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Modelling the long-term strength of timber columns

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Summary

This paper studies the influence of the used creep function, and the duration of the experimental sustained loading from which the creep function was derived, in modelling the long-term buckling strength of timber columns. The sensitivity of this buckling strength to creep and initial deflection is numerically studied using an energy approach that takes into account the initial deflection. Various creep functions — power laws as well as exponential laws — derived from bending experiments of different durations are used for the numerical simulation. The crucial need for experimental results issued from very long load period experiments is identified. Such experiments may lead to a more credible creep analysis of timber structures.

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Abbreviations

i:

radius of giration

s:

stress level

EL :

effective MOE

E0 :

instantaneous MOE

I:

inertia moment

Kσ,K′σ :

geometrical matrices

L:

length of beam or column

Lf :

effective length

Ncr :

axial force, buckling load

U:

elastic strain energy

W:

external forces work

t:

time variable

u:

moisture content (m.c.)

v:

total deflection

vc, ve, v0 :

creep, instantaneous elastic and initial deflections respectively

α(t):

time function

ɛ, ɛe, ɛ0 :

total, instantaneous and initial strains respectively

ψ:

twist rotation

φ(t):

creep coefficient or fractional creep or relative creep

ϕ(x):

shape function

λ:

load factor

δ:

longitudinal shortening

Π:

total potential energy

ξ:

creep factor

τ:

relaxation time

References

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Ayina, O., Morlier, P., Reynouard, J. et al. Modelling the long-term strength of timber columns. Wood Sci.Technol. 30, 491–503 (1996). https://doi.org/10.1007/BF00244443

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Keywords

  • Timber
  • Period Experiment
  • Material Processing
  • Energy Approach
  • Timber Structure