COST 508


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Wood mechanics: Workshop on service life assessment of wooden structures with special emphasis on the effect of load duration in various environments
Industrial research and development



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ISSN 1018-5593
European Cooperation
on Scientific and
European Commission Technical Research m
COST 508 — Wood mechanics
Workshop on service life assessment
of wooden structures
with special emphasis on the effect of load duration
in various environments
18 and 19 May 1994
Technical Research Centre of Finland
Building technology — wood technology
Espoo, Finland
EUR 16895 EN ***
European Commission • •
•Directorate-General XII
*•* Science, Research and Development
COST 508 — Wood mechanics
Workshop on service life assessment
of wooden structures
with special emphasis on the effect of load duration
in various environments
18 and 19 May 1994
Technical Research Centre of Finland
Building technology — wood technology
Espoo, Finland
Edited by:
Shankare S. Gowda, Ph. D.
for the management committee
1996 EUR 16895 EN Published by the
Directorate-General XII
Science, Research and Development
B-1049 Brussels
Neither the European Commission nor any person acting
on behalf of the Commission is responsible for the use which might be made of
the following information
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1996
ISBN 92-827-7187-3
©ECSC-EC-EAEC, Brussels »Luxembourg, 1996
Reproduction is authorized, except for commercial purposes,
provided the source is acknowledged
COST 508 Wood Mechanics is a joint action of 17 European member countries. One of its
activities has been to organize workshops in wood mechanics related topics selected to
respond to the actual need of expanding co-operation between researchers. The previous
topics and venues of workshops have been as follows:
1991 - Fundamental aspects on creep in wood, Lund University, Sweden.
1992 - Fracture mechanics in wooden materials, LRBB, Bordeaux, France.
1993 - Plasticity and damage in wood, University of Limerick, Ireland.
Workshop 1994 was held at the Technical Research Centre of Finland (VTT) in Espoo,
Finland, on service life assessment of wooden structures with special emphasis of the effect
of load duration in various environments. About 60 participants from many countries took
part in the workshop. The program included 4 invited papers and 21 voluntary presentations
which are all printed in this book. The programme also included a technical visit to Kerto-
LVL Factory of Finnforest company in Lohja and a visit to VTT's underground research
My warm thanks are extended to all the speakers for the prompt delivery of their papers and
to Dr.Gowda for editing the proceedings. The financial support of CEC and Finnforest Co.
is gratefully acknowledged.
October 1994 Alpo Ranta-Maunus
- Ill -COST 508
Fourth Workshop
with special emphasis on the effect of load duration in various environments
Table of contents
Disclaimer ii
Session1-Theories for creep and strengthι
ReviewoftheTheories on long term strength and time to failure3
Morlier, G. Valentin and T. Toratti
Chemical kinetic modelling of creep of wood 29
P. Bonfield, J. Dinwoodie and J. Mundy
Deformation kinetics based modelforthecreep of wood with accountofthe
mechano­sorptive effect 45
Applicationofthetheoryofdeformation kinetics on toothed­plate joints 57
J. W.vandeKuilen
Possiblecontributionoffibreslippage to the longitudinal creep of wood 69
D. HuntandJ.Gril
Relationship between water binding energy in wood and its mechanical strength
determined by acoustic emission method 83
S. Poliszko, W. Molinski and J. Raczkowski
Cracks accumulationinwoodundercyclicchanges of its moisture contentas
investigated by acousticemissionmethod93
W. Molinski, J. RaczkowskiandS.Poliszko
­ iv ­Session 2 - Fatigue and fracture 103
Fatigue of laminated woodbeams105
L. P. Hansen and A. Rathkjen
Fatigue behaviour of curved beams under constant amplitude loading 115
S. S. Gowda
Life duration of wood joints under high stress level ­ experimentation and
modelling 127
