Within this paper a comparison of different reinforcement concepts for timber beams with round holes is carried out. Therefore currently applied standardized methods and two recently developed approaches are considered. By means of numerical and analytical investigations it becomes apparent that the analysed reinforcement methods divergent to those given in current standards have great potential: shear stresses as well as tensile stresses perpendicular to the grain in the critical areas around the beam opening can be reduced significantly. Hence, the maximum load carrying capacities of the new reinforcement concepts supposedly exceed the standardized ones considerably. For verification of the results experimental investigations on beams with different reinforcement methods are planned.
The topic of this paper is the discussion of a proposal for the design of ribbed plates built-up with CLT (plate)- and GLT (ribs)- members. The suggested elastic model is based on the work of Abdelouahed  and Smith and Teng  for the strengthening of concrete members with FRP plates and will be applied for the mentioned loadcarrying timber elements. As a result so far it could be observed, that high peaks of shear and tensile stresses perpendicular to the interface (glue-line) occur due to the elastic consideration of the material. The model was evaluated by some pre-test which showed an acceptable correlation between the predictions of the model and a 2D-FEM analysis. It is evident, that the notches at the end of the rips must be reinforced by e.g. self-tapping screws or glued in rod to achieve effective solutions for this load carrying element. With the discussed model the shear and tensile stresses and forces resp. perpendicular to the interface can be computed.
The usage of holes in glulam and LVL beams is a common practice in timber constructions and requires in many cases the application of reinforcement. At present, Eurocode 5 does not contain design rules for holes, nor for their reinforcement, which are, however, regulated in the German National Annex to EC5. Although it has been proven that internal rod-like reinforcements improve the shear force capacity of a beam with holes, several problems still remain, particularly the inability to successfully reduce peak stresses at the periphery of the hole, especially shear stresses. Inclined internal steel rod reinforcements were studied and compared with vertically oriented rods, which is currently the only regulated application. The analysis revealed a reduction of both perpendicular to grain tensile stresses and shear stresses, which for the case of vertical rods are not reduced at all. A first attempt at the design of such inclined reinforcements was made by deriving an equation based on the results from FEM simulations. The design approach was then applied to an example case. Experimental verification of the theoretical observations is still necessary and ongoing, though a very promising approach for an improved internal reinforcement and its respective design can already be observed.
The interlaminar shear stresses of the three-layer, five-layer, and seven-layer cross laminated timber (CLT) and those of the oriented laminated beams were calculated according to Hooke's law and the differential relationship between the beam bending moment and shear force. The interlaminar and maximum shear stresses of the CLT beam are related to the number of CLT layers and to the elastic modulus ratio EL/ET (or EL/ER) of the parallel and perpendicular layers. The interlaminar shear strength of the Hemlock CLT was positively correlated with the elastic modulus of its parallel layer. The results showed that the CLT short-span beams had three failure modes when subjected to a three-point bending test, namely perpendicular layer rolling shear failure, CLT interlaminar shear failure, and parallel layer bending failure. The shear stress of the oriented laminated beam followed a parabolic distribution along the height of the section, while the shear stress of the orthogonally laminated beams tended to be balanced, rather than parabolically distributed along the height of section. The short beam three-point bending method was able to effectively test the interlaminar shear strength of CLT due to its stable and readable load.