In timber–concrete composite members with notched connections, the notches act as the shear connections between the timber and the concrete part, and have to carry the shear flow necessary for composite action. The shear transfer through the notches generates shear and tensile stresses in both parts of the composite member, which may lead to brittle failure and to an abrupt collapse of the structure. Although simplified design formulas already exist, some structural aspects are still not clear, and a reliable design model is missing. This paper summarizes current design approaches and presents analytical models to understand the shear-carrying mechanism, to estimate the shear stresses acting in the timber and concrete, and to predict failure. The analysis concentrates on three problems: the shearing-off failure of the timber close to the notch, the shear failure of the concrete, and the influence of the shear flow on the gap opening between the timber and concrete. Parts of the model calculations could be compared to experimental observations. The conclusions of this paper contribute to improving current design approaches.
The objective of this research is to develop optimum notch profile to achieve maximum connection stiffness and strength properties, characterize notched timber connection MTP-concrete floor systems, including concrete shrinkage and develop floor system details and design procedure.
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.
For the design of timber-concrete composite (TCC) elements with notches, the slip modulus Kser represents an important property of the connection. In this paper available research results were gathered and further experimental tests were carried out in order to define the slip modulus of a notched connection. Therefore experimental push-out and beam tests have been conducted on timber-concrete composite specimens. Test series included specimens with and without screws in the notches. Also the failure mode of the connection as well as the application of the slipmodulus (obtained from the push-out tests) in TCC elements have been investigated.
CLT-concrete composite floor systems are a solution for timber buildings with a long-span floor. It yields a reduction of carbon footprint and even eco-friendly structure at the end of its service life. This study will evaluate the structural performance of notched connectors in the CLT-concrete composite floor, comprised of the serviceability stiffness, maximum load, and behavior at failure. The parameters of the test plan are the loaded edge length, the notch depth, the concrete thickness, and the screw length. Other secondary variables are also assessed, such as different loading sequences, speed of test, and timber moisture content. Experimental results prove that the performance of the connector depends significantly but not linearly on the notch depth and the length of the loaded edge. The connector with a deeper notch and a shorter heel will be stiffer and more robust, but it also tends to have a brittle rupture. The test results also help validate a solution for deconstructable connector systems. A nonlinear finite element model of the connector is built and validated versus the experimental results. It yields reasonably good predictions in terms of resistance and can capture the load-slip relationship.
The objective of this research is to conduct acoustic testing of MTP-concrete floor systems with STS and notched timber connections, develop optimum construction details for various occupancy requirements and generate design guide that addresses various performance attributes, including structural, vibration, acoustics and possibly fire.