Experimental testing of anchoring devices for bottom rails in partially anchored timber frame shear walls

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Experimental Testing of Anchoring Devices for Bottom Rails in Partially Anchored

Timber Frame Shear Walls

Giuseppe Caprolu

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Timber Frame Shear Walls

Giuseppe Caprolu

Luleå University of Technology

Department of Civil, Environmental and Natural resources engineering Division of Structural and Construction Engineering

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Printed by Universitetstryckeriet, Luleå, 2011 ISSN: 1402-1536

ISBN 978-91-7439-302-6 Luleå 

www.ltu.se

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1 Background ... 6

2 Test setup and material ... 7

2.1 Test specimens and setup ... 7

2.2 Material properties... 8

2.3 Moisture content and density ... 9

2.4 Test programme ... 9

3 Test results ...11

3.1 Failure modes ...12

3.2 Load – time curves ...16

4 Summary of test results ...25

4.1 Influence of anomalies ...43

5 Conclusions ...46

Appendix A – Load vs. time curves ...47

A.1 Series 1 – Anchor bolt at centre, 60 mm from the sheathing ...47

A.1.1 Set 1 – Size of washer 40x40 mm ...47

A.1.1.1 Pith Down ...47

A.1.1.2 Pith Up ...52

A.1.2.1 Pith Down ...57

A.1.2.2 Pith Up ...62

A.1.3.1 Pith Down ...67

A.1.3.2 Pith Up ...72

A.1.4 Set 4 – Size of washer, 100x70 mm ...77

A.1.4.1 Pith Down ...77

A.1.4.2 Pith Up ...82

A.2 Series 2 – Anchor bolt at 45 mm from sheathing ...87

A.2.1.1 Pith Down ...87

A.2.1.2 Pith Up ...95

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A.2.2.1 Pith Down ...102

A.2.2.2 Pith Up ...110

A.2.3.1 Pith Down ...118

A.2.3.2 Pith Up ...126

A.3 Series 3 – Anchor bolt at 30 mm from the sheathing ...134

A.3.1.1 Pith down ...134

A.3.1.2 Pith Up ...138

A.3.2.1 Pith Down ...143

A.3.2.2 Pith Up ...148

Appendix B – Chronological summary of the conduction of the tests ...153

Appendix C – Planning of the experimental series (in Swedish) ...157

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4 2010.

Bo Källsner and Ulf Arne Girhammar have initiated this study as part of their research work on a plastic design method for partially anchored light-frame shear walls. Per-Anders Daerga has planned the test series and initiated the testing program. Giuseppe Caprolu has performed the experiment and written the report.

I would like to thank Bo Källsner and Ulf Arne Girhammar for reviewed the report and Helena Johnsson for reading and commenting the manuscript.

Finally, we would like to thank The European Union’s Structural Funds – The Regional Fund for its financial support.

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5

Summary

Källsner and Girhammar have presented a new plastic design method of wood-framed shear walls at ultimate limit state. This method allows the designer to calculate the load-carrying capacity of shear walls partially anchored, where the leading stud is not anchored against the uplift.

The anchorage system of shear walls is provided from anchor bolts and hold downs. Anchor bolts provide horizontal shear continuity between the bottom rail and the foundation. Hold downs are directly connected from the vertical end stud to the foundation. When hold downs are not provided, the bottom row of nails transmits the vertical forces in the sheathing to the bottom rail (instead of the vertical stud) where the anchor bolts will further transmit the forces into the foundation.

Because of the eccentric load transfer, transverse bending is created in the bottom rail and splitting often occurs.

Bottom rail experimentally studied with respect to two primary failure modes, splitting along the bottom of the bottom rail due to cross-wise bending and splitting along the edge side of the bottom rail due forces perpendicular to the grain for the sheathing-to-framing connections.

The parameters varied are the location of the anchor bolt, the size of the washer and the orientation of the pith.

The bottom rail was subjected to loading perpendicular to grain through one-sided sheathing.

