Project manager Patrick Jordaens has selected a project that nicely illustrates Vestad’s expertise in timber structures. "It may not be a huge project", Patrick explains, "but it is definitely a project with an extraordinary story.
In particular, this story concerns the restoration of an old timber shed that was built as a garden room against a residence in Killowen (Ireland) according to a design by Tatsuro Miki (Mood Architecture, Brussels). The timber garden shed has (literally!) gone through quite an extraordinary journey before ending up in Killowen.
This small building originally stood in the Netherlands, where it was carefully dismantled by Borg-Bouw, a Belgian contracting company specialising in restoring buildings, furniture, and joinery. Borg-Bouw then had the 5 trusses of the original timber structure rebuilt at their own premises to prepare for the final realisation in Ireland. Because of our expertise in timber frame construction, they got in touch with us and asked us to perform all structural engineering analyses.
To model the original load-bearing structure as accurately as possible, Borg-Bouw carried out a 3D scan of the timber trusses. Based on the point cloud describing the shape of those trusses, the centrelines were determined in AutoCAD. And as this load-bearing oak structure is quite old, the centrelines were anything but straight and vertical. Via a DXF file, we imported the centrelines as a wire-frame model into BuildSoft's Diamonds structural analysis software before completing it with cross-section and material properties. Finally, straight bar elements were added to model the new wooden roof structure on top of the original load-bearing structure.
It's worth spending a moment to reflect on the cross-section properties of the load-bearing oak structure as derived from the 3D scan. Since those cross-sections have an irregular shape, they were entered in Diamonds as variable cross-sections to build a geometry model that approaches reality as closely as possible. But in the end, of course, any geometry model remains an approximation of an all-but-perfect geometry. We, therefore, developed a second model in which we somewhat reduced the cross-section properties of the original load-bearing structure.
That provided an excellent tool to assess the sensitivity of the structural analysis results to model imperfections. And that, of course, is the big advantage of using structural analysis software such as Diamonds, which sets great store on usability and user-friendliness. Because it’s so easy to experiment with various model variants, we can provide reliable structural advice and do it very fast.
After completing the geometry model with the relevant load groups and load combinations (especially wind loads were important in this case), we used Diamonds to calculate the internal forces in ultimate limit states and deformations in serviceability limit states. This showed that interventions were required to keep the horizontal deformations due to wind loads within acceptable limits.
To complete the structural analysis, we then performed all mandatory verifications regarding the strength and stability of timber bar members (including the buckling resistance of compression members) following the Eurocodes and the Irish National Annexes, starting from the internal forces calculated in the previous step.
This small but charming restoration project is an excellent example of how easy it is to validate structural concepts efficiently using BuildSoft's exceptionally practical structural analysis software. That makes our life as structural design engineers much easier and more enjoyable!"