Högre byggnader i KL-trä kräver ett ökat fokus på dynamiska egenskaperså att brukaren inte upplever obehag vid hög vindlast. Utvärderingarhar gjorts på tre byggnader där resultaten stämmer in påbefintlig forskning: akustikisolering placerad under väggar i KL-träreducerar den horisontella skjuvstyvheten och kan leda till signifikantaminskningar av egenfrekvenserna. Effekten bör beaktas vid framtagningav förutsättningar för dimensionering av höga trähus.

There is a growing interest in timber buildings in Sweden and increased availability of Glulam (GLT) andparticularly Cross Laminated Timber (CLT) products. Timber buildings, though, often have difficulties in fulfilling theperformance requirements of a building project. The use of concrete elements in addition to timber elements in the load-bearing structure is a widespread solution, introducing timber-concrete hybrid buildings. The study presents responsesfrom interviews regarding ten different timber-concrete hybrid building projects in Sweden with a load-bearing structureabove the foundation level in both timber and concrete. Four main types of timber-concrete hybrids were found: a CLTstructure on top of a concrete structure, a post-beam system in GLT with CLT slabs and concrete walls, a post-beamsystem in GLT with concrete hollow core slabs, and a timber structure with some slabs in concrete. The results show thattimber-concrete hybrid buildings are flexible and suitable for various construction types. The reasons for using concretein timber construction were primarily to increase self-weight, obtain longer span lengths, and overcome shear wallcapacity issues. There is still a lack of competence in the design of structural timber projects, and at most, five differentstructural designers were involved in the load-bearing design of a single building. This highlights issues regarding projectmanagement of the design process within timber-concrete hybrid buildings

 This paper describes the in-situ ambient vibration tests of a lightweight timber frame building, performed in order to obtain its modal properties. Our case study is a six-story lightweight timber frame building in Varberg, Sweden. Five battery-driven wireless data acquisition units with a total of 14 uni-axial accelerometers were used to perform the in-situ measurements. Accelerations along the two horizontal directions were recorded with a duration of approximately 40 minutes. Two different only-output frequency and time domain Operational Modal Analysis (OMA) methods were used to evaluate the dynamic properties of the building. The modal parameters obtained from the in-situ measurements, such as natural frequencies and mode shapes, were compared with the parameters obtained from the Finite Element (FE) model of the structure. To perform a detailed numerical analysis of the light-frame timber building, all lateral-load resisting system components were modelled. The FE model was calibrated in function of the results obtained from the OMA of the building. Based on the obtained results from the calibrated FE model, it was possible to conclude that the non-structural elements have an influence on the global dynamic response of the building.

Wood is widely used in the construction sector and gaining increased market share. It isinteracting with the surrounding so that its mechanical and geometrical properties (stiffness,strength, swelling, density, …) change with temperature and humidity levels. In a full-scalebuilding, the eigenfrequencies are hence also varying with the climate. In the current paper,results from a preliminary experimental study are presented. A beam made from cross-laminated timber was hanging freely supported inside a climate chamber. Enforced vibrationsfrom a controlled shaker were taken to obtain the eigenfrequencies. With decreasing moisturecontent, the first and third eigenfrequencies were increasing (bending modes) while the secondeigenfrequency was decreasing (torsional mode). A finite element study allowed for checkingwhich parameters is influencing to which degree so that individual changes can be combined.

The dynamic action of footbridge users in different forms of activity (especially during walking andrunning) may cause an excessive vibration of the footbridge deck and may disturb the comfort of use of the structure. Thedynamic susceptibility of the footbridges varies depending on the construction material used to build the footbridge andthe typical construction solutions (construction details) resulting from the construction material used. The paper presentsthe basic dynamic characteristics of timber footbridges of various structural solutions, collected during dynamic field testsof these structures. The obtained results indicate relatively high dynamic resistance of timber footbridges to the dynamicloads generated by users under normal conditions of use. In addition, the results show that in the case of timberfootbridges, it is possible to consider changing the requirements of international standards defining the range of naturalfrequencies sensitive to the dynamic impact of users. In the case of timber footbridges, characterized by a relatively highself-weight (compared to steel footbridges), high stiffness and high damping, it is possible to consider changing therequirements for performing forced vibration analyses only for structures with fundamental vertical vibration frequency f_v <= 3.0 Hz instead of the currently defined f_v <= 5.0 Hz.