In this report the different test series are presented. Three series were conducted depending on the location on the anchor bolt. In each series different sets were studied depending on the size of the washer and in each set the pith was placed upwards or downwards.

The tests showed three different failure modes. In addition to the failure modes that the testing program was aimed at, splitting along the bottom or side of the bottom rail, the final failure was due to plastic bending and withdrawal of the sheathing-to-framing nails.

The results show that the size of the washer and the position of the bolt have a significant influence on the maximum load and the failure modes. It was found that decreasing the distance of the washer to the loaded edge of the bottom rail increases the maximum load.

Key words: timber shear walls, partially anchored, sheathing-to-framing joint, bottom rail, cross-wise bending, splitting of bottom surface, splitting of side surface.

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top and bottom rails and sheathing connected with fasteners (see figure 1).

Horizontal forces in timber frame structures (e.g. wind or earthquake forces) are transferred onto the shear walls at the level of the top rail via the floor structure. The horizontal forces creates a tipping moment on the shear wall and therefore create uplift forces on one side and compression on the other side of the wall. The strength of the wall is dependent upon three components: timber frame members, sheathing and fasteners.

Figure 1: Details of Shear Wall

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2 Test setup and material

2.1 Test specimens and setup

The specimens were built with a rail of length 900 mm with a cross section of 45x120 mm, joined with a hardboard sheet of 900x500 mm and width 8 mm by nails.

The rails were chosen according to their density. This was provided using for each set the rails cut from the same board, however sometimes by mistake this was not respected.

The specimens were usually tested the same day or the day later of their built. Sometime due problems of the test machine this was impossible to respect and the specimens were tested some days later (see Appendix B for a chronological summary of the conduction of the tests).

Figure 2 shows the test setup.

Figure 2: Test configuration

The bottom rail was fixed to a steel plate with two anchor bolts. To tighten the bolts a torque moment of 50 N∙m was used. A rigid square or rectangular washer (figure 3) was inserted between the bottom rail and the head bolt throughout all tests. Its size and shape varied from the set tested. A hydraulic piston was then attached to the upper panel by connection using a C steel beam and four bolts Ø 16 inducing a tensile force with a rate of 10 mm/min (by mistake it was 10 mm/min instead of 2 mm/min; the testing rate should ideally be such that the failure occurs after 5 minutes).

The displacements were measured using a Linear Voltage Displacement Transducer (LVDT) see figure 4. The displacement was measured as the upward movement of the upper surface of the rail in the line of the anchor bolts of the inner edge of the washer relative to the foundation. However, in some tests, it was measured on the head of the bolt (tests 213N and 213 U), on the upper surface of the washer (unfortunately from the pictures is not possible to recognize these tests) and in the distance between the washer edge and the loaded edge of the bottom rail (test 212U).

The rails are free to rotate during loading, i.e. the inclined bars are removed from the lifting device. This provides a well-defined boundary condition (figure 5).

150 600 150

500

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Figure 5: Lifting device

2.2 Material properties

The following material was used for the specimens:

· Bottom Rail: Spruce (Picea Abies), C24, 45x120 mm;

· Sheathing: Hardboard, C40, 8 mm (wet process fibre board, HB.HLA2, Masonite AB);

· Sheathing-to-timber joints: Annular ringed shank nails, 50x2.1 mm (Duofast, Nordisk Kartro AB). The joints were nailed manually and the holes were pre-drilled, 1.7 mm. Nail spacing was 25 mm or 50 mm. Edge distance was 22.5 mm along the bottom rails;

· Anchor bolt: Ø 12 (M12). The holes in the bottom rails were pre-drilled, 14 mm.

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At first it was thought of planning the top and bottom surface of the rail, in order to eliminate any influence of cupping and possible pre-cracking, when tightening the anchor bolts, on the ultimate load. However it was not necessary because the surfaces of the bottom rail were acceptable with regard to with regard to plainness.

