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Long-term analysis of the environmental effects on the global dynamic properties of a hybrid timber-concrete building
Linnaeus University, Faculty of Technology, Department of Building Technology.ORCID iD: 0000-0002-1234-7461
Linnaeus University, Faculty of Technology, Department of Building Technology.ORCID iD: 0000-0003-0530-9552
Skanska Sverige AB, Sweden.
Linnaeus University, Faculty of Technology, Department of Building Technology.ORCID iD: 0000-0002-1181-8479
2022 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 268, article id 114726Article in journal (Refereed) Published
Sustainable development
SDG 11: Make cities and human settlements inclusive, safe, resilient, and sustainable, SDG 9: Build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation, SDG 12: Ensure sustainable consumption and production patterns
Abstract [en]

With the increased availability of timber materials, such as cross-laminated timber, the number of buildings using timber as a structural material has been rapidly increasing. As these buildings are new to the market, limited data and research on their long-term structural modal performance are available. This is particularly important in timber buildings since the material properties of wood are highly affected by environmental factors, especially the moisture content. Over time, the evolution of the dynamic properties is essential for damage indication in structural health monitoring systems since natural changes can mask the influence of damage. This work presents three years of observations from a structural monitoring system collecting data ever since completing a four-story timber-concrete hybrid building in Sweden. Ambient vibrations of the building were measured using geophones, resulting in 3,100 datasets. The temperature and relative humidity were measured both externally using a weather station and internally using sensors embedded in several walls and a slab in the building. The observed natural frequencies of the building vary with +/- 0.2 Hz around the mean value over time. Linear regression analysis shows a significant correlation between the moisture content of a cross-laminated timber slab and the natural frequencies (coefficient of determination R2 up to 0.84). A predictive model for the natural frequencies is presented, taking seasonal variations and a dry-out of the structure into account. Variations from the expected values are +/- 0.1 Hz at most. The model clearly narrows the error margins for damage indication in a structural health monitoring system.

Place, publisher, year, edition, pages
Elsevier, 2022. Vol. 268, article id 114726
Keywords [en]
Structural health monitoring, Ambient vibration monitoring, Environmental monitoring, Timber-concrete hybrid building
National Category
Civil Engineering
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
URN: urn:nbn:se:lnu:diva-116512DOI: 10.1016/j.engstruct.2022.114726ISI: 000852741900001Scopus ID: 2-s2.0-85135387546OAI: oai:DiVA.org:lnu-116512DiVA, id: diva2:1698375
Funder
Svenska Byggbranschens Utvecklingsfond (SBUF), 13721Knowledge Foundation, 20190026Available from: 2022-09-23 Created: 2022-09-23 Last updated: 2023-03-02Bibliographically approved
In thesis
1. Timber-concrete hybrid structural systems: Examples, long and short-term dynamic monitoring, and numerical analysis
Open this publication in new window or tab >>Timber-concrete hybrid structural systems: Examples, long and short-term dynamic monitoring, and numerical analysis
2023 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Timber-concrete hybrid buildings are an innovative solution to increase the amount of timber materials in modern buildings. Due to its lower impact on the environment than materials like steel and concrete, the demand for timber products is rising as the construction industry aims to decrease its environmental footprint.Timber is naturally grown, and certain characteristics must be considered when used in buildings, such as strength and stiffness properties depending on variables like fiber direction and moisture content. In addition, timber is a lightweight material, which influences dynamic performance of timber elements and structures.To fulfill the requirements of a modern building, timber elements are sometimes combined with concrete elements, introducing timber-concrete hybrid buildings.This study aims to expand the use of timber-concrete hybrid buildings within the construction industry. The objective is to present different types of timber-concrete hybrid buildings and evaluate their structural performance to improve the level of knowledge for structural designers for the safe and robust design of such buildings. Typically, four different types of timber-concrete hybrid structures are found in building projects in Sweden. These types of building projects usually involve additional designers than regular projects due to a lack of knowledge in timber design. Additionally, different designers uses different statical models for their designs, even within the same building project. A mobile measurement system was developed to perform in-situ dynamic measurements. The system was used in a nine-story timber-concrete hybrid building during construction to investigate the dynamic properties and validate structural design models. A parameter study highlights different design parameters that have a large influence on these models. These parameters include the inplane shear stiffness of CLT wall elements, the foundation properties, as well as non-load-bearing internal walls. In addition, the long-term dynamic response of a four-story office timber concretehybrid building is presented. Over a three-years evaluation period, the results show a clear seasonal variation of the natural frequencies which correlates well with the moisture content within a CLT slab element. The results show that environmental effects are to be considered when comparing with finite  . A predictive model is presented that can be implemented in a structural health monitoring system for damage detection so that these environmental effect scan be filtered out.

