DynaTTB : Dyna mic Response of Tall
Timber Buildings under Service Load
26th Japan-France Building Colloquium
5 th june 2023

Manuel MANTHEY, Olivier FLAMAND

DynaTTB is a project bringing
together industrial and academic
partners
from5
Europeancountries(Slovenia,United
Kingdom, Norway, Sweden andFrance).
Project Dyna-TTB is supported under the umbrella ofERA-NET Cofund ForestValue by Vinnova Sweden´sInnovation Agency, Agence Nationale de la recherche,
Ministry of Education, Science and Sport, The ResearchCouncil of Norway and Forestry Commission .
ForestValue has received funding from the EuropeanUnion's Horizon 2020 research and innovation
programme under grant agreement N° 773324.

Starting point of the DynaTTB project
Dynamic Response of Tall Timber Buildings underService Load (Dyna-TTB)
Starting point :The world's tallest wooden tower (Norway,Mjøstårnet, 85m) has been "weighted down" tomeet comfort requirements.
The top 7 floors have a 30cm thick concretefloor. The top floor exceeds the chosen comfort
criteria. It is sold by specifying it to the buyer.
Most all-wood buildings
requirement (even forfloors).

can meet thisheights of 4-505/06/2023

Manuel MANTHEY

Olivier FLAMAND

3In-situ measurements: 9 buildings have been shaken !

05/06/2023

Manuel MANTHEY

Olivier FLAMAND

4

2 buildings in France, hybrid structure (timber-concrete)
THE HYPÉRION TOWER 56 M
Located in Bordeaux
17 floors (R+16)
Construction from March 2019 to June 2021
Residential use
Highest hybrid wood/concrete tower in France
Large balconies

THE « TREED IT » TOWER 36 M
In Champs sur Marne
12 floors (R+11)
Construction from mas 2018 to December 2020Student residence : Many interior partitions (rooms)

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Manuel MANTHEY

Olivier FLAMAND

Hybrid / multi-material structures

Philosophy :- The right material in the right place.
- Lighter structures.
- Optimization of material quantities (frugality).
- Favors the use of bio-sourced materials.

1st Treed-It campaign- Reduction of the carbon footprint of buildings.

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Manuel MANTHEY

Olivier FLAMAND

6

Geometry and Materials
What is special about these two towers is their hybrid character. The concrete cores, for reasons of fire
protection in particular, are made of reinforced concrete. With this structural system, it is to be expected thatthe concrete core will mainly guide the lateral stiffness of the tower. Tests conducted at various times during
construction have shown that this is not so simple.
Concrete core all along the tower

Timber-concrete floors
CLT floors
Timber columns
Steel columns
Timber beams
1st levels in concrete
Piles for foundations

Treed-It FEM

Hyperion FEM
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Manuel MANTHEY

Olivier FLAMAND

7

Manuel MANTHEY

Olivier FLAMAND

8

How to get rid of the weather for testing ?
The mass shaker
With a heavy shaker input force is such that the amplitude of noise becomes
negligible.
Two levels of amplitude, two levels of moving mass.
Lever arm can be set to 158mm or 248mm
Moving mass is 400kg; 150kg addition is possible
The applied force increases according to the frequency²
2. A

When the force of the shaker exceeds the frictional resistance, the exciterslides on the floor.
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The mass shaker in action at Hyperion
Ballast per bag of sand

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Manuel MANTHEY

Olivier FLAMAND

9Acceleration and relative displacement measurements
Location of sensors: 3 accelerometers on 3 different floors

1 st Treed-It campaign

1st Hyperion campaign(without partitional walls)(without partitional walls)

1 st, 7th and 11 th floors.

1st, 9 th and 16th levels.

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Manuel MANTHEY

Olivier FLAMAND

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Four different kinds of tests have been achieved, eachhaving a particular purpose
The measurement of vibrations under ambient excitation, by turbulent wind, nearby traffic or works
inside the building, gives way to long lasting records (10 to 60 minutes) with the aim to identify modal
frequencies. It provides a good insight of modal frequencies.
An artificial excitation by a mass shaker delivering a horizontal sinusoidal force, with a continuousand slow variation of the frequency of which, called swept sine test. Because input force is controlled,
the dynamic response of the building, i.e. accelerations measured at various locations, shows thefrequencies of increased amplitude, pointing out the modal frequencies.
An artificial excitation by a mass shaker delivering a continuous horizontal sinusoidal force at a fixedfrequency. This constant excitation test must be brief to avoid beating, due to the unavoidable small
difference between the frequency of the applied force and the modal frequency of the building which isexcited. It was lasting 60s in this series of tests limiting data processing to time domain approach only.
An interrupted excitation by the mass shaker, called a shutdown test, is used to measure modal
damping. The initial excitation frequency is the one of a selected mode, then amplitude decreasing after
the excitation has been stopped gives a good approach of modal damping.
05/06/2023

