This thesis deals with the shear design of Cross Laminated Timber (CLT) elements stressed by concentrated loads which are locally reinforced by means of self-tapping screws with continuous threads. A simplified model is presented using an effective width for the calculation of the shear stresses in the vicinity of point supports or concentrated loads. Laboratory tests supply material-mechanical principles to determine the interaction of rolling shear stresses and compression perpendicular to the grain. In addition to experimental tests theoretical models are developed to examine the load bearing behaviour of CLT-elements reinforced by self-tapping screws. Preliminary tests with plate elements provide initial experience with these reinforcements under biaxial load transfer. Finally a design concept validated by means of the test results is proposed.
Point-supported flat slabs made of cross laminated timber (CLT) for multi-storey buildings pose various challenges to structural timber design. One aspect are concentrated compressive loads, which cause stress concentrations in the form of shear and compression perpendicular to the grain at the point supports. The present work deals with this problem and shows a method, how the support area can be reinforced with a system connector. After a specification of the connector, the functionality of this construction element is described on the basis of experimental, numerical and analytical studies for a symmetrical loading. The interaction of the connector with the (CLT) is presented with an anlaytical model and numerical simulations, and evaluated with mechanical tests.
In this paper, the dynamic properties of a point-supported cross-laminated timber slab are studied in order to determine the elastic material parameters on this basis. A detailed experimental modal analysis of the slab with dimensions 16.0 m x 11.0 m is performed, and seven modes including the natural frequencies, damping ratios and mode shape components at 651 sensor positions are identified. The found mode shapes are complex due to environmental influences that occurred during the two-day measurement campaign. This error is corrected by eliminating these influences. A finite element model of the slab is presented, whose parameters in terms of material properties and boundary conditions are determined by a model updating procedure. Based on the modal properties of the seven experimentally identified modes, an accurate and robust parameter set is obtained, which can be used in further numerical studies of the considered CLT to check serviceability limit criteria.
This paper presents an experimental investigation of the structural behaviour and dynamic characteristics of an innovative, double-span, point-supported Cross Laminated Timber (CLT) floor system for an 18-stroey woodhybrid student residence building at the University of British Columbia Campus in Vancouver, Canada. Eighteen CLT floor specimens with or without service openings were fabricated by three manufacturers and tested. The fundamental natural frequency, stiffness and deformability, load-carrying capacity, two-way action, compression perpendicular to grain at the supports, and the failure mechanism of the floor systems were investigated. In addition, the effect of openings in the floors was investigated along with the manufacturer-related properties of the CLT floors were examined. The tests gave an insight into the structural behaviour of this innovative floor system, provided test data that was used for calibration of the Finite Element Models of the building, and helped choose the right product for the floors.
The challenge with point-supported flat slabs is the stress concentration at the supporting points. The small strength of the wood perpendicular to the grain should not reduce the load carrying capacity of the CLT –Panels. Therefore, there are some existing state of the art methods of reinforcement with self-tapping screws, which open up the...