The material was kept in the laboratory. The rails were not used in any previous tests and they were enclosed in a plastic cover. The temperature in the lab was about 20°C. The specimens were assembled manually.

2.3 Moisture content and density

For each specimen the moisture content and the density of the bottom rail was measured after the test according to ISO 3130:1975 and ISO 3131:1975 respectively.

The moisture content (ω) was calculated according to the following equation:

=!_"− !_$

!_$ ∙ 100 [%]

where:

m1 is the mass of the test specimen before drying [g];

m0 is the mass of the test specimen after drying [g].

The density of the bottom rail (ρ) was calculated according to the following equation:

'_$,( =!_$ )₍ * +

!!^-. where:

m0 is the mass of the test specimen after drying [g];

Vω is the volume of the test specimen before drying [mm³].

After conducting the tests each specimen was dried in an oven for 24 hours at a temperature of 103° C. The density and the moisture content were then measured for each specimen .

2.4 Test programme

A total number of 142 specimens were tested. The specimens were divided into three different series, each series were divided into several sets. The series were subdivided regarding the orientation of the pith of the bottom rail, the washer size and the position of the anchor bolt in the bottom rail.

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10 Series

Anchor bolt position

Set washers [mm]

of tests

to rail edge [mm]

1

Centre 60 mm from

sheathing

1 40x40x15 16¹⁾ 40

2 60x60x15 16¹⁾ 30

3 80x70x15 16¹⁾ 20

4 100x70x15 16¹⁾ 10

2

3b/8 45 mm from

sheathing

1 40x40x15 14²⁾ 25

2 60x60x15 16¹⁾ 15

3 80x70x15 16¹⁾ 5

3

b/4

30 mm from sheathing

1 40x40x15 16¹⁾ 10

2 60x60x15 16¹⁾ 0

1) 8 specimens with the pith downwards and 8 upwards.

2) 7 specimens with the pith downwards and 7 upwards.

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3 Test results

The load vs. time graphs are displayed for each test in Appendix A. Load vs. displacement graphs could not be displayed as the displacement measurement system was inaccurate.

For each test the maximum load and the max displacement at the moment of the crack was recorded by the hydraulic piston. The distances between the loaded edge of the bottom rail and the fracture line of the bottom rail in the anchor bolt position (figure 6) and the distances from fracture line to loaded edge on both sides, not always possible due to mistake recording data, (figure 7) were documented. Using these distances is possible to understand when the crack line is present on the whole bottom surface of the bottom rail or when it finish before to arrive at the end of the bottom rail. The side of the first crack as well as the moisture content and the density were also documented.

Figure 6: Example of distance between the edge loaded of the bottom-rail and the fracture line of the bottom rail.

Figure 7: Example of distance between the edge loaded of the bottom rail and the fracture line on side 1 (Rail 215 N) and side 2 (Rail 212 N)

In order to identify the specimen the Swedish convention is used where N means ner (downwards in English) and U means Upp (upwards in English) according to pith orientation.

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Failure Mode 1: Failure due to splitting of the underneath side of the bottom rail (figures 8 and 9 ).

Figure 8: The steel plate where the rail was fixed was shorter than the rail, this is way in the pictures above the rail edges don’t have the same length of the steel plate.

Figure 9: Failure mode 1, splitting of the underneath side of the bottom rail.

Failure Mode 2a: Failure of the bottom rail with fracture along the line of nails and at the edge side of the bottom rail (figure 10).

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Figure 10: Failure mode 2a, fracture of the bottom rail along the line of nails.

Failure Mode 2b: Splitting of the bottom rail along the line of nails between the anchor bolts (figure 11).

Figure 11: Failure mode 2b, splitting of the bottom rail along the line of nails between the anchor bolts.

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Figure 12: Failure mode 3, pull out of nails.

