Published article “Model updating of seven-storey cross-laminated timber building designed on frequency-response-functions-based modal testing” by Kurent et al.
Blaž Kurent, Boštjan Brank (both from University of Ljubljana, Slovenia) and Wai Kei Ao (University of Exeter, UK) authored an open access article on model updating on seven storey cross-laminated timber building Yoker in Glasgow, UK. The article was published in Structure and Infrastructure Engineering journal and can be accessed here:
Full scale tests on Trinity College building, Cambridge, UK
Researchers from University of Exeter, in collaboration with industrial partner in DynaTTV project, Smith and Wallwork, performed in-situ vibration serviceability test on a 5-storey hybrid CLT-concrete building Trinity College in Cambridge, UK. A set of three shakers was used to perform FRF measurements and shaker shutdown test within the successful forced vibration testing campaign.
Ambient vibration test on 4-storey InnoRenew building in Izola, Slovenia
In March 2021 two independent sets of ambient vibration tests were performed on the 4-storey InnoRenew building in Izola, Slovenia, which is to be completed in autumn 2021. In addition to timber structure, roof and secondary glass elements (windows, doors), this building phase included partial screed on the floor plates, partition walls and partly finished internal CLT walls. The first set of tests was performed with data acquisition system Bruel&Kjaer (Type 3053-B-120), 1-axial accelerometers Bruel&Kjaer, Type 4507 B 004 and the data was processed with Bruel&Kjaer, BK Connect, PULSE Operational Modal Analysis software. The second set of tests was performed with Dewesoft 16-channel acquisition unit, 3-axial MEMS accelerometers and the data was processed with Dewesoft X3 processing software. In both sets measurements, matching results were achieved for the first three natural frequencies: f1 = 4,80 Hz, f2 = 6,27 Hz, f3 = 7,08 Hz. The next measurement will be performed also with excitation shaker.
The 5th DynaTTB project partner meeting (online)
The fifth project partner meeting took place from the 18th to the 19th March 2021 online instead of in-person meeting due to Covid-19 travel restrictions. Each of the partners presented updated on numerical modelling of selected tall timbe buildings and new on-site measurements and experimental data were presented. The ongoing work on the preparation of final Design guidelines was also discussed and the action points for the following months were set. The next meeting is planned to take place in Exeter, UK on 6-7th September 2021 (if Covid-19 travel restrictions will allow). In addition, a joint meeting with all timber building related ongoing ForestValue projects is planned to take place between 22-25th of February 2022 in Skellefteå, Sweden. The meeting will be held in the newly built 20-storey tall timber Sara Culture house.
Horizon Results Booster – Module A
ForestValue was granted Horizon Results Booster (HRB) “Portfolio Dissemination & Exploitation Strategy” services (www.horizonresultsbooster.eu) funded by the European Commission as a result of a successful application. Horizon Results Booster is a package of specialised services to maximise the impact of R&I public investment and further amplify the added value of the Framework Programmes (FPs). It helps to bring a continual stream of innovation to the market and beyond.
Within this HRB service, a project group of 17 ongoing ForestValue projects was formed with a common aim to disseminate effectively and boost exploitation potential of the research results of the projects. Representatives of each of the projects provided their input in individual project questionnaires and after an online meeting was organized in January 2021 for further discussions. Based on all the provided inputs HRB will prepare a portfolio of results that are suitable for dissemination and which includes a comprehensive mapping of the relevant stakeholders/target audience for each particular portfolio with a final report “Portfolio of R&I Results”. This portfolio aims to provide the first mapping of complementarities between the projects and will form the basis of Module B, which aims to design a common dissemination plan for the portfolio and to carry out the actual dissemination of the portfolio results.
Laboratory tests at NTNU
Over the past months, a series of laboratory tests have been carried out at NTNU with focus on the energy dissipation of different structural components, namely a composite timber floor and timber connections. The timber composite floor was subjected to dynamic testing both by use of the modal hammer and forced vibrations applied by an oscillator. A viscous damping ratio equal to approx. 0.70% of the critical damping ratio was quantified by both methods for the fundamental mode of vibration. The energy dissipation of timber connections with screws and threaded rods was quantified on the basis of quasi-static cyclic tests under service load by use of the equivalent viscous damping ratio which was of the order of 5-8%. In the near future, cyclic testing of a glulam connection with slotted-in steel plates and dowels will be carried-out.
