PULL-OUT RESISTANCE OF SELF-TAPPING WOOD SCREWS …

PULL-OUT RESISTANCE OF SELF-TAPPING WOOD SCREWS

WITH CONTINUOUS THREAD

by

MAIK GEHLOFF

Dipl.-Ing. (FH), University of Applied Sciences, Eberswalde, Germany, 2002

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF

THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF APPLIED SCIENCE

in

THE FACULTY OF GRADUATE STUDIES

(Forestry)

THE UNIVERSITY OF BRITISH COLUMBIA

(Vancouver)

July 2011

© Maik Gehloff, 2011

ii

ABSTRACT

Over the past centuries the use of timber in structures has seen waves of decline and

rediscovery. Timber structures have evolved from empirical structures using timber

within its natural boundaries in terms of shape, size and length to modern day

engineering design approach using computers and sophisticated numerical models; this

has led to the need of high performance connections in such structures.

With the help of mechanical fasteners the envelope was pushed time and time again,

creating ever stronger connections. However, the capacity of such connections is not only

governed by the mechanical properties of the connectors, but also by the mechanical

properties of the connecting wood members. Researchers have been developing different

methods of reinforcing the inherent weakness of wood, namely the low strength in

tension and compression perpendicular to the grain, as well as the low capacity in

longitudinal shear.

This thesis examines experimentally the pull-out resistance of self-tapping wood screws

with continuous thread, a new type of fastener that can be used as a fastener, but also as

reinforcement considering Canadian major wood species. Utilizing its high withdrawal

capacity and high tensile strength, this type of connector can potentially be used to

transfer internal forces in the wood along the length-axis of the screw instead of loading

the wood in its weak directions.

The results show that self-tapping wood screws (STSs) have a high resistance to pull-out

and are an economical alternative to other reinforcement methods. Besides the superior

capacities of STSs in withdrawal and tensile strength to other methods, they are also very

easy to install since no pre-drilling of holes is required and thus, give an economical

solution to many challenges in engineered timber construction.

iii

TABLE OF CONTENTS

ABSTRACT ........................................................................................................................ ii

TABLE OF CONTENTS ................................................................................................... iii

LIST OF TABLES ............................................................................................................. iv

LIST OF FIGURES ............................................................................................................ v

ACKNOWLEDGEMENTS ............................................................................................. xiii

1. INTRODUCTION ...................................................................................................... 1

1.1. History .................................................................................................................. 1

1.2. Self-tapping wood screws .................................................................................... 7

2. EXPERIMENTAL DESIGN / EQUATIONS .......................................................... 13

2.1. Parameter considerations.................................................................................... 13

2.2. Test setup............................................................................................................ 15

2.3. European code equations .................................................................................... 19

2.4. Equivalency calculations .................................................................................... 22

3. RESULTS / DISCUSSION....................................................................................... 25

3.1. Results ................................................................................................................ 25

3.2. Discussion .......................................................................................................... 36

4. CONCLUSIONS AND RECOMMENDATIONS ................................................... 58

4.1. Conclusions ........................................................................................................ 58

4.2. Recommendations .............................................................................................. 59

BIBLIOGRAPHY ............................................................................................................. 61

APPENDIX – SUPPLEMENTAL MATERIAL .............................................................. 64

iv

LIST OF TABLES

Table 1: Effective embedment depths ............................................................................... 18

Table 2: Average densities ................................................................................................ 25

Table 3: Withdrawal test results for 90° ........................................................................... 26



Table 6: Comparison of test results to code equation predictions for STS ....................... 37

v

LIST OF FIGURES

Figure 1: Development of wood design since 1750............................................................ 2

Figure 2: Knitted glass and aramid fibre fabric (spiral) ...................................................... 4

Figure 3: Transversally reinforced carbon fibre loop ......................................................... 4

Figure 4: Typical load-displacement curve......................................................................... 4

Figure 5: Beam splice using glued-in rods ......................................................................... 6

Figure 6: Screw thread in accordance with DIN 7998 ........................................................ 8

Figure 7: Self-tapping wood screws ................................................................................... 9

Figure 8: Self-tapping wood screw drill-tips ...................................................................... 9

Figure 9: Shank cutter on partially threaded screw ............................................................ 9

Figure 10: STS as embedment and splitting reinforcement .............................................. 11

Figure 11: Test setup for 90º tests ..................................................................................... 15



Figure 14: Transducer to measure deflection .................................................................... 17

Figure 15: Effective embedment depth ............................................................................. 18

Figure 16: Average withdrawal resistance for 6 mm screw @ 90º................................... 27


Figure 18: Average withdrawal resistance for 10 mm screw @ 90º................................. 28






vi


Figure 25: Typical screw failure ....................................................................................... 34

Figure 26: Typical load deformation plot ......................................................................... 35

Figure 27: Wood density distribution ............................................................................... 36

Figure 28: Comparison of 6 mm results with DIN 1052:2004-8 predictions @ 90° ........ 39

Figure 29: Comparison of 6 mm results with EC 5 predictions @ 90° ............................ 39











Figure 40: Comparison of 10 mm results with DIN 1052:2004-8 predictions @ 90° ...... 45

Figure 41: Comparison of 10 mm results with EC 5 predictions @ 90° .......................... 45





Figure 46: Comparison of 6 mm results with DIN 1052:2004-8 adjustments @ 90° ...... 49

Figure 47: Comparison of 6 mm results with EC 5 adjustments @ 90° ........................... 49

vii











Figure 58: Comparison of 10 mm results with DIN 1052:2004-8 adjustments @ 90° .... 55

Figure 59: Comparison of 10 mm results with EC 5 adjustments @ 90° ......................... 55





Figure 64: Load – Deformation (6mm, 4d, 90°, Douglas-fir) .......................................... 64

Figure 65: Load – Deformation (6mm, 4d, 90°, S-P-F) ................................................... 64

Figure 66: Load – Deformation (6mm, 4d, 90°, Hemlock) .............................................. 65






viii


Figure 73: Load – Deformation (6mm, 10d, 90°, Douglas-fir) ........................................ 68

Figure 74: Load – Deformation (6mm, 10d, 90°, S-P-F) ................................................. 69

Figure 75: Load – Deformation (6mm, 10d, 90°, Hemlock) ............................................ 69





















ix














Figure 109: Load – Deformation (8mm, 10d, 90°, Douglas-fir) ...................................... 86

Figure 110: Load – Deformation (8mm, 10d, 90°, S-P-F) ............................................... 87

Figure 111: Load – Deformation (8mm, 10d, 90°, Hemlock) .......................................... 87









x

















Figure 136: Load – Deformation (10mm, 4d, 90°, Douglas-fir) .................................... 100

Figure 137: Load – Deformation (10mm, 4d, 90°, S-P-F) ............................................. 100

Figure 138: Load – Deformation (10mm, 4d, 90°, Hemlock) ........................................ 101






xi


Figure 145: Load – Deformation (10mm, 10d, 90°, Douglas-fir) .................................. 104

Figure 146: Load – Deformation (10mm, 10d, 90°, S-P-F) ........................................... 105

Figure 147: Load – Deformation (10mm, 10d, 90°, Hemlock) ...................................... 105





















xii





xiii

ACKNOWLEDGEMENTS

I would like to thank Dr. Frank Lam for his guidance throughout this project and

Maximilian Closen as well as the TEAM technicians for the help provided during testing.

I would also like to express my gratitude to Natural Sciences and Engineering

Research Council of Canada for the financial support in this research project.

The cooperation received from Adolf Würth GmbH & Co. KG (http://www.Würth.de) for

the supply of the ASSY screws and Hans Hundegger - Maschinenbau GmbH

(http://www.hundegger.com) for the use of the Hundegger K2 milling machine is also

appreciated.

http://www.nserc-crsng.gc.ca/index_eng.asp

http://www.nserc-crsng.gc.ca/index_eng.asp

http://www.wuerth.de/

http://www.hundegger.com/

1

1. INTRODUCTION

1.1. History

Wood is one of the oldest and most common building materials. In the past, if wood was

not readily available or available in limited quantities then other materials like loam,

stone, bamboo etc. were used in buildings. Wood was primarily used in its natural form

and shape, only the development of tools enabled builders to shape wood into desired

components and allowed wood to be usable beyond its natural limitations, like length for

example. The desire and move toward planned structures was the cradle of timber design

and planned timber construction. Until late in the 19th

century a timber structure was a

mere testimony to craftsmanship and was carried out without structural analysis. These

structures were built by empirical considerations and experience only. The first structures

fully analyzed by engineers were bridges and trestles. They were designed either as

timber arches or timber trusses to reach spans of 20 m and up to 60 m. Illustrated in

Figure 1 is the evolution of timber structure design over a period of about 250 year (years

rounded to decade). Shown are the results of the great craftsmanship of Swiss carpenter

Ulrich Grubenmann (Killer, 1998) using only sawn wood and few mechanical fasteners

in 1756. The American Thompson S. Brown designed the RW Bridge about 100 years

later utilizing structural analysis of arched trusses as it was available at that time by

incorporating mechanical fasteners (Zimmer, 2002). Howard Hughes (Herzog et al, 2003)

conquered yet another new challenge when put in charge of building an airplane, a task

that would have been impossible to undertake without the use of adhesives. In modern

day design of timber structures the computer has become an indispensable tool to allow

2

the completion of each task for complex structures such as the shell roof structure for the

2000 World Exposition EXPO in Hannover Germany (Herzog et al, 2003) (Herzog,

2000).

