high-fire-resistance glulam connections for tall timber

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

SMART HOUSING SMÅLAND

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E-MAIL [email protected]

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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


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


2 x 5S355JOsteel dowelsd=12mml=108mm


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


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


4 x 8 screws:WFD 8x100

GL30c beam215x450mm machinedto 190mm width at end

of beam


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).





Yield shear force


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


members

d=18mm

Load

Support

Support


between thebeams

Support

Support

GL30c beam115 x 330 x2000mmmachined down

to 94mm widthat the end

Drilled hole

with depth

of 70mmd=45mm

S355JO steel



DVW plate297 x 330 x15mm1300 kg/m3


8 galvanized

mild steel tubes17.2 x 2.35mm

to becompressed inconnection

8 wooden plugs

d=45mmt=70mm

8 M18 steelwashers


8 M18 steelwashers

8 wooden plugs

d=45mmt=70mm




Slotted hole


Connection 4

Connection 3

Connection 2




S355JO Steel

shoe 205 x 395 x5mm


2 x 5S355JO

steel dowelsd=12mm

l=108mm




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



260 x 260mm


M36steel


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




of beam


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.





Yield shear force


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


members

d=18mm

Load

Support

Support


between the

beams

Support

Support



Drilled hole

with depth

of 70mmd=45mm

S355JO steel



DVW plate

297 x 330 x15mm1300 kg/m3


8 galvanized


to be


8 wooden plugs

d=45mmt=70mm

8 M18 steelwashers


8 M18 steelwashers

8 wooden plugs

d=45mmt=70mm




Slotted hole


Connection 4

Connection 3

Connection 2




S355JO Steel

shoe 205 x 395 x5mm


2 x 5S355JO

steel dowelsd=12mm

l=108mm




Fire sealant

aroundgypsum board

near shoe

Connection 1

GL30c beam215x360mm

Wooden plug

d=68mmt=70mm

DVW plate

260 x 260 x 18mm1300 kg/m3


tube 33.7 x3.25mm

to be



260 x 260mm


M36steel


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




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


members

d=18mm

Load

Support

Support


between the

beams

Support

Support



Drilled hole

with depth

of 70mmd=45mm

S355JO steel



DVW plate297 x 330 x15mm1300 kg/m3


8 galvanized


to be


8 wooden plugs

d=45mmt=70mm

8 M18 steelwashers


8 M18 steelwashers

8 wooden plugs

d=45mmt=70mm




Slotted hole


Connection 4

Connection 3

Connection 2




S355JO Steel

shoe 205 x 395 x5mm


2 x 5S355JOsteel dowelsd=12mm

l=108mm




Fire sealant

aroundgypsum board

near shoe

Connection 1

GL30c beam215x360mm

Wooden plug

d=68mmt=70mm

DVW plate

260 x 260 x 18mm1300 kg/m3


tube 33.7 x3.25mmto be



260 x 260mm


M36steel


Drilled hole

with depthof 70mmd=68mm

(bothbeams)

drilled holes

through all

membersd=35mm

M36steelwasher

GL30c

beam180 x260 x985mm


15mmtype Fgypsum

board




of beam


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.



Ultimate bending moment

Yield bending moment


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.

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35

Nu

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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.


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Karine Laplanche (2006) Etude du comportement au feu des assemblages de structures bois :

approche expérimentale et modélisation. Génie mécanique [physics.class-ph]. Université 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


5

2


12

3


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


Plate thickness: 8 mm

Dowels


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


plate

3Slotted in glued


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

high-fire-resistance glulam connections for tall timber

Documents