Experimental setup at Mjøstårnet
A measurement setup consisting of triaxial accelerometers was installed on the roof of the building in March 2019. This setup measures ambient vibrations of the building due to wind load. The goal of the experimental setup was to obtain modal dynamic properties of the building, including fundamental frequencies and damping ratios.
Collaboration between DynaTTB and InnoCrossLam Forest Value projects
Within the InnoCrossLam project one of the tasks is to use modern FEM
tools to analyse complex high-rise CLT buildings located in seismically active
areas. For the purpose of the study a joint cooperation was established with
the DynaTTB project to reach a mutual goal of more reliable modelling of tall
timber buildings. DynaTTB is focused on the dynamic response of tall timber
building under service load with the emphasis on wind loading. As a case study,
a 4-storey asymmetrical CLT building was taken into consideration. The building
is situated in Ljubljana and was designed by the company CBD, also an
associated partner of InnoCrossLam.
Vibrational testing and FE-modelling of a large glulam truss that stabilizes a tall timber building
The dynamics of a 4300 kg large timber truss with slotted-in steel plates and dowel connection have been examined. The truss is part of the structural lateral bracing of a six-storey residential house in Skövde in Sweden. Series of forced vibration tests with an impact hammer and accelerometers were performed at the glulam plant. Modes in the plane of the truss have been identified. Their damping values were estimated to be between 0.6 and 1 % of the critical viscous damping.
The experimental data are compared with results from a Finite Element (FE) model consisting of more than 2 million solid elements. The Modal Assurance Criterion is used to pair the experimental modes to the most similar numerical ones. The comparison shows that the natural frequencies of the paired numerical eigenmodes are all about 10 % higher than the one stemming from tests, before any calibration of the FE-model.
The investigation and the results will be presented at the EURODYN 2020 conference, 23rd-26th of November 2020 (https://eurodyn2020.org/).
Bayesian (finite element) model updating webinar
Bayesian (finite element) model updating webinar was organized by U Ljubljana from 25 September 2020 until 30 September 2020. The lecturers were prof. Hermann G. Matthies (TU Braunschweig) and dr. Noémi Friedman (Computer Science and Automation Research Institute, Budapest). There were 35 attendants (mostly doctoral students) from Slovenia, France and Croatia. The lectures are available on YouTube channel of U Ljubljana (Faculty of Civil and Geodetic Engineering):
Second campaign of full-scale dynamic testing on Treed-It building, in Paris
When the building was first tested, in December 2019, the main structure was achieved but not the internal partitions. In June 2020 the building was very close to its final stage and all internal walls in place, adding more mass but at the same time giving additional stiffness to the building.
The 500kg shaker was transported to the 11th floor by the lift, with great care when rolling on the definitive floors. The three first modes that have been identified during the first campaign have been excited once again with frequencies shifted a bit. The first frequency was shifted up, what means the stiffness added on this bending mode was larger than the added mass, when the second and third modes were observed at smaller frequencies. The amplitude dependency of the structural damping was confirmed. The three modes have the same mean amplitude damping, 1.7% of critical. In parallel the Finite Element Modelling of the building was improved, especially by a better model of the foundations, to fit with the measured mode shapes and frequencies.
Full-scale dynamic testing on Hyperion building, in Bordeaux
The Hyperion tower is a 56m high, 16 storeys dwelling with a concrete core and CLT floors.
The 500kg shaker was lifted to the 17th floor by a tower crane, as water tightness was not done. The three first modes have been identified by ambient excitation measurement and by swept sine tests. Damping ratio was found to be strongly dependent on the amplitude of vibration. The torsion mode, mode 2, showed a typical decrease of a solid damping, that can be explained by the way the CLT floor is connected to the concrete core. As the three modes were well separated, recorded vibrations are easy to analyze.
The next step will be to perform the same kind of tests, with smaller amplitudes of excitation, when the tower will be completed in March 2021.
