System reliability of timber trusses based on non-linear structural modelling |
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Authors: | M Hansson P Ellegaard |
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Affiliation: | (1) Division of Structural Engineering, Lund University, P.O. Box 118, SE-221 00 Lund, Sweden;(2) Department of Building Technology and Structural Engineering, Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark |
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Abstract: | Structural design is today concerned with single component performance where each limit state is related to a single mode
of failure of a single component. Further, in limit state codes the strength variables are related to a deterministic value
(usually the 5-percentile). However, in a structure with a number of elements, two different effects (called system effects)
can be found:
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The probabilistic system effect that is based on the reduced probability that weak sections coincide with the most stressed
sections.
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Structural load-sharing that is the ability to redistribute load between members. |
In this paper, Monte Carlo simulations of a timber W-truss with punched metal plate fasteners (nail plates) are performed.
Structural timber displays a significant variability in strength and stiffness both within and between members and is described
by a statistic model calibrated against data from Norway spruce (Picea abies). Most studies found in the literature are based
on linear-elastic theory and the variability within members is neglected mainly because of lack of data. The FE calculations
are performed by TrussLab – a toolbox for MATLAB developed at Aalborg University. TrussLab considers contact between timber
members and non-linear behaviour of the joints. The timber members are given linear properties.
The system effect is based on reliability analyses. The system effect found depends on the coefficient of variation, the distribution
of the random load variable and the reliability level. Depending on the assumptions, the system effect was found to be in
the range 8–25%. |
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Keywords: | |
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