At a
recent anchor installers installation seminars, the discussion got
around to anchors and metal fatigue. So out of interest, we decided
to examine specific diameters of the twelve anchors that had been
loaded to the ultimate failure load and pulled from the rock.
It is
quite apparent that certain parts of the Eco anchor undergo local
extrusion at specific points. The degree of reduction of the diameter,
is consistent with the amount of loading and the direction of loading.
I should add at this point that all these anchors we loaded in an
axial pull.
The diagrams
and tables below should give you an insight into the stresses that
result in reduction of specific diameters during loading.
Each
Eco anchor from the test bed dated 17 August 1995 has had specific
diameters measured. The areas from where the measurements were taken
are indicated below on the diagram of the Eco anchor.
The reduction
in the measurements at the point diameter D, we believe is caused
by the manufacturing process and although a reduction means a reduced
maximum load, significant work-hardening will make up for any loss.
But it may become more brittle in this area.
|
Anchor
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
9
|
10
|
11
|
12
|
New
|
|
Ave
|
|
Egress
(KN)
|
36
|
46.8
|
25.2
|
36
|
45
|
36
|
23.4
|
45
|
54
|
34.2
|
18
|
34.4
|
|
|
36.17
|
|
Max
Load (KN)
|
46.8
|
54
|
29
|
54
|
52.2
|
48.6
|
36.8
|
50.4
|
54
|
44
|
40
|
37.8
|
|
|
45.63
|
|
Diameter
A
|
7.62
|
7.67
|
7.75
|
7.62
|
7.67
|
7.64
|
7.75
|
7.72
|
7.69
|
7.77
|
7.71
|
7.77
|
7.92
|
|
7.72
|
|
Diameter
Reduction (mm)
|
0.3
|
0.25
|
0.17
|
0.3
|
0.25
|
0.28
|
0.17
|
0.2
|
0.23
|
0.15
|
0.21
|
0.15
|
0
|
|
0.2
|
|
Diameter
Reduction (%)
|
3.788
|
3.157
|
2.146
|
3.788
|
3.157
|
3.535
|
2.146
|
2.525
|
2.904
|
1.894
|
2.652
|
1.894
|
0
|
|
2.584
|
|
Diameter
B
|
7.92
|
7.9
|
7.95
|
7.92
|
7.92
|
7.92
|
7.95
|
7.95
|
7.84
|
7.92
|
7.92
|
7.92
|
7.92
|
|
7.94
|
|
Diameter
Reduction (mm)
|
0
|
0.02
|
-0
|
0
|
0
|
0
|
-0
|
-0
|
0.08
|
0
|
0
|
0
|
0
|
|
0
|
|
Diameter
Reduction (%)
|
0
|
0.253
|
-0.38
|
0
|
0
|
0
|
-0.38
|
-0.38
|
1.01
|
0
|
0
|
0
|
0
|
|
0.01
|
|
Diameter
C
|
7.9
|
7.91
|
7.92
|
7.9
|
7.9
|
7.92
|
7.92
|
7.92
|
7.9
|
7.9
|
7.91
|
7.89
|
7.92
|
|
7.908
|
|
Diameter
Reduction (mm)
|
0.02
|
0.01
|
0
|
0.02
|
0.02
|
0
|
0
|
0
|
0.02
|
0.02
|
0.01
|
0.03
|
0
|
|
0.0115
|
|
Diameter
Reduction (%)
|
0.25
|
0.13
|
0
|
0.25
|
0.25
|
0
|
0
|
0
|
0.25
|
0.25
|
0.13
|
0.38
|
0
|
|
0.15
|
|
Diameter
D
|
7.67
|
7.67
|
7.77
|
7.8
|
7.82
|
7.72
|
7.77
|
7.66
|
7.57
|
7.87
|
7.71
|
7.84
|
7.9
|
|
7.75
|
|
Diameter
Reduction (mm)
|
0.25
|
0.25
|
0.15
|
0.12
|
0.1
|
0.2
|
0.15
|
0.26
|
0.35
|
0.05
|
0.21
|
0.08
|
0.02
|
|
0.17
|
|
Diameter
Reduction (%)
|
3.16
|
3.16
|
1.89
|
1.52
|
1.26
|
2.53
|
1.89
|
3.28
|
4.42
|
0.63
|
2.65
|
1.01
|
0.25
|
|
2.13
|
|
Diameter
E
|
7.92
|
7.92
|
7.92
|
7.92
|
7.92
|
7.92
|
7.92
|
7.92
|
7.92
|
7.92
|
7.95
|
7.92
|
7.92
|
|
7.922
|
|
Diameter
Reduction (mm)
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
-0.03
|
0
|
0
|
|
-0
|
|
Diameter
Reduction (%)
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
-0.38
|
0
|
0
|
|
-0.03
|
|
Diameter
F
|
7.92
|
7.92
|
7.92
|
7.92
|
7.92
|
7.92
|
7.92
|
7.92
|
7.92
|
7.92
|
7.92
|
7.92
|
7.92
|
|
7.92
|
|
Diameter
Reduction (mm)
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
|
0
|
|
Diameter
Reduction (%)
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
|
0
|
Andy
McCarron...
andy.mccarron@yss.uk.com
|