The 4th DynaTTB project partner meeting (online)
The fourth project partner meeting took place from the 22nd to the 23rd September 2020 online instead of originally planned location in Exeter, UK due to Covid-19 travel restrictions. Updates on laboratory and in-situ test measurements were presented by the partners and a plan for the remaining in-situ test measurements were discussed due to Covid-19 restricted international travel. Several international conference papers were submitted and ongoing work on scientific journal papers were discussed. Special attention was given to defining the structure of the final Design guidelines document.
3rd ambient vibration test on a 4-storey CLT building in Ljubljana
In September 2020 the third phase of ambient vibration tests was performed on the 4-storey “Flower Valley” CLT building in Ljubljana, Slovenia. In addition to timber structure, roof and secondary glass elements (windows, doors), this phase included screed on the floor plates, façade, partition walls and partly finished external and internal CLT walls. The next measurement is expected to be performed also with excitation shaker.
The 3rd DynaTTB project partner meeting (online)
The third project partner meeting took place on 24th of March 2020 online instead of originally planned location in Paris, France due to Covid-19 travel restrictions. Each of the partners presented different approaches on numerical modelling and/or on-site measurements and experimental data processing. In addition, adaptations of originally planned activities due to Covid-19 were discussed. The partners discussed also about the preparation of the mid-term reporting to ForestValue as well as about preparation of joint publications at international conferences and in scientific journals.
Full scale dynamic testing on Treed-It building, in Paris
In December 2019 the first measurement campaign was performed on the 11 storey Treed-It building, in the suburb of Paris. The building is designed by Vinci Engineering with Arbonis as main contractor of the timber parts. For the measurements a 500kg shaker was lifted to the 10th floor with the site crane and Seismic accelerometers were placed at three levels to measure horizontal displacements during shaking. The shaker was operated with various amplitudes and various frequencies; abruptly stopping the excitation allows to measure the decay of vibration, giving structural damping for each mode. Damping was close to 3.5% of critical for large amplitudes in torsion and decreases to less than 1% for small amplitudes. For the flexion mode structural damping was close to 2.5% of critical for large amplitudes and reduced to 1.5% of critical for smaller amplitudes.
2nd ambient vibration test on a 4-storey CLT building in Ljubljana
In November 2019 the second set of ambient vibration tests was performed on the 4-storey “Flower Valley” CLT building in Ljubljana, Slovenia. In this phase, all the secondary glass elements (windows, doors) were installed, which was expected to increase the structure’s stiffness. In addition, the roof was also completed in this stage, which increased the total mass of the building, mainly due to added gravel on the roof.
The 2nd DynaTTB project partner meeting (Ljubljana, Slovenia)
The second project partner meeting is taking place in Ljubljana from the 16th to the 17th September 2019. It is being hosted by the University of Ljubljana. During the two days of meetings the ongoing work is being presented; in-situ building cases are being presented as well as the modelling concepts. The first day finished with the visit of the 4-storey CLT building in Slovenia, also part of the testing. In addition to project partner presentations, two additional invited presentations took place at the second day of the meeting; Boris Azinović from National building institute of Slovenia presented ForestValue project InnoCrossLam and common point in collaboration among both projects were identified; Mike Burnard from InnoRenew CoE gave presentation on Data Management, Open Access and Open Data.
Ambient vibration test on a 4-storey CLT building in Ljubljana
In July 2019 the first series of ambient vibration tests was performed on a 4-storey CLT building in Ljubljana, Slovenia. This building is still under construction and it will be tested in various building stages in order to study the influences of secondary elements to the natural frequency of the building. In this phase, the measurements were performed on load bearing structure. In the following months, the structure with added doors and windows will be tested.
The DynaTTB project has started: Kick-off meeting (Brummundal, Norway)
The kick-off meeting took place on the 28th March 2019 in the world’s tallest timber construction, the 85 m tall Mjøstårnet in Brummundal, Norway. The building itself will also be analysed within the project. The partners presented themselves and their work and set more detailed plans for future work. In addition, structural design project and a presentation of the Mjøstårnet building was given by partners in the project, structural design office Sweco, and the manufacturer and contractor of the Mjøstårnet’s timber structure, Moelven.