high-fire-resistance glulam connections for tall timber
TRANSCRIPT
Daniel Brandon, Pierre Landel, Rune Ziethén, Joakim Albrektsson, Alar Just – RISE, Research Institutes of Sweden
SMART HOUSING SMÅLAND RISE rapport 2019:26
ISBN 978-91-88907-52-3
High-Fire-Resistance Glulam
Connections for Tall Timber
Buildings
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Foreword
This report provides a brief overview of relevant results as required by one of the project sponsors
Smart Housing Småland. The project consists of 4 timber connection fire resistance tests and 4 tests
of similar connections at room temperature. A more detailed discussion of the tests of connection 3
and 4 is given in the Master Thesis of Ronstad and Ek (2018).
The research presented in this report was conducted by RISE (Sweden). The study was funded by
Smart Housing Småland (Sweden), Formas (Sweden).
The timber beams used for the tests were sponsored by Moelven (Sweden).
Densified veneer wood for tests of connections 3 and 4 were sponsored by Lignostone BV (the
Netherlands).
The melamine-formaldehyde adhesive used to assemble connections 3 and 4 were sponsored by
Akzo Nobel (Sweden).
The presented study is part of a multi-disciplinary research project on the conceptual design of two
22-storey timber buildings, named: Tall Timber Buildings – Concept Studies.
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Table of contents
Foreword _______________________________________________________________________ 2
Table of contents _________________________________________________________________ 3
Summary _______________________________________________________________________ 4
Background _____________________________________________________________________ 4
Literature review of timber connection fire tests _________________________________________ 5
Method _________________________________________________________________________ 6
Most important results _____________________________________________________________ 8
Connection 1 – Steel shoe connection ______________________________________________ 8
Connection 2 – Dowelled flitch plate connection ______________________________________ 10
Connection 3 – DVW-Reinforced connection with a steel tube fastener ____________________ 12
Connection 4 – DVW-Reinforced connection with a steel tube fastener ____________________ 14
Summary and conclusions _________________________________________________________ 16
Continuation of research __________________________________________________________ 17
References ____________________________________________________________________ 18
Annex A: Connection 1 drawings, photos, results _______________________________________ 20
Annex B: Connection 2 drawings, photos, results _______________________________________ 22
Annex C: Connection 3 drawings, photos, results _______________________________________ 24
Annex D: Connection 4 drawings, photos, results _______________________________________ 27
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Summary
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.
Background
The maximum height of timber buildings has increased rapidly in the last 15 years, due to changes of
building regulations in many European countries and due to the development of mass timber
materials, such as glued laminated timber beams and cross-laminated timber (CLT) panels. If their
size is sufficient, mass timber members can achieve fire resistance ratings that are relevant for tall
timber buildings without the need for fire protective encapsulation. There is, therefore, a potential to
expose mass timber members, although it should be noted that there are additional fire safety risks
involved. The connections between especially glued laminated timber beams do not, however,
always easily obtain a fire resistance rating that is required for realizing tall buildings without the
presence of fire protection.
Connections between glued laminated timber members often comprise steel fasteners, such as
dowels, bolts, nails and screws, often in combination with steel plates. If steel fasteners and/or plates
are exposed to a fire, the fasteners conduct the heat rapidly into the timber connection. This causes
timber under high mechanical stresses adjacent to these fasteners to heat up rapidly. At increasing
temperatures timber weakens significantly quicker than steel and has no significant strength left at
the charring temperature of approximately 300°C. For this reason, timber connections with exposed
steel members rarely have fire resistance ratings of 30 minutes or higher (Carling, 1989), while fire
resistance ratings of 90 minutes or higher are required for tall timber buildings in Sweden and in
many other countries.
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Recent architectural trends include having visible timber surfaces in tall buildings. Therefore, there is
a need for high fire resistance timber connections without fire protective encapsulation (Gerard et al.
2014).
Literature review of timber connection fire tests
Fire resistance tests of connections between timber beams have been analysed for this study. Table
1 indicates the number of tests performed in previous experimental studies and the nature and
direction of the load acting on the connections during the fire test. Figure 1 indicates the frequency of
tests that resulted in different fire resistance ratings. The figure also makes a distinction based on the
nature of the applied load.
The most common connection type between glued laminated timber members in tall timber buildings
is a column-beam connection loaded in shear. To be applicable for implementation in tall buildings a
fire resistance of at least 90 minutes is required in most countries. In Figure 1 it can be seen that
there are only 2 previous tests that meet both of these descriptions, which strongly indicates that
there is a need for fire tests of connections relevant for tall timber buildings.