Timber-concrete hybrid buildings are an innovative solution to increase the amount of timber materials used in modern buildings. This study presents a dynamic evaluation of a nine-story timber-concrete hybrid residential building during construction. The building consists of a seven-story structure in cross-laminated timber (CLT) on top of two stories in concrete. Ambient vibration tests were conducted seven times during the 13-month construction period, including tests with only the structural elements in place and tests of the finished building with the façade, non-structural walls, and other internal finishing. The results show a clear decrease in the natural frequencies of the building as the building gets higher and more elements are installed. However, a slight increase in the natural frequency was observed following the installation of the non-structural walls in the final construction stage. A corresponding finite element analysis is presented for each test, providing additional insights into the parameters typically used in the structural design process. The study demonstrates the importance of properly selecting reduction factors for CLT elements in a dynamic finite element analysis. It also shows the importance of considering non-structural walls, both regarding weight and stiffness, even in buildings where the number of non-structural walls is relatively small compared to structural walls.

Wood used outdoors is often surface treated with a paint to protect the wood from moisture anddeterioration. If coated with a dark colour, the albedo value is lowered. A lower surface albedo generates greater amountsof energy absorption and makes the surface, and subsequently the wood, warmer and dryer. This study was carried out to increase knowledge of how different coating colours impact the temperature of the underlaying wood, and the effect this has on the moisture content (MC). The study was performed by exposing panels of Norway spruce [Picea abies (L.) H.Karst.] painted with three different colours (white, red, and black) to natural sunlight over a month during summer. Each panel fitted with a dry-bulb humidity sensor inside. The results showed a greater variation in calculated equilibrium moisture content (EMC) in the darker panels, since the temperature reached higher levels than the white panels when exposed to sunlight. The maximum recorded temperature was around 50 °C for the dark panels while the maximum forwhite was around 40 °C. Furthermore, it was shown that the temperature inside the panel reaches its maximum around the same time as the outside air, while the maximum values for EMC were recorded approximately 8-9 hours apart between the panels and the outside air.

Korslimmat trä (KL-trä) tillverkas av brädor som limmas ihop korsvis i flera skikt. Skivorna som erhållsanvänds som byggelement, mestadels för väggar och bjälklagselement. Utgångsmaterialet trä tarstår i jämvikt med det omgivande klimatet och kommer därför ändra fuktkvoten. I studien undersöktesen skiva av KL-trä under varierande fuktförhållanden i en klimatkammare hos Linnéuniversitetet.Egenfrekvenser samt fuktkvoten följdes upp och sambandet med klimatet studerades. Det visade sigatt första och tredje uppmätta egenfrekvensen (böjning) visade negativ korrelation med omgivandefukten, den gick upp när fukten minskades (och tvärtom). För andra egenfrekvensen (torsion)däremot visade sig ett mer komplicerat samband. Ett flertal möjliga orsaker presenteras som förklaring. Medverkande organisationer var Linnéuniversitetet som huvudpart samt SödraSkogsägarna och Saab som bidragit som stödfunktionen och bollplank.

Ambient vibrations of a six-story lightweight timber frame building were measured under different environmental conditions in order to obtain the modal parameters of the structure. Changes in temperature and relative humidi-ty in timber can influence its response in terms of modal parameters. Namely, a moisture content change in the timber can affect stiffness, strength, and shape of the elements as well as the properties of the connections. Monthly measure-ments have been performed on a six-story lightweight timber frame building in Varberg, Sweden, built in 2021. The in-situ tests were performed using five bat-tery-driven data acquisition units with 14 uni-axial accelerometers. Additional-ly, the building is permanently monitored using temperature and humidity sen-sors, starting ever since its construction phase. The ambient vibration data have been analyzed using two different only-output methods. The results obtained under different temperature and humidity conditions were compared in order to assess the effect of the environmental conditions in the building. This infor-mation can be used to ensure the building meets safety and performance re-quirements, as well as to identify potential issues that may need to be addressed during building design.