TEMTIS seminar Horsens 2008
Eurocode 5: Compression
perpendicular to the Grain
H J Larsen
Denmark
A J M Leijten
TU-Eindhoven – The Netherlands
T A C M van der Put
TU-Delft – The Netherlands
TEMTIS seminar Horsens 2008
Acknowledsments
Based on paper for CIB-W18 2008 by
H J Larsen, Denmark
A J M Leijten, TU-Eindhoven – The Netherlands
T A C M van der Put, TU-Delft – The Netherlands
TEMTIS seminar Horsens 2008
Problem
Introduction of a ”scientific” test method and
definition for compression perpendicular to
grain has halved the characteristic
strength
TEMTIS seminar Horsens 2008
Problem
Introduction of a ”scientific” test method and
definition for compression perpendicular to
grain has halved the characteristic
strength
Many traditional structures and details e. g.
in timber frame houses will no longer be
acceptable
TEMTIS seminar Horsens 2008
TEMTIS seminar Horsens 2008
Standard Test Methods
ASTM – D143
Australian
(technological) test
51x51x152mm
51
152
European
(scientifical) test
EN 408
Compressive strength =
45
f c,90
Poussa et all.
Proc.:CIB-W18-2007:
paper 40-2-2
TEMTIS seminar Horsens 2008
Standard Test Methods
Compressive stress [MPa]
Compressive stress
 c,90
8
7
6
5
4
3
2
1
0
0
2
4
6
Strain [%]
8
10
12
TEMTIS seminar Horsens 2008
Definition Compressive strength
European test
EN 408
1%
Compressive strength
f c,90
1% off-set
TEMTIS seminar Horsens 2008
Comparison of test results
Ref: Poussa et al.
Helsinki CIB-W18
paper 40-2-2
TEMTIS seminar Horsens 2008
Proposal
Thelandersson & Mårtensson and others
Regard exceedance of scientific
compression strength as violation of a
serviceability state (and not an ultimate
limit state)
TEMTIS seminar Horsens 2008
Limit states
Ultimate limit states
Serviceability limit states
TEMTIS seminar Horsens 2008
Ultimate limit states
Failure of whole structure or part of it
Precise internationally agreed definitions
On the whole agreed safety level
TEMTIS seminar Horsens 2008
Topping-up day
TEMTIS seminar Horsens 2008
Next day - failure
TEMTIS seminar Horsens 2008
Failure (at least in lower story)
TEMTIS seminar Horsens 2008
Failure (at least in lower story)
TEMTIS seminar Horsens 2008
Deformations preceding failure
TEMTIS seminar Horsens 2008
Serviceability limit states
Unacceptable behaviour at normal use
TEMTIS seminar Horsens 2008
Serviceability limit states
Unacceptable behaviour at normal use, e. g.
visually unacceptable
TEMTIS seminar Horsens 2008
Serviceability limit states
Unacceptable behaviour at normal use, e. g.
visually unacceptable
TEMTIS seminar Horsens 2008
Serviceability limit states
Unacceptable behaviour at normal use, e. g.
visually or functionally unacceptable
deformations
TEMTIS seminar Horsens 2008
Serviceability limit states
In most cases: No precise requirements
Criteria fixed by designer in agreement with
client
National tradition and taste
TEMTIS seminar Horsens 2008
Serviceability limit states
Formally it is not required to perform a
serviceability verification as long as it is
possible to perform the ultimate state
verification
TEMTIS seminar Horsens 2008
Serviceability, compression perp.
It is difficult, to put it mildly, to understand why exceeding a
marginal deformation in a block compression test should
be taken as the governing criteria for structures where
much larger deformations are normally acceptable and
loaded in a completely different way.
TEMTIS seminar Horsens 2008
Serviceability, compression perp.
It is difficult, to put it mildly, to understand why exceeding a
marginal deformation in a block compression test should
be taken as the governing criteria for structures where
much larger deformations are normally acceptable and
loaded in a completely different way.
Especially when the use of the Serviceability limit state is
accepted only half heartedly and without a proper
definition and understanding
TEMTIS seminar Horsens 2008
Eurocode design equation
EN1995-1-1
Impirical model
Hilmer Riberholt
Incomplete, discontinous, strange jumps
TEMTIS seminar Horsens 2008
New design equation
EN1995-1-1:2005/A1
Blass and Görlacher based on
Borg Madsen (2000)
 c ,90

