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.

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.

Multi-story residential and commercial timber buildings are an efficient solution for sustainable cities. Numerous projects have been and are expected to be realized in Sweden. In-situ wind-induced ambient vibrations tests have been conducted on a six-story light-weight timber-frame building in Varberg (Sweden). The load-bearing structure is composed of outer walls and some interior walls. For horizontal stabilization, the walls are supported by a bracings system realized with steel rods. To perform the in-situ measurements, multiple battery-driven data acquisition units, with uni-axial accelerometers have been used. Repeated measurements at different positions have been performed to be able to collect data at each floor and along both directions (longitudinal and transversal). Two different Operational Modal Analysis (OMA) methods have been used to evaluate the modal parameters: frequency, damping and mode shapes. The in-situ dynamics properties have been compared with the dynamic properties obtained from the Finite Element (FE) model of the structure.

Growing interest in the preservation of architectural heritage has revealed a need for tools that are capable to reliably analyze masonry structures. For decades, finite element modeling approach has been commonly used in engineering society to simulate these structures under different conditions; but most of the time, the responses obtained from experiments differ from those of simulations due to the complexity in inherent physical aspects such as material properties, boundary conditions, mass and/or stiffness uncertainties. From this perspective, model updating techniques have the potential to overcome these inaccuracies and become essential tools in developing verified finite element models compatible with experiments. In this paper, sensitivity-based finite element model updating studies of the courtyard walls of the historical Isabey Mosque located in Selcuk/Izmir are presented. Dynamic characteristics of the structure are estimated from two sets of ambient vibration measurements by the EFDD operational modal analysis technique. The initial numerical model of the courtyard walls is constituted by macro modeling strategy. In order to obtain a much better correlation with in situ tests, the uncertain parameters such as mass density, Young's modulus, and boundary conditions of the initial numerical model are updated. Thus, a reliable finite element model that is more representative than the initial one is obtained to be used in future numerical assessment studies. In the presented paper, it is highlighted that the boundary conditions are often the most uncertain parts of a structural system, so they should be included in the updating process for realistic updating results.

This paper presents modal parameter estimation work on a steel railway bridge at three different temperature conditions using ambient vibration test data. The bridge was built at the end of the 19th century using the available technology of its time. It is composed of six spans, each 30 m long, with a total length of 180 m. It is slightly curved in the horizontal plane with a radius of 300 m, and has a vertical grade of 2.5%. Modal parameters of the bridge were estimated using two different output-only system identification methods. The identified results obtained under different temperature conditions were compared in assessing the effects of temperature variation in the identification results. A comparative study in assessing method-to-method and test-to-test variability was also conducted. A three-dimensional finite-element model of the bridge was developed. In order to match the experimentally obtained modal parameters with the numerical ones, a trial-and-error–based model updating study was conducted. This way, a benchmark model of the 199+325 steel railway bridge was obtained for future capacity assessment, prediction, and sensitivity-based model updating work.

Sciarapotamo Bridge, located in Reggio Calabria Province, Italy, has been recently retrofitted by replacing its deteriorated concrete bridge deck with a composite steelconcrete deck, and isolating the new deck with eight high damping rubber, and four multidirectional sliding bearings. Full-scale ambient and forced vibration dynamic commissioning tests were performed on the bridge just before the bridge has become operational. Three different output-only system identification methods with ambient vibration measurements were used for modal parameter identification, namely: (1) multiple reference natural excitation technique in conjunction with eigen-system realization algorithm, (2) enhanced frequency domain decomposition, and (3) data driven stochastic subspace identification methods. Modal parameter estimation results using different output-only identification methods were presented and compared within the paper. In addition, relatively higher level forced vibration test data was used for estimating frequency response functions, identifying isolated natural frequencies, and damping ratios of the retrofitted bridge in as-built condition. Estimated damping coefficients under different excitation levels are of great value, showing the total damping in the system at low level ambient and relatively higher level forced vibration tests. Experimentally obtained modal parameters of the bridge set the undamaged benchmark state of the bridge for future potential condition assessment studies.

This study presents a comprehensive investigation of the dynamic behavior of a six-story lightweight timber frame building through periodic and continuous ambient vibration tests. Seasonal changes in temperature and relative humidity can influence the dynamic response of timber buildings, by affecting stiffness, strength, and connection properties due to changes in moisture content. Systematic tests were performed from October 2022 until May 2024 to identify natural frequencies, damping ratios, and mode shapes of the building using five battery-driven data acquisition units equipped with 15 uni-axialaccelerometers. Two different only-output frequency and time domain Operational Modal Analysis (OMA) methods were used to evaluate the dynamic properties of the building. Additionally, the building has been continuously monitored with temperature and humidity sensors since its construction. Results obtained from the periodic measurements highlighted the need for a permanent system to capture the transient changes in the modal parameters. A complementary permanent system to record the accelerations at the roof level was installed in May 2024. The modal parameters from in situ measurements were compared with those obtained from the Finite Element (FE) model of the structure. The FE model, calibrated through a multi-stage approach, incorporating non-structural elements, and varying imposed loads, showed good agreement with experimental data. Comparative analysis of the results obtained under different temperature and humidity conditions showed the effect of the environmental conditions on the building dynamics properties, for both periodic and permanent measurements. This study highlights the importance of continuous monitoring and detailed FE modeling in understanding the dynamic properties and long-term structural behavior under varying conditions. This information can be used to ensure that the building meets safety and performance requirements and to identify potential issues that may need to be addressed during the design and maintenance phases.