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Analysis of underground concrete pipelines subjected to seismic high-frequency loads
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Buried pipelines are tubular structures that are used for transportation of important liquid materials and gas in order to provide safety for human life. During an earthquake, imposed loads from soil deformations on concrete pipelines may cause severe damages, possibly causing disturbance in vital systems, such as cooling of nuclear power facilities. The high level of safety has caused a demand for reliable seismic analyses, also for structures built in the regions that have not traditionally been considered as highly seismically active. The focus in this study is on areas with seismic and geological conditions corresponding to those in Sweden and Northern Europe. Earthquakes in Sweden for regions with hard rock dominated by high-frequency ground vibrations, Propagation of such high-frequency waves through the rock mass and soil medium affect underground structures such as pipelines.

The aim of this project is investigating parameters that affect response of buried pipelines due to high-frequency seismic excitations. The main focus of the study is on reinforced concrete pipelines. Steel pipelines are also studied for comparison purposes. The effects of water mass, burial depth, soil layer thickness and non-uniform ground thickness caused by inclined bedrock are studied. The results are compared to those obtained for low-frequency earthquakes and the relationship between strong ground motion parameters and pipelines response is investigated. It is shown that, especially for high frequency earthquake excitations, non-uniform ground thickness due to inclined bedrock significantly increase stresses in the pipelines. For the conditions studied, it is clear that high-frequency seismic excitation is less likely to cause damage to buried concrete pipelines. However, the main conclusion is that seismic analysis is motivated also for pipelines in high-frequency earthquake areas since local variation in the ground conditions can have a significant effect on the safety.

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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , 70 p.
Series
TRITA-BKN. Bulletin, ISSN 1103-4270 ; 138
Keyword [en]
Earthquake, High-frequency, Underground, Pipelines, Reinforced concrete, Inclined bedrock
Keyword [sv]
Jordbävning, Högfrekvent, Underjordisk, Rörledningar (pipelines), Armerad betong, Lutande berggrund
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering
Identifiers
URN: urn:nbn:se:kth:diva-194076ISBN: 978-91-7729-168-8 (print)OAI: oai:DiVA.org:kth-194076DiVA: diva2:1037283
Presentation
2016-11-15, B24, Brinellvägen 23, KTH Byggvetenskap, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20161014

Available from: 2016-10-14 Created: 2016-10-14 Last updated: 2016-10-17Bibliographically approved
List of papers
1. Analysis of shallowly buried reinforced concrete pipelines subjected to earthquake loads
Open this publication in new window or tab >>Analysis of shallowly buried reinforced concrete pipelines subjected to earthquake loads
2014 (English)In: Nordic Concrete Research, ISSN 0800-6377, no 51, 111-130 p.Article in journal (Refereed) Published
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.

National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-159224 (URN)
Note

QC 20150128

Available from: 2015-01-26 Created: 2015-01-26 Last updated: 2017-12-05Bibliographically approved
2. Analysis of buried reinforced concrete pipelines subjected to seismic waves
Open this publication in new window or tab >>Analysis of buried reinforced concrete pipelines subjected to seismic waves
2014 (English)Conference paper, Published paper (Refereed)
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-182571 (URN)
Conference
XXII Symposium on Nordic Concrete Research & Development, Reykjavik, 2014
Note

QC 20160226

Available from: 2016-02-19 Created: 2016-02-19 Last updated: 2016-12-05Bibliographically approved
3. Seismic response of buried concrete pipelines subjected to highfrequency earthquakes
Open this publication in new window or tab >>Seismic response of buried concrete pipelines subjected to highfrequency earthquakes
(English)In: Geotechnical and Geological Engineering, ISSN 0960-3182, E-ISSN 1573-1529Article in journal (Refereed) Submitted
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.

Keyword
Buried pipelines, high frequency, finite element, seismic analysis, irregular ground, soil
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-194062 (URN)
Note

QC 20161014

Available from: 2016-10-14 Created: 2016-10-14 Last updated: 2017-11-29Bibliographically approved

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