Influence of Moisture Content and Reinforcement on LoadCarrying Capacity of Housings in Solid Timber Beams
By

Rafid Shams Huq

B.Sc., Bangladesh University of Engineering and Technology (BUET), Dhaka,
Bangladesh, 2016

THESIS SUBMITTED IN PARTIAL
FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
MASTER OF APPLIED SCIENCE
IN
ENGINEERING

UNIVERSITY OF NORTHERN BRITISH COLUMBIA
July 2022

© Rafid Shams Huq, 2022
i

Abstract
Timber construction is a sustainable solution to address the increasing global demand for
housing. Timber framing currently uses mostly mechanical fasteners, which are made from
metals with high carbon footprint, and – depending on the type of fasteners– provide poor
aesthetics. These challenges can be addressed by using traditional joints such as timber
housings. However, there are no design guidelines available that account for the joint geometric
parameters, the wood moisture content during fabrication and when loaded as well as the
impact of mechanical reinforcements.
This thesis extends on previous research to investigate the influence of wood moisture and
reinforcement on the load-carrying capacity of solid timber beams with housings. A total of 60
beams with single housings and 30 beams with double housings were prepared and tested while
varying the moisture condition (either wet or dry) at the time of cutting the housings and at the
time of testing the beams. Along with 32 test data from previous research, statistical analysis
was conducted to evaluate the statistical significance of the investigated parameters. In
addition, 198 small-scale specimens were tested for shear, tension and compression to evaluate
the impact of small clear specimen material strength on the beam load-carrying capacity.
The tests confirmed that larger depth below the mortise and the use of self-tapping screws as
reinforcement lead to increase of load-carrying capacity; however, the moisture condition
during cutting and testing was only shown to have a significant impact on the load-carrying
capacity of double housings, but not single housings. The correlation between the material
strength tests and load-carrying capacities demonstrated that the strength of small clear
specimens from the same beam had no influence on the load-carrying capacity of the housings.

ii

Table of Contents
Abstract .....................................................................................................................................ii
List of Figures ........................................................................................................................... v
List of Tables ..........................................................................................................................vii
Acknowledgements .............................................................................................................. viii
1

2

3

Introduction ...................................................................................................................... 1
1-1

Background ................................................................................................................. 1

1-2

Load Bearing Timber Housing .................................................................................... 1

1-3

Load and Moisture Induced Stresses in Housings ...................................................... 2

1-4

Reinforcements of Connection Details ....................................................................... 2

1-5

Objectives .................................................................................................................... 2

1-6

Scope and Limitations ................................................................................................. 3

Literature Review ............................................................................................................. 4
2-1

Material Properties of Wood ....................................................................................... 4

2-2

Timber Housings ......................................................................................................... 6

2-3

Reinforcing Wood Joints ............................................................................................. 8

2-4

Preceding Work at UNBC ........................................................................................... 9

2-5

Summary of Literature Review ................................................................................. 12

Experimental Investigations .......................................................................................... 13
3-1 Materials ........................................................................................................................ 13
3-2 Specimen Description and Test Matrix.......................................................................... 16
3-3 Test Methods .................................................................................................................. 18
3-4 Statistical Analyses ........................................................................................................ 20
3-5 Results ............................................................................................................................ 21

iii

3-5-1 Compression, Tension and Shear Tests .................................................................. 21
3-5-2 Single Housing Beams ............................................................................................ 26
3-5-3 Double Housing Beams .......................................................................................... 30
3-6 Discussion ...................................................................................................................... 33
3-6-1 Correlation between material strengths and housing load-carrying capacity ......... 33
3-6-2 Single Housing Beams ............................................................................................ 37
3-6-3 Double Housing Beams .......................................................................................... 41
4

Conclusions and Outlook ............................................................................................... 46

References ............................................................................................................................... 48
Appendices .............................................................................................................................. 51
Appendix 1 – Test results from previous research (Heal et al., 2019) ................................. 51
Appendix 2 – Detailed test results of all specimens in S-0.80 series ................................... 52
Appendix 3 – Detailed test results of all specimens in S-0.65 series ................................... 60
Appendix 4 – Detailed test results of all specimens in D-0.80 series .................................. 68
Appendix 5 – Detailed test results of all specimens in D-0.65 series .................................. 76

iv

List of Figures
Figure 1-1: Load bearing housing (Nehil & Trojniak, 2013) .................................................... 1
Figure 2-1: Effect of moisture content on wood strength properties ......................................... 5
Figure 2-2: a) Typical single and double timber housings (Heal et al., 2019) and b) photo ..... 7
Figure 2-3: Failure Modes (a) Splitting, (b) Bearing, (c) Combined Bearing/Splitting .......... 11
Figure 2-4: Typical load-displacement curves for failure modes (a) Splitting, (b) Bearing, (c)
Combined Bearing/Splitting (Heal et al., 2019) ...................................................................... 11
Figure 3-1: Test Assembly for (a) Compression Perpendicular to Grain Test (b) Tension
Perpendicular to Grain Test (c) Shear Test .............................................................................. 14
Figure 3-2: Fully threaded STS of 120mm, 180mm and 200mm from left to right ................ 15
Figure 3-3: Schematic of a) single housing and b) double housing ......................................... 16
Figure 3-4: Single & Double Housing Specimens with Reinforcements ................................ 17
Figure 3-5: Specimen naming convention ............................................................................... 17
Figure 3-6: Experimental setup: a) photo, b) detail sensor, and c) schematic ......................... 19
Figure 3-7: Failure modes of Compression, Tension and Shear Tests .................................... 21
Figure 3-8: Failure Modes: a) Splitting, b) Bearing c) Combined Bearing/Splitting .............. 27
Figure 3-9: Typical load-displacement curves for different failure modes ............................. 27
Figure 3-10: Load-displacement tests of typical 0.80 series under bearing load (a) Load vs
Beam Displacement (b) Load vs Mean Crack Opening .......................................................... 30
Figure 3-11: Load-displacement tests of typical 0.65 series under bearing load (a) Load vs
Beam Displacement (b) Load vs Mean Crack Opening .......................................................... 30
Figure 3-12: Failure Modes Observed (a) Splitting Failure, (b) Bearing Failure, (c) Combined
Bearing/Splitting Failure .......................................................................................................... 31
Figure 3-13: Load-displacement of D-0.80 series: a) Load vs Beam Displacement (b) Load vs
Crack Opening for Side #1, c) Load vs Crack Opening for Side #2 ....................................... 33

v

Figure 3-14: Load-displacement of D-0.65 series: a) Load vs Beam Displacement, b) Load vs
Crack Opening for Side #1, c) Load vs Crack Opening for Side #2 ....................................... 33
Figure 3-15: Relation between capacity and material strength ................................................ 34
Figure 3-16: Relation between material strength and density ................................................. 35
Figure 3-17: Capacity vs Mechanical Strength based on Failure Modes ................................ 36
Figure 3-18: Relation between Load-carrying capacity and Mortise Depth (Single Housings)
.................................................................................................................................................. 38
Figure 3-19: Relation between load-carrying capacity and reinforcement (Single Housings) 39
Figure 3-20: Relation between load-carrying capacity and moisture condition (single housings)
.................................................................................................................................................. 40
Figure 3-21: Relation between load-carrying capacity and mortise depth (double housings) 42
Figure 3-22: Relation between load-carrying capacity and moisture condition (double
housings) .................................................................................................................................. 43
Figure 3-23: Relation between load-carrying capacity and reinforcement (double housings) 44

vi

List of Tables
Table 2-1: Parameter overview and results of tests by Heal et al. (2021) ............................... 10
Table 3-1: Overview test series................................................................................................ 18
Table 3-2: Compression Test Results ...................................................................................... 23
Table 3-3: Tension Test Results .............................................................................................. 24
Table 3-4: Shear Test Results .................................................................................................. 25
Table 3-5: Estimated Bearing Capacity ................................................................................... 26
Table 3-6: Load-carrying capacity, crack opening, and density: single housing specimens ... 28
Table 3-7: Load-carrying capacity, beam displacement and crack opening: double housing . 32
Table 3-8: Proportion of failure modes: single housing .......................................................... 37
Table 3-9: Three Factor ANOVA results: single housing ....................................................... 41
Table 3-10: Proportion of failure modes: non-reinforced double housing .............................. 42
Table 3-11: Two factor ANOVA (Analysis 1) results: double housing .................................. 45
Table 3-12: Two factor ANOVA (Analysis 2) results: double housing .................................. 45

vii

Acknowledgements
I am grateful to Allah for all His blessings. I thank my parents and wife for their unwavering
support throughout the entire journey of graduate studies.
It has been an honor and great privilege working with Dr. Thomas Tannert. His prompt and
detailed feedback kept me going in the right direction. His continuous guidance and support
made it possible to get this thesis to the present state. I also appreciate the valuable suggestions
provided by the committee members Dr. Jianhui Zhou and Maik Gehloff. I want to take this
opportunity to thank Maik Gehloff for ensuring that I had the beams with required dimensions
on time for my tests. Finally, I thank the entire team at Wood Innovation Research Laboratory
–Michael Billups, James Andal and Ryan Stern– for preparing the test samples, setting up the
equipment/test assembly and ensuring smooth running of everything required for completing
all my tests related to my thesis.

viii

1 Introduction
1-1

Background

The increasing global population requires extensive levels of construction. The construction
sector contributed 39% of energy and process-related carbon dioxide emissions in 2018, out of
which one third was due to manufacturing building materials and products such as cement and
steel (IEA, 2019). In comparison, timber requires little energy for processing, about 60 to 80%
less than an equivalent structure made of concrete (Börjesson & Gustavsson, 2000). Increased
use of wood and engineered wood products in construction along with sustainable forestry is
required. Hence, increased use of traditional joints such as housings can be a potential solution.
1-2 Load Bearing Timber Housing
Load bearing housings are quite common; these consist of a joist (secondary beam) with a
tenon attached to a main beam (primary beam) resting on a mortise, as shown in Figure 1-1.

Mortise
Tenon

Figure 1-1: Load bearing housing (Nehil & Trojniak, 2013)

Such joints are also known as beam pockets, butt cogs, or partial-width notches (Sobon, 2014).
Previous research on load bearing timber housings is limited, but provides valuable
understanding of its performance. Amongst other findings, a linear relationship was observed
between the load-carrying capacity and depth below the notch (Nehil & Trojniak, 2013), (Heal

1

et al., 2019). However, most previous tests were done under constant service conditions, and
the effect of changes in moisture content (MC) due to seasoning has not been evaluated.
1-3

Load and Moisture Induced Stresses in Housings

Wood is a natural and anisotropic material with low strength in the perpendicular to grain
direction. Hence, it is preferable to avoid or reduce stresses perpendicular to the grain.
However, such stresses inevitably develop in housings, caused by loads and increased due to
changes in moisture content. Since wood is also hygroscopic in nature, surrounding
environmental conditions such as relative humidity and temperature impact its moisture
content, which in turn influences mechanical properties of wood. Drying of wood not only
leads to shrinkage, but can also lead to internal tensile stresses and internal cracks (United
States Department of Agriculture, 2010), (Dietsch, 2017).
1-4

Reinforcements of Connection Details

To counteract the effect of moisture-induced stresses, and to increase a connection detail’s
load-carrying capacity, several reinforcement methods exist. Self-tapping screws (STS) are
quite popular in modern construction as means of reinforcement (Tannert & Lam, 2009).
Previous work on load bearing housings established that STS increased the load-carrying
capacity and the deformation capacity (Heal et al., 2019).
1-5

Objectives

The objective of this study is to investigate the structural performance of timber housings. The
specific objectives are to:
1) Investigate the effect of moisture changes on housings by testing dry specimens, which
were fabricated under both wet (wet-dry) and dry (dry-dry) conditions and compare these
to previous results obtained by testing wet specimens (wet-wet).

2

2) Investigate the relationship between the wood mechanical properties (such as shear parallel
to grain, tension and compression perpendicular to grain strength properties) and the
housing load-carrying capacities.
3) Investigate the influence of reinforcement with self-tapping screws (STS) on load-carrying
capacities and the failure modes of housings.
1-6

Scope and Limitations

This research focused on testing solid timber beams under wet and dry conditions, but not any
range of moisture contents in between. Therefore, all conclusions are limited to these two
extreme conditions. The development of design provisions for housings was beyond the scope
of this thesis. In addition, all tests were conducted under quasi-static monotonic short-term
loading at room temperature. Hence, long-term creep effects, influence of fire and durability
on load-carrying capacity are outside the scope of this research. Moreover, the present study is
limited to the use of Douglas fir grade # 1 and fully threaded 8 mm diameter STS. Hence, the
performance of housings in different species or different reinforcement methods is not known.

3

2

Literature Review

2-1

Material Properties of Wood

Wood is the most widely used renewable construction material. It has high strength-to-weight
ratio and good thermal insulation properties. As a naturally grown material, its properties are
highly variable and vary not only between species, but also between trees of one species and
even within an individual tree. The latter may be due to difference in density and presence of
knots, spiral grain, slope of grain, etc. Hence, timbers are graded to satisfy the requirements of
diverse usage and to ensure reliability of product quality (Harte, 2009).
Wood is an organic composite of cellulose fibers and lignin in which the orientation of microfibers in cell wall has great influence on strength and shrinkage properties of wood. It is an
orthotropic material having higher strength and stiffness in parallel-to-grain direction while
being weaker in the perpendicular-to-grain direction (Harte, 2009). Therefore, tension stresses
perpendicular to grain should be minimized. Barrett et al. (1975) used Weibull’s theory of
brittle fracture to derive allowable stresses while taking into account the size effect, proving
that the allowable stress is related to the structure’s volume.
Wood is a hygroscopic material; it exchanges moisture with the surrounding environment to
attain an equilibrium state (Sjödin & Johansson , 2007), which equilibrium is called
Equilibrium Moisture Content (EMC). The EMC depends on the surrounding environment, i.e.
relative humidity and temperature (Harte, 2009). The MC during construction varies based on
construction material and surrounding conditions, from as low as 6% to up to 20%. However,
unseasoned green wood has MCs higher than 30%, and kiln-drying (expensive) or air drying
(time consuming) are used to reduce MC.
Moisture exchange with the surrounding on the wood surface is much faster compared to inner
regions due to the distance of diffusion. Hence, moisture content depends on both time and

4

location inside the cross section. It should be noted that both physical and mechanical
properties of wood change mostly below the Fiber Saturation Point (FSP); the FSP ranges from
28% to 30% depending on species. Widehammar (2004) showed that wood exhibits higher
strength in dry condition compared to wet condition. Note: Wood is called dry if MC is less
than 19%, wet if the MC is higher but still below the (MC of approx. 28%), and green if the
MC is higher than the FSP.
The change of different strength properties (A: Tension parallel to grain, B: Bending, C:
Compression parallel to grain, D: Compression perpendicular to grain, E: Tension
perpendicular to grain) as a function of moisture content is shown in Figure 2-1, (United States
Department of Agriculture, 2010).

