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Eurocode 5: Compression perpendicular to the GrainPowerPoint Presentation

Eurocode 5: Compression perpendicular to the Grain

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### 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

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

45

51

152

Standard Test MethodsASTM – D143

Australian

(technological) test

European

(scientifical) test

EN 408

Compressive strength =

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

Standard Test Methods

Compressive stress

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)

Ultimate limit states

Failure of whole structure or part of it

Precise internationally agreed definitions

On the whole agreed safety level

Failure (at least in lower story)

Failure (at least in lower story)

Deformations preceding failure

Serviceability limit states

Unacceptable behaviour at normal use

Serviceability limit states

Unacceptable behaviour at normal use, e. g.

visually or functionally unacceptable deformations

Serviceability limit states

In most cases: No precise requirements

Criteria fixed by designer in agreement with client

National tradition and taste

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

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

l + 60mm

New design equationEN1995-1-1:2005/A1

Blass and Görlacher based on

Borg Madsen (2000)

lef =

A B C D E F

Model comparisonLoad cases reported

- 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

Comparison 1 % off-set D E F

Model comparison D E F

Comparison D E F

Comparisons D E Fln(model/test)=ln(R) ideally: ln(R)=0 R=1

Model evaluation D E F

Model evaluation D E F

Conclusion D E F

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 D E F

Compression perpendicular to grain

for h < 4 b

Deformation limit 1%

Deformation limit 10%

Proposal for EC5 adoption D E F

Compression perpendicular to grain

for h < 4 b

Deformation limit 1%

Deformation limit 10%

Restriction D E F

Formally verified only for continously supported beams

Restriction D E F

Formally verified only for continously supported beams

Not too difficult to extend

to concentrated supports

Future D E F

Formally verified only for continously supported beams

Not too difficult to extend

to concentrated supports

No tests for unsupported

loads

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