Figure 1: Development of wood design since 1750

With the industrial revolution and the technological developments in the second half of

the 18th

century came the mass production of iron and later, steel and concrete. The

development of these materials and their “superior” mechanical properties compared to

wood almost led to the complete disappearance of wood as building material in

commercial and high rise construction. Only the limited availability of iron and steel

after the Second World War and the targeted development in timber construction

facilitated the revival of larger wood structures. Some key developments like that of glue

laminated timber by Otto Hetzer (Müller, 2000) at the beginning of the 20th

century along

with the development of connections and connectors further helped that revival.

3

It became apparent in recent years that the topic of connections in timber construction

and design is a crucial one. Researchers around the world are targeting some inherent

weaknesses of wood and moreover, connections in timber structures and revising current

design rules and codes accordingly. These activities also led to the development of new

connections and connection systems with superior structural properties. With these

innovative connection systems, safer and more economical timber structures can be built

since connection design is critical and often governing in timber engineering.

Timber connections with dowel-type fasteners are typically designed based on the

European-Yield model or Johansen theory (Johansen, 1949) and its ductile failure modes.

Splitting failure becomes more and more severe due to the relatively low tension

perpendicular to grain strength of the wooden connection members with an increase in

the number of fasteners and the fastener diameter. Defects like cracks, specifically end-

cracks in the wood, further reduce the resistance of a connection. Such cracks occur not

only during drying and seasoning, but can also occur in glue laminated beams in indoor

application during the service life of the beam. Furthermore, be it intended or non-

intended by design, if moments were imposed onto the connection, splitting failure will

occur.

In the recent past more and more research is being conducted on the topic of

reinforcement of such connections to increase their resistances and capacity. With the

inherent low tension perpendicular to grain strength of wood and defects like cracks

being a big concern for the splitting of connections, a lot of focus was set to reinforce

dowel-type connections with the goal of minimizing splitting. The types of

reinforcements are ranging from glued in rods over reinforcement with glued and

4

screwed on plywood and glued on high tensile fibres at the connection to more recently

developed self-tapping wood screws (STS) with continuous threads. Figure 2 and Figure

3 show specimens that were reinforced using different types of high tensile fibres as well

as a different method on applying the reinforcement. Although some reinforcement

against splitting of the wood is provided, this method is used primarily to reinforce the

embedment strength of the wood (Haller et al, 2006). The load displacement curve in

Figure 4 shows the effectiveness of the reinforcement.

Figure 2: Knitted glass and aramid fibre fabric (spiral)

Figure 3: Transversally reinforced carbon fibre loop

Figure 4: Typical load-displacement curve

5

Madsen (2000) summarizes the research work done on glued-in steel rods and its broad

applicability to multiple common problems in timber engineering. These applications

reach from knee-joints, beam splices and moment connections to reinforcing the bearing

strength as well as tension perpendicular to grain strength. An example of a beam splice

using glued-in rods is shown in Figure 5.

On the other hand Hockey (1999) and Blaß et al. (2000) used commonly available and

well know truss plates to reinforce bolted connections in both embedment strength as

well as splitting perpendicular to the grain. Findings show an increase in ultimate

capacity of the connection as well as a change in failure mode from brittle failure to a

much more desirable ductile failure. The method of using truss plates as reinforcement

offers an economical approach to the problem. First of all, the truss plates are comparably

inexpensive as they are widely used in the manufacturing of conventional 2-by trusses.

Another advantage of using truss plates is the fact that it eliminates the need for pre-

drilled holes in the timber member, as they are required for glued in rods, but also is

easier and cleaner to apply than fibre reinforces plastics that require epoxy resins for their

application.

6

Figure 5: Beam splice using glued-in rods

Self-tapping wood screws with continuous threads have also proven to not only to be an

effective but also an economical method of reinforcing connections with dowel-type

fasteners (Bejtka Blaß, 2005). When compared to glued in rods and glued on fibre

reinforcements for example, self-tapping wood screws are relatively inexpensive, fast and

easy to install. The self-tapping wood screws, as their name implies, do not require any

pre-drilling, similar to the afore mentioned truss plates, and can be installed virtually

invisibly. This is another big advantage of such self-tapping wood screws especially

when they are used in retrofit applications to restore and reinforce existing connections.

However, the use of self-tapping wood screws is not limited to reinforcing connections,

7

but to generally reinforce inherent weaknesses of timber beams like the tension

perpendicular to grain and compression perpendicular to grain strengths.

1.2. Self-tapping wood screws

STSs provide economical means of assembling components, especially where materials

must be joined together or reinforced. Thread forming and thread cutting are the two

major types of self-tapping screws. The thread cutting screws remove the material

physically from which they are drilled into and are typically used in timber connections.

Thread forming STSs, however, plastically deform the material that they are driven into,

providing a permanent thread. This distinguished mechanical and form giving bond with

the wood, offers a great method of transferring tensile and compressive forces along the

axis of the STS.

The development of STSs occurred primarily in Europe where earlier, more common,

wood screws are widely used. These more common screws used the same principle of

transferring loads, but were limited in dimensions. These types of wood screws are

standardized according to DIN 96, DIN 97 or DIN 571 with a thread type in accordance

with DIN 7998 for all of them. Screws with a thread type standardized in DIN 7998

require a pilot hole; their thread length makes up about 60% of the length of the screw

with a length limited to about 150 mm. The limited length meant that these screws could

not be used to connect members with larger cross-section. The commonly used lag-

screws in North America are of similar nature and have essentially the same restrictions

and a comparable thread type like the screws in accordance with DIN 7998 as shown in

Figure 6.

8

Figure 6: Screw thread in accordance with DIN 7998

With the emergence of ever larger cross-sectional glue laminated timbers, the need for

new longer screws was becoming more and more apparent. The development of self-

tapping wood screws was filling that need with screw lengths of now up to 1,000 mm and

diameters of up to 12 mm. STSs are manufactured as partially threaded screws and as

screws with continuous thread depending on their application. A variety of different STSs

are shown in Figure 7. To achieve such long, large diameter screws that can be installed

without a pilot hole, the screws are hardened after the thread has been rolled onto them.

The hardening of the screws is a highly secretive process; it is different for each

manufacturer, which can increase the mechanical properties such as the yield strength,

tensile and compressive strength, as well as the torsional strength of the screws. Self-

tapping wood screws are manufactured with a drill-tip (Figure 8) and coated with a

company specific lubricant to reduce the torque required to install the STS and to prevent

splitting of the wood during installation. When partially threaded self-tapping wood

screws are used, the introduction of a shank cutter as seen in Figure 9 helps to further

reduce friction. Unlike the standardized conventional wood screws, self-tapping wood

screws are not standardized and need a technical or general construction approval. In

Germany the “Deutsche Institut für Bautechnik” DIBt provides the technical approvals

for non-standardized construction materials like STSs.

9

Figure 7: Self-tapping wood screws

Figure 8: Self-tapping wood screw drill-tips

Figure 9: Shank cutter on partially threaded screw

The use of self-tapping screws, which eliminated the need for a pilot hole, has increased

considerably over the past decade in Europe. Initially, a conceivably big disadvantage of

self-tapping wood screws compared to nails, was the fact that little experimental work

10

had been done on these new types of screws. Most mechanical properties in wood-wood

or wood-steel joints were estimated mainly by giving self-tapping screws the same

properties as nails with similar dimensions. Therefore, the strongest attribute, the

withdrawal resistance, of a self-tapping screw was not taken into account. In shear

connections only their dowel action was taken into consideration during design.

Furthermore, self-tapping screws could only be applied in timber connections without a

pilot hole where the density of timber was less than 500-600 kg/m3 and if the shank

diameter of the threaded part was less than 5-6 mm. Further research (Blaß & Bejtka,

2004) concerning lateral and withdrawal resistance of STSs in European species found

that the lateral strength of self-tapping wood screws varied almost linearly with the

specific gravity of the wood and the square root of the diameter of the screw. In addition,

the withdrawal strength of self-tapping wood screws varies almost linearly with the

embedment depth or, more specifically, the effective embedment length of the screw’s

thread. No practical difference was observed between radial and tangential withdrawal

strengths.

