Project

DynaTTB - Dynamic Response of Tall Timber Buildings under Service Load

Goal: The project's goal is to quantify the structural damping in as-built tall timber buildings (TTB), identify and quantify the effects of connections and non-structural elements on the stiffness, damping and wind-induced dynamic response of TTBs, develop a bottom-up numerical finite element model for estimating the dynamic response of multi-storey timber buildings, validate the predicted response with in-situ measurements on TTBs and disseminate findings via a TTB Design Guideline for design practitioners.

The project is supported under the umbrella of ERA-NET Cofund ForestValue.

Project coordinator: RISE Research Institute of Sweden

Project partners:
- NTNU Norwegian University of Science and Technology (Norway)
- University of Exeter (UK)
- University of Ljubljana (Slovenia)
- InnoRenew CoE (Slovenia)
- CSTB Centre Scientifique et Technique du Bâtiment (France)
- Linnaeus University (Sweden)
- Moelven Töreboda AB (Sweden)
- Moelven Limtre AS (Norway)
- SWECO Norge AS avd Lillehammer (Norway)
- Smith and Wallwork Engineers Ltd (UK)
- GALEO (France)
- EIFFAGE (France)
- ARBONIS (France)

Date: 1 March 2019 - 1 March 2022

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Project log

Pierre Landel
added a research item
Climate change and densification of cities are two major global challenges. In the building and construction industry, there are great expectations that tall timber buildings will constitute one of the most sustainable solutions. First, vertical urban growth is energy and resource-efficient. Second, forest-based products store carbon and have one of the highest mechanical strength to den-sity ratios. If the structural substitution of concrete and steel with wood in high-rise buildings awakens fears of fire safety issues, engineers and research-ers are particularly worried about the dynamic response of the trendy tall tim-ber buildings. Indeed, due to the low density of wood, they are lighter, and for the same height, they might be more sensitive to wind-induced vibrations than traditional buildings. To satisfy people’s comfort on the top floors, the ser-viceability design of tall timber buildings must consider wind-induced vibra-tions carefully. Architects and structural engineers need accurate and verified calculation methods, useful numerical models and good knowledge of the dynamical properties of tall timber buildings. Firstly, the research work presented hereby attempts to increase the under-standing of the dynamical phenomena of wind-induced vibration in tall build-ings and evaluate the accuracy of the semi-empirical models available to esti-mate along-wind accelerations in buildings. Secondly, it aims at, experimen-tally and numerically, studying the impact of structural parameters – masses, stiffnesses and damping – on the dynamics of timber structures. Finally, it suggests how tall timber buildings can be modeled to correctly predict modal properties and wind-induced responses. This research thesis confirms the concerns that timber buildings above 15-20 stories are more sensitive to wind excitation than traditional buildings with concrete and steel structures, and solutions are proposed to mitigate this vibra-tion issue. Regarding the comparison of models from different standards to estimate wind-induced accelerations, the spread of the results is found to be very large. From vibration tests on a large glulam truss, the connection stiff-nesses are found to be valuable for predicting modal properties, and numerical reductions with simple spring models yield fair results. Concerning the struc-tural models of conceptual and real tall timber buildings, numerical case stud-ies emphasize the importance of accurately distributed masses and stiffnesses of structural elements, connections and non-structural building parts, and the need for accurate damping values.
Saule Tulebekova
added a research item
Currently, there is limited knowledge of the dynamic response of taller glue laminated (glulam) timber buildings due to ambient vibrations. Based on previous studies, glulam frame connections, as well as non-structural elements (external timber walls and internal plasterboard partitions) can have a significant impact on the global stiffness properties, and there is a lack of knowledge in modeling and investigation of their impact on the serviceability level building dynamics. In this paper, a numerical modeling approach with the use of “connection-zones” suitable for analyzing the taller glulam timber frame buildings serviceability level response is presented. The “connection-zones” are generalized beam and shell elements, whose geometry and properties depend on the structural elements that are being connected. By introducing “connection-zones”, the stiffness in the connections can be estimated as modified stiffness with respect to the connected structural elements. This approach allows for the assessment of the impact of both glulam connection stiffness and non-structural element stiffness on the dynamic building response due to service loading. The results of ambient vibration measurements of an 18-storey glulam timber frame building, currently the tallest timber building in the world, are reported and used for validation of the developed numerical model with “connection-zones”. Based on model updating, the stiffness values for glulam connections are presented and the impact of non-structural elements is assessed. The updating procedure showed that the axial stiffness of diagonal connections is the governing parameter, while the rotational stiffness of the beam connections does not have a considerable impact on the dynamic response of the glulam frame type of building. Based on modal updating, connections exhibit a semi-rigid behavior. The impact of non-structural elements on the mode shapes of the building is observed. The obtained values can serve as a practical reference for engineers in their prediction models of taller glulam timber frame buildings serviceability level response.
Blaz Kurent
added a research item