Table 1: Number of timber connection tests performed for different configurations
Reference Configuration
Tension 0° Tension 90° Tension 45° Bending Shear
Dhima (1999) 19
Laplanche (2006) 17
Frangi and Mischler (2004) 6
Lau P.H. (2006) & Chuo (2007)
9
Peng (2010) 15
Audebert (2010)
4 3 6
Palma (2016)
19
Barber (2017) 3
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Figure 1: Overview of previous fire resistance tests and fire resistance times of timber connections
In response to the lack of fire resistance tests of glued laminated timber connections with acting
shear loads and bending moments, this study includes fire resistance tests of three column-beam
connections with shear loads acting upon them. Additionally, the fire resistance of one moment
resisting connection is determined in this study. This study also includes destructive tests of all
connections performed at room temperature prior to the fire tests, to determine the capacity of all
connections.
Method
Three shear connections and a moment connection were designed aiming to achieve a fire
resistance rating of 90 minutes while bearing 36% +/- 4% of their initial capacity. To determine the
initial capacity, three tests of similar connections were performed at room temperature. The loading
procedure of these tests was in accordance with ISO 6891 (1983).
Fire resistance tests of the connections were performed according to EN1363-1 (2012) to determine
a fire resistance rating. The tests that were performed first (connection 3 and 4) were performed in an
intermediate scale furnace of 1.0 x 1.0 x 1.0m. Due to the complexity of the setup, it was decided to
perform the subsequent tests in a large scale furnace of 3.0 x 5.0 x 3.0m (width x length x depth),
with the same exposure. Figure 3 and 4 show the setups for the intermediate scale furnace of a shear
connection and the moment connection, respectively.
Technical drawings of all specimens can be found in Annex A.
0
5
10
15
20
25
30
35
Nu
mb
er o
f te
s re
sult
s
Shear
Bending
Tension 45°
Tension 90°
Tension 0°(parallel)
Tall timber buildings
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Figure 2: Fire resistance test setup of a shear connection
Figure 3. Fire resistance test setup of the moment connection
Hydraulic
jack with
load cell
Timber beams
Furnacecovers
Steel supports
Furnace
door
Hydraulic
jack with
load cell
Timber column
Locations to attach
specimen
Furnace
door
Hydraulic
jack with
load cell
Steel connector
Steel I beam
(450mm)Timber
beams
Furnacecovers
Hydraulic
jack with
load cell
Timber beams
Furnacecovers
Steel supports
Furnace
door
Hydraulic
jack with
load cell
Timber column
Locations to attach
specimen
Furnace
door
Hydraulic
jack with
load cell
Steel connector
Steel I beam
(450mm)Timber
beams
Furnacecovers
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Most important results
The connection details and results are summarised in this section. In addition, specific information is
given in the annexes. The master thesis by Ronstad and Ek (2018) discuss the background,
preparation, tests and results corresponding to connection 3 and 4 in detail.
Connection 1 – Steel shoe connection
Connection 1 was included on request of practitioners and partners of the project. This connection
has been applied in practice and comprises of a steel shoe that is screwed onto the column and
bears the beam. High fire resistance is achieved by encapsulation with 2 layers of 15mm type F
gypsum board around the beam and steel shoe and 1 similar layer around the column. Fire sealant
Bostik Fire Bond Silmax Pro was used to seal the gypsum joints around the steel shoe. Figure 4
shows an exploded view of Connection 1 next to the drawing of the assembled connection. An
overview of results is given in Table 2.
Figure 4: Exploded view of connection 1 (left) and assembled connection 1 (right)
Table 2: Overview of results of tests of connection 1 (calculated shear force in the connection)
Room temperature test Fire test results
Ultimate shear force
Yield shear force
Stiffness, Ki, ISO 6891
Failure mode Applied shear force
Failure mode
Failure time
Fire resistance
232.3 kN
130.3 kN
19.7 kN/mm
Embedment of screws & tensile failure perp. to
grain in column
82 kN (35%)
Embedment of screws in
column
122min R120
Support
Load
Support
Support
Load
Support
Support
Load
Load
Load
Drilled holesthrough all
membersd=18mm
Load
Support
Support
Fire sealantaround thesteel plate
between the
beams
Support
Support
GL30c beam115 x 330 x2000mmmachined downto 94mm widthat the end
Drilled hole
with depthof 70mmd=45mm
S355JO steel
flitch plate600 x 264 x15mm
DVW plate297 x 62 x15mmscrewed onDVW
DVW plate
297 x 330 x15mm1300 kg/m3
to be gluedon timber
8 galvanizedmild steel tubes17.2 x 2.35mm
to be
compressed inconnection
8 wooden plugs
d=45mmt=70mm
8 M18 steelwashers
15mm type Fgypsum board
8 M18 steelwashers
8 wooden plugsd=45mmt=70mm
15mm type Fgypsum board
Fire sealantaround the steel
plate between thebeam and column
Slotted hole
(hidden)210 x 380 x12mm
Connection 4