In this study, basic strength data on the withdrawal capacity of self-tapping screws with

major Canadian wood species is evaluated. This basic information is needed for the

development of design rules for these types of screws with Canadian species. The

establishment of such design rules would allow engineers and builders to facilitate the

full potential of these types of screws. This is of great interest to engineers in North

America as they are facing similar technical issues as their European colleagues in that

right now STSs can only be designed as lag-screws or nails. As previously mentioned,

using the lag-screw or nail equivalent approach; the greatest benefit of the self-tapping

11

screws, the high withdrawal capacity, is entirely neglected. By establishing evaluation

data the full benefit of the screws could be explored.

The use of STSs is vast and many different kinds of applications have been tried and

looked at by researchers (Blaß & Bejtka, 2004). In Europe these screws are used as

reinforcements for longitudinal shear, tension perpendicular to the grain, and

compression perpendicular to the grain. They are also used to reinforce embedment

strength in dowel-type connections and, more recently, have been discovered as primary

fasteners as well. The application as reinforcements is wide-spread and ranges from

rehabilitation of old existing structures and members to reinforcement for connections, as

shown in Figure 10.

Figure 10: STS as embedment and splitting reinforcement

Research done by Lam et al. (2008) at the University of British Columbia (UBC)

investigated the use of STS in moment resisting bolted connections as reinforcement

12

perpendicular to the grain. The study compared results of unreinforced specimens to

specimens that were previously broken and rehabilitated using STS as well as specimens

that were reinforced using self-tapping wood screws. The results revealed that the

ultimate capacity as well as ductility of the connections could be improved using STS as

reinforcement. It is worth noting that even the previously broken specimens that were

rehabilitated using STS had significantly higher values of capacity than the unreinforced

specimens. Additional work done by Lam et al. (2010) and Gehloff et al. (2010) at UBC

looked at further increasing the capacity of such moment resisting bolted connections by

using larger diameter bolts with reduced end and edge distances. The results confirmed

that the reinforcement with self-tapping wood screws is a viable method to increase the

capacity and ductility of bolted connections subjected to cyclic loading; even for

connections with larger diameter bolts, which are more prone to splitting, and reduced

end and edge distances.

13

2. EXPERIMENTAL DESIGN / EQUATIONS

2.1. Parameter considerations

The focus of this work is the pull out resistance or withdrawal resistance of self-tapping

screws with continuous thread. Experiments are conducted by testing the pull out

resistance at different angles to the grain in different wood species. The angles of the

screw to the grain are 90 degrees (perpendicular), 45 degrees and 30 degrees. The pull

out resistance will be compared under the afore mentioned angles and different

embedment depths in three different wood species. The chosen wood species are

Douglas-fir and S-P-F glulam, as well as, Hemlock solid sawn timber to cover the most

commonly used construction materials in Canadian heavy timber construction and

density range. The screws used for the tests are Würth ASSY plus VG®, where VG

denotes continuous thread. The Würth ASSY plus VG® screws are of 6 mm, 8 mm and

10 mm in diameter and are provided in various lengths of up to 800 mm for the 10 mm

diameter screws.

Preliminary withdrawal tests were conducted by pulling the screws from the specimens.

Results have shown that the tensile strength of the screw itself became the limiting factor

at embedment depths of ~12d (d = diameter of the screw). The test setup was

re-configured in a way that instead of pulling on the screws, the screws were pushed into

the wood. Preliminary tests also revealed that the heads of the screws failed at the

shoulder between the shaft of the screw and the head when the screws were tested by

pulling them through the specimen. This stress concentration resulted from the grip

device of the test setup which would not be present in real applications. When the screws

14

are used with steel side plates, the screws have to be counter-sunk into the steel plates to

ensure proper contact of the screw head and shoulder with the steel plate to avoid stress

concentrations and premature failure. Further preliminary tests proved that the new

compression based setup was more suitable to get results at higher embedment depths of

up to 16d before the screws failed in buckling. Based on these preliminary results, four

different embedment depths were selected: 4d, 10d, 12d and 16d. The low embedment

depth of 4d was selected to gather insights on the reinforcement of bolted connection

with smaller edge distances.

For each combination of screw diameter, embedment depth, angle to the grain and wood

species, 10 replications were tested. With 108 different setups and 10 replicates for each

setup, a total of 1080 test were conducted and evaluated. Furthermore, the results are

compared to predictions based on the German building code DIN 1052:2004-8 and the

Eurocode 5. Both building codes predict the withdrawal resistance of this type of screws

and therefore their potential as reinforcement in tension perpendicular to grain in dowel-

type connections. Input parameters in the equations in the German code are the mean

specific gravity of the wood, the angle to the grain, the screw diameter and the

embedment depth. These parameters coincide with the studied parameters in the tests

conducted for this study.

15

2.2. Test setup

The machine used for the tests was the Sintech 30/D with a 1,500 kN load cell. Wooden

blocks were used to create enough clearance above the machine test table for the screws.

Steel rectangular tubing was used to reduce the span and therefore limit the deflection of

the specimens. A transducer was used to measure the wood deflection near the tested

screw as correction value. Figures 11to13 show the test setup for the 90, 45 and 30 degree

tests respectively. The transducer used to measure the deflection of the specimen is

shown in Figure 14.

Figure 11: Test setup for 90º tests

16



17

Figure 14: Transducer to measure deflection

As shown in Figures 11 to 13, the screws were driven all the way through the specimen to

eliminate any resistance at the screw tip during testing, as well as to reduce the

slenderness ratio. The reduced slenderness will help prevent buckling of the screws at

higher loads and greater embedment depths. The embedment depth was controlled by the

thickness of the specimens. All specimens were cut and planed to the thickness that

equalled the embedment depth for the specific tests. Table 1 and Figure 15 show the

effective embedment depth for the different screw inclinations. The embedment depths

were chosen to remain constant since, otherwise, not enough material would have been

left to properly install the screws and test the screws without breaking the wood first. In a

situation where the screws are used to reinforce bolted connections the approach would

be similar. The calculated minimum edge distances, even if reduced due to the presence

of self-tapping wood screws as reinforcement for the bolts would, be a value that is

18

perpendicular (90°) to the edges of the beam. Thus, the obtained withdrawal resistance

values are applicable to such reinforcements even if it means that the values for different

screw inclinations cannot be compared directly.

Table 1: Effective embedment depths

Figure 15: Effective embedment depth

Embedment

depth

Effective embedment depth

90° 45° 30°

4d 4d (1/sin 45°) 4d (1/sin 30°) 4d

~ 5.656 d 8 d

10d 10d (1/sin 45°) 10d (1/sin 30°) 10d

~ 14.142 d 20 d

12d 12d (1/sin 45°) 12d (1/sin 30°) 12d

~ 16.968 d 24 d

16d 16d (1/sin 45°) 16d (1/sin 30°) 16d

~ 22.624 d 32 d

19

To transfer the load from the load cell to the head of the self-tapping screw, a harden hex-

head screw was used. Due to the hardness of the self-tapping screw the hex-head was

introduced to avoid damage to the load cell.

Testing was done in accordance with the German standard DIN EN 1832, which specifies

the speed of testing such that failure can be reached in 90 seconds ± 30 seconds. Multiple

screws were placed in the specimens to speed up testing. The row spacing of ≥ 5d as well

as the end, edge and screw spacing of ≥ 10d was followed as given in the standard.

2.3. European code equations

The German wood building code DIN 1052:2004-08 defines the withdrawal resistance of

screws by taking the tensile strength min. fu,k = 400 N/mm2 of the screw, the axial

capacity of the thread in wood and the head-pull through into account. Given that, head

pull through of full threaded screws is neglected, the main parameters influencing

withdrawal resistance are the penetration depth of the thread (lef) including the tip

embedded in the wood, the diameter (d), the angle (α) and the characteristic value of the

withdrawal resistance ( Kf .1 ). Further influencing parameters are the apparent density, as

well as the axial capacity of the threaded part embedded in the wood. Wood screws are

separated into three different strength groups regarding their characteristic axial capacity

parameter ( Kf .1 ). For group one to three, the parameter is 26

,1 10 kKf where the

value ( ) can vary from 60 for group one, 70 for group two and 80 for group three,

respectively. Group one represents any wood screw other than screws that can be placed

into either of the other two groups. Screws with threads in accordance with DIN 7998

20

(Figure 6) can be placed in group two without the need of further proof. Group three, on

the other hand, represents a group for hardened screws that are proven to withstand a

certain threshold capacity and generally require a general construction approval. Self-

tapping wood screws require a general construction approval and fall into group three

unless stated otherwise in the approval of the particular screw. The characteristic value of

the withdrawal resistance kaxR , is calculated by Equation 1.