Based on the experimental estimation of the key dynamic properties of a seven-storey building made entirely of cross-laminated timber (CLT) panels, the finite element (FE) model updating was performed. The dynamic properties were obtained from an input-output full-scale modal testing of the building in operation. The chosen parameters for the FE model updating allowed the consideration of the timber connections in a smeared sense. This approach led to an excellent match between the first six experimental and numerical modes of vibrations, despite spatial aliasing. Moreover, it allowed, together with the sensitivity analysis, to estimate the stiffness (affected by the connections) of the building structural elements. Thus, the study provides an insight into the as-built stiffness and modal properties of tall CLT building. This is valuable because of the currently limited knowledge about the dynamics of tall timber buildings under service loadings, especially because their design is predominantly governed by the wind-generated vibrations.
Pierre Landel
added a research item
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.
Wai Kei Ao
added 3 research items
Wind-induced dynamic excitation is becoming 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. vibration serviceability failure. Although some TTBs have been instrumented and measured 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 provide key elements to FE modelers.
This paper describes an experimental validation of a novel FRF-based modal testing system designed to measure experimentally sway modes of tall timber and other building structures. The test uses a set of synchronised electrodynamic shakers and oven-controlled crystal oscillator (OCXO) high-precision synchronised wireless accelerometers for simultaneous force and response measurements. This modal testing system makes no use of cables or radio-waves to connect all accelerometers simultaneously with the multi-channel data acquisition system but provides a perfect synchronised measurement of a practically unlimited number of force and response channels. The system will be used to to estimate experimentally sway modes of as-built tall timber buildings. Therefore, the aim of this paper is to demonstrate the feasibility of the OCXO-based system in high-rise building FRF measurements. Two nominally identical FRF-based modal testing exercises were carried out on a 15-tonne laboratory-based test floor structure supported by 4 columns in order to measure its horizontal 'swaying' modes of vibration using: (1) a well-established and quality assured 'wired' system based on a 20-channel spectrum analyser, and (2) OCXO-based wireless system. It was shown that the two methodologies produce almost identical modal testing results and that the OCXO-based method is robust and reliable for field utilisation on high-rise buildings.
Wind-induced dynamic excitation is becoming 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. vibration serviceability failure. Although some TTBs have been instrumented and measured 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 ForrestValue research program, mixes on site measurements on existing buildings excited by heavy shakers and/or white noise measurements, 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 provide key elements to FE modelers. This paper presents the results of one of the buildings being studied, the 7-storey CLT building, called Yoker, in Glasgow UK.
Igor Gavrić
added an update
Timber buildings are regarded as one of the best carbon sequestration tools available in the built environment, addressing key environmental challenges and are capable of contributing to circular economy initiative within the construction industry. Tall Timber Buildings (TTBs) provide the opportunity for cost and space efficiency. However, little is understood regarding vibrations in these structures under wind loads, which contribute to size, shape, and mass design of TTBs in order to minimize effects on physical well-being of users. Considering the resonant nature of wind-induced vibrations of tall structures, more information on their natural frequencies and damping properties are crucial. Despite the increasing popularity of Tall Timber Buildings, currently only some information and knowledge regarding the damping and distribution of mass and stiffness in sway from these structures is available. Te dynamic properties of timber buildings are primarily driven by the damping in connections but also by the effects of non-structural elements. To solve this problem, we are designing new, more detailed experimental research, with calibrated numerical models, that will enable us to better describe and predict Tall Timber Buildings behavior under wind load. The methodology involves experimental measurements of components of building structures (mainly timber connections) as well as measurements on already built timber buildings. The experimental data will serve to verify numerical models based on the finite element method. By using this approach, it will be possible to evaluate more accurately the parameters that are currently given as an estimate and are not consistently scientifically verified. The objective of this research project is to develop knowledge and reliable models, so as to assist designers in predicting the dynamic performance of Tall Timber Buildings under service load. The secondary impact will be to encourage the greater use of Tall Timber Buildings as part of the solution for urban development, with the opportunity to create value and market growth for forest based renewable products.
 
Igor Gavrić
added a project goal
The project's goal is to quantify the structural damping in as-built tall timber buildings (TTB), identify and quantify the effects of connections and non-structural elements on the stiffness, damping and wind-induced dynamic response of TTBs, develop a bottom-up numerical finite element model for estimating the dynamic response of multi-storey timber buildings, validate the predicted response with in-situ measurements on TTBs and disseminate findings via a TTB Design Guideline for design practitioners.
The project is supported under the umbrella of ERA-NET Cofund ForestValue.
Project coordinator: RISE Research Institute of Sweden
Project partners:
- NTNU Norwegian University of Science and Technology (Norway)
- University of Exeter (UK)
- University of Ljubljana (Slovenia)
- InnoRenew CoE (Slovenia)
- CSTB Centre Scientifique et Technique du Bâtiment (France)
- Linnaeus University (Sweden)
- Moelven Töreboda AB (Sweden)
- Moelven Limtre AS (Norway)
- SWECO Norge AS avd Lillehammer (Norway)
- Smith and Wallwork Engineers Ltd (UK)
- GALEO (France)
- EIFFAGE (France)
- ARBONIS (France)