Environmental and urbanisation challenges have encouraged steady growth of mass timber structures where cross laminated timber (CLT) stands out in applications as full-size wall, floor, or beam elements. Beam elements are used mainly in situations where cross layers have a reinforcing effect on the tensile stress perpendicular to the beam axis, such as when introducing holes or notches, which is common practice in beams, due to engineering, installation, or architectural requirements. This paper presents experimental investigations of CLT beams with holes or notches for comparison and validation of an analytical model provided in the literature. Different sizes of holes and notches as well as different placements of the holes were considered in the experiments. All relevant failure modes were analysed and discussed in detail. Two predominant failure modes were indicated, i.e., bending failure and shear failure in crossing areas (mode III). Results further indicate that reduced lamination widths near the hole, notch, or element edges have a relatively small influence on the beam strength. Parametric studies indicate net shear failure (mode II) and tensile failure perpendicular to the beam axis as the critical failure modes in most of the considered cases, indicating their strong underestimation in design verifications according to the analytical model.
This paper provides a systematic review of research on glued laminated timber beams with circular and rectangular openings. Experiments on girders with unreinforced openings varied several parameters, including the girder span and shape, opening position and shape, and the relationship between the stress state near the opening and the ratio of opening size to girder size. We compare experimental results with recommendations given by DIN 1052:2004-08, DIN EN 1995-1-1/NA: 2010, prEN 1995-1-1: Final Draft, analytical expressions, and other relevant standards, as well as with the results of numerical models using the finite element method. Because of its myriad complexities and uncertainties, this area remains open for further research and for implementation of that research into practical design guidelines and rules.
Cross laminated timber (CLT) is a versatile engineered timber product that is increasingly well-known and of global interest in several applications such as full size plane or linear timber elements. The aim of this study involves investigating the performance of CLT beams loaded in-plane by considering bending and shear stress analysis with a special emphasis on the in-plane shear behavior including the complex internal structure of CLT. Numerical analysis based on 3D-FE models was used and compared with two existing analytical approaches, namely representative volume sub element (method I) and composite beam theory (method II). The separate verification of bending and shear stresses including tree different shear failure modes was performed, and a good agreement was obtained. The main difference between the results relates to shear failure mode in the crossing areas between the orthogonally bonded lamellas in which the distribution of shear stresses tzx over the crossing areas per height of the CLT beam is not in accordance with the analytical assumptions. The presented analyses constitute the first attempt to contribute to the on-going review process of Eurocode 5 with respect to CLT beams loaded-in plane. Currently, regulations on designing these types of beams do not exist, and thus experimental and numerical investigations are planned in the future.