2

.222

.1

. ;

cos3

4sin

min kK

efK

Kax dfldf

R

[N] (1)

where;

26

,1 10 kKf ,

with ρk = characteristic density, kg/m3

d = outside screw diameter, mm

lef = effective embedment depth including the tip, mm

α = angle between screw length axis and wood grain, degree (°)

The second part of Equation 1 is used to calculate the head pull-through resistance of the

screws, where Kf .2 denotes the characteristic head pull-through parameter and kd the

outside head diameter, or if a washer is used the outside diameter of the washer. In case

of fully threaded self-tapping wood screws, however, the head pull-through resistance is

not considered since the loads are transferred through the thread and the shaft of the

screws and not the head.

21

Equation 1 can only be applied for angles 45°≤ α ≤90°. Blaß and Bejtka (2004) show that

the equation holds true for angles (α) down to 30°. In addition, Blaß et al. (2006) found

that the predicted withdrawal resistance kaxR , is very conservative. Thus, the

characteristic axial capacity Kf .1 could be increased by increasing the value ( ) up to 113

for 90° angles and up to 109 for angles less than 90°.

Contrary to the value of kaxR , presented in DIN 1052:2004-08 where the screw tip is

included in the effective embedment depth of the thread in the wood, Equation (2) of the

Eurocode (EC) 5-2004 considers the screw tip by subtracting one time the diameter (d)

from the embedded length. Furthermore, a possible group effect is taken into

consideration by an exponent for the number of fasteners (n).

22

5.138.09.0

.cos5.1sin

106.3

k

efKax ldnR [N] (2)

where;

d = outside screw diameter, mm

lef = effective embedment depth excluding the tip, mm

ρk = characteristic density, kg/m3

α = angle between screw length axis and wood grain, degree (°)

The findings by Blaß and Bejtka (2003) show Equation 2 over-predicted the withdrawal

resistance kaxR , compared to their test results and, in conclusion, the parameter of 3.6 was

lowered to 2.85 to match the test results.

22

2.4. Equivalency calculations

Neither the Canadian timber building code CSA-O86-09, nor the National Design

Specifications (NDS) in the United States give indication for the calculation of the

withdrawal resistance of wood screws similar to the self-tapping wood screws. As no

technical approvals are in existence to date in North America for this type of screw, only

equivalency calculations can be done. The only dowel type fasteners that are of similar

type and are permitted to be loaded axial in withdrawal are nails and spikes, wood screws

and lag-bolts or lag-screws.

When looking at the Canadian CSA-O86-09, paragraph 10.9.5.1 states that nails and

spikes may only be loaded in withdrawal for wind and earthquake design. The same is

stated for wood screws in paragraph 10.11.5.1. Consequently, an equivalency calculation

is only given for wood screws as they have more similarity to self-tapping wood screws

than nails and spikes. The only fastener permitted to be designed in withdrawal in

accordance with CSA-O86-09 that is similar in shape and function to the self-tapping

wood screw is the lag-bolt or lag-screw. The NDS in the United States, however, permits

the axial loading in withdrawal for all three types of fasteners, the nail and spike, wood

screw as well as the lag-bolt or lag-screw; both terms are used interchangeably.

The withdrawal resistance of lag-bolts in accordance with the Canadian CSA-O86-09 is

calculated with Equation 3 and CSA-O86-09 Table 10.6.5.1 as follows;

eFtwrw JnLYP [N/mm] (3)

23

where;

ɸ = 0.6

Yw = yw (KDKSFKT)

yw = basic withdrawal resistance per millimeter of penetration, N/mm (Table 10.6.5.1)

Lt = length of penetration of threaded portion of lag-bolt in main member, mm

nF = number of lag-bolts in the connection

Je = end grain factor for lag-bolts; 0.75 in end grain, 1.00 in all other cases

For wooden side members an appropriate washer has to be used to prevent the head of the

lag-bolt from pulling through the side member.

The withdrawal resistance of wood-screws in accordance with the Canadian CSA-O86-09

is calculated with Equation 4 and CSA-O86-09 Tables A.10.1 and 10.11.1 as follows;

Ftpwrw nLYP [N/mm] (4)

where;

ɸ = 0.6

Yw = yw (KTKSF)

yw = basic withdrawal resistance per millimeter of threaded shank penetration in main

member; = 68 dF0.82

G1.77

, N/mm

G = mean relative density of main member (Table A.10.1)

df = nominal wood screw diameter, mm (Table 10.11.1)

Lpt = threaded length penetration in the main member, mm

nF = number of wood screws in the connection

For a joint with three members, the threaded length penetration shall be the maximum

24

threaded length within any member other than the head-side member. For wooden side

members an appropriate washer has to be used to prevent the head of the wood screw

from pulling through the side member.

In accordance with the United States NDS, the withdrawal resistance is calculated by

multiplying the reference withdrawal resistance W with all applicable adjustment factors

as they can be found in Table 10.3.1 in the NDS. The reference withdrawal resistance is

calculated with Equations 5 to 7 for lag-bolts, wood screws and nails and spikes

respectively. These values are also tabulated in NDS Tables 11.2A, 11.2B and 11.2C

respectively.

4/32/31800 DGW [lb/in] (5)

DGW 22850 [lb/in] (6)

DGW 2/51380 [lb/in] (7)

The calculations for the withdrawal resistance in Canada as well as the United States are

limited to the fastener being installed perpendicular to the grain, meaning an angle of 90°

between the axis of the screw and the grain. No other installation angles are allowed; thus

limiting design parameters to the diameter of the fastener, the penetration depth of the

fastener, and the density of the wood member the fastener is driven into. A comparison of

the calculated withdrawal resistances using the DIN and Eurocode code equations as well

as the equivalency calculations is given in Chapter three. The results of various calculated

predictions are also compared to the test results in an effort to evaluate their respective

applicability.

25

3. RESULTS / DISCUSSION

3.1. Results

The withdrawal test results are shown in Table 3 through Table 5 for all 108 test series.

Each test configuration was tested with 10 replicates bringing the total number of tests to

1080 individual screws. The tables are formatted to group the results for all screws with

the same angle between the axis of the screw relative to the grain. It should be mentioned

that the results in Tables 3 to 5 showing average values for the 6 mm, 8 mm and 10 mm

screws respectively, are taken from all 10 test replicates and are not calculated based on

the shown minimum and maximum values alone. To display the results a little more

clearly and to be able to understand the effects of different parameters, the results are also

shown in Figures 16 to 24. The figures are divided not only into the angle of screw

installation with respect to the grain, but also split into single screw diameters in order to

keep the graphs legible. The error bars show the minimum and maximum test values.

The data below clearly shows the effect the individual parameters have on the results.

With an increase in embedment depth, the withdrawal resistance also increased. The

same can be said for the increase in screw diameter and the different densities of the

wood samples. The effect of the density, however, can only really be discussed on the

bases of the different wood species (Table 2) as multiple screws were tested in the same

specimen and local density variations like knots within the specimen were present.

Table 2: Average densities

Douglas-fir Spruce - Pine - Fir Hemlock

Average density [kg/m3] 530.58 463.89 512.88

Standard Deviation [kg/m3] 37.20 34.78 38.164

26

Table 3: Withdrawal test results for 90°

Test configuration Withdrawal Capacity [kN]

Ø [mm] Embedment Angle [°] Species Min Max Average STDV

6 4d 90 DF 2.709 4.510 3.508 0.570

6 4d 90 SPF 2.357 4.270 3.195 0.658

6 4d 90 H 2.487 3.478 2.926 0.371

6 10d 90 DF 9.456 18.070 13.285 3.094

6 10d 90 SPF 7.216 8.152 7.725 0.320

6 10d 90 H 10.793 18.304 13.426 2.251

6 12d 90 DF 11.441 16.700 14.180 1.779

6 12d 90 SPF 8.846 10.698 9.627 0.699

6 12d 90 H 13.396 18.383 15.859 2.070

6 16d 90 DF 15.599 18.071 16.884 0.790

6 16d 90 SPF 13.904 16.308 14.890 0.829

6 16d 90 H 14.389 15.869 15.111 0.543

8 4d 90 DF 6.024 9.200 7.160 0.852

8 4d 90 SPF 4.427 5.779 5.058 0.475

8 4d 90 H 3.944 8.027 4.892 1.193

8 10d 90 DF 14.817 19.218 17.284 1.502

8 10d 90 SPF 12.062 13.765 12.751 0.555

8 10d 90 H 13.042 16.842 15.324 1.131

8 12d 90 DF 18.162 25.547 22.136 2.541

8 12d 90 SPF 16.460 20.857 18.255 1.295

8 12d 90 H 14.172 26.745 19.228 3.826

8 16d 90 DF 23.607 27.561 25.889 1.228

8 16d 90 SPF 20.746 26.298 23.420 2.162

8 16d 90 H 21.741 28.413 24.396 2.651

10 4d 90 DF 6.819 9.331 8.150 0.905

10 4d 90 SPF 6.263 7.215 6.921 0.299

10 4d 90 H 6.892 9.923 8.017 0.830

10 10d 90 DF 22.783 30.383 27.904 2.126

10 10d 90 SPF 15.343 21.701 19.237 1.955

10 10d 90 H 14.123 20.906 18.485 2.984

10 12d 90 DF 25.489 38.549 33.235 5.460

10 12d 90 SPF 22.654 27.909 25.529 1.628

10 12d 90 H 19.867 38.995 29.353 6.608

10 16d 90 DF 32.237 37.842 35.948 1.726

10 16d 90 SPF 25.158 31.425 28.956 2.120

10 16d 90 H 25.264 36.096 29.615 4.043 Note: DF = Douglas-fir, SPF = Spruce-Pine-Fir, H = Hemlock