Figure 2-1: Effect of moisture content on wood strength properties

Reduction in moisture content also leads to shrinkage of wood and the shrinkage varies based
on direction. Shrinkage is lowest in the longitudinal to fiber orientation (0.1 to 0.2%) and
maximum in the tangential orientation (6 to 13%) (Green, 2001). The differential shrinkage or
swelling based on orientation is reflection of the anisotropic nature of wood and leads to strains
of different degrees across the cross-section. During drying, the inner wood restrains the wood
near the surface which results in tensile stresses perpendicular to the grain near the surface.

5

Whereas, there are compressive stresses inside the cross-section to counterbalance the tensile
stresses in order to maintain stress equilibrium in the section. Although such stresses reduce
over time due to relaxation processes, these stresses can lead to cracks if the local tensile
strength perpendicular to grain of timber is exceeded. Hence, the load-carrying capacity of
structural member will be reduced (Dietsch, 2017).
Häglund (2007) investigated moisture penetration and moisture gradients at various climatic
location over 23 years to conclude that rapid daily changes do not affect inner part of the
timber. However, slow annual variations have a significant effect. Chaplain & Valentin (2010)
demonstrated that cyclic change in air humidity produced rapid change of the crack velocity
and this was more prominent during drying change.
Drying of wood not only leads to shrinkage, but can also lead to internal tensile stresses and
which in turn can lead to cracks (Franke & Franke, 2014). It occurs when the strength of
bending, shear or tension of the timber is exceeded, for example in beams with notches.
Rammer & Winistorfer (2001) proved the effect of moisture content on the stiffness and the
load-carrying capacity of connections. Although, temperature treatment is a viable option to
improve the hygroscopic properties of wood (Roszyk et al., 2020), moisture content may vary
due to change in ambient conditions inducing stress perpendicular to the grain.
2-2

Timber Housings

Timber-framing is a load-bearing wooden structure usually held together with mortise and
tenon (or similar) joinery. Currently, there are no design guidelines for housings and use of
such connections are limited based on experience of the engineers. Limited research focused
on carpentry-type joints. Tannert (2008) tested rounded dovetail connections of different
materials, geometry, loading conditions, moisture contents, manufacturing tolerances and
reinforcement with STS and concluded that capacity and failure mode is impacted by the load

6

transfer mechanism with size effect playing a major role in capacity. A housing is a mortise
cut on the side of the primary beam to support a secondary beam, enabling load to be
transferred. Housings can be either single or double housings i.e. mortise cut on only one side
or both sides of a beam respectively. Schematics and a photo for typical timber housings are
shown in Figure 2-2.

a)

b)

Figure 2-2: a) Typical single and double timber housings (Heal et al., 2019) and b) photo

Nehil & Trojniak (2013) tested load-bearing housings in green timbers with different depth of
material remaining below the mortise. They concluded that the capacity is linearly proportional
to the depth of material below notch and strength of the specimens themselves. The weaker
softwoods failed in sudden rupture (tension perpendicular to grain), whereas the stronger
hardwoods showed ductile-like splitting with increased load-carrying capacity after the split
developed. Although not related to the observed failure mechanisms, results were consistent
with the National Design Specification (NDS) Equation 3.4-7 (Wood Design Standards
Committee, 2018). Similar consistency with the NDS Equation was observed by (Iuliano,
2013), based on 36 tests on load-bearing housings in 8" × 8" timber beams with varying
housing heights.
Garbin et al. (2006) tested four different configurations of dovetail connections in shear, with
two configurations designed to fail the mortises and the other two designed to fail the tenons.
They concluded that the location of defects and pith (if present) had a substantial impact and

7

they proposed an empirical model based on the slip of the joint for the tested configurations.
However, the results may be skewed as only short lengths of joist and beams were tested. Thus,
the supports may have provided additional resistance against splitting which would be absent
in reality. More recently, Heal et al. (2019) investigated housings in timber beams to analyze
the influence of variations in housing depth, housing width, use of reinforcement, shape of
housing, etc. to provide insightful findings on the stated parameters.
2-3

Reinforcing Wood Joints

Timber strength perpendicular to the wood grain is significantly lower than parallel to the
grain, hence timber structures and joints should be detailed minimizing stresses perpendicular
to the grain (Blass & Bejtka, 2004), (Dietsch & Brandner 2015). Where it is inevitable, the
timber should be reinforced to compensate for the low strength properties. Reinforcement is
possible using various means, such as glued-in rods, bolts, STS, etc. STS are considered the
best choices for many applications as they are fast to install (Dietsch & Brandner 2015).
Angst & Malo (2012) studied the effectiveness of STS as reinforcement under variable climatic
conditions and concluded that during wetting season in comparison to unreinforced glulam,
tensile stresses were reduced significantly by 70% to 30%. However, slight increase in tensile
stress was observed during the drying season due to the additional restraint of reinforcing STS.
It was shown by Jockwer (2014) and later confirmed by Danzer et al. (2016) that installation
of screws at an angle to the grain is an efficient way to increase the capacities both for tension
perpendicular to the grain and in shear for the notched timber members.
Dietsch (2017) investigated the effect of reinforcement on shrinkage stresses in timbers. He
concluded that restraining effect of reinforcement was more critical for timber members in
buildings with a constant dry climate. A reduction of moisture content of 3% around
reinforcement could lead to critical tensile stresses perpendicular to the grain, even after

8

considering the influence of relaxation processes. In fact, even a 1% reduction in moisture was
shown to nullify the comparable stress transfer by the reinforcement in the un-cracked member.
When the reinforcements were placed at an angle of 45°, the moisture induced stresses were
reduced to half whereas the stressed volume was reduced to about 15%. Hence, for areas of
high stresses, e.g. near notches, he recommended placing reinforcements at an angle to
allowing release and proportionate transfer of shear stresses.
Zhang et al. (2019) compared between the effectiveness of fully threaded screws (100% thread
length) and partially threaded screws (33% thread length) in improving the mechanical
properties of single-dowel timber connections with artificial cracks of three different widths
which represented splitting of the wood due to variation in moisture. They concluded that
partial threaded STS were sufficiently suitable to reinforce cracks up to 4.5 mm, but not
effective for higher cracks of 6 mm width.
2-4

Preceding Work at UNBC

In previous research by Heal et al. (2019), a total of 110 Douglas-Fir (No.1 or better) simply
supported beams with 13 series for single-sided connections and 8 series for double-sided
connections were tested. The specimens were all 1,830 mm (6 feet) in length and the crosssections were 89 mm × 285 mm (4″ × 12″), 89 mm × 235 mm (4″ × 10″), or 184 mm × 235
mm (8″ × 10″). The mortise depth and width were mostly 25 mm and 89 mm, respectively.
The specimens were also tested with reinforcement using two STS on either side of the mortise.
Hence, two STS for single housing series and four STS for double housing series. It should be
noted that all these tests were conducted on specimens where the housings were cut under wet
conditions (mean moisture content of 29%). The parameters and test results of all test series
are summarized in Table 2-1 The test series marked with asterisk (*) will later be referred to
as wet-wet (WW) series in the research work presented in this thesis and the detailed results of
these wet-wet series from the previous research are provided in Appendix 1.
9

Table 2-1: Parameter overview and results of tests by Heal et al. (2021)
Mortice
Height [mm]
142

Housing
Width [mm]
89

Single/Double

Reinforcement

Single

No

Fult
[kN]
31.4

S-0.5-89-25-RR

142

89

Single

Yes

52.0

S-.65-89-25

100

89

Single

No

28.2

S-.65-89-25-Sq

100

89

Single

No

19.6

S-.65-89-25-RR

100

89

Single

Yes

21.1

S-0.8-89-25

57

89

Single

No

14.9

S-0.8-89-25-RR

57

89

Single

Yes

18.0

S-0.8-89-25-R

57

89

Single

Yes

18.3

S-0.65-50-25

100

50

Single

No

19.7

S-0.65-130-25

100

130

Single

No

22.6

S-0.65-89-38

100

89

Single

No

26.4

S-0.65-WW*

100

89

Single

No

20.1

S-0.80-WW*

57

89

Single

No

15.0

D-0.5-89-25

118

89

Double

No

45.6

D-0.65-89-25*

82

89

Double

No

43.5

D-0.65-89-25-RR

82

89

Double

Yes

51.0

D-0.8-89-25*

47

89

Double

No

31.3

D-0.8-89-25-RR*

47

89

Double

Yes

39.8

D-0.8-89-25-R*

47

89

Double

Yes

43.7

D-0.65-50-25

82

50

Double

No

34.4

D-0.65-130-25

82

130

Double

No

54.1

ID
S-0.5-89-25

Three different failure modes - bearing, splitting and combined splitting/bearing, shown in
Figure 2-3, were identified. Bearing failures were characterized by localized crushing of wood
fibers at the mortise base. Sustained load pick-up was observed without reaching a peak load
because of wood densification as shown in Figure 2-4. Splitting failures were characterized by
the separation of timber into two parts; small cracks generated at small loads, which continued
to grow with increasing load. A peak “ultimate” load was reached until a sudden failure led to
drop of load carrying capacity. The majority of splitting occurred at the bottom corner of the
mortise but this depended on the presence and location of knots. The third failure mode was a

10

combined one of localized splitting of each side of the mortise base together with crushing
below the mortise. Splitting usually happened after bearing and this can be verified from the
graphs. On rare occasions, some beams did show spitting first and then bearing. However, this
did not distinctly show up on graphs and were few in number out of the total number of
specimens. Thus, they were not characterized as a separate type of failure mode and considered
as combined bearing/splitting failure.

a)

b)

c)

35

35

30

30

30

25

25

20
15

20

15

25
20
15

10

10

10

5

5

5

0
0

a)

Load [kN]

35
Load [kN]

Load [kN]

Figure 2-3: Failure Modes (a) Splitting, (b) Bearing, (c) Combined Bearing/Splitting

10
20
Displacement [mm]

0

0
0

b)

10
20
Displacement [mm]

0

c)

10
20
Displacement [mm]

Figure 2-4: Typical load-displacement curves for failure modes (a) Splitting, (b) Bearing, (c)
Combined Bearing/Splitting (Heal et al., 2019)

As in previous research (Nehil & Trojniak, 2013), mortise height had the highest influence on
load-carrying capacity. An overall decrease in load-carrying capacity was observed with

11

increase in the mortise height. On the other hand, load-carrying capacity increased with the
increase of the mortise width. An increased bearing area in a mortise with greater width was
beneficial. Reinforcement led to higher capacities and greater deformation before failure. It
was shown that housings with square bases achieved lower load-carrying capacities than
mortise with rounded base; however, this mechanism was not studied further. The specimens
which were retested after reinforcement showed higher capacities and greater deformation than
when they were tested unreinforced, however there was a reduction in stiffness.
2-5

Summary of Literature Review

The hygroscopic nature of wood makes it susceptible to changes in MC, which in turn
influences the mechanical properties. Reduction in MC slightly increases the compressive
strength perpendicular to grain, and significantly the compressive strength parallel to grain.
Wood is inherently weak in perpendicular to the grain direction, and drying can induce stresses
perpendicular to grain. The limited previous research on housings showed that the ultimate
load-carrying capacity increased with increase in mortise depth, mortise width and height
below mortise. In addition, capacity improvements were possible with STS reinforcement.
Also, use of reinforcement is more effective in improving capacity when used before testing
rather than using them to reinforce an already tested beam i.e. retest with reinforcement.
However, there are gaps in the literature regarding the understanding of how moisture
conditions during fabrication and loading of housing, influence the load-carrying capacity for
both unreinforced and reinforced beams. Also, the relationship between load-carrying capacity
and properties of timber such as shear strength, compressive strength perpendicular to grain,
tension perpendicular to grain and density are unavailable. Such information would eventually
make it possible to have detailed design guidelines for traditional housing connections.

12

3

Experimental Investigations

3-1 Materials
All timbers tested were Douglas-fir purchased in 2018, grade of No. 1 or better. A paraffin
wax end sealer (AnchorSeal) was applied to the cut ends of all members to limit drying defects.
The beams were air-dried by leaving them inside the Wood Innovation Research Laboratory
(WIRL) for three years (till 2021). The beams were originally in green condition, were cut to
length, and the mortises were machined using a CNC machine, with mortise bases squared off
by hand. The beams that were cut wet to be tested dry did shrink resulting in different actual
depth below the mortise. In addition, the beams also warped along the length. However, it was
possible to minimize these in the dry-dry specimens (housings cut dry and tested dry) by
making adjustments when cutting the housings. The wet-dry specimens they were tested as is.
Moisture content was measured using a Delmhorst RDM-2 pin-type moisture meter prior to
testing, with an average moisture content of 29.2% at 25 mm below the surface when it was
wet in 2018. During the research presented herein, the mean moisture content was 7.0% for
the single housing specimens, while 6.7% for the double housing specimens. The means are
based on one reading taken for each beam specimen at a depth of 25 mm from the surface,
individual values varied between 6.2% to 7.4% and 6.1% to 7.5% for single housing specimens
and double housing specimens, respectively.
While CSA-086 provides specified design values for Douglas Fir-Larch, beam and stringer
grades for longitudinal shear (fv = 1.5 MPa), compression perpendicular to the grain (fcp = 7.0
MPa), tension perpendicular to the grain (ft = 2.0 MPa, value from Glulam). These values were
adjusted to the 7% moisture content using the Wood Handbook procedure (United States
Department of Agriculture, 2010) as 7.5 MPa, 2.4 MPa and 8.6 MPa for compression
perpendicular to grain, tension perpendicular to grain, and shear parallel to grain, respectively.

