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.

Knots are usually regarded as defects when grading lumber. In order to evaluate a member under out-of-plane loading, shear strength is one of the major mechanical properties, specifically, rolling shear (RS) strength is one of the critical mechanical properties of Cross-Laminated Timber (CLT), which determines the flexural strength of CLT under short-span bending loads. Lower grade lumber with a higher percentage of knots is recommended to be utilized for the cross-layer laminations which are mainly responsible for resisting shear stresses. Firstly, shear tests were performed in order to evaluate the effect of knots on longitudinal shear strength using shear blocks. After that, the effect of knots on the RS strength of 3-ply southern yellow pine CLT were investigated by experimental tests and an analytical model. Center-point bending tests with a span-to-depth ratio of 6 and two-plate shear tests with a loading angle of 14° were conducted on six CLT configurations composed of different types of cross layer laminations: clear flatsawn lumber with/without pith, lumber with sound knots with/without pith, and lumber with decayed knots with/without pith. The shear analogy method was implemented to evaluate the RS strength values from the bending test results, which were also compared against the results from the two-plate shear tests. It was found that: (1) The shear blocks containing sound knots had higher shear strength than matched clear shear blocks, the shear blocks containing unsound knots had lower shear strength than the matched clear shear blocks. (2) CLT specimens with cross-layer laminations with either sound knots or decayed knots had higher RS strength. (3) In general, the shear analogy method underestimated the RS strength of CLT specimens containing knots and pith.