Connection 3
Connection 2
GL30c column215x360mm
Wooden plugsd=12mmt=53mm
Slotted hole(hidden)212 x 270 x12mm
S355JO Steel
shoe 205 x 395 x5mm
S355JO steelflitch platet=8mm
2 x 5S355JO
steel dowelsd=12mm
l=108mm
Wooden plugsd=12mmt=53mm
2 x 5S355JOsteel dowelsd=12mml=108mm
Wooden plugsd=12mmt=53mm
Fire sealant
aroundgypsum board
near shoe
Connection 1
GL30c beam215x360mm
Wooden plug
d=68mmt=70mm
DVW plate
260 x 260 x 18mm1300 kg/m3
to be glued on timberGalvanizedmild steeltube 33.7 x3.25mm
to be
compressed inconnection
Wooden plugd=68mmt=70mm
260 x 260mm
area machinedto t=162mm
M36steel
washerGL30c 180 x260 x 2600mm
Drilled holewith depthof 70mm
d=68mm
(bothbeams)
drilled holesthrough all
membersd=35mm
M36steelwasher
GL30c
beam180 x260 x985mm
15mm type F
gypsum board
15mmtype Fgypsum
board
GL30c column215x360mm
4 x 8 screws:WFD 8x100
GL30c beam215x450mm machinedto 190mm width at end
of beam
2 x 9 screws:WFD 8x80
on each side
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The measured temperatures of the steel members at the time of failure ranged between 350 and
480°C, indicating that the timber around the steel screws was close to these temperatures and
started to char. The picture of the beam cross-section (Figure 7) shows that also in the beam, the
screws started to cause charring deeper in the timber. This indicates that embedment failure
occurred, which is confirmed by video evidence. Pictures taken after the room temperature test and
the fire test are shown in Figure 5 and 6, respectively. Annex A shows the technical drawings
deflection and steel temperatures of connection 1.
Figure 5: Connection 1 after room temperature test
Figure 6: Connection 1 fire test 10 minutes after failure
Figure 7: Photo of cross-section of beam with charred screw holes.
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Connection 2 – Dowelled flitch plate connection
Connection 2 was based on connections implemented in existing buildings. The connection
comprises of a protected 8mm thick steel flitch plate in a 12mm thick slot and ten 12mm dowels
(hammered in 12mm holes) in each timber member to transfer shear loads from the beam to the
column. High fire resistance is achieved by 53mm long timber plugs protecting the dowel and two
approx. 2cm wide barriers of fire sealant around the steel plate between the beam and the column
(Figure 9). Figure 8 shows an exploded view of Connection 2 next to the drawing of the assembled
connection. An overview of results is given in Table 3. The first failure occurring during the fire test
was at the end support of the beam (not in the connection).
Figure 8: Exploded view of connection 2 (left) and assembled connection 2 (right)
Table 3: Overview of results of tests of connection 2 (calculated shear force in the connection)
Room temperature test Fire test results
Ultimate shear force
Yield shear force
Stiffness, Ki, ISO 6891
Failure mode
Applied shear force
Failure mode
Failure time
Fire resistance
133.5 kN
66.8 kN
22.3 kN/mm
Splitting failure of column
54 kN (40%)
Failure not in connection (at support)
100min (≥)R90
Support
Load
Support
Support
Load
Support
Support
Load
Load
Load
Drilled holesthrough all
members
d=18mm
Load
Support
Support
Fire sealantaround thesteel plate
between thebeams
Support
Support
GL30c beam115 x 330 x2000mmmachined down
to 94mm widthat the end
Drilled hole
with depth
of 70mmd=45mm
S355JO steel
flitch plate600 x 264 x15mm
DVW plate297 x 62 x15mmscrewed onDVW
DVW plate297 x 330 x15mm1300 kg/m3
to be gluedon timber
8 galvanized
mild steel tubes17.2 x 2.35mm
to becompressed inconnection
8 wooden plugs
d=45mmt=70mm
8 M18 steelwashers
15mm type Fgypsum board
8 M18 steelwashers
8 wooden plugs
d=45mmt=70mm
15mm type Fgypsum board
Fire sealantaround the steel
plate between thebeam and column
Slotted hole
(hidden)210 x 380 x12mm
Connection 4
Connection 3
Connection 2
GL30c column215x360mm
Wooden plugsd=12mmt=53mm
Slotted hole(hidden)212 x 270 x12mm
S355JO Steel
shoe 205 x 395 x5mm
S355JO steelflitch platet=8mm
2 x 5S355JO
steel dowelsd=12mm
l=108mm
Wooden plugsd=12mmt=53mm
2 x 5S355JOsteel dowelsd=12mml=108mm
Wooden plugsd=12mmt=53mm
Fire sealant
aroundgypsum board
near shoe
Connection 1
GL30c beam215x360mm
Wooden plug
d=68mmt=70mm
DVW plate
260 x 260 x 18mm1300 kg/m3
to be glued on timberGalvanizedmild steel
tube 33.7 x3.25mm
to be
compressed inconnection
Wooden plugd=68mmt=70mm
260 x 260mm
area machinedto t=162mm
M36steel
washerGL30c 180 x260 x 2600mm
Drilled hole
with depthof 70mm
d=68mm
(bothbeams)
drilled holes
through all
membersd=35mm
M36steelwasher
GL30c
beam180 x260 x985mm
15mm type F
gypsum board
15mmtype Fgypsum
board
GL30c column215x360mm
4 x 8 screws:WFD 8x100
GL30c beam215x450mm machinedto 190mm width at end
of beam
2 x 9 screws:WFD 8x80
on each side
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Pictures taken after the room temperature test and the fire test are shown in Figure 10 and 11,
respectively. The average 1-dimensional charring rate determined by thermocouples was 0.7mm/min.