13

Herein, the actual average strengths in shear parallel to grain, compressive and tensile
perpendicular to grain were determined on small clear samples cut from the beams with
housings after testing. The two beams with the highest and the lowest load-carrying capacity
(obtained from the housing tests) in the unreinforced state were identified from each series
(resulting in 20 specimens), and samples were cut following the specifications of ASTM D143
(2021). For the compression tests, 20 beams, which exhibited either bearing or combined
bearing/splitting failure, were identified along with 6 beams, which exhibited splitting failure.
Three samples were tested for each property (compression, tension and shear) from each beam,
for a total of 198 small clear specimens. The small clear specimens were obtained at random
locations along the beam to assure these were without knots, cracks or other defects.
The corresponding test specimens and the test assemblies for each test are shown in Figure
3-1. ASTM D143 (2021) was followed for testing. The compression, tension and shear tests
were conducted using rates of loading of 2.0 mm/min, 2.5 mm/min and 0.6 mm/min
respectively. For tension and shear tests, strengths were determined at failure, whereas for the
compression tests, strength was determined at displacements of 2.5 mm as per ASTM D 143
(2021), and at displacements of 5.0 mm (to get additional perspective).

a)

b)

c)

Figure 3-1: Test Assembly for (a) Compression Perpendicular to Grain Test (b) Tension
Perpendicular to Grain Test (c) Shear Test
14

For reinforcement, fully-threaded STS (Heco-Topix) with product approval ETA-11/0284
(DIBt, 2019) with 8.0 mm diameter and lengths of 120 mm, 180 mm or 200 mm, as shown in
Figure 3-2, were selected. Length of reinforcement was at least double of height below mortise
i.e. 120 mm STS for 57 mm or 47 mm depth, 180 mm STS for 82 mm depth and 200 mm STS
for 100 mm depth below the mortise. So, the difference in reinforcement length was as required
to match the difference in depth below the mortise. Two screws were used for each connection
as per the product approval. For the selected diameter, the screws have characteristic tensile
strength of 20 kN and withdrawal resistance of 22.7 kN for S-0.65 series and 13.7 kN for S0.80 series (calculated based on ETA specifications). For calculations embedment length was
assumed to be the difference between screw length and height below mortise i.e. for S-0.80 it
is 63 mm (120 mm of screw – 57 mm of length below mortise) and for S-0.65 it is 100 mm
(200 mm of screw – 100 mm below mortise). These values were assumed irrespective of failure
modes and location of splitting failure (if applicable) as the exact location of splitting was not
recorded. Hence, for computational convenience it was assumed that the splitting was below
the mortise corner. The screws were installed at the minimum edge distances (S) away from
the mortise base, 3d, but which was taken as 25 mm for convenience.

Figure 3-2: Fully threaded STS of 120mm, 180mm and 200mm from left to right

15

3-2 Specimen Description and Test Matrix
Similar to the preceding work at UNBC, simply supported beam specimens with single-sided
and double-sided housings were tested. For the single housings, 10 test series with 6 replicates
each, therefore 60 specimens were manufactured. Whereas, the double housings have 6 test
series each with 5 replicates, therefore a total of 30 specimens as shown in Figure 3-3. The
single housing specimens had a length of 1,830 mm, width of 100 mm, beam height of 250
mm with mortise cut in to them having depth of 25 mm and width of 89 mm. The mortise
height varied among the series, with the depth below mortise either 57 mm for S-0.80 series
or 100 mm for S-0.65 series. The double housing specimen length was 1,825 mm, width was
130 mm, height was 225 mm, with the same mortise width and depth as the single housing
connections. However, the depths below the mortise were 47 mm for D-0.80 series and 82 mm
for D-0.65 series. For S-0.80, 80% mortise height would mean 0.8 × 250 = 200 mm, hence
height below mortise should have been 50 mm, but the actual height was 57 mm. Similarly,
for S-0.65 it should have been 87.5 mm, but it was actually 100 mm. Similar double housing
depths below the mortise should have been different that those used. These 57 mm and 100
mm for the single housings and 47 mm and 82 mm for the double housings were maintained
to match the heights used in the previous research by Heal et al. (2019).

a)

b)
Figure 3-3: Schematic of a) single housing and b) double housing

16

Each housing was reinforced with two STS (i.e., two STS for single housing and four STS for
double housing series), as shown in Figure 3-4. Reinforcement was installed either for
specimens that were already tested or – in some double housing series – before testing. All
parameters are summarized in Table 3-1.

a)

b)
Figure 3-4: Single & Double Housing Specimens with Reinforcements

The naming convention (ID) of each test series is explained in Figure 3-5. The first letter refers
to single (S) or double housing (D), the decimal number 0.80 or 0.65 (80% or 65%) refers to
housing depth. The third term (WW, WD or DD) refers to the moisture conditions (wet or dry)
during fabrication (first letter) and testing (second letter). Exception to this exists in the form
of WWD where WW specimens were retested with reinforcement under dry conditions. The
last part refers to reinforcement: none (blank), retested with STS (RR) or tested reinforced (R).

Figure 3-5: Specimen naming convention
17

Table 3-1: Overview test series
# of
Tests

Mortise
Backcut

Moisture
Condition

Reinforcement

S-0.65-WWD-RR

6

100 mm, 0.65

Cut Wet, tested
Wet

Reinforced with Heco-Topix 8.0
Ø × 200mm & retested

S-0.8-WWD-RR

6

57 mm, 0.8

Reinforced with Heco-Topix 8.0
Ø × 120mm & retested

S-0.65-WD

6

100 mm, 0.65

Cut Wet, tested
Wet
Cut Wet, tested
Dry

S-0.65-WD-RR

6

100 mm, 0.65

Cut Wet, tested
Dry

Reinforced with Heco-Topix 8.0
Ø × 200mm & retested

S-0.80-WD

6

57 mm, 0.8

S-0.80-WD-RR

6

57 mm, 0.8

S-0.65-DD

6

100 mm, 0.65

S-0.65-DD-RR

6

S-0.80-DD

Series ID

Unreinforced

Cut Wet, tested
Dry
Cut Wet, tested
Dry
Cut Dry, tested
Dry

Reinforced with Heco-Topix 8.0
Ø × 120mm & retested

100 mm, 0.65

Cut Dry, tested
Dry

Reinforced with Heco-Topix 8.0
Ø × 200mm & retested

6

57 mm, 0.8

Cut Dry, tested
Dry

Unreinforced

S-0.80-DD-RR

6

57 mm, 0.8

Cut Dry, tested
Dry

Reinforced with Heco-Topix 8.0
Ø × 120mm & retested

D-0.65-DD

5

82 mm, 0.65

Cut Dry, tested
Dry

Unreinforced

D-0.65-DD-RR

5

82 mm, 0.65

Cut Dry, tested
Dry

Reinforced with Heco-Topix 8.0
Ø × 180mm & retested

D-0.65-DD-R

5

82 mm, 0.65

Cut Dry, tested
Dry

Reinforced prior to Testing with
Heco-Topix 8.0 Ø × 180mm

D-0.80-DD

5

47 mm, 0.8

Cut Dry, tested
Dry

Unreinforced

D-0.80-DD-RR

5

47 mm, 0.8

Cut Dry, tested
Dry

Reinforced with Heco-Topix 8.0
Ø × 120mm & retested

D-0.80-DD-R

5

47 mm, 0.8

Cut Dry, tested
Dry

Reinforced prior to Testing with
Heco-Topix 8.0 Ø × 120mm

Unreinforced

Unreinforced

3-3 Test Methods
The housing specimens were tested in a Universal Test Machine (UTM) using a custom
loading frame, see Figure 3-6a, such that the mortise was loaded in shear only. The force from
the secondary beam was simulated by use of loading block inside the mortise, made of

18

Laminated Veneer Lumber (LVL). Restraints were provided on the outside surface to ensure
that they did not deflect outwards when loads were applied to the mortise. EN 26 891 (CEN,
1991) was followed for loading where the specimens were initially loaded to approx. 40% of
their expected load-carrying capacity to place the loading block properly on the mortise and
thus reducing any alignment problems. After holding this 40% load for 30 seconds, the beam
was unloaded to 10%, with that load kept constant for another 30 seconds. Afterwards, the
beam was loaded to failure, with failure defined as 80% drop in the load-carrying capacity
(F ). A displacement controlled loading rate of 5.0 mm/min was used for all the 90 specimens.
In case of specimens where no sudden drop of failure was achieved due to nature of failure
mode, loading was stopped when capacity continued to drop consistently.

a)

b)

b)
Figure 3-6: Experimental setup: a) photo, b) detail sensor, and c) schematic

19

The load-displacement data were obtained from the UTM data acquisition system, while the
crack opening data were collected using string pots attached close to the housings as shown in
Figure 3-6b. When the housing was loaded, it would cause a crack to develop near the base of
the mortise. The relative displacement between was measured. The screw was placed mid-way
below the base of mortise for all test series. Two sets of data were obtained from the two
sensors with the results being averaged to get mean crack opening for each test specimen.
Bearing capacities were estimated by multiplying the compressive strength with the bearing
area (89 mm × 25 mm) of the housing.
3-4 Statistical Analyses
In this research, analysis of variance (ANOVA) (Montgomery & Runger, 2003) was conducted
to determine the statistical significance of mortise depth, moisture condition and reinforcement
along with their interactions on

. In order to accept or reject a null hypothesis (normally

stating that there is no effect of the factor), a p-value is computed. A significance level (α) of
0.05 which is typical in engineering practice (Tannert et al., 2012) was selected to compare the
p value against. For the single housing tests, a three-way factorial design was chosen. The first
factor, mortise depth had two levels (S-0.80 and S-0.65). The second factor, moisture
conditions, had three levels (WW, WD and DD) and the third factor, reinforcement, had again
two levels (unreinforced and reinforced). For double housings, two-way ANOVA was
performed twice: 1) with mortise depths (two levels: D-0.80 and D-0.65) and reinforcement
(three levels: unreinforced, retested with reinforcement and reinforced) as factors. This
analysis was only for dry (DD) specimens of all the double housing series; and 2) for the D0.80 series with different moisture conditions (two levels: WW and DD) and reinforcement
(three levels: unreinforced, retested with reinforcement and reinforced) as factors. The test
results for WW series for both the single and double housing series were taken from previous
study in 2018 at UNBC (Heal et al., 2019) and all the rest from this research.

20

3-5 Results
3-5-1 Compression, Tension and Shear Tests
The small clear specimen tests resulted in the failure modes shown in Figure 3-7. In the
compression perpendicular to the grain tests, as per ASTM D143, the load at 2.5 mm
compression was recorded as strength, as shown in Figure 3-7 (a). In the tension perpendicular
to grain tests, all specimens showed distinct failure at the middle of the cross-section, as shown
Figure 3-7 (b). In the shear tests, all specimens failed by fracture through the shear plane with
the majority completely separating into two pieces, as shown in Figure 3-7 (c).

a)

b)

c)

Figure 3-7: Failure modes of Compression, Tension and Shear Tests

The weights and volumes were measured for the specimens from each of the selected
representative beams to calculate the apparent density. These densities and the recorded mean
strengths are presented in Table 3-2 for compression perpendicular to grain tests, Table 3-3 for
tension perpendicular to grain tests and Table 3-4 for shear tests. The specimens marked with

21

asterisk (*) refer to the specimens taken from beams tested in the previous research by Heal
(Heal et al., 2019) and the numbers ‘1-6’ refer to the small clear specimens being collected
from the replicate number for that series. These data are later used to correlate the specimen
strength to the load-carrying capacity of then housing and the density of timber.
The mean compressive strengths at 2.5 mm displacements were 9.8 MPa with a coefficient of
variation (CV) of 16% for the S-0.80 series, 10.4 MPa (18%) for the S-0.65 series, 9.5 MPa
(24%) for the D-0.80 series and 8.1 MPa (16%) for the D-0.65 series. The corresponding mean
densities were determined as 457 kg/m3, 435 kg/m3, 528 kg/m3 and 503 kg/m3.
The mean tensile strengths were determined 1.9 MPa with a CV of 20% for the S-0.80 series,
2.2 MPa (17%) for the S-0.65 series, 2.0 MPa (35%) for the D-0.80 series, and 1.9 MPa (27%)
for the D-0.65 series. The corresponding mean densities were determined as 465 kg/m 3, 525
kg/m3, 518 kg/m3 and 535 kg/m3.
The mean shear strengths were determined as 8.6 MPa (10%) for the S-0.80 series, 9.7 MPa
(12%) for the S-0.65 series, 10.0 MPa (9%) for the D-0.80 series and 10.5 MPa (15%) for the
D-0.65 series. The corresponding mean densities were 456 kg/m 3, 511 kg/m3, 495 kg/m3 and
524 kg/m3.
The compressive strengths of single housing specimens (S-0.65 and S-0.80 series) were used
to estimate the bearing capacity of the housing to compare with the load-carrying capacity of
the housing as shown in Table 3-5. It was observed that the mean differences between bearing
capacities and load-carrying capacities for splitting, bearing and mixed bearing/splitting failure
modes were respectively 31%, 10% and 24%. This indicates that compressive strength of wood
is certainly crucial for the specimens which failures in bearing failure modes.

