Notches in CLT and CLT ribbed plates

Project duration 09/2019 - 08/2021

Cross Laminated Timber (CLT) is mainly applied as a plate or a panel element in Timber construction. This industrially produced product consists of orthogonally glued boards, produced as plates, beams or panels. CLT elements are capable of transferring shear and normal forces as well as bending moments, while at the same time acting as a space-enclosing element. Within the scope of this research project, the focus is on the use of CLT as a plate element.

In case of the connection of two CLT elements with a half lap joint connection or support of CLT element on a steel profile, the notches in CLT elements are often utilized. These geometric discontinuities lead to stress concentrations which considerably reduce the load-bearing capacity of such elements. This is due to the fact that in the area of these notches high tensile stresses perpendicular to the grain in combination with shear stresses occur, which can lead to a crack formation. 

In contrast to notches in CLT elements, notches in solid timber or glulam as well as veneer lumber (LVL) are well known. The verification of such notches is currently based on a fracture mechanics approach according to Gustafsson (1988). The product dependant properties are considered with a factor kn, which is still not sufficiently examined for CLT. Main goal of this research is to examine whether an analogous application of this currently available verification method for solid wood, glulam and LVL is also possible for the CLT panel, despite the orthogonal layered structure. Under these conditions, the factor kn or a corresponding function describing the same shall be developed. Otherwise, the goal is to develop an alternative approach for CLT. 

Similar stress peaks and interacting tensile stresses perpendicular to the grain and shear stresses also occur with notched BSP ribbed plates, where Glulam rip delaminates from a CLT plate. A first approach for the calculation of load-bearing capacity of such elements was published by Augustin et al. (2016) based on the approach of an elastic interface model and a beam on elastic foundation. Furthermore, within the scope of this project, a comparison of the model presented by Augustin et al. (2016) together with existing test results and the fracture mechanics approach shall be performed. The overall goal is to achieve an equivalent handling and methodology for all timber construction products relevant for construction.

Funding programme Collective Research

Collective Research | General Programmes

The funding of cooperative research projects (sector projects) in Collective Research supports pre-competitive research projects which do not include any directly exploitable product and process or service developments.

Collective Research stands for cooperative research projects for whose results are made available to the industry and is open to all topics.