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Structural health assessment of in-situ timber

An interface between service life planning and timber engineering
: Kasal, B.

Brischke, C. (Ed.) ; Nordic Forest Research Cooperation Committee -NFRCC-:
9th Meeting of the Northern European Network for Wood Science and Engineering, WSE 2013. Proceedings : September 11-12, 2013, Hannover, Germany
Hannover, 2013
Northern European Network for Wood Science and Engineering (WSE Meeting) <9, 2013, Hannover>
Fraunhofer WKI ()
in-situ; evaluation; wood; nondestructive; semi-destructive; reliability; service life

The in-situ assessment of timber structures has gained considerable attention in recent years due to some unexpected failures of public buildings. The assessment of timber, however, has been used in the evaluation of historic structures for a number of years and methods employed have enveloped from visual observation (which is still one of the most effective ways of evaluating in-situ timber) to more sophisticated methods that use various physical phenomena such as stress wave or x-ray energy attenuation. In the health assessment of timber, effects of biotic elements such as insects and fungi are of interest, which of course is always connected with the presence of water in wood. The structural assessment encompasses questions related to the structural integrity of in-situ members and the performance of components and the system. The structural health assessment not only focuses on biotic elements but also attempts to quantify engineering properties of the material such as strength degradation, modulus of elasticity, loss of cross section, extent of check and other quantitative parameters needed for subsequent evaluation of the structural system, frequently expressed as loadbearing capacity. Service life planning of a structure is a complex issue that is complex issue that is related not only on the materials, but also the environment and use of the structure. Assessment of the health and properties of existing timber elements yields a piece of information that is necessary but not sufficient for the service life estimate.
In the evaluation of structural timber, a mere use of various assessment techniques is not sufficient and usually an involvement of disciplines such as wood anatomy, wood physics and statistics is needed. A reliable estimate of the parameters of in-situ timber requires careful planning of measurements (experiments) since the material is highly variable and any statement about the properties of an element or even the entire system must reflect the random character of the wood properties. This paper will summarize the state-of-the art methods used in the assessment of in-situ timber and analyze the strengths and weaknesses of selected methods. An attempt will be made to outline future directions in the development of in-situ assessment methods.