22

Table 3-2: Compression Test Results
ID

Density
[kg/m3]

Strength at 2.5
mm [MPa]

CV
[%]

Strength at 5
mm [MPa]

CV
[%]

S-0.80-WW* ‘2’

420

9.5

5

10.1

2

S-0.80-WW* ‘3’

517

11.2

1

12.8

2

S-0.80-WD

‘2’

492

11.4

1

12.2

2

S-0.80-WD

‘5’

500

11.6

2

13.3

4

S-0.80-DD

‘1’

420

7.9

4

9.0

5

S-0.80-DD

‘2’

419

8.7

2

9.5

2

S-0.80-DD

‘6’

428

8.5

2

9.6

4

Average

457

9.8

16

10.9

16

S-0.65-WW* ‘1’

396

8.8

6

9.4

6

S-0.65-WW* ‘4’

532

14.3

2

16.7

1

S-0.65-DD

‘5’

428

8.5

3

9.3

2

S-0.65-WW* ‘3’

419

8.5

3

9.3

3

S-0.65-WW* ‘6’

428

11.5

1

13.4

1

S-0.65-WD

‘2’

425

9.1

2

10.2

1

S-0.65-WD

‘4’

426

9.6

4

10.8

5

S-0.65-DD

‘2’

425

11.3

4

12.4

7

S-0.65-DD

‘4’

418

11.7

1

13.8

4

S-0.65-DD

‘6’

453

11.0

2

12.1

1

435

10.4

18

11.7

21

Average
D-0.80-DD

‘3’

452

7.0

4

7.6

5

D-0.80-DD

‘5’

556

9.0

1

9.3

3

D-0.80-DD-R

‘3’

525

12.5

3

15.4

4

D-0.80-DD-R

‘2’

577

9.5

7

10.0

3

528

9.5

24

10.6

32

Average
D-0.65-DD

‘5’

459

9.0

3

10.4

3

D-0.65-DD

‘4’

559

9.7

4

11.4

4

D-0.65-DD-R

‘3’

430

6.9

2

7.3

2

D-0.65-DD-R

‘2’

478

6.7

2

7.1

0

D-0.65-DD-R

‘5’

589

8.3

5

8.5

4

503

8.1

16

8.9

21

Average

23

Table 3-3: Tension Test Results
ID

Density
[kg/m3]

Strength
[MPa]

CV
[%]

S-0.80-WW*

‘2’

454

1.7

22

S-0.80-WW*

‘3’

537

2.5

67

S-0.80-WD

‘2’

500

1.9

17

S-0.80-WD

‘5’

422

2.1

3

S-0.80-DD

‘1’

428

1.4

7

S-0.80-DD

‘2’

448

1.8

21

465

1.9

20

Average
S-0.65-WW*

‘1’

431

1.6

17

S-0.65-WW*

‘4’

564

2.1

34

S-0.65-WD

‘5’

549

2.8

2

S-0.65-WD

‘6’

578

2.1

9

S-0.65-DD

‘3’

552

2.4

5

S-0.65-DD

‘5’

480

2.4

5

525

2.2

17

Average
D-0.80-DD

‘3’

480

1.0

15

D-0.80-DD

‘4’

500

2.4

12

D-0.80-DD-R

‘1’

523

2.5

2

D-0.80-DD-R

‘3’

569

1.9

10

518

2.0

35

Average
D-0.65-DD

‘2’

566

1.7

9

D-0.65-DD

‘5’

503

1.3

43

D-0.65-DD-R

‘3’

506

2.5

8

D-0.65-DD-R

‘4’

566

1.9

23

535

1.9

27

Average

24

Table 3-4: Shear Test Results
ID

Density
[kg/m3]

Strength
[MPa]

CV
[%]

S-0.80-WW*

‘2’

431

8.9

4

S-0.80-WW*

‘3’

531

9.5

2

S-0.80-WD

‘2’

524

9.5

8

S-0.80-WD

‘5’

424

7.5

3

S-0.80-DD

‘1’

397

7.6

3

S-0.80-DD

‘2’

431

8.8

8

Average

456

8.6

10

S-0.65-WW* ‘1’

415

7.8

3

S-0.65-WW* ‘4’

554

9.4

9

S-0.65-WD

‘5’

537

10.7

7

S-0.65-WD

‘6’

577

10.9

12

S-0.65-DD

‘3’

540

10.2

3

S-0.65-DD

‘5’

445

8.8

3

511

9.7

12

Average
D-0.80-DD

‘3’

475

8.8

2

D-0.80-DD

‘4’

494

10.2

3

D-0.80-DD-R ‘1’

484

10.9

2

D-0.80-DD-R ‘3’

526

10.0

5

Average

495

10.0

9

D-0.65-DD

‘2’

572

11.1

6

D-0.65-DD

‘5’

471

8.6

8

D-0.65-DD-R ‘3’

461

10.0

3

D-0.65-DD-R ‘4’

593

12.4

12

Average

524

10.5

15

25

Table 3-5: Estimated Bearing Capacity
ID

Failure Modes

Compression
Strength at 2.5
mm [MPa]

Bearing
Capacity
[kN]

Fult
[kN]

%
Difference

S-0.80-WW*

2/6

Splitting

9.5

21.1

10.9

48

S-0.80-WW*

3/6

Splitting

11.2

25.0

17.9

28

S-0.80-WD

2/6

Splitting

11.4

25.3

17.7

30

S-0.80-WD

5/6

Splitting

11.6

25.7

13.9

46

S-0.80-DD 1/6

Splitting

7.9

17.6

13.8

21

S-0.80-DD 2/6

Splitting

8.7

19.4

16.6

14

S-0.65-WW*

1/6

Bearing

8.8

19.5

17.2

12

S-0.65-DD 5/6

Bearing

8.5

19.0

15.5

18

S-0.65-WW*

3/6

Bearing

8.5

19.0

20.8

-10

S-0.65-WD

2/6

Bearing

9.1

20.3

16.8

17

S-0.65-WD

4/6

Bearing

9.6

21.3

21.4

0

S-0.65-DD 2/6

Bearing

11.3

25.2

18.9

25

S-0.65-DD 6/6

Bearing

11.0

24.4

22.4

9

S-0.80-DD 6/6

Bearing/Splitting

8.5

19.0

14.5

24

S-0.65-WW*

4/6

Bearing/Splitting

14.3

31.8

22.6

29

S-0.65-WW*

6/6

Bearing/Splitting

11.5

25.7

19.0

26

S-0.65-DD 4/6

Bearing/Splitting

11.7

26.0

21.0

19

Mean %

3-5-2 Single Housing Beams
Three different failure modes: splitting, bearing, and combined bearing/splitting were observed
as shown in Figure 3-8; typical load-displacement curves corresponding to these failures are
shown in Figure 3-9. The splitting failures were typically characterized by reaching loadcarrying capacity followed by sudden drop in load. Horizontal splits along the length and width
of beams were observed, mostly at the mortise base, but in some specimens also at higher
locations. The bearing failures were not characterised by a distinct drop after reaching loadcarrying capacity as the load was usually maintained due to continuous crushing and
densification of wood fibres at the base of the mortise. Hence, tests were stopped after 6

26

31

10

24

minutes or when localized tear-out occurred, whichever came first. Otherwise, a combined
failure, with mostly splitting happing after bearing occurred, where the load continued to
increase due to densification of the wood fibres followed by sudden drop at load-carrying
capacity similar to pure splitting. However, the splitting observed here were mostly limited to
corners of the mortise base.
The mean values along with their CVs for density, load-carrying capacity (F ), as well as
mid-span displacement and crack opening at F

are presented in Table 3-6. All individual

results for series S.80 are provided in Appendix 2, and for series S-0.65 in Appendix 3.

a)

b)

c)

Figure 3-8: Failure Modes: a) Splitting, b) Bearing c) Combined Bearing/Splitting

25
S-0.80-WD-RR-4
(Bearing-Splitting)

Load [kN]

20

S-0.80-WD-RR-6
(Bearing)

15
10

S-0.80-DD-4
(Splitting)

5
0
0

5

10
15
Displacement [mm]

20

25

Figure 3-9: Typical load-displacement curves for different failure modes

27

Table 3-6: Load-carrying capacity, crack opening, and density: single housing specimens
ID

Density [kg/m3]

Fult [kN]

Disp. [mm]

Crack Opening [mm]

S-0.80-WWD-RR

479

9%

17.3

26%

10.7

23%

2.0

40%

S-0.80-WD

455

10%

15.4

9%

7.2

12%

0.3

27%

S-0.80-WD-RR

455

10%

20.6

16%

16.6

28%

1.9

39%

S-0.80-DD

451

8%

14.9

8%

7.0

22%

0.8

99%

S-0.80-DD-RR

451

8%

19.0

17%

10.0

28%

1.5

16%

S-0.65-WWD-RR

475

11%

26.5

16%

23.6

17%

2.4

27%

S-0.65-WD

479

10%

18.9

14%

11.9

47%

0.5

41%

S-0.65-WD-RR

479

10%

26.0

18%

18.8

33%

1.2

37%

S-0.65-DD

490

9%

21.9

21%

12.4

45%

0.9

71%

S-0.65-DD-RR

490

9%

23.0

30%

14.8

30%

1.0

72%

The mean density varied from 451 kg/m3 for S-0.80-DD to 490 kg/m3 for S-0.65-DD with
lowest CV (8%) for S-0.80-DD and highest CV (11%) for S-0.65-WWD-RR. The mean F
ranged from 14.9 kN for S-0.80-DD to 26.5 kN for S-0.65-WWD-RR, where lowest CV (8%)
was obtained for S-0.80-DD and largest CV (30%) was for S-0.65-DD-RR. In case of beam
displacement, lowest was 7.0 mm for S-0.80-DD and highest was 23.6 mm for S-0.65-WWDRR. However, lowest CV (12%) was not for S-0.80-DD as in previous two parameters, but for
S-0.80-WD while largest CV (47%) was for S-0.65-WD. Mean crack opening varied largely
from 0.3 mm for S-0.80-WD to 2.4 mm for S-0.65-WWD-RR. The lowest CV (16%) was for
S-0.80-DD-RR and largest CV (99%) was for S-80-DD. High CV indicated that the crack
opening varied significantly. Although crack opening is shown for all specimens (to maintain
consistency with previous research), practically for beams with bearing failure this represents
how much the end of the sensor string displaced vertically. For beams with splitting or
bearing/splitting it is assumed that sensor provides the crack opening as string pot is fixed at
the beam top while the end of string is placed below the mortise base.

28

Specimens from the S-0.65 series reached higher load-carrying capacity and beam
displacement at failure than the specimens from the corresponding S-0.80 series within the
same moisture conditions. Re-testing with reinforcement increased the capacity irrespective of
the moisture conditions. It is worth noting that the CV (for capacity) is higher when reinforced,
suggesting large dispersion of the results around mean. It is also interesting to note that CV of
mean crack opening is large for all series and hence obtaining precise measurements is quite
difficult for this parameter. Calculating the average CV for S-0.80 series and S-0.65 series
shows that for both load-carrying capacity and beam displacement, S-0.65 has larger CV (20%
and 34% respectively), than S-0.80 (15% and 23% respectively). Hence, failure mechanism in
S-0.65 series is such that it has higher dispersion of obtained results.
Representative graphs for each test series are shown in Figure 3-10 and Figure 3-11. All
individual load-displacement and load-crack opening graphs are also provided for both series
in Appendix 2 and 3. It is seen in Figure 3-10 (a) that specimens with reinforcement (S-0.80WD-RR-1, S-0.80-DD-RR-4 and S-0.80-WWD-RR-2) have higher load-carrying capacity
than the unreinforced ones (S-0.80-WD-3 and S-0.80-DD-4), and also fail after significant
displacement of the beam. The trend is more prominent when load vs mean crack-opening
curves are considered as shown in Figure 3-10 (b). In the reinforced specimens, the beams
reach load capacity when the cracks have opened up significantly more than the unreinforced
beams. It is observed in the representative curves shown here in Figure 3-11 (which is also
applicable to individual curves provided in the appendixes), the load-displacement path for S0.65 series is much more variable than those of the S-0.80. However, similar to S-0.65 series
reinforcement increases the load-carrying capacity with possibility of reaching greater
displacement at capacity load. Similar to the unreinforced specimens, the reinforced specimens
also show wide range of variation in results.

29

S-0.80-WD-3
S-0.80-DD-4
S-0.80-WWD-RR-2

S-0.80-WD-RR-1
S-0.80-DD-RR-4

S-0.80-WD-3
S-0.80-DD-4
S-0.80-WWD-RR-2
30

30
25

25

20

20

Load [kN]

Load [kN]

S-0.80-WD-RR-1
S-0.80-DD-RR-4

15
10

15
10
5

5

0

0
0

5

10
15
20
Displacement [mm]

25

0

30

1

2
3
Crack Opening [mm]

4

5

a)
b)
Figure 3-10: Load-displacement tests of typical 0.80 series under bearing load (a) Load vs
Beam Displacement (b) Load vs Mean Crack Opening

30

30

25

25

20

20

15
10

S-0.65-WD-RR-3
S-0.65-DD-RR-6

15
10

5

a)

S-0.65-WD-3
S-0.65-DD-6
S-0.65-WWD-RR-3

S-0.65-WD-RR-3
S-0.65-DD-RR-6

Load [kN]

Load [kN]

S-0.65-WD-3
S-0.65-DD-6
S-0.65-WWD-RR-3

5

0
0

5

10

15

20

25

30

Displacement [mm]

b)

0
0

5

10
15
20
Crack Opening [mm]

25

Figure 3-11: Load-displacement tests of typical 0.65 series under bearing load (a) Load vs
Beam Displacement (b) Load vs Mean Crack Opening

3-5-3 Double Housing Beams
Similar to the specimens with singe housing, the specimens with double housings failed in
three different modes: splitting, bearing, and combined splitting/bearing, as shown in Figure
3-12. However, the presence of two housings did complicate the observations made in the form
of two different sides seemingly failing in two different modes. Hence, conclusion on the
global mode of failure for each specimen was to some extent subjective in some cases.