Figure 13: *Bolt position, ** Size of washer [mm]. Failure mode 1: splitting of the bottom rail, failure mode 2a: splitting of the bottom rail along the line of the nails, failure mode 2b: splitting of the bottom rail along the line of the nails between the anchor bolts, failure mode 3: pull-out of the nails.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Serie 1 (b/2)*

Serie 2 (3b/8)*

(14 test)

Serie 3 (b/4)*

Serie 1 (b/2)*

Serie 2 (3b/8)*

Serie 3 (b/4)*

Serie 1 (b/2)*

Serie 2 (3b/8)*

Serie 1 (b/2)*

40** 60** 80** 100**

Percentage Failure Mode vs.

Size of Washer and Bolt Position

Mode 3 Mode 2b Mode 2a Mode 1

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Figure 14: *Bolt position, ** Size of washer [mm]. Failure mode 1: splitting of the bottom rail, failure mode 2a: splitting of the bottom rail along the line of the nails, failure mode 2b: splitting of the bottom rail along the line of the nails between the anchor bolts, failure mode 3: pull-out of the nails.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Set 1 (40)**

Set 2 (60)**

Set 3 (80)**

Set 4 (100)**

Set 1 (40)** (14

tests)

Set 2 (60)**

Set 3 (80)**

Set 1 (40)**

Set 2 (60)**

Serie 1 (b/2)* Serie 2 (3b/8)* Serie 3 (b/4)*

Percentage Failure Mode vs.

Size of Washer and Bolt Position

Mode 3 Mode 2b Mode 2a Mode 1

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Figure 15: Load vs. time curves for bottom rail with pith down. 8 failure mode of type 1.

Figure 16: Load vs. time curves for bottom rail with pith up. 8 failure mode of type 1.

0 2000 4000 6000 8000 10000 12000

0 20 40 60 80 100 120 140

Load [N]

Time [s]

Rail 111 N Rail 112 N Rail 113 N Rail 114 N Rail 115 N Rail 116 N Rail 117 N Rail 118 N

0 2000 4000 6000 8000 10000 12000 14000

0 20 40 60 80 100 120 140

Load [N]

Time [s]

Pith up (U)

Rail 111 U Rail 112 U Rail 113 U Rail 114 U Rail 115 U Rail 116 U Rail 117 U Rail 118 U

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Figure 18: Load vs. time curves for bottom rail with pith up. 8 failure of type 1.

0 2000 4000 6000 8000 10000 12000 14000 16000 18000

0 20 40 60 80 100 120 140 160

Load [N]

Time [s]

Pith down (N)

0 2000 4000 6000 8000 10000 12000 14000 16000 18000

0 20 40 60 80 100 120 140

Load [N]

Time [s]

Pith up (U)

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Figure 19: Load vs. time curves for bottom rail with pith down. 4 failure of type 1 (131N, 132N,134N and 136N), 1 failure of type 2a (135N) and 3 failure of type 3 (133N, 137N and 138N).

Figure 20: Load vs. time curves for bottom rail with pith up rail. 7 failure mode of type 1 and 1 failure mode of type 3 (134U).

0 4000 8000 12000 16000

0 20 40 60 80 100 120 140

Load [N]

Time [s]

Rail 134 N Rail 135 N Rail 136 N Rail 137 N Rail 138 N

0 4000 8000 12000 16000 20000 24000

0 20 40 60 80 100 120 140

Load [N]

Time [s]

Pith up (U)

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Figure 21: Load vs. time curves for bottom rail with pith down. 2 failure mode of type 1 (142N and 145N), 1 failure mode of type 2a (141N) and 5 failure mode of type 3 (143N, 144N, 146N, 147N and 148N ).

Figure 22: Load vs. time curves for bottom rail with pith up. 6 failure mode of type 1, 1 failure mode of type 2a (142U) and 1 failure mode of type 3 (147U).

0 4000 8000 12000 16000 20000 24000 28000

0 20 40 60 80 100 120 140 160 180 200

Load [N]

Time [s]

Pith down (N)

0 4000 8000 12000 16000 20000 24000

0 20 40 60 80 100 120 140

Load [N]

Time [s]

Pith up (U)

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Figure 24: Load vs. time curves for bottom rail with pith up. 7 failure mode of type 1.

