Within the project Dyna-TTB, vibrational tests have been conducted on eight high-rise timber buildings, in Europe. A main objective of the project is to gain knowledge about damping in timber buildings to assist in predicting the accelerations, at the top of a building, due to wind-induced vibrations. One of the buildings is Eken (the oak) in Mariestad in Sweden. That building is seven stories tall, thus questionable as a tall timber building, yet an interesting test object. The building structure is made up of glue laminated timber beams and columns stabilized with glulam trusses. Forced vibration were conducted on Eken with the aim to estimate the building’s dynamic properties from test data. Estimates of the eigenfrequencies, mode shapes, and their scalings are useful both in the calculations of wind-induced vibrations and to calibrate numerical models. However, the most important outcome is estimates of the modal damping values. The damping impacts the acceleration and thus the serviceability of the building, and at the same time, it is very hard to model damping. So, during the design phase, one must rely on previous test data (of which very few exist for taller timber buildings) and rule of thumbs. It is therefore important to gain knowledge about the damping for timber buildings in order to enable good designs of future and taller timber buildings.

A modular wooden wind turbine tower has been developed by the Swedish company Modvion AB, where the prefabricated modular elements are connected by glued timber-timber edge joints and by hybrid timber joints with bonded-in perforated steel plates. The application of wood-based products in such a demanding application and highperformance structure is challenging and a variety of questions had to be solved to ensure a reliable performance. The fatigue performance of the adhesive bonded connections has been evaluated in a research project and is presented in this paper. Test specimens of the fatigue resistance of the adhesive and the bond line has been developed. Different stress ratios with alternating loads and high numbers of load cycles have been tested. The results of the tests are presented in this paper.

Forced vibration tests have been conducted on the seven-storey timber building Eken in Mariestad in Sweden. The main objective is to estimate the building’s dynamic properties from test data. The eigenfrequencies, mode shapes and their scaling are useful to calibrate numerical models. However, the most important outcomes are the estimates of the modal damping values. The reason is that the damping impacts the acceleration, and thus the serviceability of the building, and at the same time, it is very hard to model damping. So, during the design phase, one must rely on previous test data (of which very few exist for taller timber buildings) or rule of thumbs. It is therefore important to gain knowledge about the damping for timber buildings in order to enable good designs of future and taller timber buildings. The test data shows that the modal damping is roughly equal to 2% of the critical viscous ones for the eigenmodes extracted. The test campaign on Eken is made as a part of the project Dyna-TTB in which vibrational tests have been performed on eight high-rise timber buildings, in Europe, of which Eken is one.

Modvion develops modular wind turbine towers made of wood. The application requires strong and stiff connections and to achieve the desired performance, a hybrid connection with perforated steel plates slotted into LVL modules is used. The parts will be glued together on site, using a polyurethane adhesive (PUR), providing high strength and stiffness to the connection. This paper presents a preliminary screening on how temperature and relative humidity of the surrounding air during assembly and curing will influence the strength of the bond glued on-site. Static tests were performed on the hybrid connections which were glued and cured in different climates. Tests were also performed at different hardening times to evaluate strength growth in the studied climates. The test results show that at cold temperatures of 9 °C to 12 °C there is a breakpoint where the rate of strength growth starts to decline. The experiments show also that the relative humidity may influence the final strength of the bond. However, the low number of tested specimens brings uncertainties to this observation. High temperatures up to 27 ºC and dry climates down to 20% RH did not impact the strength of the tested hybrid connections.

Wind-induced dynamic excitation is a governing design action determining size and shape of modern Tall Timber Buildings (TTBs). The wind actions generate dynamic loading, causing discomfort or annoyance for occupants due to the perceived horizontal sway, i.e. a vibration serviceability problem. The DynaTTB project, funded by the ForestValue research program, mixed on-site measurements on timber buildings, for identification of the structural system, with numerical modelling of timber structures. The goal was to identify and quantify the causes of vibration energy dissipation in modern TTBs and provide key elements to finite element models. This paper presents an overview of the project.    The paper also presents measurements using forced vibration conducted on the seven-storey timber building Eken in Mariestad in Sweden. The main objective is to estimate the building’s dynamic properties from test data. The eigenfrequencies, mode shapes and their scalings are useful to calibrate numerical models. However, the most important outcomes are the estimates of the modal damping values. The test data shows that the modal damping is roughly equal to 2% of the critical viscous ones for the eigenmodes extracted.