30

a)

b)

c)

Figure 3-12: Failure Modes Observed (a) Splitting Failure, (b) Bearing Failure, (c)
Combined Bearing/Splitting Failure

The mean values along with their CVs for density, load-carrying capacity (F ), as well as
mid-span displacement and crack opening at F

are presented in Table 3-7. All individual

results are included in Appendix 4 for D-0.80 series and Appendix 5 for D-0.65 series.
Similar to the single housing series, specimens in the double housing series with greater height
below housing (i.e. in the D-0.65 series) have higher load-carrying capacity and beam
displacement at failure than the specimens from the corresponding D-0.80 series. Also,
retesting with reinforcement helped in reaching greater capacity and displacement. However,
reinforcing the beams first and then testing them lead to even higher increase of capacity, at a
lower displacement irrespective of housing depth. It was not possible to directly compare
between single and double housing capacities (i.e. whether the capacity in double housing is
double of the single housing capacity) because the depths below the mortise were not identical.
The density varied within a close range of 503 kg/m3 (CV of 6%) to 515 kg/m3 (CV of 9%) for
D-0.80-DD-R and D-0.65-DD-R, respectively. The load-carrying capacity ranged from 22.0
kN (CV of 52%) to 49.6 kN (CV of 14%) for D-0.80-DD and D-0.65-DD-R, respectively.
Beam displacement ranged from 8.6 mm (20%) for D-0.80-DD to 20.0 mm (29%) for D-0.65DD-RR. Similar to the single housings, double housings also had large variation in crack
openings; values ranged from 0.9 mm (largest CV of 108%) for D-0.65-DD-R to 8.2 mm (CV
31

of 81%) for D-0.80-DD-RR. The mean crack opening results being most dispersed with large
CV in general. It is interesting to note that the specimens, which were reinforced and then
tested (D-0.80-DD-R and D-0.65-DD-R) had the lowest CV (9% and 14% respectively).
Hence, reinforcing the specimens before testing ensured lower variations in capacity compared
to testing an unreinforced beam or retesting a beam with reinforcement.

Table 3-7: Load-carrying capacity, beam displacement and crack opening: double housing
ID

Density
[kg/m3]

Fult [kN]

Disp.
[mm]

Crack Opening
[mm]

D-0.80-DD

510

6%

22.0

52%

8.6

20%

3.7

86%

D-0.80-DD-RR

510

6%

26.1

28%

13.7

41%

8.2

81%

D-0.80-DD-R

503

6%

32.7

9%

10.7

12%

1.0

33%

D-0.65-DD

506

6%

44.3

19%

15.6

41%

1.2

91%

D-0.65-DD-RR

506

6%

45.6

24%

20.0

29%

1.9

29%

D-0.65-DD-R

515

9%

49.6

14%

17.5

37%

0.9

108%

Representative graphs for each test series are shown in Figure 3-13 and Figure 3-14. Individual
graphs are provided in the appendix 4 for D-0.80 series, and appendix 5 for D-0.65 series. The
reinforced series (D-0.80-DD-R-4) showed higher capacity than unreinforced (D-0.80-DD-1)
or series retested with reinforcement (D-0.80-DD-RR-1). The reinforcing seemed to reduce
ductility; failure occurred without the crack opening up significantly. The STS reduced the
opening width at failure. Ductility would give warning of failure and thus be preferable over a
sudden failure observed in unreinforced housings. A similar trend was observed in Figure 3-14
with reinforced series (D-0.65-DD-R-1) showing higher capacity than the unreinforced (D0.65-DD-4) and retested beam with reinforcement (D-0.65-DD-RR-2). Mean crack opening
stays low for the reinforced series (D-0.65-DD-R-1) with the retested beam reinforcement (D0.65-DD-RR-2) showing very large crack openings before failure.

32

Load [kN]

D-0.80-DD-1
D-0.80-DD-RR-1
D-0.80-DD-R-4

D-0.80-DD-1
D-0.80-DD-RR-1
D-0.80-DD-R-4

40
35
30
25
20
15
10
5
0

D-0.80-DD-1
D-0.80-DD-RR-1
D-0.80-DD-R-4

40
35
30
25
20
15
10
5
0
0

2
4
6
8
Displacement [mm]

10

40
35
30
25
20
15
10
5
0
0

2

4

6

8

10

0

Crack Opening #1 [mm]

2

4

6

8

10

Crack Opening #2 [mm]

a)
b)
c)
Figure 3-13: Load-displacement of D-0.80 series: a) Load vs Beam Displacement (b) Load
vs Crack Opening for Side #1, c) Load vs Crack Opening for Side #2

Load [kN]

D-0.65-DD-4
D-0.65-DD-RR-2
D-0.65-DD-R-1
70

70

70

60

60

60

50

50

50

40

40

40

30

30

30

20

20

20

10

10

10

0

0
0

a)

D-0.65-DD-4
D-0.65-DD-RR-2
D-0.65-DD-R-1

D-0.65-DD-4
D-0.65-DD-RR-2
D-0.65-DD-R-1

5 10 15 20 25 30
Displacement [mm]

0
0

b)

5

10 15 20 25 30

Crack Opening #1 [mm]

0

c)

5

10 15 20 25 30

Crack Opening #2 [mm]

Figure 3-14: Load-displacement of D-0.65 series: a) Load vs Beam Displacement, b) Load
vs Crack Opening for Side #1, c) Load vs Crack Opening for Side #2

3-6 Discussion
3-6-1 Correlation between material strengths and housing load-carrying capacity
The Wood Handbook (United States Department of Agriculture, 2010) tabulated mean
strengths for compression perpendicular to grain, tension perpendicular to grain and shear
parallel to grain at 7% moisture content were 7.5 MPa, 2.4 MPa and 8.6 MPa, respectively.
The experimentally determined compressive strength values were on average 35% higher: 9.8
MPa and 10.4 MPa for single housings, S-0.80 and S-0.65 series, respectively. Similarly, the
33

shear strengths (8.6 MPa and 9.7 MPa) were higher. On the contrary, the tensile strengths (1.9
MPa and 2.2 MPa) were on average 15% lower.
The results from the small specimen tests (compression, tension and shear) were correlated to
the housing load-carrying capacity (Figure 3-15) and densities (Figure 3-16). The loadcarrying capacity values were normalized for variation in depths of mortise (0.65 and 0.80)
and number of housings (single or double housing). The R2 value which describes the
proportion of the variation in the dependent variable (i.e., load-carrying capacity) which can
be attributed to the independent variable (i.e., compressive strength/tensile strength/shear
strength) are low for all three material strengths having R2 values of 0.20, 0.24 and 0.25
respectively.

Shear

Tension

Compression

Load-carrying capacity [kN]

35
30

R² = 0.2421
R² = 0.2471

25
R² = 0.1985
20
15
10
0

3

6
9
Strength [MPa]

12

15

Figure 3-15: Relation between capacity and material strength

Figure 3-16 illustrates that compressive and shear strengths are more strongly correlated to
specimen densities with higher R2 values of 0.51 and 0.59 respectively. However, tensile
strength values are less dependent on densities with lower R2 value of 0.21, demonstrating the
high variability involved of tensile strength of timber perpendicular to the grain direction.

34

16
R² = 0.5142

Strength [MPa]

12

R² = 0.5859

8

Shear
Tension

4

Compression

R² = 0.2126

0
350

400

450

500

550

600

Density [kg/m3]

Figure 3-16: Relation between material strength and density

To get a better perspective on the relationship between material strengths and failure modes of
the beam from which the small specimens were prepared, data were analysed of failures modes
of the unreinforced single housing beams, see Figure 3-17. As before the load-carrying
capacity values were normalized for variation in depths of mortise (0.65 and 0.80) and number
of housings (single or double housing). For the compressive strength, 21 beam specimens
were considered with 6 splitting failures, 10 bearing failures. and 5 mixed failures. For the
shear and tensile strengths, 16 beam specimens were considered with 11 splitting failures, 4
bearing failures and 1 combined failure. A limitation that should be noted is that all three tests
were conducted on dry specimens whereas the load-carrying of beams included beams tested
wet which accounted for 30% of the small specimens tested (for compression) and 25% (for
shear and tension). While the compressive strength is expected to be an indicator for possibility
of bearing failure modes (if beam have higher depth below the mortise) based on the relatively
lower difference between expected bearing capacity and housing capacity as seen in Table 3-5
, the low R2 values in Figure 3-17 confirm that the small clear specimen strengths are not a
good predictor of housing load-carrying capacity of timber housings. This is most applicable
for tensile strength which has the lowest R2 value of 0.1. All data were normalised as before.

35

Load-carrying capacity [kN]

24
R² = 0.2522

22
20
18

R² = 0.1408

16

Splitting Failures

14

Bearing and Mixed
Bearing/Splitting Failures

12
6

8

a)

10
12
14
Compressive strength [MPa]

16

35

Load-carrying capacity [kN]

30
R² = 0.0907
25
20

R² = 0.4503

15

Splitting Failures

10

Bearing and Mixed
Bearing/Splitting Failures

5
1.0

1.5

b)

2.0
2.5
Tensile strength [MPa]

3.0

Load-Carrying Capacity [kN]

35
30
R² = 0.3118
25

20
R² = 0.0632
15

Splitting Failures

10

Bearing and Mixed
Bearing/Splitting Failures

5
7

c)

8

9
10
Shear Strength [MPa]

11

12

Figure 3-17: Capacity vs Mechanical Strength based on Failure Modes
36

3-6-2 Single Housing Beams
Analysis of the failure modes, (photos of each failed specimen are included in the appendices)
reveal that for S-0.80 series the proportion of splitting, bearing, combined bearing/splitting and
failures are respectively 64%, 0% and 36%, see Table 3-8. Whereas, for the S-0.65 series the
proportions are respectively 28%, 44% and 28%. It is evident that the S-0.80 series have higher
proportion of splitting failures owing to less material below the mortise. The S-0.65 series with
thicker depth below the mortise exhibit lower proportion of splitting failures. On closer
inspection into the unreinforced specimens (WD and DD), the arguments are even more
conclusive with splitting accounting for 89% of failure in S-0.80 series and only 33% in the S0.65 series. However, reinforcing the specimens significantly reduces the splitting failures to
39% and 22% respectively. It should be taken into consideration that the splitting failures are
different from the previous splitting failures as the resistance perpendicular to grain now
includes the additional withdrawal capacity of the STS. Hence, the use of fully threaded STS
in housing connections load them in withdrawal shifting the connection failure modes towards
bearing or combined bearing/splitting which are primarily governed by crushing of wood fibers
under compressive stresses. Specimens which still failed by splitting after reinforcement, the
peak load corresponds to withdrawal failure.

Table 3-8: Proportion of failure modes: single housing
ID

Splitting

Bearing

Bearing/Splitting

S-0.80 (All)

64%

0%

36%

S-0.65 (All)

28%

44%

28%

S-0.80 (Unreinforced)

89%

11%

S-0.80 (Reinforced)

39%

61%

S-0.65 (Unreinforced)

33%

67%

S-0.65 (Reinforced)

22%

78%

37

Figure 3-18 presents the relation between capacity and mortise depth. The mean load-carrying
capacity while ignoring variation in moisture and reinforcement conditions (mean of
unreinforced and reinforced WW, WD and DD specimens) are 17.0 kN (S-0.80 series) and
22.7 kN (S-0.65 series). Hence, greater height below the mortise in S-0.65 series resulted in an
increase of load-carrying capacity by 34%. Thus, confirming the findings of previous research
(Heal et al., 2019) that depth of material below mortise directly influences the load-carrying
capacity of housing in beams. Less material below the mortise increases the likelihood of
separation of wood fibers induced by tension perpendicular to the grain. Moisture reduction
induced internal cracks are widely known in literature as shown by Rammer & Winistorfer
(2001), Franke & Franke (2014), Dietsch (2017), etc. The higher capacity in S-0.65 is primarily
due to the compressive strength perpendicular to grain governing the failure mechanism.

WW

WD

DD

Load-carrying capacity [kN]

25
20

15
10
5
0
S-0.80

Mortise depth

S-0.65

Figure 3-18: Relation between Load-carrying capacity and Mortise Depth (Single Housings)

Inspection of the influence of reinforcement, illustrated in Figure 3-19, showed that STS
increased the load-carrying capacity in all specimens irrespective of moisture conditions (WW,
WD or DD) and mortise depth (S-0.80 or S-0.65). However, for both S-0.80 and S-0.65 series,
the largest increase was observed in the wet-wet (WW) series (34% and 38% respectively)

38

along with less brittle failure modes in the form of higher displacement achieved. The
corresponding dry-dry (DD) series showed increases of 28% and 5% in load-carrying capacity.

Load-carrying capacity [kN]

30

S-0.80-WW

S-0.80-WD

S-0.80-DD

S-0.65-WW

S-0.65-WD

S-0.65-DD

25
20
15
10
5
0

Unreinforced
Reinforced
Reinforcement condition

Figure 3-19: Relation between load-carrying capacity and reinforcement (Single Housings)

The relation between load-carrying capacity and moisture conditions is demonstrated in Figure
3-20. Different moisture conditions did not substantially affect the load-carrying capacity in
the S-0.80 series. However, in the S-0.65 series, the highest capacity was observed in the drydry specimens which conforms with the existing literature that reduction in moisture content
below FSP leads to higher strength. At the same time, reduction in moisture induces internal
stresses in wood. The influence of which was clearly observed in the WD specimens (having
lowest capacity) which were cut wet, but tested dry. The WW specimens have higher capacity
than the WD specimens, suggesting that the influence of shrinkage like shrinkage defects and
the induced internal stresses are significantly more than the increase of strength due to
reduction in MC. Otherwise, both the WD and the DD specimens would have had higher
capacity than the WW specimens with the WD specimens perhaps having slightly lower
capacity than the DD specimens.