27

Figure 16: Average withdrawal resistance for 6 mm screw @ 90º


0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

4d 10d 12d 16d

Ava

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wit

hd

raw

al

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stan

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kN

]

Embedment depth

Würth 6 mm @ 90º angle

Douglas-fir

S-P-F

Hem.-fir

0.00

5.00

10.00

15.00

20.00

25.00

30.00

4d 10d 12d 16d

Avare

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kN

]

Embedment depth


Douglas-fir

S-P-F

Hem.-fir

28


Results shown in Figures 16 to 18 indicate a general trend that the average values for the

withdrawal resistance following the same trend as the average densities. With an

increased average density, the values for the average withdrawal resistance are also

increased. The above stated effect of the embedment depth as well as the screw diameter

is also clearly seen in the graphs.

The permissible characteristic tensile strength of the screws as per the German general

construction approval are 11.3 kN for the 6 mm screws, 18.9 kN for the 8 mm screws and

24.0 kN for the 10 mm screws. Granted the fact that the permissible characteristic values

for the tensile strength of the steel are 5th

percentile value and the shown withdrawal

values are average values, it can still be seen that the embedment depth of 16d almost

always cause the screw to fail not the wood in withdrawal. A closer look at this will be

taken in the discussions section of this study.

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

4d 10d 12d 16d

Avare

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kN

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Embedment depth


Douglas-fir

S-P-F

Hem.-fir

29




6 4d 45 DF 3.978 4.729 4.313 0.243

6 4d 45 SPF 2.370 3.163 2.929 0.223

6 4d 45 H 2.627 6.000 3.278 1.007

6 10d 45 DF 12.447 14.115 13.090 0.553

6 10d 45 SPF 10.559 14.018 11.882 1.131

6 10d 45 H 13.575 15.998 14.419 0.887

6 12d 45 DF 14.111 16.428 15.039 0.654

6 12d 45 SPF 12.492 15.715 13.985 0.915

6 12d 45 H 13.881 15.534 14.701 0.513

6 16d 45 DF 13.347 16.264 15.306 0.831

6 16d 45 SPF 13.915 15.483 14.849 0.487

6 16d 45 H 12.941 16.143 14.635 0.792

8 4d 45 DF 3.494 6.494 5.686 0.947

8 4d 45 SPF 5.727 6.407 6.041 0.218

8 4d 45 H 3.938 7.151 5.177 1.157

8 10d 45 DF 22.388 25.738 23.740 1.071

8 10d 45 SPF 16.722 22.843 19.354 1.859

8 10d 45 H 15.680 23.638 19.864 2.958

8 12d 45 DF 19.805 24.611 22.844 1.549

8 12d 45 SPF 21.311 23.327 22.310 0.559

8 12d 45 H 20.299 23.057 21.760 0.821

8 16d 45 DF 19.942 24.062 21.902 1.130

8 16d 45 SPF 19.811 24.916 21.805 1.474

8 16d 45 H 18.018 23.052 20.833 1.622

10 4d 45 DF 5.795 9.590 7.921 1.260

10 4d 45 SPF 7.012 8.762 7.897 0.624

10 4d 45 H 3.281 12.477 8.563 3.432

10 10d 45 DF 24.315 31.525 29.074 2.107

10 10d 45 SPF 22.840 30.619 27.473 1.988

10 10d 45 H 23.657 30.682 27.798 2.310

10 12d 45 DF 26.833 32.862 30.214 1.730

10 12d 45 SPF 24.673 33.323 29.104 2.463

10 12d 45 H 28.547 33.579 31.241 1.759

10 16d 45 DF 25.259 32.731 29.418 2.124

10 16d 45 SPF 24.369 32.343 28.883 2.180


30



0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

4d 10d 12d 16d

Avare

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kN

]

Embedment depth


Douglas-fir

S-P-F

Hem.-fir

0.00

5.00

10.00

15.00

20.00

25.00

30.00

4d 10d 12d 16d

Avare

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kN

]

Embedment depth


Douglas-fir

S-P-F

Hem.-fir

31


The values for inclination angles of 45°, as well as 30°, are exhibiting similar trends as

seen for the perpendicular to the grain installed screws. However, the effect of the

increased effective embedment depth leads to screw failure in a few cases at a depth of

10d since the effective depth would be about 14d compared to the 90 degree tests (Table

1). This is even more apparent for angles of 30 degrees where almost all specimens at

10d already shown steel failure in the screw instead of withdrawal failure in the wood.

The calculated embedment depth for perpendicular installed screws would be in the range

of 12d to 14d depending on the density of the wood. Figure 25 depicts typical screw

failure as it is reached when the embedment depth exceeds the limit the steel of the screw

can transfer into the wood. Figure 26 shows a typical load displacement plot of the

withdrawal test, all plots can be found in the appendix.

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

4d 10d 12d 16d

Avare

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kN

]

Embedment depth


Douglas-fir

S-P-F

Hem.-fir

32




6 4d 30 DF 4.618 7.090 5.893 0.851

6 4d 30 SPF 3.672 6.179 4.430 0.755

6 4d 30 H 4.598 8.079 6.100 1.061

6 10d 30 DF 13.615 15.312 14.511 0.489

6 10d 30 SPF 11.435 14.556 13.087 1.187

6 10d 30 H 13.624 14.519 14.124 0.282

6 12d 30 DF 13.036 15.181 14.179 0.793

6 12d 30 SPF 13.108 14.899 13.978 0.668

6 12d 30 H 12.379 14.568 13.908 0.627

6 16d 30 DF 13.328 14.904 14.059 0.471

6 16d 30 SPF 11.735 14.543 13.517 0.867

6 16d 30 H 13.879 15.175 14.605 0.449

8 4d 30 DF 9.994 16.214 12.789 1.884

8 4d 30 SPF 6.559 13.664 8.522 2.061

8 4d 30 H 8.822 13.466 10.443 2.216

8 10d 30 DF 19.691 23.128 21.451 1.113

8 10d 30 SPF 19.816 24.581 22.273 1.428

8 10d 30 H 19.108 24.780 21.110 1.540

8 12d 30 DF 22.047 26.307 23.875 1.147

8 12d 30 SPF 21.678 24.163 22.679 0.827

8 12d 30 H 19.762 22.221 21.339 1.046

8 16d 30 DF 21.153 23.549 22.201 0.931

8 16d 30 SPF 20.192 22.922 21.526 0.950

8 16d 30 H 17.609 22.266 20.132 1.407

10 4d 30 DF 17.485 20.391 19.083 1.021

10 4d 30 SPF 11.044 17.409 15.224 1.782

10 4d 30 H 12.454 21.633 16.258 3.102

10 10d 30 DF 29.572 34.166 31.217 1.434

10 10d 30 SPF 27.677 31.918 29.731 1.203

10 10d 30 H 25.441 31.039 29.363 1.853

10 12d 30 DF 28.549 31.746 30.727 1.103

10 12d 30 SPF 29.787 33.906 31.389 1.141

10 12d 30 H 26.334 33.890 29.618 2.642

10 16d 30 DF 29.229 35.660 31.540 1.794

10 16d 30 SPF 28.602 32.158 29.936 0.953


33



0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

4d 10d 12d 16d

Avare

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Embedment depth


Douglas-fir

S-P-F

Hem.-fir

0.00

5.00

10.00

15.00

20.00

25.00

30.00

4d 10d 12d 16d

Avare

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kN

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Embedment depth


Douglas-fir

S-P-F

Hem.-fir

34


Figure 25: Typical screw failure

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

4d 10d 12d 16d

Avare

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kN

]

Embedment depth


Douglas-fir

S-P-F

Hem.-fir

35

Figure 26: Typical load deformation plot

The densities and moisture content for all specimens have been recorded during the

testing. A needle moisture meter was used to measure the moisture content, driving the

needles about 25 mm in to the specimen. The moisture content varied from 7.25% to

13.00% with most specimens having moisture contents between 8.00% and 10.00%. To

establish the density of the specimens, the specimens were weighed at the ambient

climate and their respective moisture contents and measured in all dimensions to establish

their volume. The density was then calculated using the measured weight and volume of

the specimens. Densities for all specimens, regardless of species, have been sorted in

density groups with 20 kg/m3 increments and a normal distribution has then been fitted,

as shown in Figure 27. Figure 27 shows that a normal distribution fits quite well to the

recorded density values.

