In-situ assessment of timber structures - Assessment methods and case studies

Doctoral thesis, 2013

In the assessment of timber structures, diagnostic investigations with reference to the condition and structural performance of these structures are necessary and often require appropriate health monitoring techniques. This thesis covers four aspects within the research area of the in-situ assessment of timber structures based on scientific knowledge and guidelines to perform assessment of existing timber structures: I Determination of density of wood with portable X-ray The mechanical performance of timber is often strongly related to the density of wood. This work focused on the development of an in-situ calibration procedure to determine the density using X-ray, thereby enabling the prediction of the mechanical properties of timber as well as to evaluate the internal condition of the structure. II Property assessment of oak from the Vasa warship X-ray density measurements combined with mechanical tests from present and previous studies were used in the evaluation to non-destructively predict the mechanical properties in the proposed methodology for the special case of Vasa oak. III In-situ assessment of historical timber structures Systematic assessment strategies were applied to assess the mechanical performance and structural health monitoring techniques to preserve historical structures without interfering with their structural integrity and capacity. This is of vital importance to minimise interventions and prolong the service life of timber structures. IV Pilot study of the assessment of stresses in loaded structures A resonance frequency analysis procedure was investigated in this pilot study to evaluate the opportunity to determine the tensile capacity on site for peaks of unexpected increased loads and to detect the most loaded vulnerable members. It has been shown that a systematic assessment strategy is valuable and effective in the evaluation of the structural condition and performance of the structure in order to preserve (historical) timber structures to the greatest extent possible. The combination of structural health monitoring techniques is necessary to achieve accurate results for the analysis of the structural performance and they require further specific development.