39

S-0.80

S-0.65

Load-carrying capacity [kN]

25

20
15
10
5
0
WW

WD

DD

Moisture condition

Figure 3-20: Relation between load-carrying capacity and moisture condition (single
housings)

To investigate these findings statistically, ANOVA was conducted to know the significance of
the results. The ANOVA results for the single housing tests are shown Table 3-9. It is noted
that there was no significant three-way interaction among the factors nor any two-way
interactions. Hence, the impact of all factors can be evaluated separately. It is observed that for
an alpha value of 0.05, p values for the dependent variables (Housing Depth and
Reinforcement) are much less than 0.05. Hence, the differences in load-carrying capacity due
to variation in housing depth and presence or absence of reinforcement are statistically
significant. However, the influence of environment (moisture condition) on the load-carrying
capacity having a p-value of 0.86 is not statistically significant. Hence, previous observation
regarding the WD specimens having the lowest capacity and the DD specimens having the
highest capacity in the S-0.65 series, could not be confirmed.
It can be concluded that the capacity is controlled by depth below mortise, reinforcement,
bearing area (mortise depth and width). In addition, usually splitting failures have lower
capacity and it is best to avoid such failure due to its abrupt nature. As an optimum mortise

40

depth, 50% of the beam depth should be selected, considering the possible failure in the tenon
of the secondary beam (instead of failure of mortise in primary beam).

Table 3-9: Three Factor ANOVA results: single housing
Parameters

SS

df

MS

F

p-value

A (Housing Depth)

584

1

584.31

41.32

<0.01

B (Reinforcement)

344

1

344.23

24.34

<0.01

C (Environment)

4.14

2

2.07

0.15

0.86

AxB

4.13

1

4.13

0.29

0.59

AxC

20.9

2

10.49

0.74

0.48

BxC

39.3

2

19.66

1.39

0.26

AxBxC

39.6

2

19.82

1.40

0.25

Within

848

60

14.14

Total

1885

71

26.55

3-6-3 Double Housing Beams
Investigating the individual failure modes, provided in appendix A-4 and appendix A-5,
showed that for both unreinforced D-0.80 series (D-0.80-DD) and unreinforced D-0.65 series
(D-0.65-DD) the proportion of splitting failure is 60%, as summarized in Table 3-10. In
contrasts to what was observed in the single housing series where only S-0.80 series had the
higher proportion of splitting, this suggests that the failure mechanism in unreinforced double
housings is significantly influenced by tension perpendicular to grain directions irrespective of
the depths of housings. However, similar to single housings, the D-0.80 series fail in splitting
(60%) while only 27% of the specimens in the D-0.65 series fail in splitting. Hence, the general
trend of data in the double housings is similar to that in single housings where series with lower
height below mortise predominantly failed in splitting.

41

Table 3-10: Proportion of failure modes: non-reinforced double housing
ID

Splitting (%)

Bearing (%)

Bearing/Splitting (%)

D-0.80 (All)

60

13

27

D-0.65 (All)

27

13

60

D-0.80 (Unreinforced)

60

40

D-0.65 (Unreinforced)

60

40

Figure 3-21 compares between the load-carrying capacities under different reinforcement
conditions and mortise depth for dry-dry specimens. Calculating the mean F

for all

specimens from the D-0.80 and D-0.65 series (ignoring difference in reinforcements), showed
that D-0.65 series had significantly (73%) higher capacity of 46.5 kN than the D-0.80 series
with 26.9 kN. Hence, mortise depth has a significant influence on load capacity.

Load-carrying capacity [kN]

DD

DD-RR

DD-R

50
40
30
20
10
0

D-0.80

Mortise depth

D-0.65

Figure 3-21: Relation between load-carrying capacity and mortise depth (double housings)

This research only considered the dry-dry series for double housings and to evaluate the
influence of moisture, results are compared with wet-wet series tested previously (Heal et al.,
2019). The relation between the load-carrying capacity and the moisture conditions of D-0.80
series is illustrated in Figure 3-22. All the wet-wet series (D-0.80-WW, D-0.80-WW-RR and
D-0.80-WW-R) had higher load carrying capacity than their corresponding dry-dry series (D0.80-DD, D-0.80-DD-RR and D-0.80-DD-R) except the D-0.65-WW series, which showed
42

slightly lower F

than the D-0.65-DD series; however this series also had comparatively

larger spread of data for the dry-dry series (CV of 19%) than the wet-wet series (CV of 10%).
It was also observed that the dry-dry series of D-0.65 had higher percentage of splitting
failures, while the wet-wet series of D-0.65 had higher percentage of mixed failure. The lower
load-carrying capacity of dry-dry series suggest change in moisture conditions having strong
influence, where reduction in moisture content induces early initiation of cracks due to tension
perpendicular to the grain. The reduction in moisture content led to greater shrinkage and
internal stresses in wood, resulting in lower load-carrying capacity for specimens likely to fail
in splitting. The increase of tension perpendicular to grain strength due to reduction of moisture
seems to be of lower influence in comparison to the reduction of strength due to development
of moisture change induced internal cracks.

UR

Load-carrying capacity [kN]

50

RR

R

40
30
20
10
0
Wet-Wet

Moisture conditions

Dry-Dry

Figure 3-22: Relation between load-carrying capacity and moisture condition (double
housings)

Figure 3-23 illustrates that reinforcement increased the load-carrying capacity in beams
irrespectively of moisture condition or relish depth. Here, only D-0.80 series are considered,
as D-0.65 did not have reinforced wet-wet specimens from previous research to compare with.
It is also observed that beams, which were reinforced and then tested, always had higher
capacity than those beams, which were tested first and then again retested with reinforcement.
43

In other words, reinforcement of uncracked beams leads to higher capacity as the load is carried
by both the reinforcement and the tensile strength of wood. However, in cracked beams the
load is carried only by the screw in withdrawal leading to lower capacity. Thus, STS always
increased the load-carrying capacity, but if the bonding of wood fibers had already been
compromised during the initial test, the effectiveness was lower. Hence, having STS from the
beginning delays crack propagation in the wood fibers, contributing in higher capacity.

Wet-Wet

Dry-Dry

:Load-carrying capacity [kN]

50
40
30
20
10
0
UR

RR
Reinforcement conditions

R

Figure 3-23: Relation between load-carrying capacity and reinforcement (double housings)

Two ANOVAs were performed to evaluate the impact of the parameters, housing depth,
moisture, reinforcement on

for alpha = 0.05. In Analysis 1, presented in Table 3-11, only

the dry-dry specimens from series D-0.80 and D-0.65 were considered. ANOVA showed that
the interaction between housing depth and reinforcement was not statistically significant;
therefore, the factors can be evaluated independently. Housing depth was significant (p < 0.01),
but reinforcement (p = 0.13) was shown not to be statistically significant in influencing the
capacity. However, the reinforcement would still be statistically significant if a lower
confidence level of 85% was considered.
In Analysis 2, results presented in Table 3-12, all specimens from the D-0.80 series were
considered. The two-factor ANOVA showed that the interaction between environment and

44

reinforcement was not statistically significant; therefore, the factors can be evaluated
independently. Both the moisture conditions and reinforcement were statistically significant in
influencing the load-carrying capacity with p-values <0.01. While lower moisture content in
timber is expected to result in higher strength properties due to better bonding between
cellulose, in this research conflicting results were obtained for the S-0.80 or D-0.80 series.
Considering the predominant mode of failure (splitting), it seems reasonable to conclude that
the internal stresses induced by shrinkage significantly affected the load-carrying capacity. The
moisture-induced internal stresses from shrinkage led to lower capacities in D-0.80 specimens
and almost unchanged capacities in the S-0.80 specimens. However, the failure mechanism in
S-0.65 or D-0.65 were initiated by compression perpendicular to grain which increases slightly
at lower moisture contents leading to an expected higher capacity in dry conditions.

Table 3-11: Two factor ANOVA (Analysis 1) results: double housing
Parameters

SS

df

MS

F

P-value

Housing Depth

2876.89

1

2876.89

39.16

<0.01

Reinforcement

331.62

2

165.81

2.26

0.13

Interaction

36.43

2

18.22

0.25

0.78

Within

1763.32

24

73.47

Total

5008.27

29

Table 3-12: Two factor ANOVA (Analysis 2) results: double housing
Parameters

SS

df

MS

F

P-value

Environment

1002.25

1

1002.25

21.04

<0.01

Reinforcement

549.47

2

274.73

5.77

<0.01

Interaction

17.03

2

8.52

0.18

0.84

Within

1143.28

24

47.64

Total

2712.04

29

45

4

Conclusions and Outlook

In this thesis, the influence of mortise depth, wood moisture and reinforcement on the loadcarrying capacity of solid timber beams with housings was investigated. A total of 60 beams
with single housings and 30 beams with double housings were prepared while varying the
moisture condition (either wet or dry) at the time of cutting the housings and at the time of
testing. In addition, 198 small-scale specimens were tested for compression, tension and shear
to evaluate the impact of local material strength on the beam load-carrying capacity. Along
with 32 previous tests, statistical analyses were conducted to evaluate the statistical
significance of the investigated parameters. Based on the findings in this research, the
following conclusions can be drawn:
·

Housing depths have significant influence on the failure mode. With lower mortise depths,
predominantly bearing failure or mixture of bearing and splitting were observed. The
greater height below the mortise leads to compression due to bearing forces to govern
instead of tension perpendicular to grain. The housing depth consequently also has affected
the load-carrying capacity F . The beams failing in pure splitting (beams with higher
mortise depth) exhibited significantly lower F . This finding was confirmed to be
statistically significant for both single and double housings.

·

Reinforcement with self-tapping screws increased the load-carrying capacity irrespective
of depth. Again, this finding was confirmed to be statistically significant for both single
and double housings. However, the increase in capacity is more prominent in the series
with higher mortise depth as the withdrawal capacity of STS reduces the crack propagation
in the beam due to tensile forces perpendicular to the grain. Also, increase in the loadcarrying capacity is more when un-cracked section is reinforced instead of reinforcing a
cracked section.

46

·

For the single housing series, the moisture conditions did not prove to be statistically
significant as factor influencing the load-carrying capacity

. For double housings,

however, lower moisture contents were shown to decrease

. and the result was

statistically significant.
·

Splitting occurs suddenly and hence not a desirably mode of failure in housing connections.
Bearing failure or a combined bearing/splitting failure would generally provide visible
warning concerning failure and hence the more preferable mode of failure. Based on the
experimental results, to achieve such failure modes, a large depth below the mortise should
be provided and fully-threaded STS should be used to reinforce the housing. Although
design driven by how much load it should take is expected to lead to higher depth below
the mortise and in other words, higher capacity-non splitting failure modes with ample
warning. In case load requirements are not as high, still larger depths should be provided
below the mortise to achieve bearing or mixed failure.

Based on these results and observations, future investigations should address the following:
·

Only solid Douglas fir beams were tested. Future testing should validate the findings by
testing other species and glue-laminated timber (GLT) beams.

·

Fracture mechanics could be used to evaluate the load-carrying capacity of housings as a
function of the mortise parameters. In this context, fracture mechanics parameters need to
be determined on samples taken from the timber beams.

·

Analytical and numerical methods can be used for parametric studies and developing
empirical equations to predict the load-carrying capacity of housings.

·

The fire resistance of housing connections, both un-reinforced and reinforced should be
determined to provide guidance for the fire resistance of exposed structures with housings.

47

References
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Fir. Canadian Journal of Civil Engineering, 50-57.
Blass, H. J., & Bejtka, I. (2004). Reinforcements perpendicular to the grain using self-tapping
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2804-2812). Vienna: TU Verlag Wien.
DIBt. (2019). ETA 11/0284: HECO-FIX-plus, HECO-TOPIX, HECO-TOPIX-T and HECOTOPIX-CC screws. Schramberg: European Organisation for Technical Assessment
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Dietsch, P. (2017). Effect of reinforcement on shrinkage stresses in timber members.
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Franke, B., & Franke, S. (2014). Causes, assessment and impact of cracks in timber elements.
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Jockwer, R. (2014). Structural behaviour of glued laminated timber beams with unreinforced
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Montgomery, D. C., & Runger, G. C. (2003). Applied statistics and probability for engineers
(3rd ed.). New York: Wiley.
Nehil, T. E., & Trojniak, B. I. (2013). Capacity of Load-Bearing Housings: Preliminary
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Rammer , D. R., & Winistorfer , S. G. (2001). Effect of moisture content on dowel-bearing
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Sjödin , J., & Johansson , C. (2007). Influence of initial moisture induced stresses in multiple
steel-to-timber dowel joints. Holz Roh Werkst, 71-77.
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Framers Guild.
Tannert, T. (2008). Structural Performance of Rounded Dovetail Connections. Vancouver,
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Tannert, T., & Lam, F. (2009). Progress in Structural Engineering and Materials : Timber
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Tannert, T., Vallée , T., & Hehl , S. (2012). Experimental and numerical investigations on
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Rate, Moisture Content and Loading Direction. Experimental Mechanics, 44-48.
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reinforcement on single-dowel connections with artificial cracks. Engineering
Structures, 656 - 664.