0

2

4

6

8

10

12

0 0.5 1 1.5 2 2.5 3

Load

[kN

]

Deformation [mm]

Würth 6mm 12d @ 90 deg. - S-P-F

SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

36

Figure 27: Wood density distribution

3.2. Discussion

In Table 6, calculated characteristic values are compared to the minimum value of the

test, in lieu of the 5th

percentile value, due to the low number of test replicates. The

results in general confirm the findings by Blaß and Bejtka (2004). In most cases the

German DIN 1052:2004-8 (Equation 1) seems to produce conservative results for 90°,

especially for higher embedment depths. It is also confirmed that the Equation 2 used in

the EC 5 over-predicts the withdrawal resistance in most cases. Neither the US code nor

the Canadian code allow for the calculation of withdrawal capacities at an angle other

than 90°. Thus, the comparisons shown in Table 6 were chosen for an angle to the grain

of 90°. The densities used in the calculations are taken from the averages measured

during the tests as shown in Table 2.

0

0.002

0.004

0.006

0.008

0.01

0.012

380 430 480 530 580

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

22%

24%

26%

28%

400 420 440 460 480 500 520 540 560 580 600 620

Rela

tiv

e f

req

uen

cy [

%]

Density [kg/m3]

Wood density distribution

37

Table 6: Comparison of test results to code equation predictions for STS

Code predictions @ 90° Withdrawal Capacity [kN]

Ø

[mm]

Embed.

Depth

Species

(G)

Min.

Test DIN EC5

CSA

lag

CSA

screw

NDS

lag

NDS

screw

NDS

nail

6

4d 24 DF 0.53 4.51 3.24 5.85 1.78 2.92 1.03 0.84 0.30

4d 24 SPF 0.46 2.36 2.44 4.73 0.74 2.27 0.83 0.63 0.21

4d 24 H 0.51 2.49 3.00 5.52 0.89 2.73 0.97 0.78 0.27

10d 60 DF 0.53 9.46 8.09 12.18 4.44 7.30 2.58 2.10 0.74

10d 60 SPF 0.46 7.22 6.09 9.84 1.86 5.68 2.09 1.58 0.52

10d 60 H 0.51 10.79 7.49 11.49 2.22 6.82 2.44 1.95 0.67

12d 72 DF 0.53 11.44 9.71 14.09 5.33 8.76 3.10 2.52 0.89

12d 72 SPF 0.46 8.85 7.31 11.39 2.23 6.81 2.50 1.90 0.62

12d 72 H 0.51 13.40 8.99 13.30 2.66 8.18 2.92 2.34 0.81

16d 96 DF 0.53 15.60 12.94 17.73 7.10 11.68 4.13 3.36 1.19

16d 96 SPF 0.46 13.90 9.75 14.34 2.98 9.09 3.34 2.53 0.83

16d 96 H 0.51 14.39 11.99 16.74 3.55 10.91 3.90 3.12 1.08

8

4d 32 DF 0.53 6.02 5.75 9.27 3.10 3.89 1.63 1.40 0.49

4d 32 SPF 0.46 4.43 4.33 7.49 1.34 3.03 1.32 1.06 0.35

4d 32 H 0.51 3.94 5.33 8.75 1.76 3.64 1.54 1.30 0.45

10d 80 DF 0.53 14.82 14.38 19.29 7.76 9.73 4.07 3.51 1.24

10d 80 SPF 0.46 12.06 10.83 15.60 3.36 7.57 3.29 2.64 0.87

10d 80 H 0.51 13.04 13.32 18.21 4.40 9.09 3.84 3.25 1.12

12d 96 DF 0.53 18.16 17.26 22.32 9.31 11.68 4.88 4.21 1.48

12d 96 SPF 0.46 16.46 13.00 18.05 4.03 9.09 3.95 3.17 1.04

12d 96 H 0.51 14.17 15.98 21.07 5.28 10.91 4.61 3.89 1.35

16d 128 DF 0.53 23.61 23.01 28.10 12.42 15.57 6.51 5.61 1.98

16d 128 SPF 0.46 20.75 17.33 22.72 5.38 12.12 5.26 4.22 1.39

16d 128 H 0.51 21.74 21.31 26.52 7.04 14.54 6.14 5.19 1.80

10

4d 40 DF 0.53 9.33 8.99 13.25 4.80 4.86 2.33 2.10 0.74

4d 40 SPF 0.46 6.26 6.77 10.71 2.44 3.79 1.89 1.58 0.52

4d 40 H 0.51 6.89 8.32 12.50 2.80 4.54 2.20 1.95 0.67

10d 100 DF 0.53 22.78 22.47 27.57 12.00 12.16 5.83 5.26 1.85

10d 100 SPF 0.46 15.34 16.93 22.29 6.10 9.47 4.71 3.96 1.30

10d 100 H 0.51 14.12 20.81 26.02 7.00 11.36 5.50 4.87 1.68

12d 120 DF 0.53 25.49 26.97 31.90 14.40 14.59 6.99 6.31 2.22

12d 120 SPF 0.46 22.65 20.31 25.79 7.32 11.36 5.66 4.75 1.56

12d 120 H 0.51 19.87 24.97 30.11 8.40 13.63 6.60 5.84 2.02

16d 160 DF 0.53 32.24 35.96 40.15 19.20 19.46 9.33 8.41 2.97

16d 160 SPF 0.46 25.16 27.08 32.47 9.76 15.14 7.54 6.34 2.08

16d 160 H 0.51 25.26 33.29 37.90 11.20 18.18 8.80 7.79 2.69 Note: DF = Douglas-fir, SPF = Spruce-Pine-Fir, H = Hemlock

* ** ** ** ** *** ***

* of 10 tests; ** characteristic value (5th

percentile); *** allowable stress design value

***

38

Using the CSA O86-09 wood screw withdrawal resistance equivalent (Equation 4) gives

the closest values of any of the equivalent methods, but still significantly under-predicts

the test results.

The screw diameter and angle to the grain are considered in Figures 28 to 45, which show

the relationship between DIN and EC5 predicted characteristic withdrawal resistance

compared to test results. The figures show the withdrawal capacities calculated using the

respective code equations of DIN and EC5, which for larger embedment depth is higher

than the tensile strength of the screw itself. The tensile strength of the screws are shown

in the figures as dotted lines, meaning values that are beyond that line would be governed

by the screws tensile strength rather than the withdrawal capacity from the wood. Thus,

the values in the lower left part of the graph are the pivotal ones and considered in the

discussions below.

The results show trends that could generally confirm the work done by Blaß and Bejtka

(2004). The design equation given in the German DIN (Equation 1) are valid for wood of

densities up to 500 kg/m3 and should be carefully checked for applicability to North

American species, especially at higher densities. On the other hand, the EC5 design

equation does not specify a limit in density. When looking at the figures for the

comparison to EC5 (Figures 29 to 45) it shows that the EC5 equation over-predicts the

withdrawal capacities especially when compared to the minimum test values as

mentioned before. The equation according to DIN also over-predicts for the 4d

embedment depths and even more for other depths for screw diameters of 8 mm and 10

mm. For withdrawal values at angles other than 90° the tensile strength of the screw

becomes limiting in most cases due to the increased effective embedment depths.

39

Figure 28: Comparison of 6 mm results with DIN 1052:2004-8 predictions @ 90°

Figure 29: Comparison of 6 mm results with EC 5 predictions @ 90°

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Exp

erim

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kN

]

Predicted withdrawal resistance DIN 1052:2004-8 [kN]


Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Exp

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kN

]

Predicted withdrawal resistance Eurocode 5 [kN]

Würth 6 mm @ 90º angle Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

40



0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

41



0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

42



0

5

10

15

20

25

30

35

40

45

50

55

0 5 10 15 20 25 30 35 40 45 50 55Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

0

5

10

15

20

25

30

35

40

45

50

55

0 5 10 15 20 25 30 35 40 45 50 55Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

43



0

5

10

15

20

25

30

35

40

45

50

55

0 5 10 15 20 25 30 35 40 45 50 55Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

0

5

10

15

20

25

30

35

40

45

50

55

0 5 10 15 20 25 30 35 40 45 50 55Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

44



0

5

10

15

20

25

30

35

40

45

50

55

0 5 10 15 20 25 30 35 40 45 50 55Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

0

5

10

15

20

25

30

35

40

45

50

55

0 5 10 15 20 25 30 35 40 45 50 55Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

45



05

101520253035404550556065707580

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

05

101520253035404550556065707580

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

46



05

101520253035404550556065707580

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

05

101520253035404550556065707580

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

47



05

101520253035404550556065707580

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

05

101520253035404550556065707580

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

48

Results of the study by Blaß et al. (2006) suggested adjustments to Equation 1. Changing

the characteristic axial capacity Kf .1 by increasing the values of to 109 are shown in

Figures 46 to 62. The comparisons of the calculations to the observed test values are un-

conservatively over-predicted and undesirable. The values of should actually be

slightly reduced for major Canadian species, although a larger number of tests than done

in this study are required to make more definitive statements. In case of the by Blaß and

Bejtka (2004) suggested adjustment to Eurocode 5 (Equation 2), the parameter of 3.6 was

lowered to 2.85 to better match the test results and avoid over-predicting the withdrawal

resistance. Figures 47 to 63 show that the adjusted EC5 equation predicts more

conservatively than the unadjusted equation, especially at higher embedment depths. For

embedment depths of 4d the adjusted EC5 equation still over-predicts the withdrawal

capacity, but the results are closer to the observed test results as they were when using the

current, uncorrected EC5 equation. However, neither adjustment properly predicts the

results of the tests and needs to be revisited. For major Canadian species the equations

need to be further optimized, but more test data is required to do so effectively and

accurately.

