In situ assessment of the timber floor structure of the Skansen Lejonet fortification, Sweden

• We examine the structural soundness and performance of the timber floor structures.
• Resistance drilling metod is usefull to estimate the depth of wood decay.
• None of NDT techniques provides complete data.
• It is recommended to use and combine different NDT methods for in situ testing.

Historical structures represent part of the cultural heritage of every nation and societies pay considerable attention to their preservation and maintenance. In historical structures, it is essential to preserve the original structure to the greatest degree possible. It is therefore of great importance to adopt structural health monitoring techniques to assess the remaining load-bearing capacity of timber structures. The main aim of this study was to examine the structural soundness and performance of the timber floor structures in Skansen Lejonet. Non-destructive testing (NDT) was used to evaluate mechanical properties and the general condition, without interfering with the structural integrity. It has been shown that the general structural condition and performance is good and fulfils the requirements for the intended use of the structure both in the past and at the present time, according to Eurocode standards. To assess the general quality of the timber, stress-wave measurements in combination with resistance drilling and X-ray measurements were applied. The quantitative evaluation of the mechanical properties and the density using stress-wave timing and radiographic measurements provided both good agreement and sufficiently good input for the structural analysis. The accurate use of non-destructive measurements, considering their crucial aspects and limitations, enables reliable results to be obtained, thereby increasing the potential to minimise interventions and prolong the service life of buildings as a part of sustainable development.