CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL ...
CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL ...
CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL ...
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to draw an approximate value for same from a graph (diagram). The residual<br />
load-bearing capacity <strong>of</strong> existing, structures or components can be<br />
checked and verified by means <strong>of</strong> the timber cross sections reduced by d.<br />
In the draft <strong>of</strong> the new GDR Code "<strong>Timber</strong> Construction - Loadbearing<br />
Systems" adopting the method <strong>of</strong> limit states, for timber the most<br />
significant agents have been assigned to ranges (grades) <strong>of</strong> aggressivity,<br />
and stress degrees have been defined accordingly. Subject to the stress degree<br />
and to the cross-sectional dimension <strong>of</strong> the timber component concerned,<br />
adaptation factors for the influence <strong>of</strong> aggressive media have been<br />
fixed.<br />
29-11-1 P Galimard, P Morlier<br />
Load duration effect on structural beams under varying climate influence<br />
<strong>of</strong> size and shape<br />
Abstract<br />
The Duration <strong>of</strong> Load effect has been <strong>of</strong> increasing interest for both the<br />
understanding <strong>of</strong> wood or wood products in long term behaviour and for<br />
the determination <strong>of</strong> safety factors for engineering purposes. Many kinds<br />
<strong>of</strong> testing, mainly in bending, have been made but the large amount <strong>of</strong><br />
configurations has always been reduced to few moisture contents and load<br />
histories. However, it is still not easy to compare all the results for the protocol<br />
<strong>of</strong> testing and presenting the results is not yet a standard.<br />
Different attempts <strong>of</strong> evaluating the stress level have been done and<br />
their accuracy depends on what is wanted to be shown. The methods are<br />
applied on 2 meter LVL beams subjected to bending in natural environment.<br />
Forty beams are stepwise loaded in an open shed in the Laboratoire<br />
de Rhéologie du Bois de Bordeaux in order to have a failure <strong>of</strong> 80% <strong>of</strong> the<br />
beams within two months. The step levels are from 50% to 90% <strong>of</strong> the average<br />
short term strength. Two beam depths (100 & 150 mm) are tested.<br />
The beams can be sealed or unsealed. The curvature, the time-to-failure<br />
and the climatic conditions are monitored.<br />
A ranking method is used to show the main trends <strong>of</strong> the duration <strong>of</strong><br />
load results: the time-to-failure are not affected by daily or short time variations<br />
<strong>of</strong> hygrothermal conditions, but by the two month mean variation <strong>of</strong><br />
the moisture content.<br />
The long term strength reductions are evaluated and finally compared<br />
to standard (EC5) ones. This work is a part <strong>of</strong> a European AIR-Project<br />
which has been set up to get experimental data on DOL <strong>of</strong> LVL and glulam<br />
straight, notched and curved sized beams.<br />
Conclusion<br />
<strong>–</strong> We have shown, on straight LVL beams that opposite conclusions can<br />
appear from the same data depending on the way <strong>of</strong> presenting the results.<br />
<strong>–</strong> However, the influence <strong>of</strong> the general changing <strong>of</strong> the climate was<br />
more important than the absolute moisture content.<br />
<strong>–</strong> The strength reduction estimation has roughly given the same results<br />
from the two tested methods; so #50% beams can be accurately used.<br />
<strong>–</strong> The short term strength has been influencing the results in a large scale,<br />
because <strong>of</strong> the moisture content reference and <strong>of</strong> the definition <strong>of</strong> the<br />
stress level.<br />
<strong>–</strong> The duration <strong>of</strong> load effect is fairly depending on the tested shape: it is<br />
more important on straight beams than on notched beams.<br />
<strong>–</strong> The EC5 krnod factor, for LVL beams, seems to be optimistic for EC5<br />
Service Class 2 and conservative for EC5 Service Class 3.<br />
A protocol <strong>of</strong> Duration <strong>of</strong> Load test and analysis is still needed because <strong>of</strong><br />
the numerous testing configurations, the variability <strong>of</strong> the result analysis,<br />
and the influence <strong>of</strong> the analysis on the conclusions that can be contradictory.<br />
30-11-1 R H Leicester, C H Wang, M N Nguyen, G C Foliente<br />
Probabilistic design models for the durability <strong>of</strong> timber constructions<br />
Introduction<br />
The theory <strong>of</strong> structural engineering for timber construction is now sufficiently<br />
well defined that computational design procedures can be developed<br />
and even codified. By contrast, design for durability is still very<br />
much <strong>of</strong> an art, with design solutions varying from person to person. More<br />
usually, design for durability is omitted and the control <strong>of</strong> performance is<br />
undertaken by complying with 'good building practice'.<br />
The key to developing a design procedure is first to have predictive<br />
models for durability. Because <strong>of</strong> the uncertainties associated with these<br />
models, they will <strong>of</strong> necessity have to be probabilistic models. Once such<br />
models are available computational design procedures can be developed<br />
<strong>CIB</strong>-<strong>W18</strong> <strong>Timber</strong> <strong>Structures</strong> <strong>–</strong> A <strong>review</strong> <strong>of</strong> <strong>meeting</strong> 1-<strong>43</strong> 2 <strong>MATERIAL</strong> PROPERTIES page 2.24