Another observation is that starting at an embedment depth of about 10d to 12d,

depending on the screw angle, the tensile capacity (as per German General Construction

Approval) of the Würth ASSY plus VG screw is reached.

49

Figure 46: Comparison of 6 mm results with DIN 1052:2004-8 adjustments @ 90°

Figure 47: Comparison of 6 mm results with EC 5 adjustments @ 90°

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]

Adjusted withdrawal resistance DIN 1052:2004-8 [kN]


SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]

Adjusted withdrawal resistance Eurocode 5 [kN]


SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

50



0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

51



0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

52



0

5

10

15

20

25

30

35

40

45

50

55

0 5 10 15 20 25 30 35 40 45 50 55Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

0

5

10

15

20

25

30

35

40

45

50

55

0 5 10 15 20 25 30 35 40 45 50 55Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

53



0

5

10

15

20

25

30

35

40

45

50

55

0 5 10 15 20 25 30 35 40 45 50 55Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

0

5

10

15

20

25

30

35

40

45

50

55

0 5 10 15 20 25 30 35 40 45 50 55Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

54



0

5

10

15

20

25

30

35

40

45

50

55

0 5 10 15 20 25 30 35 40 45 50 55Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

0

5

10

15

20

25

30

35

40

45

50

55

0 5 10 15 20 25 30 35 40 45 50 55Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

55



05

101520253035404550556065707580

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

05

101520253035404550556065707580

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

56



05

101520253035404550556065707580

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

05

101520253035404550556065707580

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

57



05

101520253035404550556065707580

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

05

101520253035404550556065707580

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80Exp

erim

enta

l w

ith

dra

wal

resi

stan

ce [

kN

]



Douglas-fir - 4d

SPF - 4d

Hem.-fir - 4d

Douglas-fir - 10d

SPF - 10d

Hem.-fir - 10d

Douglas-fir - 12d

SPF - 12d

Hem.-fir - 12d

Douglas-fir - 16d

SPF - 16d

Hem.-fir - 16d

tens. capacity

58

4. CONCLUSIONS AND RECOMMENDATIONS

4.1. Conclusions

Results of this study show that self-tapping wood screws have a high resistance against

pull-out in Canadian Major Species. Combined with their hardened high tensile strength

steel, these STS connectors can be effectively used in reinforcement applications and

direct connections. To utilize the high withdrawal capacity of self-tapping wood screws

most efficiently, they should be installed in such way that the main path of load transfer

is along the length axis of the self-tapping wood screw.

This study has shown that in most cases the equation given in the German DIN predicts

the withdrawal capacity conservatively. However, some cases are under-predicted and

therefore seem unsafe. The EC 5 equation over-predicts the withdrawal capacities of the

screws. The findings clearly show that improvements to the equations need to be done in

order to apply them to major Canadian species. Nevertheless, more data on the

withdrawal resistance of self-tapping wood screws in major Canadian species is required

to develop such improved equations.

When comparing the test results to the equivalency calculations according to CSA O86-

09 and the NDS 2005 (Equations 3 to 7), it becomes apparent that none of the currently

available calculation methods for mechanical fasteners can predict the withdrawal

capacity of self-tapping wood screws. Not only are the predicted values much too

conservative, but the currently available equations also failed to include a parameter for

the angle of the screw axis relative to the angle of the grain. While the European

59

equations are valid for screw inclinations between 90 degree and 30 degrees, the North

American equations are only valid for 90 degree screw angles.

In order to fully utilize the high capacities and therefore advantages of STSs,

modifications to CSA O86-09, as well as NDS 2005 are required. In lieu of changing the

available equations in the North American code, they could be complimented by adopting

an additional section for self-tapping wood screws or fasteners with a thread type similar

to that of STSs. Alternatively, for the immediate future, proprietary construction

approval, or product evaluation reports valid for an individual screw type and

manufacturer could be used to overcome the missing calculation methods in the available

codes.

4.2. Recommendations

The experimental research needs to be continued to 1) increase sample size to allow

proper estimation of characteristic values and 2) complete the parameter study for the

withdrawal resistance of screws from different manufacturers such as the

HECO TOPPIX CC and SPAX to confirm the findings of the study. Furthermore, the

effects of multiple self-tapping screws and respective end and edge distances, as well as

spacing’s of these screws between each other need to be studied. Such studies should

include conditions like changing moisture conditions during the service life of a

connection, as well as during the seasons of the year.

In the Canadian context reliability based design procedures need to be considered to

establish design equations for STS.

60

In order to fully understand the behaviour of connections using self-tapping wood screws,

further studies of the capacities of such screws perpendicular to their length axis as well

as combined forces applied parallel and perpendicular to the axis of the screw are needed.

In most cases combined forces will have to be transmitted and resisted by the self-tapping

wood screws. Such tests have been conducted in Europe by Blaß and Bejtka (2004) to

increase the range of application of STSs.

In addition, more studies should be conducted to build on UBC’s work on using these

screws to reinforce moment resistant connections against perpendicular to the grain and

shear failures. The feasibility of reducing end and edge distances, as well as bolt and row

spacing in moment resisting connections and heavy timber connections in general could

be studied. The reduction of such parameters would allow for more economical use of

timber members in structures and potentially lead to a greater use of wooden members in

mid-rise and commercial structures. In almost all cases, the current minimum distances

are the limiting factor in sizing wooden members in structures of such nature.

61

BIBLIOGRAPHY

ANSI / AF&PA NDS-2005 (2005), NDS: National Design Specifications for Wood

Construction. AF&AP American Wood Council, Washington

Bejtka I., Blaß H.J. (2005) Self-tapping screws as reinforcements in connections with

dowel-type fasteners. International Council for Research and Innovation in Building and

Construction, Working Commission W18 - Timber Structures. Meeting Thirty-Eight,

Karlsruhe, Germany

Blaß H.J., Bejtka I. (2004) Selbstbohrende Holzschrauben und ihre

Anwendungsmöglichkeiten. Holzbaukalender 2004, 3. Jahrgang, Bruderverlag Karlsruhe,

ISBN 3- 87104-136-X, S. 516-541 (2004)

Blaß H.J., Bejtka I., Uibel I. (2006) Tragfähigkeit von Verbindungen mit selbstbohrende

Holzschrauben mit Vollgewinde. Karlsruher Berichte zum Ingenieurholzbau 4,

Universität Karlsruhe, Germany

Blaß H.J., Schmid M., Litze H., Wagner B. (2000) Nail plate reinforced joints with

dowel-type fasteners. World Conference on Timber Engineering 2004. Whistler, British

Columbia, Canada. Proceedings pp. 8.6.4-1 – 8.6.4-8

CEN (Comité Européen de Normalisation) (2004). EN1995-1-1: 2004 (D), Eurocode 5:

Bemessung und Konstruktion von Holzbauten- Teil 1-1: Allgemeines- Allgemeine

Regeln und Regeln für den Hochbau CEN/ TC 250 Structual Eurocodes.

CSA (Canadian Standards Association) Standard (2009). CSA O86-09: Engineering

Design in Wood. Canadian Standards Association, Mississauga

DIBt (Deutsches Institut für Bautechnik) (2006) Allgemeine Bauaufsichtliche Zulassung,

Würth ASSY VG plus Vollgewindeschrauben als Holzverbindungsmittel. DIBt, Berlin

DIN (Deutsches Institut für Normung e.V.) (1975) DIN 7998: Gewinde und

Schraubenenden für Holzschrauben. Beuth Verlag, Berlin

62

DIN (Deutsches Institut für Normung e.V.) (2004) DIN 1052:2004-08: Entwurf,

Berechnung und Bemessung von Holzbauwerken- Allgemeine Bemessungsregeln und

Bemessungsregeln für den Hochbau. Beuth Verlag, Berlin

DIN (Deutsches Institut für Normung e.V.) (2010) DIN 96: Halbrund-Holzschrauben mit

Schlitz. Beuth Verlag, Berlin

DIN (Deutsches Institut für Normung e.V.) (2010) DIN 97: Senk-Holzschrauben mit

Schlitz. Beuth Verlag, Berlin

DIN (Deutsches Institut für Normung e.V.) (2010) DIN 571: Sechkant-Holzschrauben.