The rise of wood buildings in the skylines of cities forces structural dynamic and timber experts to team up to solve one of the new civil-engineering challenges, namely comfort at the higher levels, in light weight buildings, with respect to wind-induced vibrations. Large laminated timber structures with mechanical joints are exposed to turbulent horizontal excitation with most of the wind energy blowing around the lowest resonance frequencies of 50 to 150 m tall buildings. Good knowledge of the spatial distribution of mass, stiffness and damping is needed to predict and mitigate the sway in lighter, flexible buildings. This paper presents vibration tests and reductions of a detailed FE-model of a truss with dowel-type connections leading to models that will be useful for structural engineers. The models also enable further investigations about the parameters of the slotted-in steel plates and dowels connections governing the dynamical response of timber trusses. © 2022 The Author(s)

The height and the market share of multi-story timber buildings are both rising. During the last two decades, the Architectural and Engineering Construction industry has developed new reliable solutions to provide strength, structural integrity, fire safety and robustness for timber structures used in the mid- and high-rise sectors. According to long-time survey and lab experiments, motion sickness and sopite syndrome are the main adverse effects on the occupants of a wind sensitive building. For tall timber buildings, wind-induced vibrations seem to be a new critical design aspect at much lower heights than for traditional steel-concrete buildings. To guarantee good comfort, the horizontal accelerations at the top of tall timber buildings must be limited. Two methods in the Eurocode for wind actions (EN1991-1-4), procedure 1 in Annex B (EC-B) and procedure 2 in Annex C (EC-C), provide formulas to estimate the along-wind accelerations. The Swedish code advises to follow a method specified in the National Annex to the Eurocode (EKS) and the American ASCE 7-2016 recommend another method. This study gives an overview on the background of the different methods for the evaluation of along-wind accelerations for buildings. Estimated accelerations of several tall timber buildings evaluated according to the different methods are compared and discussed. The scatter of the accelerations estimated with different codes is big and increases the design uncertainty of wind induced response at the top of tall timber buildings

Wind-induced dynamic excitation is becoming a governing design action determin-ing size and shape of modern Tall Timber Buildings (TTBs). The wind actions generate dynamic loading, causing discomfort or annoyance for occupants due to the perceived horizontal sway – i.e. vibration serviceability failure. Although some TTBs have been instrumented and meas-ured to estimate their key dynamic properties (natural frequencies and damping), no systematic evaluation of dynamic performance pertinent to wind loading has been performed for the new and evolving construction technology used in TTBs. The DynaTTB project, funded by the Forest Value research program, mixes on site measurements on existing buildings excited by heavy shakers, for identification of the structural system, with laboratory identification of building elements mechanical features coupled with numerical modelling of timber structures. The goal is to identify and quantify the causes of vibration energy dissipation in modern TTBs and pro-vide key elements to FE modelers.

The first building, from a list of 8, was modelled and tested at full scale in December 2019. Some results are presented in this paper. Four other buildings will be modelled and tested in spring 2020.

The dynamic response to time varying loads, e.g. wind loads or earthquakes, is in many cases decisive when designing a tall timber building. The structural parameters governing the dynamic behaviour are the mass, the damping and the stiffness. The last two parameters are not well-known at serviceability levels for timber structures in general and for timber connections specifically. Results from forced vibration tests on single components and on a full-scale truss for an eight-storey residential building have been analyzed. In parallel, a detailed Finite Element (FE) model of a large Glulam truss with slotted-in steel plates and dowels connections has been developed and simulations have been made. The damping caused by the structural components, the embedment of fasteners and friction of mating surfaces of components in the selected connection types is quantified experimentally. The materials' stiffness values in the model were evaluated. The results from this study bring knowledge on the structural dynamic properties of large timber structures with mechanical connections and will facilitate the performance prediction of new tall timber buildings for better comfort at higher levels in environmentally friendly expansions of our cities. 

Tall timber buildings generally require fire resistance ratings of 90 minutes, 120 minutes or more. The vast majority of fire tested structural timber connections, however, did not reach a fire resistance that was relevant for these buildings. Commonly timber connections between glued laminated timber members comprise of exposed steel fasteners, such as bolts, screws, nails and dowels. However, it has previously been concluded that connections with exposed steel fasteners, generally do not achieve fire resistance ratings of 30 minutes and are, therefore, inadequate to be implemented in tall timber buildings without fire encapsulation. The research project presented in this report consists of four connection fire tests that are designed to achieve structural fire resistance ratings of 90 minutes, using different design strategies. This goal was achieved for all tested column-beam connections. A single test of a moment resisting connection did not lead to a fire resistance rating of 90 minutes, due to timber failure at the smallest cross-section after 86 minutes. The low temperature of the steel fasteners and the limited rotation of the connection, however, suggest that the connection would have been capable of achieving a 90 minutes fire resistance rating if larger beam cross-sections would be used.