita elementberäkningar, där geometriska dimensioner och materialegenskaper har implementerats i en modell av en referensbro belägen i Falkenberg. Plattrambron modellerades i BRIGADE Plus med lastfall både inklusive och exklusive temperaturlaster. Därefter har minimiarmering och armering för sprickviddskrav beräknats baserat på de resultat som extraherats från plattan.
Vid jämförelse mellan armeringsbehov med och utan temperatur indikerar resultatet att tillskottet i armeringsbehov på grund av temperaturlast är betydligt större i tvärgående riktning än i längsgående. För det studerade referensfallet medför även den minimiarmering som beräknats i bruksgränstillståndet ett större armeringsbehov i tvärriktning än det som erhålls vid dimensionering i brottgränstillståndet. Förändrade riktlinjer avseende minimiarmeringen kan därför uppfattas som en av orsakerna till den ökade mängden armering som placeras i dagens broar, särskilt när denna beräknas med avseende på ren dragning. Minimiarmering vid ren dragning innebär i vissa fall att ingen sprickviddsberäkning behövs för den befintliga bron.
För att minska armeringsbehovet, särskilt i de fall där temperaturskillnader mellan broelement är dimensionerande, kan en temperaturskillnad mellan platta och ramben på 10 °C, istället för 15 °C, bidra till en tydlig minskning. Vid en temperaturskillnad på 5 °C blir denna minskning ännu tydligare. (Less) - Popular Abstract (Swedish)
- Det finns indikationer på att armeringsmängderna i plattrambroar har ökat under de senaste 50 åren.
Ökningen kopplas bland annat till krav på tredimensionell modellering och förändrade normkrav.
Detta gör det nödvändigt att analysera utvecklingen och identifiera metoder som kan reducera armeringsmängden.
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/student-papers/record/9249569
- author
- Shaheen, Diana LU
- supervisor
- organization
- course
- VSMM01 20261
- year
- 2026
- type
- H3 - Professional qualifications (4 Years - )
- subject
- keywords
- Minimiarmering, plattrambro, sprickviddskontroll, temperaturlaster, temperaturskillnad
- publication/series
- TVSM-5000
- report number
- TVSM 5283
- ISSN
- 0281-6679
- language
- Swedish
- id
- 9249569
- alternative location
- https://www.byggmek.lth.se/english/publications/tvsm-5000-present-2014/
- date added to LUP
- 2026-08-31 14:58:31
- date last changed
- 2026-09-03 13:17:23
@misc{9249569,
abstract = {{Portal frame bridges are common in Sweden and are continuously subjected to temperature variations. These variations give rise to restraint forces when the structure is prevented from moving freely during thermal expansion or contraction. Previous studies indicate that the amount of reinforcement in portal frame bridges has increased substantially over the past 50 years, which can partly be attributed to stricter requirements for three-dimensional modelling as well as changes in design standards. At the same time, clear guidelines are lacking in both the Eurocodes and the Swedish Transport Administration regarding how temperature actions should be modelled and which temperature distributions ought to be considered in three-dimensional analyses.
This study aims to analyse how temperature actions influence the reinforcement demand in portal frame bridges and to examine the effects of different temperature load cases, creep, and boundary conditions.
The investigation was carried out using finite element analysis, where geometric dimensions and material properties were implemented in a model of a reference bridge located in Falkenberg. The portal frame bridge was modelled in BRIGADE Plus with load cases both including and excluding temperature actions. Minimum reinforcement and reinforcement required for crack-width control were subsequently calculated based on the results extracted from the deck slab.
A comparison between reinforcement demand with and without temperature actions indicates that the additional reinforcement required due to thermal effects is significantly larger in the transverse direction than in the longitudinal direction. For the studied reference case, the minimum reinforcement calculated in the serviceability limit state also results in a greater transverse reinforcement demand than that obtained in the ultimate limit state. Revised guidelines regarding minimum reinforcement may therefore be perceived as one of the reasons behind the increased amount of reinforcement placed in modern bridges, particularly when this reinforcement is governed by pure tension. Minimum reinforcement under pure tension implies that, in some cases, no crack-width calculation is required for the existing bridge.
To reduce the reinforcement demand, especially in cases where temperature differences between bridge components are governing, a temperature difference of 10 °C between the deck slab and the frame legs, instead of 15 °C, can lead to a noticeable reduction. At a temperature difference of 5 °C, this reduction becomes even more pronounced.}},
author = {{Shaheen, Diana}},
issn = {{0281-6679}},
language = {{swe}},
note = {{Student Paper}},
series = {{TVSM-5000}},
title = {{Modellering av temperaturbelastade plattrambroar - utvärdering av tvångslaster och armeringsbehov}},
year = {{2026}},
}