Manuel MANTHEY

Olivier FLAMAND

11ADAPTED METHODS FOR THE MEASUREMENT OFSTRUCTURAL DAMPING
Example of shutdown test record for bending mode and the evaluations of damping by various methods.
Spectral density
0 .3 5

FFT 4096 points
FFT 2048 overlap 50 %TFD 6000 points
maximum likelihood method
2884 points after stopping shaker= 1,81 %0 .3= 1,47 %0 .2 5= 2,23 %= 2,02 %0 .2

0 .1 50 .1

0 .0 501 .7 8

1 .7 91 .81 .8 1

1 .8 2

1 .8 3

1 .8 4

1 .8 5

1 .8 61 .8 7

1 .8 8

1 .8 91 .9

1 .9 1

1 .9 2

1 .9 3

1 .9 4Frequency (Hz)Examples of damping evaluation from repeated shutdown test records for bending mode with shaker located in the south corner o f
the building and with small amplitude (left) and on the east side with large amplitude (right)
Maxima of oscillation amplitudes ofafter stopping the shaker

0.18= 1,87 %= 1,87 %

0.16
0.14
0.12

increase of damping with amplitude
on bending mode

0.1
0.08
0.06
0.04
0.02
005

1015Time (s)202505/06/2023

Manuel MANTHEY

Olivier FLAMAND

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How does this relate to numericalsimulations?
-SITU TRIALS> The model gives an estimate of the natural frequencies and modal deformations(choice and settings of the exciter, location of the sensors).
> The model helps to convince the client before the tests: via a temporal simulation ofthe excitation by the machine and the demonstration that the amplitude of thedeformation remains very limited (deformation verified by LVDT during tests).
IMPROVEMENT OF THE MODEL BY COMPARISON WITH TRIALS> The measured frequencies and modal shapes are compared with the numericalresults and an optimisation process is started.
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Manuel MANTHEY

Olivier FLAMAND

13Analysis of the simulations
INITIAL FINITE ELEMENT MODEL

The measured frequencies are directlycompared with the numerical results

The modal shapes are compared with thenumerical results (Modal Assurance Criterion)
Bending 1Torsion

Bending 2 + Torsion

An optimisation process can be started parameter by parameter. In addition to updating the material parameters used, or theconnections between elements, it has sometimes been necessary to add components that were initially neglected.
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Manuel MANTHEY

Olivier FLAMAND

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What role for non-structural elements?
In simulation, lightweight partitions were initially considered more as a distributed
mass than as a discrete element bringing a gain in rigidity to the structure.

1st round of testing

2nd round of testing
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Manuel MANTHEY

Olivier FLAMAND

15

What role for non-structural elements?
On-site measurements were made twice for each of the two towers :1/ With all the structural elements implemented (walls, floors, beams, etc.)
2/ After the addition of non-structural elements (light partitions, facade, balconies, etc.)

Treed-It

Mode 1bending X

Mode 2
bending Y

Mode 3 torsion

Hyperion

Mode 1bending X

Mode 2
torsionMode 3
bending Y

1.37

1.54

1.69

1st round oftesting(mass shaker)

0.95

1.67

1.88

1.62

2nd round of
testing(ambient)

0.95

1.50

1.81

1st round oftesting(mass shaker)
2nd round oftesting(mass shaker)

1.39

Numerous partitions(student residence)

1.49

Mass
+43%

Frequencies- 21% ???

! Balcony weight (+700t)
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Manuel MANTHEY

Olivier FLAMAND

16Consideration of internal partitions in the simulations
Example on the Treed-It tower adding shell elements for the partitions

Initial model

View of the interior partitions
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Manuel MANTHEY

Olivier FLAMAND

17Conclusions
Timber buildings (and hybrid building) are lightweight and subject to wind excitation, which
poses a serious problem for occupant comfort --- DynaTTB project.
In-situ tests of towers with a timber or hybrid structure were performerd => providing modal
frequencies and modal shapes that were compared with numerical simulations.
Damping was found to be amplitude dependent: a large amplitude excitation is needed tocapture it, the FE model is of great help to prepare these tests.
The FE models need to be improved by :-Optimising the parameters (initial values can be poorly estimated).

-Taking into account the stiffness of so-called "non-structural" elements as partitions orscreeds, whose relative stiffness may have a role here in the overall stiffness of thestructure
05/06/2023

Manuel MANTHEY

Olivier FLAMAND

18Merci pour votre attention