M.Chaplain,E. Fournely and A. Vergne
Rateeffectintangential tension fracture softening performance137
P.Olejniczakand P. J. Gustafsson
Delayedfracture of spruce notched beams 149
C. Jourdain, P. RacoisandG.Valentín
Fracture mechanics andacousticemissionin wood­based panel products 157
V. Morris, J. Adams andD.Hunt
Session 3 - Experimental research on load duration effect 169
Overview of duration­of­load research on lumber and wood composite panels in
North America 171
Long­termstrengthofcurvedglulam beams at cyclically varyingclimate207
Short­termandlong­termexperiments of laminated veneer lumber227
Damagequantificationofwood based thin­flanged beams with thehelpof
modal analysis237
P. Kuklik and K. Mikes
Behaviour of old timber (roof) structures in Tallinn 257
K. öiger
Introduction of AIR­project: Durationofloadeffectondifferent sized timber
beams 267
­ ν ­Session 4 - Moisture effects in wood m
Densified veneer wood effects of moisture on some physical and mechanical
properties - A review 279
Ad. J. M. Lejten
Spring-forward of laminated bends in sitka spruce 29
M. Redington and S. Ramsbottom
Cycbc tensile loading and creep-recovery test on thin wood specimens 309
P. Navi and V. Pittet-Gress
Large transverse compression of small specimens of wet spruce 319
A. Uhmeier, D. Vansteenkiste and L. Sahnen
Varying climate and size effect in moisture transport modeling of wood 327
L Absetz and S. Koponen
Long-term behaviour of wood composites - shear creep and crack formation
in cross veneered structures 341
S. Koponen
Conclusions of COST 508 wood mechanics workshop 353
A. Ranta-Maunus COST 508 List of participants and their contact address
Dr. Simon Aicher Mr. Ilmari Absetz
Forschungs- und Materialprufungsanstalt TKK
TRT Baden-Wurttemberg
Rakentajanaukio 4 A Pfaffenwaldring 4
02150 Espoo 70569 Stuttgart
fax. +358-0-451 3776 tel. 449 711685 1
fax.+49 711 685 6829
Mr. Peter Bonfield Dr. Colin Birkinshaw
Building Research Establishment University of Limerick
Materials Research Centre Timber Division
Limerick Watford WD2 7JR
IRELAND Gars ton
fax.+353 6133 8172 UNITED KINGDOM
tel.+44 923 664 815
fax. +44 923 664 785
Dr. Lars Boström Dr. Tony Bravery
Statens Provningsanstalt Building Research Establishment
P.O. Box 857 Timber Division
S-50115 Borås Watford WD2 7JR
SWEDEN Garston
fax.+46 33 13 45 16 UNITED KINGDOM
tel. +44 923 665 253
fax. +44 923 664 785
Mr. Bojau Bucar Mr. Stefano Capretti
University of Ljubljana I.T.L.-Instituto Technologia Legno
Dept. of Wood Scienc and Technology Via Biasi 75
Rozna c. VIII/34 1-38010 S. Michele
61000 Ljubljana ITALY
SLOVENIA fax.+39 461 650045
fax.+38 61 272297
Miss Helena Cruz Mr. John Dinwoodie
Laboratorio Nacional de Engenharia Civil Building Research Establishment Brasil, 101 Timber Division
1799 Lisboa Watford WD2 7JR
tel.+351 1 848 2131 UNITED KINGDOM
fax.+351 1 849 7660 tel.+44 923 664 815
fax. +44 923 664 785
vii -Dr. Ferenc Divos Mr. Christer Fellers
University of Sopron STF1 y of Foresty and Wood Sciences BOX 5604
PO Box 132 S-11486Stocholm
H-9401 Sopron SWEDEN
tel.+36 99 311 100/233
fax.+36 99 311 103
Dr. Eric Foumely Dr. Philippe Galimard
Civil Engineering Laboratory LRBB
University Blaise Pascal of Clemont- Laboratoire de Rheologie du Bois de
Ferrand Bordeaux
B.P. 206 B.P. 10
F-63174 Aubiere Cedex F-33610 Cestas Gazinet
fax.+33 73 40 75 10 fax. +33 57 97 91 02
Dipl.-Ing Martin Gier Dr. Shankare Gowda
Forschungs- und Materialprufungsanstalt VTT Building Technology
Baden-Württemberg Wood Technology
Pfaffenwaldring 4 P.O. Box 1806
70569 Stuttgart FIN-02044 VTT
tel.+4 9 711685 1 tel. +358 0 456 5552
fax.+4 9 711 685 6829 fax. +358 0 456 7027
Mr. Joseph Gril Dr. Per Johan Gustafsson
University of Montpellier Lund Institute of Technology
LMGC Dept. of Structrural Engineering
CP81 34095 Montpellier Cdx5 P.O. Box 118
FRANCE S-22100Lund
fax. +33 6754 4852 SWEDEN
E-mail:jgril@ fax. +46 46 10 44 20
Dr. Peer Haller Mr. Antti Hanhijärvi
Ecole Polytechnique Federale de Lausanne VTT Building Technology
DGC-IBOIS Wood Technology
CH-1015 Lausanne P.O. Box 1806
fax. +41 21 693 2394 FINLAND
tel. +358 0 456 5980
fax. +358 0 456 7027
- vm