The purpose of this study was to experimentally and numerically explore the effect of drilled holes in high shear zones of Laminated Veneer Lumber (LVL) beams. A total of 15 full-size shear beam tests were performed on nominal 2x10 1.9E Eastern Species LVL specimens with a span of 1829mm. Three different hole diameters were investigated: 44mm, 70mm, and 92mm drilled at quarter span and mid-depth of the beams. A finite element analysis, coupled with the Tsai-Wu strength theory, was carried out on the same beam configurations to investigate the stress distribution around the holes. It was clear from the stress contour maps that the holes disturb the flow of normal and shear stresses in such a way as to develop significant tensile stresses perpendicular to the grain at specific locations around the hole periphery. The transverse tensile stresses lead to relatively consistent failure loads for the LVL due to the lack of cross plies.
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.
A novel timber composite is presented, consisting of glued laminated timber (GLT) from softwoods and intercalated cross-layered plates of laminated veneer lumber (LVL) made of hardwood species, specifically beech. The structure is especially suited for beams with multiple, large rectangular holes, where the LVL acts as a highly efficient internal reinforcement and contributes to a damage-tolerant ultimate load behavior. The load capacity of the composite beam is not induced by the stress concentrations at the corners of the hole, which, in contrast to generic GLT, lead to a sudden propagation of cracks and brittle failure. It is shown that the structure, including the holes, can be designed analytically in a transparent manner by using beam theory, a parallel system approach, and modifications from FEM analysis for the verification of tensile forces at the hole periphery. The composite, firstly used in a recent multi-story building in Australia, significantly improves the competitiveness of timber in building works, which have been limited to steel and reinforced concrete structures.
Experimental and numerical investigations on round holes in glulam beams are presented. These were conducted in order to extend the field of practical application, to study the structural behaviour of holes arranged eccentrically or in groups and to generate basic results for deriving a design format. Within these investigations the influence of parameters like eccentricity, clear distance between holes or effect of reinforcement by fully threaded selftapping screws was considered. A comparison of estimated load-bearing capacities on the basis of the Weibull theory and test results shows good agreement. Strain gauge measurements in reinforcing elements confirm the validity of the chosen methods.
Brettsperrholz (CLT) besitzt im Gegensatz zu Brettschichtholz verhältnismäßig hohe Schub- und Querzugfestigkeiten. Bauteile aus CLT sind daher weniger empfindlich gegenüber Rissen und weisen eine größere Robustheit auf. Im Rahmen eines Forschungsvorhabens wurde das Tragverhalten von CLT-Trägern mit Ausklinkungen, Durchbrüchen und Queranschlüssen sowie Trägern mit schräg zur Faserrichtung angeschnittenen Rändern untersucht und Bemessungsansätze für die verschiedenen Trägerformen entwickelt.