0 4000 8000 12000 16000

0 50 100 150 200 250 300 350

Load [N]

Time [s]

0 4000 8000 12000 16000

0 50 100 150 200 250 300 350

Load [N]

Time [s]

Pith up (U)

Rail 212 U Rail 213 U Rail 214 U Rail 215 U Rail 216 U Rail 217 U Rail 218 U

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Figure 25: Load vs. time curves for bottom rail with pith down. 7 failure mode of type 1 and 1 failure mode of type 2a (222N).

Figure 26: Load vs. time curves for bottom rail with pith up. 5 failure mode of type 1 and 3 failure mode of type 2a (223U, 224U and 228U).

0 4000 8000 12000 16000 20000 24000

0 20 40 60 80 100 120 140 160 180

Load [N]

Time [s]

Pith down (N)

0 4000 8000 12000 16000 20000 24000

0 20 40 60 80 100 120 140 160 180

Load [N]

Time [s]

Pith up (U)

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Figure 27: Load vs. time curves for bottom rail with pith down. 1 failure mode of type 1 (235N), 4 failure mode of type 2a (231N, 232N, 233N and 234N) and 3 failure mode of type 3 (236N, 237 N and 238N).

Figure 28: Load vs. time curves for bottom rail with pith up. 3 failure mode of type 1 (234U, 235U and 238U), 4 failure mode of type 2a (232U, 233U, 236U and 237U) and 1 failure mode of type 2b (231U).

0 5000 10000 15000 20000

0 20 40 60 80 100 120 140 160

Load [N]

Time [s]

0 5000 10000 15000 20000 25000 30000

0 20 40 60 80 100 120 140 160

Load [N]

Time [s]

Pith up (U)

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Figure 29: Load vs. time curves for bottom rail with pith down. 3 failure mode of type 1 (312N, 314N and 317N), 3 failure mode of type 2a (313N, 315N and 318N) and 2 failure mode of type 3 (311N and 316N).

Figure 30: Load vs. time for bottom rail with pith up. 1 failure mode of type 1 (315U), 6 failure mode of type 2a (311U, 312U, 313U, 314U, 316U and 318U) and 1 failure mode of type 3 (317U).

0 4000 8000 12000 16000 20000 24000

0 20 40 60 80 100 120 140 160

Load [N]

Time [s]

Pith down (N)

0 4000 8000 12000 16000 20000 24000

0 20 40 60 80 100 120 140

Load [N]

Time [s]

Pith up (U)

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Figure 31: Load vs. time for bottom rail with pith down. 1 failure mode of type 2a (321N), 3 failure mode of type 2b (322N, 325 and 327N) and 4 failure mode of type 3 (323N, 324N, 326N and 328N).

Figure 32: Load vs. time for bottom rail with pith up. 5 failure mode of type 2a (322U, 323U, 324U, 325U and 327U), 1 failure mode of type 2b (321U) and 2 failure mode of type 3 (326U and 328U).

0 4000 8000 12000 16000 20000

0 20 40 60 80 100 120 140 160

Load [N]

Time [s]

0 5000 10000 15000 20000 25000

0 20 40 60 80 100 120 140 160

Load [N]

Time [s]

Pith up (U)

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4 Summary of test results

The tables below summarize the average results from the tests for each set. Failure loads and maximum displacements are shown in relation to the pith orientation as well as the density and the moisture content of the bottom rail:

Series 1 – Anchor bolt at centre, 60 mm from the sheathing

Set 1 – Washer size 40x40 mm, distance from sheathing to edge of washer 40 mm Pith Up – 8 tests

Table 2: summary of test results for series 1 – set 1 – pith up

Failure load [kN]

Max and min.

failure load [kN]

Movement of rail surface in line of the

anchor bolt of the edge of washer

[mm]

Density [kg/m³]

Moisture [%]

Average 9.49 5.14 ÷ 12.5 1.09 397.0 11.9

St. Dev. 25.88 - 1.13 28.29 0.77

Coeff. of Var.