F
F


 kc f c,90
Aeff b leff
leff
F
 kc,90 f c,90
bl
l
lef = l + 60mm
1,5 solid timber
kc  
1,75 glued laminated timber
TEMTIS seminar Horsens 2008
Alternative Model
Based on Van der Put (1986)
Slip-line theory
TEMTIS seminar Horsens 2008
Alternative Model
f s  kc f c,90
kc 
l eff
l

l  3h
l
Slope 1:1 for 1% off-set
Slope 1:1,5 for 10% deformation
TEMTIS seminar Horsens 2008
Alternative Model
Based on Van der Put (1986)
Slip-line theory
(Schoenmakers)
TEMTIS seminar Horsens 2008
Model comparison
Load cases reported
A
B
C
D
E
Test results reported by many authors
Test A:
n = 418
Tests B to F: 1% n= 582 (52 samples)
10% n= 125 (23 samples)
-Solid wood
-Glued laminated wood
F
TEMTIS seminar Horsens 2008
Comparison 1 % off-set
TEMTIS seminar Horsens 2008
Model comparison
Model comparison at 10% deformation
25
Model prediction
20
15
10
5
0
0
5
10
15
Test data
Van der Put
EC5/A1
20
25
TEMTIS seminar Horsens 2008
Comparison
Model uncertainty comparison - 1% offset
14
12
frequency
10
8
6
4
2
0
-1
-0,8
-0,6
-0,4
-0,2
0
ln(data/prediction)
van der Put
EC5/A1
0,2
0,4
0,6
TEMTIS seminar Horsens 2008
Comparisons
ln(model/test)=ln(R)
ideally: ln(R)=0  R=1
n = 582
Van der Put
EC 5
Mean
- 0,04
- 0,36
Standard
deviation
0,17
0,20
TEMTIS seminar Horsens 2008
Model evaluation
ratio Data/model prediction
Cross-section effect van de Put model
1,60
1,40
1,20
1,00
0,80
0,60
0,40
0,20
0,00
0
10000
20000
30000
40000
50000
60000
Test specimen cross-section [mm2]
1% off-set
10% off-set
70000
80000
TEMTIS seminar Horsens 2008
Model evaluation
Ratio Data/ model prediction
Depth/width effect Van der Put model
1,60
1,40
1,20
1,00
0,80
0,60
0,40
0,20
0,00
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
Test specimen depth/width ratio
1% off-set
10% off-set
4,5
5,0
5,5
TEMTIS seminar Horsens 2008
Conclusion
Compression perpendicular to grain
The evaluation of both models show that Van
der Put model is far more accurate in
predicting accurately the bearing strength
perpendicular to the grain than the model
currently in Eurocode 5/A1.
TEMTIS seminar Horsens 2008
Proposal for EC5 adoption
Compression perpendicular to grain
f s  kc f c,90
for h < 4 b
Deformation limit 1%
kc 
l  2h

4
l
l
leff
Deformation limit 10%
kc 
l  3h

4
l
l
leff
TEMTIS seminar Horsens 2008
Proposal for EC5 adoption
Compression perpendicular to grain
f s  kc f c,90
for h < 4 b
Deformation limit 1%
kc 
l  2h

4
l
l
leff
Deformation limit 10%
kc 
l  3h

4
l
l
leff
TEMTIS seminar Horsens 2008
Restriction
Formally verified only for continously
supported beams
TEMTIS seminar Horsens 2008
Restriction
Formally verified only for continously
supported beams
Not too difficult to extend
to concentrated supports
TEMTIS seminar Horsens 2008
Future
Formally verified only for continously
supported beams
Not too difficult to extend
to concentrated supports
No tests for unsupported
loads
TEMTIS seminar Horsens 2008
Future
Tests needed
for unsupported loads
!