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Kalibrering av lambda-metoden för dimensionering av stål- och samverkansbroar i Sverige - en förstudie
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.ORCID iD: 0000-0002-2833-4585
2017 (Swedish)Report (Other academic)
Abstract [sv]

Kontroll av utmattning vid dimensionering av nya broar för vägtrafik görs idag enligt Eurokoden med utmattningslastmodell 3 (ULM 3) och med s.k. skadeekvivalensfaktorer (lambda-faktorer). Denna beräkningsmodell har dock ifrågasatts både i Sverige och internationellt då den visats ge skillnader i resulatet i jämförelse med beräkningsmodeller i tidigare föreskrifter.

I föreliggande rapport föreslås en metod för kalibrering av beräkningsmodellen mot gällande krav avseende säkerhet. Metoden bygger på sannolikhetsbaserade analyser och trafiklaster bestämda utifrån BWIM-mätningar (Bridge-Weigh-In-Motion). Den sannolikhetsbaserade metoden möjliggör en validering mot en acceptabel brottsannolikhet eller det tillhörande säkerhetsindexet.

Beräkningar har utförts för nio olika brotyper och sju olika trafikmängder. Den sannolikhetsbaserade metoden har använts för att uppskatta vilket säkerhetsindex Eurokodens beräkningsmodell leder till. Resultatet visar på stor spridning med ett lägsta värde av β = 0,86 och ett högsta värde av β = 4,75. Det i sig visar på behovet av en kalibrering. Spridningen orsakas dels av skillnader mellan olika trafikkategorier, och dels av skillnader mellan olika spännvidder.

En framtida kalibrering bör inriktas mot definitionen av det totala antalet lastbilar per år i det långsamma körfältet, Nobs, och spännviddsfaktorn λ1.

Abstract [en]

In design of new bridges for road traffic, the fatigue verification should comply with the Eurocode using the fatigue load model 3 (FLM 3) together with damage equivalent factors (lambda factors). This model has, however, been questioned in Sweden and internationally, since it has shown a different result in comparison to previous assessment methods.

In this report, a method for calibration of the Eurocode model against governing safety demands is proposed. The method builds upon reliability analysis and traffic loads determined from BWIM measurements (Bridge-Weigh-In-Motion). The reliability based method enables an assessment against an acceptable probability of failure or the associated reliability index.

Calculations have been performed for nine different bridge types and seven different traffic volumes. The reliability based method has been used to estimate what reliability index the Eurocode assessment model gives. The result shows a large scatter with the lowest value of β = 0,86 and the highest value of β = 4,75. This shows in itself a need of a calibration. The scatter is caused partly by differences between traffic categories, and partly by differences between span lengths.

A future calibration should initially be focused on the number of heavy vehicles observed or estimated per year and per slow lane, Nobs, and the critical length factor λ1.

Place, publisher, year, edition, pages
Stockholm, 2017. , p. 61
Keyword [en]
Fatigue, Steel bridges, Reliability, Calibration, Eurocode
Keyword [sv]
Utmattning, Stålbroar, Tillförlitlighet, Kalibrering, Eurokoden
National Category
Civil Engineering
Research subject
Civil and Architectural Engineering
Identifiers
URN: urn:nbn:se:kth:diva-219448OAI: oai:DiVA.org:kth-219448DiVA, id: diva2:1163174
Note

QC 20180109

Available from: 2017-12-06 Created: 2017-12-06 Last updated: 2018-01-09Bibliographically approved

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