[%] 27.28 - 103.38 7.13 6.47

Char. Value 0.05 3.85 - -1.37 335.3 10.2

Distance from edge of bottom rail to crack at anchor bolt

1 [mm]

2 [mm]

Distance from edge of bottom rail to crack at

the end on side 1 [mm]

Distance from edge of bottom rail to crack at the

end on side 2 [mm]

Average 59.3 57.4 -* -*

St. Dev. 2.19 4.72 - -

Coeff. of Var.

[%] 3.69 8.22 - -

Char. Value 0.05 54.5 47.1 - -

*data available only for one test.

8 failure mode of type 1.

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Max and min.

surface in line of the anchor bolt of the

edge of washer [mm]

Average 10.24 8.24 ÷ 12.9 1.44 392.3 12.2

St. Dev. 18.39 - 0.55 37.48 0.64

Coeff. of Var.

[%] 27.28 - 38.12 9.55 5.25

Char. Value 0.05 6.24 - 0.24 310.6 10.9

1 [mm]

2 [mm]

Average 57.5 57.3 -* -*

St. Dev. 4.34 2.96 - -

Coeff. of Var.

[%] 7.55 5.18 - -

Char. Value 0.05 48.0 50.8 - -

*data available only for one test.

8 failure of type 1.

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Max and min.

[mm]

Average 10.55 7.22 ÷ 14.29 0.29 389.9 10.9

St. Dev. 20.41 - 0.20 26.89 0.38

Coeff. of Var.

[%] 19.36 - 66.61 6.90 3.44

Char. Value 0.05 6.10 - -0.13 331.4 10.1

1 [mm]

2 [mm]

Average 57.9 48.0 -* -**

St. Dev. 2.59 11.36 - -

Coeff. of Var.

[%] 4.47 23.68 - -

Char. Value 0.05 52.2 23.2 - -

*no data available, **data available only for one test.

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Max and min.

Average 13.50 11.54 ÷ 17.01 0.67 382.9 10.9

St. Dev. 20.59 - 0.31 24.01 0.27

Coeff. of Var.

[%] 15.25 - 46.06 6.27 2.52

Char. Value 0.05 9.01 - 0.00 330.6 10.3

1 [mm]

2 [mm]

Average 49.8 54.1 -* -*

St. Dev. 11.95 5.25 - -

Coeff. of Var.

[%] 24.02 9.70 - -

Char. Value 0.05 23.7 42.7 - -

* no data available.

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Max and min.

[mm]

Average 17.05 12.07 ÷ 21.08 0.65 409.0 10.7

St. Dev. 29.61 - 0.23 43.06 0.24

Coeff. of Var.

[%] 17.36 - 35.66 10.53 2.25

Char. Value 0.05 10.60 - 0.14 315.1 10.2

1 [mm]

2 [mm]

Average 57.4* 58.3* -** -**

St. Dev. 4.12 3.45 - -

Coeff. of Var.

[%] 7.17 5.92 - -

Char. Value 0.05 48.21 50.6 - -

*data about 7 tests, **data available only for one test.

7 failure mode of type 1 and 1 failure mode of type 3.

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Max and min.

Average 18.17 16.73 ÷ 20.23 0.68 425.9 10.9

St. Dev. 14.66 - 0.21 70.51 0.41

Coeff. of Var.

[%] 8.07 - 30.24 16.56 3.76

Char. Value 0.05 14.97 - 0.23 272.2 10.0

1 [mm]

2 [mm]

Average 45.5* 54.0* -** -**

St. Dev. 30.52 4.24 - -

Coeff. of Var.

[%] 67.08 7.86 - -

Char. Value 0.05 -36.3 42.63 - -

*data about 4 tests, **no data available.

4 failure mode of type 1, 1 failure mode of type 2a and 3 failure mode of type 3.

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Max and min.

