Self-tapping screws are efficient and flexible fasteners, applicable for many types of connections. Investigations on axially loaded groups of screws pointed out, that small spacing between the screws lead to block shear failure mode. So far, block and plug shear failure mode are only analysed for laterally loaded fasteners. Corresponding models cannot be simple transferred to primary axially loaded screws, because of their load insertion continuously along the effective thread featuring a thread-fibre angle perpendicular or with an angle to grain. Results gained by means of two different test configurations, with constant 90° thread-fibre angle but different configurations of group of screws and support conditions are presented. A block shear model is presented, and for mean values for stiffness and strength properties as model parameters are discussed together with values for parameters related to the force distribution over the effective thread length for the first test configuration. Agreement between model and test results was found on a conservative basis. As outlook, considerations of additional bending stresses as well as parameter optimisation are seen as prerequisites and next steps for further model improvement and practicality.
Within this paper a comparison of different reinforcement concepts for timber beams with round holes is carried out. Therefore currently applied standardized methods and two recently developed approaches are considered. By means of numerical and analytical investigations it becomes apparent that the analysed reinforcement methods divergent to those given in current standards have great potential: shear stresses as well as tensile stresses perpendicular to the grain in the critical areas around the beam opening can be reduced significantly. Hence, the maximum load carrying capacities of the new reinforcement concepts supposedly exceed the standardized ones considerably. For verification of the results experimental investigations on beams with different reinforcement methods are planned.
In this contribution bending and shear tests of cross laminated timber (CLT) plates under concentrated loads are presented. The so loaded structural members can fail either due to punching along a critical perimeter line in the vicinity of the concentrated load or in bending. Two test configurations were developed and investigated by linear elastic models. The obtained test results and observed failures as well as their correlation with the mechanical modeling are shown in this paper. The established numerical model was a 3D solid model with different material behavior for all acting stresses. The material behavior was implemented in a user subroutine for the FE program ABAQUS. By comparison of measured and computed load displacement curves numerical models could be discussed regarding their reliability and conclusions about missing input for an increasing accuracy of the model could be drawn.
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 [13] and Smith and Teng [14] 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.
Cross-laminated timber has conquered new markets since the publication of volume I Basic design and engineering principles according to Eurocode. The present volume II describing Applications provides the designer of timber structures on the one hand with basics for design factors, mechanical properties and modelling with finite element method. On the other hand it describes in detail the design of floors, ribbed plates and walls e.g. by design approaches regarding forces in joints of plates and diaphragms, concentrated loads, openings, effective width and compression perpendicular to grain. Current scientific knowledge as well as experience from practical engineers is taken into account. 15 examples demonstrate the design approaches as references for practitioners. Closing background information for the shear correction coefficient, deformations due to concentrated loads and the modelling of crosslaminated timber as general grillage will illuminate the background and facilitate deeper understanding of the design with cross-laminated timber.
Introduction of Concentrated Loads in CLT Wall Elements Parallel to Plane – Analytical Model for the Determination of Stresses and Simplification for Practice
In this paper a proposal for the computation of stresses into orthotropic panels (e.g. CLT wall elements) caused by concentrated local load introduction in plane is derived on the basis of linear elastic mechanics. In practice the concept of effective width is often applied for the approximate determination of stresses. On the basis of the elastic solution in this contribution a proposal for the determination of the effective width is submitted. In addition a proposal for the stability verifications by means of the effective width is given..
Is a wood processing company with about 1,000 employees andplants in Austria, Slovenia and Russia. In the forest around their Russian sawmill “HasslacherLes” the wood species birch (Betula pendula) is growing in large quantities and cut-able qualities. The company has also very modern equipment for the production of glued laminated and cross laminated timber. Consequently the idea was born to develop a project to produce load-carrying members to check the possibility of production of glued laminated timber and cross laminated timber without large modification of the existing production process. The goal of the project was to set up a complete profile of the mechanical properties needed for the design according to EN 1995-1-1. In addition by the means of a pilot project (detached house) erected with birch Cross Laminated Timber the effectiveness of this product for structural purposes with slender wooden components could be shown. The second pilot project was an industrial hall made of Glued Laminated Timber with birch.
In this contribution proposals for the resource optimised production of laminar, load carrying timber elements are shown. Therefore also analogies to the ship and aircraft/aerospace engineering as well as to the furniture industry have been considered.
The present contribution deals with the theoretical analysis of a selected geometry of CLT-elements combined with steel trapezoidal cross sections with a subsequent description of test specimens and the results of the conducted four-point-bending test. Used for long span floors this hybrid construction can be adjusted in its bending stiffness as needed. By placing the steel part into the tension zone a ductile failure mode can be achieved as well as notching the trapezoidal cross section is applicable easily. By performing full scale four-point-bending-tests of several test specimens it was possible to confirm the theoretical findings.
This paper will discuss the relevancy of different boundary conditions that relates to the dynamic behaviour of CLT floors to show the opportunities of adopting the findings for the verification of the serviceability limit state. Based on a literature research and measurements in the laboratory and in situ in different objects the evaluated boundary conditions are different static systems, supporting conditions, non-load bearing internal walls, flexible carriers, joints between CLT elements, elastomers and floor constructions. Furthermore a theoretical investigation on the low frequency behaviour of floating screeds was conducted. Abstracted from the results it can be stated that elastomers can generally be neglected in their influence on low frequency vibration modes except when the partial clamping due to the load of superimposed storeys at the supports should be taken into account. The effect of partial clamping on low frequency vibration can be calculated adequately but is lowered if elastomers are used to improve the building physics. A big influence was observed at non-load bearing internal walls as they are able to change the eigenmodes of a floor into ones with higher frequency. Overall the laboratory measurements agreed well with the analytic solutions while differences in comparison of calculations with in situ measurements rise with the complexity of the boundary conditions.