And the measured temperatures of the steel members at the time of failure ranged between 95 and
150°C at the moment of failure, with the majority of measurements around 100°C. Due to the rate of
temperature increase near the end of the test, it is however, not expected that the connection would
have remained intact for another 20 minutes to achieve a higher fire resistance rating than 90
minutes if the support would not have failed.
Figure 9: outer 2cm wide fire Sealant in the gap of the connection
Figure 10: Connection 1 after room temperature test
Figure 11: Connection 2 fire test 6 minutes after failure
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Connection 3 – DVW-Reinforced connection with a steel tube fastener
Connection 3 has been used in buildings in the Netherlands and is commercially known as
Lignoforce. The connection was studied before and was shown to have an evidently improved
stiffness, load bearing capacity (Leijten 1998) and seismic performance (Bakel et al. 2017) in
comparison with traditional dowel type connections. At the shear plane the timber members are
reinforced with a densified veneer wood (DVW) plate that can be glued in the factory on the
members. At the building site a tube can be compressed using a hydraulic jack as discussed by
Ronstad and Ek (2018) to achieve a tight fit and a high initial stiffness. It was chosen only to
implement one single tube in the connection, not to exceed the loading capabilities of the fire test rig.
High fire resistance is achieved by protection of the tube fasteners with a 70mm long timber plug. The
dimensions of the timber members are and can be significantly smaller than those of connections 2
and 3, while achieving a loadbearing capacity and fire resistance class that is in the same range.
Figure 5 shows an exploded view of Connection 3 next to the drawing of the assembled connection.
An overview of results is given in Table 4. The first failure occurring during the fire test was at the end
support of the beam as a screw of the setup snapped.
Figure 12: Exploded view of connection 3 (left) and assembled connection 3 (right)
Table 4: Overview of results of tests of connection 3 (calculated shear force in the connection)
Room temperature test Fire test results
Ultimate shear force
Yield shear force
Stiffness, Ki, ISO 6891
Failure mode Applied shear force
Failure mode Failure
time Fire
resistance
181.4 kN
139.4 kN
58.2.3 kN/mm
Bond line failure due to beams rotating away from column
57.4kN (32%)
Not in connection (at
support)
113min (≥)R90
Support
Load
Support
Support
Load
Support
Support
Load
Load
Load
Drilled holesthrough all
members
d=18mm
Load
Support
Support
Fire sealantaround thesteel plate
between the
beams
Support
Support
GL30c beam115 x 330 x2000mmmachined down
to 94mm widthat the end
Drilled hole
with depth
of 70mmd=45mm
S355JO steel
flitch plate600 x 264 x15mm
DVW plate297 x 62 x15mmscrewed onDVW
DVW plate
297 x 330 x15mm1300 kg/m3
to be gluedon timber
8 galvanized
mild steel tubes17.2 x 2.35mm
to be
compressed inconnection
8 wooden plugs
d=45mmt=70mm
8 M18 steelwashers
15mm type Fgypsum board
8 M18 steelwashers
8 wooden plugs
d=45mmt=70mm
15mm type Fgypsum board
Fire sealantaround the steel
plate between thebeam and column
Slotted hole
(hidden)210 x 380 x12mm
Connection 4
Connection 3
Connection 2
GL30c column215x360mm
Wooden plugsd=12mmt=53mm
Slotted hole(hidden)212 x 270 x12mm
S355JO Steel
shoe 205 x 395 x5mm
S355JO steelflitch platet=8mm
2 x 5S355JO
steel dowelsd=12mm
l=108mm
Wooden plugsd=12mmt=53mm
2 x 5S355JOsteel dowelsd=12mml=108mm
Wooden plugsd=12mmt=53mm
Fire sealant
aroundgypsum board
near shoe
Connection 1
GL30c beam215x360mm
Wooden plug
d=68mmt=70mm
DVW plate
260 x 260 x 18mm1300 kg/m3
to be glued on timberGalvanizedmild steel
tube 33.7 x3.25mm
to be
compressed inconnection
Wooden plugd=68mmt=70mm
260 x 260mm
area machinedto t=162mm
M36steel
washerGL30c 180 x260 x 2600mm
Drilled hole
with depthof 70mm
d=68mm
(bothbeams)
drilled holes
through all
membersd=35mm
M36steelwasher
GL30c
beam180 x260 x985mm
15mm type F
gypsum board
15mmtype Fgypsum
board
GL30c column215x360mm
4 x 8 screws:WFD 8x100
GL30c beam215x450mm machinedto 190mm width at end
of beam
2 x 9 screws:WFD 8x80on each side
Connection 3
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The connection itself did not fail at the end of the test. Therefore, it is relevant to discuss the
likelihood of the connection having a higher fire resistance based on analysis. Three different types of
failure modes are assessed:
- Embedment failure caused by weakening of the timber around the tube fastener.
