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 aim of this document is to report the state of the art in terms of research and practice of Timber-Concrete Composite (TCC) systems, in order to summarize the existing knowledge in the single countries and to develop a common understanding of the design of TCC.
This report was made within the framework of WG4-Hybrid Structures within COST Action FP1402. It intends to reflect the information and studies available around the world, but especially in Europe through the active contribution and participation of experts from various countries involved in this Action.
Timber-concrete composite (TCC) structures are an efficient way to combine the advantages of cross-laminated timber (CLT) and concrete plates. By cutting notches into the timber part and applying the concrete on top, efficient shear connections can be formed, eliminating the need for additional use of any type of fasteners. However, fresh concrete releases moisture after application, which is absorbed by the highly hygroscopic wood and can lead to a critical reduction in mechanical properties or to problematic situations due to a difference in expansion behavior. Therefore, a separating foil is usually applied between the two materials, which represents an additional time and cost effort and can also negatively influence the connection properties or make the use of notch-only connections impossible. Thus, we investigate numerically what effects the exclusion of such a foil has on the moisture distribution in the CLT plate. Further, the moisture propagation after a fictitious installation on site is analyzed by applying realistic indoor climates to the open wood surface on the bottom of the CLT plate for a period of two years. In addition, the numerical model allows us to study the effect of local sealings of the most critical wooden part, the end-grain surfaces in the notch region. We were able to confirm that, especially in the unsealed case, locally high moisture contents can occur in the critical region next to the notch, where the highest shear stresses are also to be expected. However, by fully sealing the end-grain surfaces in these regions, the moisture levels and thus the risk of failure could be reduced efficiently. The use of such detailed moisture simulations, where moisture uptake due to bleeding of fresh concrete has been calibrated based on experiments, allows the long-term moisture behavior of such critical situations to be studied and effective solutions to be developed.
Project contacts are Robert J. Ross at the Forest Products Laboratory and Rubin Shmulsky at Mississippi State University
Notches, particularly when incorporated on the tensile face, influence the ultimate capacity of members, such as beams and floor panels. Understanding and quantification of failure modes, ductility, and strength of notched CLT floor panels can allow the safe application of notches on building construction. Despite wood’s ductility, notches are known areas of stress concentration. The 2018 International Residential Code for one- and two-family dwellings (International Code Council 2017) restricts the use of notches on engineered wood products by requiring structural calculations instead of elucidating the ways notches might be used. To employ CLT to its maximum potential, there is a current and pressing need for better knowledge regarding the influence of notches on flexural performance.
This research seeks to review the literature regarding notches in solid and engineered beams, review typical CLT design details that employ or utilized notched panels, and conduct pilot-scale testing of notched CLT panels.
Timber-concrete composite slabs are more and more in use: the combination of timber and concrete combines the advantages of both materials and offer a valid solution for the increasing demand for sustainable construction. The connection between timber and concrete is the crucial element, yet its potential regarding material and time expenses is not exploited. This paper presents the novel connection system micro-notches, an interlocking concept between timber and concrete with indentations in the millimetre range. Micro-notches provide a continuous shear transfer without additional steel fasteners such as screws or dowels. The paper presents the development of the micro-notch concept in an extensive experimental program supplemented with analytical and numerical models, a calculation model, and practice-relevant guidelines. The results of the investigations show that micro-notches feature an approximately rigid composite action between timber and concrete and a sufficient shear strength for the use in office and residential buildings.
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.
This paper examines the load-bearing behaviour of cross-laminated-timber-concrete-composite slabs. The inhomogeneous distributed orientation of the trajectories of principal stress within the slab effected the design of the shear connection between the cross-laminated-timber (CLT) and concrete layer. Two well-known shear connection types, fully threaded screws in an angle of 45° and rectangular milled in notches, were examined in bi-axially loaded push out tests. Natural frequency tests and medium-scale test including the two shear connection types and different CLT-layer configurations determined the effective bending stiffness of the slab and the effective torsional bending stiffness of the slab respectively. The results facilitate the description of the bi-axial load-bearing behaviour, and establish a basis for a structural design model in two-way spanning CLT-concrete-composite-slab engineering. The paper eventually suggests first calculation models, a simplified FEM-model and a grid model. In this regard, a force-fitting element joint was developed and tested for practical reasons.