50

Appendices
Appendix 1 – Test results from previous research (Heal et al., 2019)
ID

Spec #

S-0.80-WW

1/6
2/6
3/6
4/6
5/6
6/6

Average
S-0.65-WW

1/6
2/6
3/6
4/6
5/6
6/6

Average
D-0.80-WW

Average
D-0.80-WW-RR

Average
D-0.80-WW-R

Average
D-0.65-WW

Average

1/5
2/5
3/5
4/5
5/5
1/5
2/5
3/5
4/5
5/5
1/5
2/5
3/5
4/5
5/5
1/5
2/5
3/5
4/5
5/5

Wet MC
[%]

Density
[kg/m3]

Fult [kN]

Ultimate
Disp [mm]

30.4
29.6
29.5
30.2
28.6
29.4
29.6
29.1
34.8
35.5
37
34.1
28.3
33.1

428.64
430.11
519.81
519.31
489.71
488.01
479.26
415.13
530.64
428.95
545.86
470.60
456.96
474.69

15.00
10.90
17.90
15.10
15.60
15.60
15.02
17.20
19.60
20.80
22.60
21.30
19.00
20.08

11.90
11.30
20.10
15.70
13.20
17.30
14.92
23.60
18.90
26.30
23.90
26.40
27.80
24.48

28.9
29.2
26.8
26.4
25.4
27.3
28.9
29.2
26.8
26.4
25.4
27.3
28.2
28.4
25.4
27.4
29.5
27.8
29.1
29.7
29.0
30.1
28.9
29.6

565.00
585.00
625.00
658.00
541.00
594.80
565.00
585.00
625.00
658.00
541.00
594.80
652.00
656.00
513.00
518.00
598.00
587.40
583.00
593.00
588.00
536.00
529.00
565.80

29.10
34.90
38.20
36.90
24.50
32.72
39.80
45.50
39.00
43.50
31.10
39.78
48.50
45.00
38.80
36.60
45.90
42.96
44.70
49.80
43.80
40.60
38.70
43.52

9.90
11.90
9.40
8.90
10.00
10.02
17.00
17.80
13.10
16.30
15.80
16.00
15.20
16.40
16.70
20.20
12.90
16.28
17.10
16.20
16.70
22.60
20.80
18.68

51

Failure Mode
Splitting
Splitting
Splitting
Splitting
Splitting
Splitting
Bearing
Splitting/ Bearing
Bearing
Bearing/ Splitting
Splitting/ Bearing
Bearing/ Splitting
Splitting
Splitting/Bearing
Splitting
Splitting

Splitting/Bearing
Bearing/Splitting
Splitting
Splitting
Bearing/Splitting
Bearing/Splitting
Bearing
Bearing/Splitting
Bearing
Splitting/Bearing
Bearing/Splitting
Splitting
Splitting
Bearing/Splitting
Bearing/Splitting

Appendix 2 – Detailed test results of all specimens in S-0.80 series
Table A-2-1: Individual test results: single housing ( S-0.80 series)
ID
S-0.80-WWD-RR

Average
S-0.80-WD

Average
S-0.80-WD-RR

Average
S-0.80-DD

Average
S-0.80-DD-RR

Average

Spec
#

Wet
MC
[%]

1/6
2/6
3/6
4/6
5/6
6/6
1/6
2/6
3/6
4/6
5/6
6/6
1/6
2/6
3/6
4/6
5/6
6/6
1/6
2/6
3/6
4/6
5/6
6/6
1/6
2/6
3/6
4/6
5/6
6/6

Dry
MC
[%]
6.9
7.1
7.3
6.7
7.0
7.1
7.0

29.2
29.2
29.2
29.2
29.2
29.2
29.2
7.2
6.9
7.1
7.1
6.7
7.1
7.0
7.1
7.0
7.0
7.1
7.1
7.3
7.1
7.1
7.0
7.0
7.1
7.1
7.3
7.1

Density
[kg/m3]

Fult
[kN]

429
430
520
519
490
488
479
412
514
421
518
433
434
455
412
514
421
518
433
434
455
431
436
528
431
451
433
451
431
436
528
431
451
433
451

19.4
19.5
16.2
15.5
23.4
10.0
17.3
15.1
17.7
15.4
15.9
13.9
14.2
15.4
21.4
25.2
19.1
22.6
20.4
15.1
20.6
13.8
16.6
13.9
14.5
15.9
14.5
14.9
21.6
23.5
17.2
19.6
14.8
17.1
19.0

52

Ultimate
Disp.
[mm]
10.0
13.5
11.5
9.5
12.8
6.9
10.7
6.9
8.1
7.8
5.8
7.8
6.9
7.2
14.1
21.9
12.4
19.5
20.6
11.1
16.6
5.4
6.8
5.5
6.9
9.1
8.6
7.0
9.2
9.4
7.0
12.7
7.7
13.9
10.0

Crack
Opening
[mm]
1.9
3.1
1.7
1.7
3.0
1.0
2.0
0.4
0.4
0.3
0.3
0.2
0.4
0.3
2.4
1.8
2.3
2.9
1.4
0.8
1.9
0.3
0.5
0.3
0.8
2.5
0.7
0.8
1.9
1.5
1.5
1.8
1.3
1.3
1.5

Failure Mode
Bearing/Splitting
Splitting
Splitting
Splitting/Bearing
Splitting
Splitting
Splitting
Splitting
Splitting
Splitting
Splitting
Splitting
Bearing/Splitting
Bearing/Splitting
Bearing/Splitting
Bearing/Splitting
Bearing/Splitting
Bearing/Splitting
Splitting
Splitting
Splitting
Splitting
Bearing/Splitting
Bearing/Splitting
Splitting
Splitting
Bearing/Splitting
Bearing/Splitting
Splitting
Bearing/Splitting

S-0.80-WD-2

S-0.80-WD-RR-1

S-0.80-WD-RR-2

S-0.80-WD-3

S-0.80-WD-4

S-0.80-WD-RR-3

S-0.80-WD-RR-4

S-0.80-WD-5

S-0.80-WD-6

S-0.80-WD-RR-5

S-0.80-WD-RR-6

30

30

25

25

20

20

Load [kN]

Load [kN]

S-0.80-WD-1

15
10

15
10
5

5

0

0
0

5

10
15
20
Displacement [mm]

25

0

30

5

10
15
20
Displacement [mm]

25

30

(b)

(a)
S-0.80-DD-2
S-0.80-DD-4
S-0.80-DD-6

30

30

25

25

20

20

Load [kN]

Load [kN]

S-0.80-DD-1
S-0.80-DD-3
S-0.80-DD-5

15

10
5

S-0.80-DD-RR-1

S-0.80-DD-RR-2

S-0.80-DD-RR-3

S-0.80-DD-RR-4

S-0.80-DD-RR-5

S-0.80-DD-RR-6

15
10
5

0
0

5

10
15
20
Displacement [mm]

25

0

30

0

10
15
20
Displacement [mm]

25

30

(d)

Load [kN]

(c)

5

30
25
20
15
10
5
0

S-0.80-WWD-RR-1

S-0.80-WWD-RR-2

S-0.80-WWD-RR-3

S-0.80-WWD-RR-4

S-0.80-WWD-RR-5

S-0.80-WWD-RR-6

0

5

10
15
20
Displacement [mm]

25

30

(e)
Figure A-2-1: Load-displacement of S-0.80 series under bearing load (a) Unreinforced Wet-Dry
Specimens, (b) Wet-Dry Specimens after Reinforcement, (c) Unreinforced Dry-Dry Specimens, (d) DryDry Specimens after Reinforcement, (e) Reinforced Wet-Wet Specimens tested Dry

53

S-0.80-WD-2

S-0.80-WD-3

S-0.80-WD-4

S-0.80-WD-5

S-0.80-WD-6

S-0.80-WD-RR-1
S-0.80-WD-RR-2
S-0.80-WD-RR-3
S-0.80-WD-RR-4

30

30

25

25

20

20

Load [kN]

Load [kN]

S-0.80-WD-1

15
10
5

15
10
5

0

0
-1

0

1

2

3

4

5

6

-1

0

Crack Opening [mm]

5

6

5

6

(b)
S-0.80-DD-1

S-0.80-DD-2

S-0.80-DD-3

S-0.80-DD-4

S-0.80-DD-5

S-0.80-DD-6

30

30

25

25

20

20

Load [kN]

Load [kN]

(a)

1
2
3
4
Crack Opening [mm]

15
10
5

S-0.80-DD-RR-1
S-0.80-DD-RR-2
S-0.80-DD-RR-3
S-0.80-DD-RR-4
S-0.80-DD-RR-5

15
10
5

0

0
-1

0

1
2
3
4
Crack Opening [mm]

5

6

-1

(c)

0

1
2
3
4
Crack Opening [mm]

(d)
S-0.80-WWD-RR-1

S-0.80-WWD-RR-2

S-0.80-WWD-RR-3

S-0.80-WWD-RR-4

S-0.80-WWD-RR-5

S-0.80-WWD-RR-6

30
Load [kN]

25
20
15
10
5
0
-1

0

1
2
3
4
Crack Opening [mm]

5

6

(e)
Figure A-2-2: Load-Mean Crack Opening S-0.80 series: (a) Unreinforced Wet-Dry Specimens, (b) Wet-Dry
Specimens after Reinforcement, (c) Unreinforced Dry-Dry Specimens, (d) Dry-Dry Specimens after
Reinforcement, (e) Reinforced Wet-Wet Specimens tested Dry

54

S-0.80-WWD-RR-6: Splitting

S-0.80-WWD-RR-5: Splitting

S-0.80-WWD-RR-4: Bearing/Splitting

S-0.80-WWD-RR-3: Bearing

S-0.80-WWD-RR-2: Splitting

S-0.80-WWD-RR-1: Bearing/Splitting

Figure A-2-3: Test Photos of S-0.80 series reinforced wet-wet specimens tested dry

55

S-0.80-WD-1: Splitting

S-0.80-WD-2: Splitting

S-0.80-WD-3: Splitting

S-0.80-WD-4: Splitting

S-0.80-WD-5: Splitting

S-0.80-WD-6: Splitting

Figure A-2-4: Test Photos of S-0.80 series unreinforced wet-dry specimens

56

S-0.80-WD-RR-1: Bearing/Splitting

S-0.80-WD-RR-2: Bearing/Splitting

S-0.80-WD-RR-3: Splitting

S-0.80-WD-RR-4: Bearing/Splitting

S-0.80-WD-RR-5: Bearing/Splitting

S-0.80-WD-RR-6: Bearing

Figure A-2-5: Test Photos of S-0.80 series reinforced retested wet-dry specimens

57

S-0.80-DD-1: Splitting

S-0.80-DD-2: Splitting

S-0.80-DD-3: Splitting

S-0.80-DD-4: Splitting

S-0.80-DD-5: Splitting

S-0.80-DD-6: Bearing/Splitting

Figure A-2-6: Test Photos of S-0.80 series unreinforced dry-dry specimens

58

S-0.80-DD-RR-6: Bearing/Splitting

S-0.80-DD-RR-5: Splitting/Bearing

S-0.80-DD-RR-4: Splitting/Bearing

S-0.80-DD-RR-3: Splitting

S-0.80-DD-RR-2: Splitting

S-0.80-DD-RR-1: Splitting/Bearing

Figure A-2-7: Test Photos of S-0.80 series reinforced retested dry-dry specimens

59

Appendix 3 – Detailed test results of all specimens in S-0.65 series
Table A-3-1: Individual test results: single housing (S-0.65 series)
ID
S-0.65-WWD-RR

Spec
#

Wet
MC
[%]

1/6
2/6
3/6
4/6
5/6
6/6

Average
S-0.65-WD

1/6
2/6
3/6
4/6
5/6
6/6

Average
S-0.65-WD-RR

1/6
2/6
3/6
4/6
5/6
6/6

Average
S-0.65-DD

1/6
2/6
3/6
4/6
5/6
6/6

Average
S-0.65-DD-RR

Average

1/6
2/6
3/6
4/6
5/6
6/6

29.2
29.2
29.2
29.2
29.2
29.2
29.2
29.2
29.2
29.2
29.2
29.2
29.2
29.2

Dry
MC
[%]

Density
[kg/m3]

Fult
[kN]

Ultimate
Disp
[mm]

7.1
7.1
7.0
7.3
7.1
7.1
7.1
6.9
6.8
7.0
6.9
7.1
7.2
7.0
6.9
6.8
7.0
6.9
7.1
7.2
7.0
7.1
6.2
7.1
7.4
7.2
7.1
7.0
7.1
6.2
7.1
7.4
7.2
7.1
7.0

415
531
429
546
471
457
475
443
446
451
448
551
535
479
443
446
451
448
551
535
479
531
446
547
458
453
508
490
531
446
547
458
453
508
490

22.6
29.1
28.7
29.7
28.9
19.8
26.5
18.4
16.8
18.3
21.4
15.7
22.7
18.9
29.0
19.4
24.0
23.3
28.3
32.1
26.0
26.1
18.9
27.7
21.0
15.5
22.4
21.9
31.6
18.1
30.8
22.7
14.3
20.4
23.0

21.2
20.8
27.0
21.6
30.1
20.6
23.6
8.5
21.0
8.2
16.6
7.2
10.0
11.9
14.5
29.1
20.2
18.8
11.0
19.5
18.8
10.2
10.5
8.4
23.6
10.4
11.6
12.4
12.5
17.1
10.7
22.5
11.9
14.1
14.8

60

Mean
Crack
Opening
[mm]
1.6
2.4
2.7
2.7
1.7
3.3
2.4
0.8
0.5
0.4
0.6
0.4
0.2
0.5
1.2
1.2
1.0
2.1
0.9
0.9
1.2
1.7
0.7
0.6
1.7
0.4
0.3
0.9
1.3
0.5
1.9
1.8
0.4
0.2
1.0

Failure Mode
Bearing
Splitting
Bearing
Splitting
Bearing/Splitting
Bearing
Splitting
Bearing
Splitting
Bearing
Splitting
Splitting
Splitting/Bearing
Bearing
Bearing/Splitting
Bearing
Splitting
Bearing
Splitting
Bearing
Splitting
Bearing/Splitting
Bearing
Bearing
Bearing/Splitting
Bearing/Splitting
Splitting
Bearing
Bearing
Bearing

S-0.65-WD-2
S-0.65-WD-4
S-0.65-WD-6

S-0.65-WD-RR-1
S-0.65-WD-RR-3
S-0.65-WD-RR-5

35
30
25
20
15
10
5
0

Load [kN]

Load [kN]

S-0.65-WD-1
S-0.65-WD-3
S-0.65-WD-5

0

5

10
15
20
25
Displacement [mm]

30

5

10
15
20
25
Displacement [mm]

30

S-0.65-DD-1

S-0.65-DD-2

S-0.65-DD-RR-1

S-0.65-DD-RR-2

S-0.65-DD-3

S-0.65-DD-4

S-0.65-DD-RR-3

S-0.65-DD-RR-4

S-0.65-DD-5

S-0.65-DD-6

S-0.65-DD-RR-5

S-0.65-DD-RR-6

35
30
25
20
15
10
5
0

Load [kN]

Load [kN]

0

35

(b)

0

5

10
15
20
25
Displacement [mm]

30

35
30
25
20
15
10
5
0

35

(c)

Load [kN]

35
30
25
20
15
10
5
0

35

(a)

S-0.65-WD-RR-2
S-0.65-WD-RR-4
S-0.65-Wd-RR-6

0

5

10
15
20
25
Displacement [mm]

30

35

(d)