- Brittle timber or densified veneer wood failure caused by reduction of the uncharred cross-
section.
- Timber column or beam failure
Temperatures measured in the tube at the shear plane at the end of the test were approximately
80°C. If the test were to continue there would have been a plateau at approximately 100°C in which
the heating rate stalls due to the energy needed to evaporate moisture of the timber and DVW
material. The temperatures at 120 minutes (only 6 minutes after the end of the test) would therefore
likely not have exceeded 100°C. Brandon et al. (2015) showed that the embedment strength of DVW
does not drop substantially under 200°C. Therefore, embedment failure before 120 minutes is
deemed very unlikely.
The average one dimensional charring rate determined from thermocouple measurements was
0.65mm/min for the first 62 minutes and 0.53mm/minutes for 112 minutes (almost the entire duration
of the test). Using this rate, at 120 minutes the edge distance can be estimated as approximately
65mm from the lower side. However, due to the downwards (realistic) direction of the load, timber or
DVW failure modes should be expected in the beam material above the tube fastener. The protection
of the floor and wall on the top and the end of the beams lead to practically unchanged end-and
upper edge distance. In addition, the char line would not have surpassed the protective plug at 120
minutes, indicating still significant beam thickness at the location of the connection. Therefore, brittle
failure modes, such as shear plug failure or splitting failure would very unlikely occur within 6 minutes
if the fire test were continued.
The weakest link in the tested structure (apart from the end support that failed) is the column. Being
exposed form 3-sides, the reduced cross section of the column reduces rapidly. Depending on the
structural design, the column will likely fail before the connection fails.
Annex D shows drawings, pictures and data of the tests of connection 4.
Figure 13: Specimen after the fire test (end support failed)
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Connection 4 – DVW-Reinforced connection with a steel tube fastener
Connection 4 is a moment-bearing variant of the DVW-reinforced tube connection, Connection 3.
Also the moment connection of this type (commercially known as Lignoforce) has been used in
buildings in the Netherlands, mainly to realise portal frame structures. This is possible due to the high
rotational stiffness, moment capacity (Leijten 1998) and, if needed, high energy absorption under
seismic loads (Bakel et al. 2017). Leijten and Brandon (2013) have shown that the flitch plate
connection can have the same rotational stiffness and moment capacity as the earlier studied 3-
member connection. High fire resistance is achieved by protection of the tube fasteners with a 70mm
long timber plug, protection of the steel plate by a 62mm wide DVW strip and fire sealant around the
steel at the gap. Figure 6 shows an exploded view and of the assembled connection.
Figure 14: Exploded view of connection 4 (top) and assembled connection 4 (bottom)
Support
Load
Support
Support
Load
Support
Support
Load
Load
Load
Drilled holesthrough all
members
d=18mm
Load
Support
Support
Fire sealantaround thesteel plate
between the
beams
Support
Support
GL30c beam115 x 330 x2000mmmachined down
to 94mm widthat the end
Drilled hole
with depth
of 70mmd=45mm
S355JO steel
flitch plate600 x 264 x15mm
DVW plate297 x 62 x15mmscrewed onDVW
DVW plate297 x 330 x15mm1300 kg/m3
to be gluedon timber
8 galvanized
mild steel tubes17.2 x 2.35mm
to be
compressed inconnection
8 wooden plugs
d=45mmt=70mm
8 M18 steelwashers
15mm type Fgypsum board
8 M18 steelwashers
8 wooden plugs
d=45mmt=70mm
15mm type Fgypsum board
Fire sealantaround the steel
plate between thebeam and column
Slotted hole
(hidden)210 x 380 x12mm
Connection 4
Connection 3
Connection 2
GL30c column215x360mm
Wooden plugsd=12mmt=53mm
Slotted hole(hidden)212 x 270 x12mm
S355JO Steel
shoe 205 x 395 x5mm
S355JO steelflitch platet=8mm
2 x 5S355JOsteel dowelsd=12mm
l=108mm
Wooden plugsd=12mmt=53mm
2 x 5S355JOsteel dowelsd=12mml=108mm
Wooden plugsd=12mmt=53mm
Fire sealant
aroundgypsum board
near shoe
Connection 1
GL30c beam215x360mm
Wooden plug
d=68mmt=70mm
DVW plate
260 x 260 x 18mm1300 kg/m3
to be glued on timberGalvanizedmild steel
tube 33.7 x3.25mmto be
compressed inconnection
Wooden plugd=68mmt=70mm
260 x 260mm
area machinedto t=162mm
M36steel
washerGL30c 180 x260 x 2600mm
Drilled hole
with depthof 70mmd=68mm
(bothbeams)
drilled holes
through all
membersd=35mm
M36steelwasher
GL30c
beam180 x260 x985mm
15mm type Fgypsum board
15mmtype Fgypsum
board
GL30c column215x360mm
4 x 8 screws:WFD 8x100
GL30c beam215x450mm machinedto 190mm width at end
of beam
2 x 9 screws:WFD 8x80
on each side
Connection 4
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Table 5 shows an overview of results. The first failure occurring during the fire test at the smallest
cross-section of the beam but did not involve the connectors, DVW plates or the flitch plate. It is
therefore expected that a small increase of the beam cross-section would have resulted in a fire
resistance classification higher than R60. The temperature of the tubes near the shear plane was 50
to 70°C, indicating no embedment failure occurred or would occur within the next few minutes.
