### Abstract

As part of the European harmonisation of building codes,
the determination of design values for loads and
materials is important and is the motivation for this
research. This report begins with a summary of the
probabilistic basis of Eurocodes, analyses the strength
distributions of wooden materials, demonstrates the
effects of different distribution functions on the
calculated safety level and shows some results of the
applications of reliability analysis.
When the number of experiments allows, determination of
the 5% fractile of strength should be based on the
function fitting on the lower tail of the strength
values, for instance 10%. All smooth functions fitted to
tail data gave good estimates of the 5% fractile. When
the 5% fractile was determined from a function fitted to
all data, up to 5% error occurred (in one case 9%) when
compared to a non-parametric estimate. Three-parameter
Weibull distribution gave, in all calculated cases, the
5% fractile within an accuracy of ±3%.
The result of structural reliability analysis depends
strongly on the load and strength distribution types
used. When fitted functions are used in reliability
analysis, it is essential that the fit is good in the
lower tail area, the lowest values being most important.
When fitted to the same data, a two-parametric Weibull
distribution gives the most pessimistic prediction for
the tail, with a normal distribution being next, and
lognormal and three-parameter Weibull being the most
optimistic. In an example, a two-parameter Weibull gave a
failure probability 10 times higher than that of a
three-parameter Weibull.
The analysis suggests that gM = 1.2 to 1.3 is reasonable
for timber structures when gG = 1.2 and gQ = 1.5.

Original language | English |
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Place of Publication | Espoo |

Publisher | VTT Technical Research Centre of Finland |

Number of pages | 107 |

ISBN (Electronic) | 951-38-5909-6 |

ISBN (Print) | 951-38-5908-8 |

Publication status | Published - 2001 |

MoE publication type | Not Eligible |

### Publication series

Series | VTT Tiedotteita - Meddelanden - Research Notes |
---|---|

Number | 2109 |

ISSN | 1235-0605 |

### Keywords

- wooden structures
- reliability
- construction
- timber construction
- strength
- building code
- design
- plywood
- Eurocode
- failure

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## Cite this

Ranta-Maunus, A., Fonselius, M., Kurkela, J., & Toratti, T. (2001).

*Reliability analysis of timber structures*. VTT Technical Research Centre of Finland. VTT Tiedotteita - Meddelanden - Research Notes, No. 2109 http://www.vtt.fi/inf/pdf/tiedotteet/2001/T2109.pdf