WHFF Project: 2016.17
Project leader: Prof. Dr. Steffen Franke
The short video about the project on Youtube can be watched under the following link (only available in German): https://youtu.be/eWMRSu8HgOc
The most important facts in brief
The effects from the local climate, the resulting wood moisture distribution, dimensional stability, residual stresses and possible cracks in the load-bearing cross-section were investigated
Concrete requirement profiles for different building categories as well as bridge structures were developed
A monitoring system for quality assurance is recommended and a numerical model for the assessment of the cross-section size or the influence of the erection period has been developed
Guidance is given for the design and erection of timber structures, particularly with regard to the moisture loads that occur and their effects.
Project description
Wooden structures are becoming increasingly sophisticated and must nowadays meet the highest requirements. The combination of modern architecture with wood, a renewable raw material, allows for an impressive appearance and slender cross-sections with large spans. Precise planning, production, logistics, commissioning and use are of great importance.
During the construction and utilization phase, risks to the timber structure must be realistically assessed. In particular, the wood moisture distribution in the timber supporting elements as well as the risk of cracking and ensuring the dimensional stability of the cross-sections play an important role. Quality assurance is of crucial importance here.
The present research project therefore deals with effects from the local climate, the resulting wood moisture distribution, dimensional stability, residual stresses and possible cracks in the load-bearing cross-section. The aim is to give concrete recommendations for the design of timber structures. For this purpose, developed numerical models and methods are to be transferred into validated recommendations for design and planning in practice.
The project is based on climate data for Switzerland, measurement data from long-term measurements of the service climate and the wood moisture content in load-bearing cross-sections, and a numerical model developed to represent moisture diffusion, dimensional change and the resulting internal stresses. In addition, required material parameters were determined in small laboratory series. The research project is thus intended to contribute to improved quality assurance and implementation of timber structures.
Conclusions
The climate data and wood moisture values from the long-term measurement were classified according to their use and processed for practical application. In addition, measurement data from other research institutes were also taken into account.
Concrete requirement profiles for different building categories and bridge structures are now available. Particular attention was paid to special influences that often led to confusion and open questions.
A monitoring system for quality assurance is recommended and a numerical model for assessing the section size or the influence of the erection period was created and validated. Taking into account the actual climatic conditions encountered in ice halls, indoor riding arenas and bridges, the change in dimensions and stresses in the cross-section was calculated and evaluated. Finally, advice is given for the design and erection of timber structures, in particular with regard to the moisture loads that occur and their effects.
The results provide planning engineers and authorities with additional guide values for estimating the expected wood moisture content in the structure, including its distribution over the cross-section width during erection and use, in addition to the values already specified in SIA 265:2012.
The full report to download:
More information about the project on ARAMIS.
The project was supported by the Swiss Forest and Wood Research Funding Switzerland (FOWO-CH) of the Federal Office for the Environment (FOEN) and the Conference for Forests, Wildlife and Landscape of the cantons.