Table 5: Overview of results of tests of connection 3 (calculated shear force in the connection)
Room temperature test Fire test results
Ultimate bending moment
Yield bending moment
Stiffness, Ki, ISO 6891
Failure mode
Applied bending moment
Failure mode Failure
time Fire
resistance
39.5 kNm
24 kNm 2319 kNm/rad
Tube def. & DVW splitting
15.8 kN (40%)
Bending failure of
timber at the smallest
cross-section
86min* R60*
*Due to a technical problem the furnace temperatures were too high for the first 12 minutes and subsequently
too low for approximately 5 minutes.
Figure 15: Two strips of fire sealant at the gap.
Figure 16: Specimen after the fire test – failure mode: bending failure at the minimum cross-section
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Summary and conclusions
An analysis of previous fire tests of glued laminated timber connection showed that there is a
shortage of tested connections that are relevant for tall timber buildings.
Four significantly different connections have been tested at a fire testing furnace to determine their
structural fire resistance. During the fire tests, a load equal to 36% +/-4% of the connections’ ultimate
load bearing capacity was implemented. To determine their load bearing capacity, similar
connections were tested to failure at room temperature prior to the fire tests.
Connection 1 was a shear connection of gypsum protected glued laminated timber. The load was
transferred from the beam to the column using a steel shoe designed by Moelven. The steel shoe
was protected using two 15mm thick layers of type F gypsum boards. The connection failed after 122
min due to embedment failure of the screws that attached the steel shoe to the column, achieving a
fire resistance R120.
Connection 2 was a shear flitch plate connection. All steel members including the dowels were
protected with at least 52mm of timber. At the gap between the column and the beam, fire sealant
was applied to protect the steel plate. During the fire test, the initial failure occurred outside of the
connection at 100 minutes, achieving a fire resistance of R90. The analysis indicates that the
connection would be able to bear the loads longer if the failure mode outside of the connection did
not occur. However, due to the char line in the proximity of the steel connection members, it is not
expected that this connection would have achieved a fire resistance rating of R120.
Connection 3 was a three-member shear connection with a tube fastener, designed in agreement
with previous studies (Leijten, 1998). To achieve high strength and stiffness while being able to have
relatively small cross-sections of timber members the connection was reinforced using densified
veneer wood plates, commercially known as Lignostone. The only measure to ensure a high fire
resistance of Connection 3, was the implementation of two timber plugs at both sides of the dowel.
During the fire test, one of the supports from the setup failed after 113 minutes achieving a fire
resistance of R90. The temperatures of the steel tube near the shear plane were still relatively low,
which indicates the connection would not have taken place for a significant time if the setup would not
have failed. In the connection design, the shear plane at the dowel was protected by a significant
amount of timber in all directions for the entire test duration. Therefore, it is not expected that
connection failure would be the governing failure mode and that the beams or the column would
failure first.
Connection 4 was a bending moment flitch-plate connection with steel tube fasteners, designed in
agreement with previous studies (Leijten and Brandon 2013). Similarly to Connection 3, to achieve
high strength and stiffness while being able to have relatively small cross-sections of timber
members, the connection was reinforced using densified veneer wood plates, commercially known as
Lignostone. Measures to achieve a high fire were similar to those of Connection 2: the
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implementation of timber plugs protecting the dowels; protection of the steel flitch plate and; fire
sealant at the gap of the connection to protect the steel plate. Failure occurred at 86 minutes
achieving a fire resistance of R60. The failure, however, did not occur in the connection, but in the
smallest cross section of the beam. This was the predicted failure mode. However, the failure
occurred a few minutes to be relevant for tall timber buildings in Sweden. A slight increase of the
timber cross-section would very likely have led to a higher fire resistance.