Abstract [sv]

Hybridkonstruktioner i trä och betong är en innovativ lösning för att öka andelen trämaterial som används i dagens byggnader. På grund av träets fördelaktiga klimategenskaper i jämförelse mot traditionella byggmaterial som t.ex. stål och betong, har både utbudet av träprodukter och efterfrågan på dessa ökat. Då trä är en naturlig råvara, finns det vissa egenskaper som måste beaktas när det används för byggproduktion. Som exempel påverkas styvhet och hållfasthet av variabler som fiberriktning och fuktkvot. Dessutom är trä ett material med förhållandevis låg densitet, som påverkar den dynamiska prestandan i byggnader som använder bärande träelement. För att möta de krav som ställs på dagens byggnader, kombineras i flera fall bärande element i trä med bärande element i betong. Denna typ av byggnad kallas hybridkonstruktioner i trä och betong. Arbetet syftar på att öka andelen hybridkonstruktioner inom byggsektorn. Målet med denna studie är att utvärdera hur den här typen av byggnader beter sig för att kunna ge konstruktörer ökad kunskap om säker och robust dimensionering. Det här arbetet presenterar fyra olika typer av hybridkonstruktioner i trä och betong som används i Sverige. I den här typen av projekt används fler konstruktörer än i traditionella byggnadsprojekt, detta då kompetensen inom träkonstruktion är bristfällig hos de traditionella konstruktörerna. Dessutom använder konstruktörer olika antaganden och statiska modeller för sina beräkningar, även om de gäller samma byggnad. Ett mobilt mätsystem har utvecklats för att kunna genomföra dynamiska mätningar på plats. Under byggtiden av ett 9-vånings flerbostadshus har det mobila mätsystemet använts för att fånga in dess dynamiska egenskaper och för att validera beräkningsmodeller. En jämförande studie visade vilka parametrar som i hög grad påverkar resultaten i dessa modeller. De avgörande parametrarna var främst skjuvstyvheten i KL-träväggarna, grundläggningen, samt icke-bärande innerväggar. Långtidsmätningar av de dynamiska egenskaperna hos en 4-vånings kontorsbyggnad presenteras. Dessa resultat visar på en tydlig säsongsvariation i egenfrekvenserna hos byggnaden som korrelerar väl med den uppmätta fuktkvoten inuti ett KL-träbjälklag över mätperioden på tre år. Resultaten visar tydligt på att det omgivande klimatet bör beaktas vid jämförandestudier med en finita elementmodell. Utöver detta presenteras en modell som predikterar egenskaperna för implementering i ett system för tillståndsövervakning för skadedetektering så att den naturliga variationen kan filtreras bort.

Place, publisher, year, edition, pages
Linnaeus University Press, 2023. p. 39
Series
Lnu Licentiate ; 42
Keywords
Timber-Concrete Hybrid Structures, Timber Design, Structural Dynamics, Structural Health Monitoring
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-119630 (URN)10.15626/LnuLic.42.2023 (DOI)9789189709973 (ISBN)9789189709980 (ISBN)
Presentation
2023-03-10, Södra salen, M1083, Växjö, 10:00 (Swedish)
Opponent
Supervisors
Available from: 2023-03-03 Created: 2023-03-02 Last updated: 2023-03-03Bibliographically approved

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Larsson, CarlAbdeljaber, OsamaBolmsvik, ÅsaDorn, Michael

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