[mm]

Average 20.01 18.06 ÷ 22.40 0.88 422.3 11.1

St. Dev. 16.22 - 0.21 55.26 0.56

Coeff. of Var.

[%] 8.11 - 23.98 13.09 5.03

Char. Value 0.05 16.47 - 0.42 301.8 9.9

1 [mm]

2 [mm]

Average 48.7* 28.67* -** -**

St. Dev. 24.22 31.49 - -

Coeff. of Var.

[%] 49.77 109.86 - -

Char. Value 0.05 -7.8 -44.7 - -

*data about 6 tests, **data available only for one test.

6 failure mode of type 1, 1 failure mode of type 2a and 1 failure mode type 3.

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Max and min.

Average 21.80 20.0 ÷ 24.95 0.91 405.6 10.9

St. Dev. 16.53 - 0.14 24.31 0.43

Coeff. of Var.

[%] 7.58 - 15.56 5.99 3.93

Char. Value 0.05 18.20 - 0.60 352.6 10.0

1 [mm]

2 [mm]

Average 56.5* 53.0* -** -**

St. Dev. - - - -

Coeff. of Var.

[%] - - - -

Char. Value 0.05 - - - -

*data about two tests, **no data available.

2 failure mode of type 1, 1 failure mode of type 2a and 5 failure mode of type 3.

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33 Series 2 – Anchor bolt at 45 mm from the sheathing

Max and min.

[mm]

Average 12.21 7.93 ÷ 14.81 1.24 405.4 9.6

St. Dev. 24.20 - 0.71 34.07 2.63

Coeff. of Var.

[%] 19.82 - 57.55 8.40 27.37

Char. Value 0.05 6.79 - -0.42 329.1 3.7

1 [mm]

2 [mm]

Average 42.0 46.0 49.3* 46.0**

St. Dev. 6.38 1.41 6.77 9.08

Coeff. of Var.

[%] 15.18 3.07 13.73 19.75

Char. Value 0.05 27.72 42.83 33.6 23.7

*data about 6 tests, **data about 5 tests.

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Max and min.

Average 14.01 9.00 ÷ 16.70 1.60 393.6 9.0

St. Dev. 28.35 - 1.42 40.20 3.44

Coeff. of Var.

[%] 20.23 - 88.37 10.21 38.18

Char. Value 0.05 7.66 - -1.70 303.5 1.3

1 [mm]

2 [mm]

Average 47.4* 45.3* 33.5** 51.2**

St. Dev. 2.44 2.14 19.65 5.34

Coeff. of Var.

[%] 5.14 4.72 58.67 10.45

Char. Value 0.05 42.0 40.5 -12.3 38.7

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Max and min.

[mm]

Average 16.91 13.83 ÷ 21.14 0.78 360.0 12.4

St. Dev. 25.62 - 0.25 31.34 0.68

Coeff. of Var.

[%] 15.15 - 31.68 8.71 5.46

Char. Value 0.05 11.32 - 0.24 291.7 10.9

1 [mm]

2 [mm]

Average 30.9* 26.43* 44.0** 32.0**

St. Dev. 21.88 19.17 11.49 12.00

Coeff. of Var.

[%] 70.91 72.55 26.11 37.50

Char. Value 0.05 -18.2 -16.5 15.7 2.5

5 failure mode of type 1 and 3 failure mode of type 2a.

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Max and min.

Average 17.86 7.70 ÷ 22.45 1.26 380.7 12.6

St. Dev. 44.84 - 0.29 35.79 0.73

Coeff. of Var.

[%] 25.10 - 23.40 9.40 5.80

Char. Value 0.05 8.09 - 0.61 302.7 11.0

1 [mm]

2 [mm]

Average 33.4 32.9 40.0* 48.0**

St. Dev. 19.75 21.42 23.18 9.30

Coeff. of Var.

[%] 59.17 65.17 57.95 19.36

Char. Value 0.05 -9.7 -13.8 -11.9 26.3

7 failure mode of type 1 and 1 failure mode of type 2a.