Figure 17 indicates the fire resistance of connections tested in this study versus, fire resistance
ratings of previously tested connections.
Figure 17: Overview of previous connection fire resistance tests and connection fire resistance tests
of this study
Continuation of research
This study only focused on connections between glued laminated timber members. Connection fire
tests relevant for CLT structures and light timber frame structures have not been studied substantially
and require research. A new study funded by the US governmental department of agriculture and
performed by RISE will look into connection performance in detail. Partnership with two of the largest
CLT manufacturers will help the project to come up with practicable and relevant solutions.
In addition, reparation of fire damages in tall timber buildings has been an upcoming question as
buildings grow taller. Restoring connections after a fire will likely be the most challenging part of the
structure and requires research. The US funded project will also look at possibilities for restoration.
0
5
10
15
20
25
30
35
Nu
mb
er o
f te
s re
sult
s
Shear this study
Bending this study
Previous studiesTall timber buildings
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References
Audebert M. (2010), Approche expérimentale et modélisation du comportement au feu
d’assemblages bois sous différents types de sollicitations. PhD Thesis, Université Blaise Pascal
Clermont-Ferrand et CSTB, 233p.
Bakel, R., Rinaldin, G., Leijten, A. J. M., and Fragiacomo, M. ( 2017) Experimental–numerical
investigation on the seismic behaviour of moment‐resisting timber frames with densified veneer
wood‐reinforced timber joints and expanded tube fasteners. Earthquake Engng Struct. Dyn., 46:
1307– 1324. doi: 10.1002/eqe.2857.
Barber D. (2017) Softwood Lumber Board - Gluelam Connection Fire Test - Summary Report. Arup
USA. Inc, Job number 246190.
Brandon, D., Maluk, C. Ansell, M.P. Harris, R. Walker, P. Bisby, L. and Bregulla, J. (2015) Fire
performance of metal-free timber connections. Proceedings of the Institution of Civil Engineers -
Construction Materials 2015 168:4, 173-186
Carling, O. (1989). Fire resistance of joint details in loadbearing timber construction - a literature
survey. BRANZ.
Chuo T.C.B. (2007) Fire performance of connections in Laminated Veneer Lumber. Fire Engineering
Research Report 07/3.
Dhima D. (1999) Vérification expérimentale de la résistance au feu des assemblages d’éléments en
bois. Saint Remy les Chevreuses: CTICM ; 61p.
EN1363-1 (2012) Fire resistance tests –Part 1: General Requirements. European Committee for
Standardization.
Frangi A., Mischler A. (2004) Fire tests on timber connections with dowel-type fasteners, Proceedings
of CIB-W18, paper 37-16-2, Edinburgh, Scotland.
Gerard R., Barber D., Wolski A. (2013) Fire safety challenges of tall wood buildings. Fire Protection
Research Foundation (FPRF), Quincy, MA, USA, and Arup North America, San Fransisco, CA, USA.
ISO 6891 (1983) ISO 6891. (1983). Timber structures - Joints made with mechanical fasteners -
General principles for the determination of strength and deformation characteristics. International
Organization for Standardization.
SMART HOUSING SMÅLAND
351 96 VÄXJÖ
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Karine Laplanche (2006) Etude du comportement au feu des assemblages de structures bois :
approche exp´erimentale et mod´elisation. G´enie m´ecanique [physics.class-ph]. Universit´e Blaise
Pascal - Clermont-Ferrand II.
Lau P.H. (2006) Fire resistance of connections in Laminated Veneer Lumber (LVL). Fire Engineering
Research Report 06/3.
Leijten, A. (1998). Densified veneer wood reinforced timber joints with expanded tube fastners.
Mekelweg: Delft University Press.
Leijten, A., & Brandon, D. (2013). Advances in moment transfering dvw reinforced timber connections
– Analysis and experimental verification, Part 1. Elsevier, 9.
Palma P. (2016) Fire Behaviour of timber connections. PhD Thesis. Diss. ETH no. 24032.
Peng L. (2010) Performance of heavy timber connections in fire. PhD Thesis, Ottawa-Carleton
Institute of Civil and Environmental Engineering, Canada ; 235p.
Ronstad and Ek (2018). Study of glue-laminated timber connections with high fire resistance using
expanded steel tubes. Master Thesis. Department of Civil, Environmental andNatural Resources
Engineering, Luleå University of Technology.