Beuth Verlag, Berlin

DIN EN (Deutsches Institut für Normung e.V. ) (1999). DIN EN 1382: Holzbauwerke,

Prüfverfahren - Ausziehtragfähigkeit von Holzverbindungsmitteln. Deutsche Fassung EN

1382. Beuth Verlag, Berlin

Gehloff M., Closen M., Lam F., (2010) Reduced edge distances in bolted timber moment

connections with perpendicular to grain reinforcement. World Conference on Timber

Engineering 2010. Riva del Garda, Italy, CD-ROM Proceedings

Haller P., Birk T., Offermann P., Cebulla H. (2006) Fully fashioned biaxial weft knitted

and stitch bonded textile reinforcements for wood connections. Science Direct,

Composites Part B 37 278-285

Herzog Th. (Hrsg.) (2000) Expodach–roof structure at the world exhibition Hanover

2000. Prestel, Munich, London, New York

Herzog Th., Natterer J., Schweitzer R., Volz M., Winter W. (2003) Holzbauatlas. Edition

DETAIL, Inst. f. internationale Architektur-Dokumentation, Muenchen. Vierte Auflage,

neu bearbeitet

Hockey B. (1999) Truss Plate reinforced bolted connections in Parallel Strand Lumber.

MASc Thesis, University of British Columbia, Department of Wood Sciences,

Vancouver

63

Johansen KW (1949) Theory of Timber Connections. International Association of Bridge

and Structural Engineering, Copenhagen, Publication No. 9, pp. 249-262

Killer J. (1998) Die Bauwerke der Baumeister Grubenmann. Lignum/Baufachverlag, 4.

Auflage

Lam F., Schulte-Wrede M., Yao C.C., Gu J.J., (2008) Moment resistance of bolted timber

connections with perpendicular to grain reinforcements. World Conference on Timber

Engineering 2008. Miyazaki, Japan, CD-ROM Proceedings

Lam F., Gehloff M., Closen M., (2010) Moment-resisting bolted timber connections.

Proceedings of the Institute of Civil Engineers, Volume 163 Issue SB4. London, UK,

ISSN 0965-0911, pp. 267-274

Madsen B. (2000) Behaviour of Timber Connections. First Edition, Timber Engineering

Ltd., North Vancouver, ISBN 1-55056-738-1

Müller Ch. (2000) Holzleimbau Laminated Timber Construction. Birkhäuser, Basel;

Berlin; Boston, ISBN 0-7643-6267-7 (2000)

Zimmer P. (2002) Die Konstruktionsgeschichte Hölzerner Brücken zwischen 1750 und

1850. Interner Forschungsbericht, Fakultät Architektur der TU Dresden

64

APPENDIX – SUPPLEMENTAL MATERIAL

Figure 64: Load – Deformation (6mm, 4d, 90°, Douglas-fir)

Figure 65: Load – Deformation (6mm, 4d, 90°, S-P-F)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 0.5 1 1.5 2 2.5 3

Load

[kN

]

Deformation [mm]

Würth 6mm 4d @ 90 deg. - Douglas-fir

SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 0.5 1 1.5 2 2.5 3

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

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SPEC 8

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SPEC 10

65

Figure 66: Load – Deformation (6mm, 4d, 90°, Hemlock)


0

0.5

1

1.5

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2.5

3

3.5

4

4.5

5

0 0.5 1 1.5 2 2.5 3

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[kN

]

Deformation [mm]

Würth 6mm 4d @ 90 deg. - Hemlock

SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

1

2

3

4

5

6

0 0.5 1 1.5 2 2.5 3 3.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

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SPEC 8

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SPEC 10

66



0

1

2

3

4

5

6

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Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

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SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

1

2

3

4

5

6

0 0.5 1 1.5 2 2.5 3 3.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

67



0

1

2

3

4

5

6

7

8

9

0 0.5 1 1.5 2 2.5 3 3.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

1

2

3

4

5

6

7

8

9

0 0.5 1 1.5 2 2.5 3 3.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

68



0

1

2

3

4

5

6

7

8

9

0 0.5 1 1.5 2 2.5 3 3.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

18

20

0 0.5 1 1.5 2 2.5 3 3.5 4

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

69



0

2

4

6

8

10

12

14

16

18

20

0 0.5 1 1.5 2 2.5 3 3.5 4

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

18

20

0 0.5 1 1.5 2 2.5 3 3.5 4

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

70



0

2

4

6

8

10

12

14

16

18

0 0.5 1 1.5 2 2.5 3

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

18

0 0.5 1 1.5 2 2.5 3

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

71



0

2

4

6

8

10

12

14

16

18

0 0.5 1 1.5 2 2.5 3

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

0 0.5 1 1.5 2 2.5 3 3.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

72



0

2

4

6

8

10

12

14

16

0 0.5 1 1.5 2 2.5 3 3.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

0 0.5 1 1.5 2 2.5 3 3.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

73



0

2

4

6

8

10

12

14

16

18

20

0 0.5 1 1.5 2 2.5 3 3.5 4

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

18

20

0 0.5 1 1.5 2 2.5 3 3.5 4

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

74



0

2

4

6

8

10

12

14

16

18

20

0 0.5 1 1.5 2 2.5 3 3.5 4

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

18

0 0.5 1 1.5 2 2.5 3

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

75



0

2

4

6

8

10

12

14

16

18

0 0.5 1 1.5 2 2.5 3

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

18

0 0.5 1 1.5 2 2.5 3

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

76



0

2

4

6

8

10

12

14

16

0 0.5 1 1.5 2 2.5 3 3.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

0 0.5 1 1.5 2 2.5 3 3.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

77



0

2

4

6

8

10

12

14

16

0 0.5 1 1.5 2 2.5 3 3.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

18

20

0 0.5 1 1.5 2 2.5 3 3.5 4

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

78



0

2

4

6

8

10

12

14

16

18

20

0 0.5 1 1.5 2 2.5 3 3.5 4

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

18

20

0 0.5 1 1.5 2 2.5 3 3.5 4

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

79



0

2

4

6

8

10

12

14

16

18

0 0.5 1 1.5 2 2.5 3

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

18

0 0.5 1 1.5 2 2.5 3

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

80



0

2

4

6

8

10

12

14

16

18

0 0.5 1 1.5 2 2.5 3

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

0 0.5 1 1.5 2 2.5 3 3.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

81



0

2

4

6

8

10

12

14

16

0 0.5 1 1.5 2 2.5 3 3.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

0 0.5 1 1.5 2 2.5 3 3.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

82



0

1

2

3

4

5

6

7

8

9

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

SPEC 11

0

1

2

3

4

5

6

7

8

9

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

83



0

1

2

3

4

5

6

7

8

9

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

84



0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

85



0

2

4

6

8

10

12

14

16

18

0 0.5 1 1.5 2 2.5 3 3.5 4

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

18

0 0.5 1 1.5 2 2.5 3 3.5 4

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

86



0

2

4

6

8

10

12

14

16

18

0 0.5 1 1.5 2 2.5 3 3.5 4

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

18

20

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

87



0

2

4

6

8

10

12

14

16

18

20

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

2

4

6

8

10

12

14

16

18

20

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

88



0

5

10

15

20

25

30

0 1 2 3 4 5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

5

10

15

20

25

30

0 1 2 3 4 5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

89



0

5

10

15

20

25

30

0 1 2 3 4 5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

5

10

15

20

25

0 1 2 3 4 5 6

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

90



0

5

10

15

20

25

0 1 2 3 4 5 6

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

5

10

15

20

25

0 1 2 3 4 5 6

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

91



0

5

10

15

20

25

30

0 1 2 3 4 5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

5

10

15

20

25

30

0 1 2 3 4 5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

92



0

5

10

15

20

25

30

0 1 2 3 4 5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

5

10

15

20

25

0 1 2 3 4 5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

93



0

5

10

15

20

25

0 1 2 3 4 5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

5

10

15

20

25

0 1 2 3 4 5

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

94



0

5

10

15

20

25

30

0 1 2 3 4 5 6

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

SPEC 5

SPEC 6

SPEC 7

SPEC 8

SPEC 9

SPEC 10

0

5

10

15

20

25

30

0 1 2 3 4 5 6

Load

[kN

]

Deformation [mm]


SPEC 1

SPEC 2

SPEC 3

SPEC 4

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Würth 10mm 16d @ 30 deg. - S-P-F - Summary -

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Date post:	13-Nov-2021
Category:	Documents
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PULL-OUT RESISTANCE OF SELF-TAPPING WOOD SCREWS …

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