compression properties of wood as functions of moisture, stress and ...

Second International Workshop Structures in Fire – Christchurch – March 2002 .
1. Initial Input
STRUCTURAL
RESPONSE MODEL
2. Input of Temperature
Distribution in the Wall
3. Determine Stiffnesses of:
Elements
Members
Supports
Frame
Increment
Time Step
4. Determine Unbalanced Actions
5. Undertake Frame Analysis to
Determine Displacements
6. Test Failure
Yes
failure
No
not
converged
yet
Yes
convergence achieved
No
no failure
7. Test Convergence
8. Output
Figure 21. Flowchart showing overview of structural response model [6].
CONCLUSIONS
Creep of wood specimens has been measured for a range of loads, moisture contents and
temperatures. The significant types of creep observed were:
• Creep due to the presence of moisture, heat and stress in the temperature range 20°-
100°C.
• Creep due to heat and stress in the temperature range 100°-300°C.
Experimentation involving desorption of moisture in wood specimens did not reveal significant
creep due to mechano-sorptive effects.
The first type of creep mentioned above was sufficient for explaining the difference between the
elastic modulus obtained by calibration and direct measurement.
The relationships for the elastic modulus of wood in compression obtained by several
researchers through the calibration of models to full scale experiments represent simple elastocreep
models for predicting the effects of creep of light-timber structures in fire. The models are
limited to applications in which the wood is subjected to temperatures, moistures and stresses
similar to values that occurred in the experiments.
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