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Annex A: Connection 1 drawings, photos, results
Figure A1: Drawings of connection 1
2 x 9 screws: WFD 8x80 on each side
10
1042
40
153
12
21
5
215x450 machined to 190 mm
width at end of beam
2 x 15mm Type F
gypsum board
11 & 1221
5
1 x 15mm Type F
gypsum board
50
4 x 8 screws: WFD 8x100
360 670
void of approximately 5mm between
gypsum board and steel shoe
40
11
.5
Connections between gypsum boards
near steel shoe sealed with fire sealant
21
5
360
1 x 15mm Type F
gypsum board
Connections between gypsum boards
near steel shoe sealed with fire sealant
100 100
8 & 9
215x450 machined to 190 mm
width at end of beam
7
45
40
6
4 x 8 screws: WFD
8x100
21
5
2 x 9 screws: WFD 8x80 on
each side
750
Steel shoe
Steel quality: S355JO
Plate thickness: 5 mm
Screws
WFD from SFS intec
Montage without pre-drilling
40
11
.5
153
12
21
2 x 15mm Type F
gypsum board
45
0
200
88
01
47
0
110
28
00
95
0
15
0
35
0Connection 1 - FireConnection 1 -
Room temperature
45
0
3
L.C.
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Figure A2: Downward displacement on top of the beam at 180mm from the column.
Figure A3: Temperatures measured on steel shoe.
0
10
20
30
40
50
60
-40 -20 0 20 40 60 80 100 120 140
Ver
tica
l d
isp
lace
men
t [m
m]
Time [min]
0
100
200
300
400
500
0 20 40 60 80 100 120 140
Tem
per
atu
re [°C
]
Time [min]
TC 8 - 100mm from the top TC 9 - 300mm from the topTC 11 - 100mm from the top TC 12 - 300mm from the top
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Annex B: Connection 2 drawings, photos, results
Figure B1: Drawings of connection 2
9
8 410
8 mm thick steel flitch plate
1
11
6 7
8 mm thick steel flitch plate
5
2
8 mm thick steel flitch plate
12
3
8 mm thick steel flitch plate
380
995
Sealant in gap
141
53
195
40
80
350
195
240
8 dowels 12x110Centered position
54
53
10 dowels 12x110
Centered position
197
54141
40
80
240
135
350
10 dowels 12x110
Centered position
Sealant in gap
25
380
210
8 dowels 12x110Centered position
Steel plate
Steel quality: S355JO
Plate thickness: 8 mm
Dowels
Steel quality: S355JO
Diameter: 12 mm
Montage with 12 mm pre-drilling
65212
270
12
360
210
65
12
200
25
215
12
102
10
110
212
L.C.
12
670
120
270
28
00
102
12
215
Connection 2 -Room temperature
102
102
750
12
360
1212101212
Connection 2 - Fire3
50
14
70
360
970
860
360
150
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Figure 6: Downward displacement on top of the beam at 180mm from the column
Figure 5: Temperatures of steel members
Figure 5: Temperatures in timber at different depths
0
20
40
60
80
100
120
-40 -20 0 20 40 60 80 100 120
Ver
tica
l d
isp
lace
men
t
[mm
]
Time [min]
0
20
40
60
80
100
120
140
160
0 20 40 60 80 100 120
Tem
per
atu
re [
°C]
Time [min]
TC 5 - top dowel at dowel end TC 6 - steel plate in gapTC 7 - top dowel at shear plain TC 8 - steel plate in gapTC 9 - steel plate in beam TC 10 - top dowel at shear plainTC 11 - top dowel at dowel end TC 12 - steel plate in beam
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Annex C: Connection 3 drawings, photos, results
Figure C1: Room temperature test
28
00
M 36 washer
18
0
Slotted in glued
densified veneer wood
plate
L.C.
7
1000
260
Ø65
Slotted in glued
densified veneer wood
plate
3Slotted in glued
densified veneer wood
plate
26
0
1
54
0
128
10
18
0
200
Ø35
Expanded tube fastener
4
Expanded tube fastener
6
13
0
21
5
9
65mm diameter 80mm long timber plug
260
5
M 36 washer
11
2
10
60
130
110260
130
13
0
Densified veneer wood plates
Density: 1300 kg/m3
Plate dimensions: 250 x 250 x 18mm
Tube
Galvanised mild steel Ø33.7 x 3.25mm
Hole diameter: 35 mm
26
0
95
0
Connection 3 - FireConnection 3 -Room temperature
Ø35
Ø65
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Figure C2: Room temperature test
Figure C3: the failure mode for high shear forced.
Figure C4: Temperature of the steel tube at the shear plane (TC2).
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Figure C5:Location of support failure (from Ronstad and Ek, 2018)
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Annex D: Connection 4 drawings, photos, results
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Figure D2. Photos during and after test
Figure D3. Preparation for the fire test of the moment connection.
Figure D4. Thermocouple positions (top view)
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Figure D5. Thermocouple positions (front view)
Figure D6. Thermocouple teadings of TC1-4 and 10-12
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Figure D7. Tubes after the test without a sign of damage