35
30
25
20
15
10
5
0

S-0.65-WWD-RR-1

S-0.65-WWD-RR-2

S-0.65-WWD-RR-3

S-0.65-WWD-RR-4

S-0.65-WWD-RR-5

S-0.65-WWD-RR-6

0

5

10
15
20
25
Displacement [mm]

30

35

(e)
Figure A-3-1: Load-displacement tests of 0.65 series under bearing load (a) Unreinforced WetDry Specimens, (b) Wet-Dry Specimens after Reinforcement, (c) Unreinforced Dry-Dry
Specimens, (d) Dry-Dry Specimens after Reinforcement, (e) Reinforced Wet-Wet Specimens
tested Dry

61

S-0.65-WD-2
S-0.65-WD-4
S-0.65-WD-6

S-0.65-WD-RR-1
S-0.65-WD-RR-3
S-0.65-WD-RR-5

35
30
25
20
15
10
5
0

Load [kN]

Load [kN]

S-0.65-WD-1
S-0.65-WD-3
S-0.65-WD-5

-1

0

1
2
3
4
Crack Opening [mm]

5

S-0.65-DD-2
S-0.65-DD-4
S-0.65-DD-6

35
30
25
20
15
10
5
0

Load [kN]

Load [kN]

-1

0

1
2
3
4
Crack Opening [mm]

5

6

(b)
S-0.65-DD-1
S-0.65-DD-3
S-0.65-DD-5

-1

0

1
2
3
4
Crack Opening [mm]

5

S-0.65-DD-RR-1

S-0.65-DD-RR-2

S-0.65-DD-RR-3

S-0.65-DD-RR-4

S-0.65-DD-RR-5

S-0.65-DD-RR-6

35
30
25
20
15
10
5
0
-1

6

0

1
2
3
4
Crack Opening [mm]

5

6

(d)

(c)
S-0.65-WWD-RR-1
S-0.65-WWD-RR-3
S-0.65-WWD-RR-5

Load [kN]

35
30
25
20
15
10
5
0

6

(a)

S-0.65-WD-RR-2
S-0.65-WD-RR-4
S-0.65-WD-RR-6

S-0.65-WWD-RR-2
S-0.65-WWD-RR-4
S-0.65-WWD-RR-6

35
30
25
20
15
10
5
0
-1

0

1
2
3
4
Crack Opening [mm]

5

6

(e)
Figure A-3-2: Load-Mean Crack Opening tests of 0.65 series under bearing load (a)
Unreinforced Wet-Dry Specimens, (b) Wet-Dry Specimens after Reinforcement, (c)
Unreinforced Dry-Dry Specimens, (d) Dry-Dry Specimens after Reinforcement, (e) Reinforced
Wet-Wet Specimens tested Dry

62

S-0.65-WWD-RR-1: Bearing

S-0.65-WWD-RR-2: Splitting

S-0.65-WWD-RR-3: Bearing

S-0.65-WWD-RR-4: Splitting

S-0.65-WWD-RR-5: Bearing/Splitting

S-0.65-WWD-RR-6: Bearing

Figure A-3-3: Test Photos of S-0.65 series reinforced wet-wet specimens tested dry

63

S-0.65-WD-1: Splitting

S-0.65-WD-2: Bearing

S-0.65-WD-3: Splitting

S-0.65-WD-4: Bearing

S-0.65-WD-5: Splitting

S-0.65-WD-6: Splitting

Figure A-3-4: Test Photos of S-0.65 series unreinforced wet-dry specimens

64

S-0.65-WD-RR-1: Splitting/Bearing

S-0.65-WD-RR-2: Bearing

S-0.65-WD-RR-3: Bearing/Splitting

S-0.65-WD-RR-4: Bearing

S-0.65-WD-RR-5: Splitting

S-0.65-WD-RR-6: Bearing

Figure A-3-5: Test Photos of S-0.65 series reinforced retested wet-dry specimens

65

S-0.65-DD-1: Splitting

S-0.65-DD-2: Bearing

S-0.65-DD-3: Splitting

S-0.65-DD-4: Bearing/Splitting

S-0.65-DD-5: Bearing

S-0.65-DD-6: Bearing

Figure A-3-6: Test Photos of S-0.65 series unreinforced dry-dry specimens

66

S-0.80-DD-RR-1: Splitting/Bearing

S-0.80-DD-RR-2: Splitting

S-0.80-DD-RR-3: Splitting

S-0.80-DD-RR-4: Splitting/Bearing

S-0.80-DD-RR-5: Splitting/Bearing

S-0.80-DD-RR-6: Bearing/Splitting

Figure A-3-7: Test Photos of S-0.65 series reinforced retested dry-dry specimens

67

Appendix 4 – Detailed test results of all specimens in D-0.80 series
Table A-4-1: Individual test results: double housings (D-0.80 series)
ID
D-0.80-DD

Average
D-0.80-DD-RR

Average
D-0.80-DD-R

Average

Spec
#
1/5
2/5
3/5
4/5
5/5
1/5
2/5
3/5
4/5
5/5
1/5
2/5
3/5
4/5
5/5

Wet
MC
[%]

Dry
MC
[%]

Density
[kg/m3]

Fult
[kN]

Ultimate
Disp.
[mm]

6.9
7.2
7.3
7.5
7.5
7.3
6.9
7.2
7.3
7.5
7.5
7.3
6.3
6.1
6.3
6.2
6.2
6.2

550
492
469
513
528
510
550
492
469
513
528
510
467
527
483
496
541
503

21.0
25.5
11.5
39.6
12.3
22.0
27.1
28.9
15.2
35.4
23.9
26.1
37.3
32.2
30.6
29.5
34.0
32.7

7.4
6.5
8.5
10.0
10.6
8.6
9.5
9.2
12.6
14.1
22.9
13.7
11.3
10.5
12.1
8.8
10.8
10.7

68

Mean
Crack
Opening
[mm]
4.4
0.6
3.6
1.2
8.6
3.7
7.7
1.7
7.5
4.8
19.3
8.2
1.3
0.9
1.4
0.6
1.0
1.0

Failure Mode
Splitting
Splitting
Bearing
Splitting
Bearing
Splitting
Splitting
Bearing/Splitting
Splitting
Splitting/Bearing
Splitting
Bearing/Splitting
Bearing/Splitting
Splitting
Splitting

D-0.80-DD-1

D-0.80-DD-2

D-0.80-DD-RR-1

D-0.80-DD-RR-2

D-0.80-DD-3

D-0.80-DD-4

D-0.80-DD-RR-3

D-0.80-DD-RR-4

D-0.80-DD-5

D-0.80-DD-RR-5

Load [kN]

Load [kN]

40
35
30
25
20
15
10
5
0
0

5

10
15
20
Displacement [mm]

40
35
30
25
20
15
10
5
0

25

(a)

0

5

10
15
Displacement [mm]

20

25

(b)
D-0.80-DD-R-1

D-0.80-DD-R-2

D-0.80-DD-R-3

D-0.80-DD-R-4

Load [kN]

D-0.80-DD-R-5
40
35
30
25
20
15
10
5
0
0

5

10
15
20
Displacement [mm]

25

(c)
Figure A-4-1: Load-displacement tests of D-0.80 series under bearing load (a) Unreinforced
Dry-Dry Specimens, (b) Dry-Dry Specimens retested after Reinforcement, (e) Reinforced DryDry Specimens

69

D-0.80-DD-1: Splitting

D-0.80-DD-2: Splitting

D-0.80-DD-3: Bearing

D-0.80-DD-4: Splitting

D-0.80-DD-5: Bearing

Figure A-4-2: Test Photos of D-0.80 series (Side 1) unreinforced dry-dry specimens

70

D-0.80-DD-1: Splitting

D-0.80-DD-2: Splitting

D-0.80-DD-3: Bearing

D-0.80-DD-4: Splitting

D-0.80-DD-5: Bearing

Figure A-4-3: Test Photos of D-0.80 series (Side 2) unreinforced dry-dry specimens

71

D-0.80-DD-RR-1: Splitting

D-0.80-DD-RR-2: Splitting

D-0.80-DD-RR-3: Bearing/Splitting

D-0.80-DD-RR-4: Splitting

D-0.80-DD-RR-5: Splitting/Bearing

Figure A-4-4: Test Photos of D-0.80 series (Side 1) reinforced retested dry-dry specimens

72

D-0.80-DD-RR-1: Splitting

D-0.80-DD-RR-2: Splitting

D-0.80-DD-RR-3: Bearing/Splitting

D-0.80-DD-RR-4: Splitting

D-0.80-DD-RR-5: Splitting/Bearing

Figure A-4-5: Test Photos of D-0.80 series (Side 2) reinforced retested dry-dry specimens

73

D-0.80-DD-R-1: Splitting

D-0.80-DD-R-2: Bearing/Splitting

D-0.80-DD-R-3: Bearing/Splitting

D-0.80-DD-R-4: Splitting

D-0.80-DD-R-5: Splitting

Figure A-4-6: Test Photos of D-0.80 series (Side 1) reinforced dry-dry specimens

74

D-0.80-DD-R-1: Splitting

D-0.80-DD-R-2: Bearing/Splitting

D-0.80-DD-R-3: Bearing/Splitting

D-0.80-DD-R-4: Splitting

D-0.80-DD-R-5: Splitting

Figure A-4-7: Test Photos of D-0.80 (Side 2) series reinforced dry-dry specimens

75

Appendix 5 – Detailed test results of all specimens in D-0.65 series
Table A-5-1: Individual test results: double housings (D-0.65 series)
ID
D-0.65-DD

Average
D-0.65-DD-RR

Average
D-0.65-DD-R

Average

Spec
#
1/5
2/5
3/5
4/5
5/5
1/5
2/5
3/5
4/5
5/5
1/5
2/5
3/5
4/5
5/5

Wet
MC
[%]

Dry
MC
[%]

Density
[kg/m3]

Fult
[kN]

Ultimate
Disp.
[mm]

6.7
6.2
6.2
6.5
6.2
6.4
6.7
6.2
6.2
6.5
6.2
6.4
6.3
6.4
6.4
7.2
7.3
6.7

475
539
536
505
473
506
475
539
536
505
473
506
499
492
459
573
551
515

38.2
53.6
50.1
46.1
33.5
44.3
39.5
47.6
49.1
60.9
31.2
45.6
54.7
44.3
42.8
59.4
46.9
49.6

9.5
10.3
14.1
19.3
24.5
15.5
12.2
19.2
23.4
27.6
17.5
20.0
19.4
10.1
26.6
12.7
18.5
17.5

76

Mean
Crack
Opening
[mm]
0.4
3.1
0.4
0.9
1.3
1.2
1.8
1.4
2.5
2.3
1.3
1.9
0.3
0.3
0.8
0.4
2.5
0.9

Failure Mode
Splitting
Splitting
Splitting
Bearing/Splitting
Bearing
Splitting
Bearing/Splitting
Splitting/Bearing
Bearing/Splitting
Bearing
Bearing/Splitting
Bearing/Splitting
Bearing/Splitting
Bearing/Splitting
Bearing/Splitting

D-0.65-DD-2
D-0.65-DD-4

70
60
50
40
30
20
10
0
0

5

10
15
20
Displacement [mm]

25

D-0.65-DD-RR-2

D-0.65-DD-RR-3

D-0.65-DD-RR-4

70
60
50
40
30
20
10
0

30

(a)

0

5

10
15
20
Displacement [mm]

25

30

(b)
D-0.65-DD-R-1
D-0.65-DD-R-3
D-0.65-DD-R-5

Load [kN]

D-0.65-DD-RR-1
D-0.65-DD-RR-5

Load [kN]

Load [[kN]

D-0.65-DD-1
D-0.65-DD-3
D-0.65-DD-5

D-0.65-DD-R-2
D-0.65-DD-R-4

70
60
50
40
30
20
10
0
0

5

10
15
20
Displacement [mm]

25

30

(c)
Figure A-5-1: Load-displacement tests of D-0.65 series under bearing load (a) Unreinforced
Dry-Dry Specimens, (b) Dry-Dry Specimens retested after Reinforcement, (e) Reinforced DryDry Specimens

77

D-0.65-DD-1: Splitting

D-0.65-DD-2: Splitting

D-0.65-DD-3: Splitting

D-0.65-DD-4: Bearing/Splitting

D-0.65-DD-5: Bearing

Figure A-5-2: Test Photos of D-0.65 series (Side 1) unreinforced dry-dry specimens

78

D-0.65-DD-1: Splitting

D-0.65-DD-2: Splitting

D-0.65-DD-3: Splitting

D-0.65-DD-4: Bearing/Splitting

D-0.65-DD-5: Bearing

Figure A-5-3: Test Photos of D-0.65 series (Side 2) unreinforced dry-dry specimens

79

D-0.80-DD-RR-1: Splitting

D-0.80-DD-RR-1: Bearing/Splitting

D-0.80-DD-RR-1: Splitting/Bearing

D-0.80-DD-RR-1: Bearing/Splitting

D-0.80-DD-RR-1: Bearing

Figure A-5-4: Test Photos of D-0.65 series (Side 1) reinforced retested dry-dry specimens

80

D-0.80-DD-RR-1: Splitting

D-0.80-DD-RR-1: Bearing/Splitting

D-0.80-DD-RR-1: Splitting/Bearing

D-0.80-DD-RR-1: Bearing/Splitting

D-0.80-DD-RR-1: Bearing

Figure A-5-5: Test Photos of D-0.65 series (Side 2) reinforced retested dry-dry specimens

81

D-0.80-DD-R-1: Splitting

D-0.80-DD-R-2: Splitting

D-0.80-DD-R-3: Bearing

D-0.80-DD-R-4: Splitting

D-0.80-DD-R-5: Bearing

Figure A-5-6: Test Photos of D-0.65 series (Side 1) reinforced dry-dry specimens

82

D-0.80-DD-R-1: Splitting

D-0.80-DD-R-2: Splitting

D-0.80-DD-R-3: Bearing

D-0.80-DD-R-4: Splitting

D-0.80-DD-R-5: Bearing

Figure A-5-7: Test Photos of D-0.65 series (Side 2) reinforced dry-dry specimens

83