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.

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 PutTU-Delft – The Netherlands


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


Problem

Introduction of a ”scientific” test method and definition for compression perpendicular to

grain has halved the characteristic strength


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



Standard Test Methods

51x51x152mm

152

51

ASTM – D143Australian(technological) test

45

European (scientifical) testEN 408

Poussa et all. Proc.:CIB-W18-2007: paper 40-2-2

Compressive strength = c,90f


0

1

2

3

4

5

6

7

8

0 2 4 6 8 10 12

Strain [%]

Co

mp

ressiv

e s

tress [

MP

a]

Standard Test MethodsCompressive stress c,90


Definition Compressive strength

European test

EN 408

Compressive strength c,90f1% off-set

1 %


Comparison of test results

Ref: Poussa et al. Helsinki CIB-W18 paper 40-2-2


ProposalThelandersson & Mårtensson and others

Regard exceedance of scientific compression strength as violation of a serviceability state (and not an ultimate limit state)


Limit states

Ultimate limit states

Serviceability limit states


Ultimate limit states

Failure of whole structure or part of it

Precise internationally agreed definitions

On the whole agreed safety level


Topping-up day


Next day - failure


Failure (at least in lower story)


Failure (at least in lower story)


Deformations preceding failure



Unacceptable behaviour at normal use



Unacceptable behaviour at normal use, e. g.

visually unacceptable




visually unacceptable




visually or functionally unacceptable deformations



In most cases: No precise requirements

Criteria fixed by designer in agreement with client

National tradition and taste



Formally it is not required to perform a serviceability verification as long as it is possible to perform the ultimate state verification


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.


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


Eurocode design equation

EN1995-1-1

Impirical model

Hilmer Riberholt

Incomplete, discontinous, strange jumps


New design equation

EN1995-1-1:2005/A1

Blass and Görlacher based on

Borg Madsen (2000)

l + 60mm

,90 c c,90eff eff

effc,90 c,90

c

F Fk f

A b l

lFk f

b l l

timberlaminated glued751

timbersolid51

,

,kc

lef =


Alternative Model

Based on Van der Put (1986)

Slip-line theory


Alternative Model

c,90fkf cs

l

hl

l

lk effc

3

Slope 1:1 for 1% off-set

Slope 1:1,5 for 10% deformation


Alternative Model

Based on Van der Put (1986)

Slip-line theory

(Schoenmakers)


Model comparison

A B C D E F

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

Load cases reported


Comparison 1 % off-set


Model comparison

Model comparison at 10% deformation

0

5

10

15

20

25

0 5 10 15 20 25

Test data

Mo

del

pre

dic

tio

n

Van der Put EC5/A1


Comparison

Model uncertainty comparison - 1% offset

0

2

4

6

8

10

12

14

-1 -0,8 -0,6 -0,4 -0,2 0 0,2 0,4 0,6

ln(data/prediction)

freq

uen

cy

van der Put EC5/A1


Comparisonsln(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


Model evaluation

Cross-section effect van de Put model

0,00

0,20

0,40

0,60

0,80

1,00

1,20

1,40

1,60

0 10000 20000 30000 40000 50000 60000 70000 80000

Test specimen cross-section [mm2]

ratio

Dat

a/m

od

el p

red

ictio

n

1% off-set 10% off-set


Model evaluation

Depth/width effect Van der Put model

0,00

0,20

0,40

0,60

0,80

1,00

1,20

1,40

1,60

0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5

Test specimen depth/width ratio

Ra

tio

Da

ta/ m

od

el p

red

icti

on

1% off-set 10% off-set


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.


Proposal for EC5 adoption

c,90s cf k f


43

l

hl

l

lk effc

Deformation limit 1%


42

l

hl

l

lk effc

for h < 4 b


Proposal for EC5 adoption

c,90s cf k f


43

l

hl

l

lk effc



42

l

hl

l

lk effc

for h < 4 b


Restriction

Formally verified only for continously supported beams


Restriction


Not too difficult to extend to concentrated supports


Future


Not too difficult to extend to concentrated supportsNo tests for unsupported loads


Future

Tests needed

for unsupported loads

!

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.

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