Composite timber structures – Ribbed plate design : Evaluation of existing and development of new design methods

Ribbed plates comprising cross-laminated timber slab, CLT, with glulam beams allow for increased span length compared to pure CLT slabs. At the moment the Eurocodes do not provide any recommendations to design a CLT plate or a ribbed plate. There are handbooks for designing ribbed plates. But are their methods the best suited? Should one use Eurocode’s gamma-method, Timoshenko, shear analogy method or maybe an FE-model? This is difficult to answer, but nevertheless important questions for a structural engineer today. This master thesis investigates some of the different design methods used today in a numerical study. The study compares analytical methods and FE-models by investigating different parameters, like span lengths 6 m, 12 m, and 18 m, or uniform load and point load. Furthermore, this thesis provides guidance and help to apply design methods for ribbed plates. The outcome of the study shows a tendency for the gamma-method and the extended gamma-method giving the lowest deflections and normal stresses in many situations. Thus, there could be a risk of underestimating these properties by using the gamma-method. On the other hand there were consistent results with the gamma-methods compared to Timoshenko- and shear analogy-method which showed more deviations from the extended gamma-method as reference. The Timoshenko-method showed anomalies with thicker CLT. In addition, an Abaqus model with 3D elements and RFEM models with 2D and 1D elements were applied. The Abaqus models gave in general higher deflections and consistent results. Concluding from this thesis the Abaqus model together with the extended gamma-method would complement each other most efficiently in the design process of ribbed plates