Experimental investigations and design provisions of steel-to-timber joints with annular-ringed shank nails for Cross-Laminated Timber structures

4siThis paper investigates the mechanical and the hysteretic behaviour of steel-to-timber joints with annular-ringed shank nails in Cross-Laminated Timber (CLT). These fasteners are used to anchor typical metal connectors, such as hold-downs and angle brackets, to the CLT panels. The experimental pro- gramme presented in the paper was carried out at the Institute of Timber Engineering and Wood Technology, Graz University of Technology (Graz, Austria). Average and characteristic values of the exper- imental strength capacities are evaluated and compared to the analytical predictions determined accord- ing to current structural design codes and literature. Furthermore, to fulfil the requirements of the capacity-based design, the overstrength factor and the strength degradation factor are evaluated and con- servative values are recommended.Link to official publication: DOI 10.1016/j.conbuildmat.2016.06.072partially_openembargoed_20180709Izzi, Matteo; Flatscher, Georg; Fragiacomo, Massimo; Schickhofer, GerhardIzzi, Matteo; Flatscher, Georg; Fragiacomo, Massimo; Schickhofer, Gerhar

Mechanical characterisation of structural laminated bamboo

Low carbon construction materials are needed to reduce CO2 emissions in the built environment. Laminated bamboo is an example of such a material, however to be used in structural applications, fundamental mechanical properties are needed to establish the design values used in architecture and engineering practice. Recent studies on laminated bamboo have focused on the use of timber standards for small clear specimens, with little work published on structural scale testing. The presented work is the first study to utilise structural scale test methods for timber in a multi-laboratory test programme to investigate all mechanical properties of an outdoor laminated bamboo product. The study provides a comparison of the full scale structural performance to conventional timber and a pathway for use in engineering design and practice. The study shows laminated bamboo is comparable to conventional timber and timber-based products in structural properties and forms the foundation to use laminated bamboo in design and construction

The influences of moisture content variation, number and width of gaps on the withdrawal resistance of self tapping screws inserted in cross laminated timber

A large experimental campaign comprised of 470 withdrawal tests was carried out, aiming to quantify the withdrawal resistance of self-tapping screws (STS) inserted in the side face of cross laminated timber (CLT) elements. In order to deeply understand the “CLT-STS” composite model, the experimental tests considered two main parameters: (i) simple and cyclic changes on moisture content (MC) and (ii) number and width of gaps. Regarding (i), three individual groups of test specimens were stabilized with 8%, 12% and 18% of moisture content and one group was submitted to a six month RH cycle (between 30% and 90% RH). Concerning (ii), different test configurations with 0 (REF), 1, 2 and 3 gaps, and widths equal to 0mm (GAP0) or 4mm (GAP4), were tested. The influences of MC and number of gaps were modeled by means of least square method. Moreover, a revision of a prediction model developed by Uibel and Blaß (2007) was proposed. The main findings of the experimental campaign were: the decrease of withdrawal resistance for specimens tested with MC=18% in most configurations; the unexpected increase of withdrawal resistance as the number of gaps with 0mm increased; and, the surprising increase of withdrawal resistance for REF specimens submitted to the RH cycle.The development of the present work was possible only thanks to the financial support of the 391 Portuguese Science Foundation (Fundação de Ciência e Tecnologia, FCT), through PhD grant SFRH / BD17392 / 79972 / 2011. Further, the valuable partnerships with the Institute of Timber Engineering and Wood393 Technology, at Graz University of Technology (Austria), and Rusticasa are gratefully acknowledged

Rolling Shear Properties of some European Timber Species with Focus on Cross Laminated Timber (CLT): Test Configuration and Parameter Study

ISSN:2199-974

Rolling Shear Strength of Cross Laminated Timber (CLT)—Testing, Evaluation, and Design

Cross laminated timber (CLT), with its typical orthogonal layering and exposure to out-of-plane bending, develops inherent rolling shear stresses. These stresses need to be checked during the ultimate limit state design process. With the ongoing revision of Eurocode 5, a discussion regarding the characteristic value of the rolling shear strength of CLT has arisen. One obstacle in the discussion is seen in the lack of harmonized regulations concerning how to determine rolling shear properties. This circumstance manifests in the greatly diverging test results of different institutions testing the rolling shear strength. The paper at hand aims to propose a candidate for such harmonized regulations. To achieve this, the most common test setups, such as the inclined shear test, three- and four-point bending tests, etc., were numerically and experimentally investigated. Within the numerical investigations, a comparison of the most common calculation methods (Timoshenko beam theory, modified γ-method, Shear Analogy Method, and Finite Element Analysis) for evaluating rolling shear stresses was included. In the experimental program, parameters such as the specimen width, number, and thickness of the cross layer(s), shear length, optional reinforcement against the stresses perpendicular to the grain, and the overall test setup were varied. It was found that the used test setups themselves and the area of the cross layer(s) (shear length, number, and thickness of the cross layer(s)) have a major impact on the rolling shear strength. In contrast, no effect was found from the calculation methods. Based on these findings and on a database of approx. 300 four-point bending rolling shear tests on CLT specimens from five well-established CLT manufacturers, a model for the regulation of the rolling shear strength of CLT is proposed, in combination with a corresponding four-point bending test setup. Afterwards, with two additionally conducted four-point bending test series, the proposed model is successfully validated. The conclusions and recommendations in respect to the test setup (four-point bending), evaluation procedure (Timoshenko beam theory), reference characteristic rolling shear strength, and the model, which allows adapting the reference rolling shear strength to individual conditions, are seen as a worthy basis for a more objective discussion on this topic

Reinforced notched cross-laminated timber plates : Load-bearing capacity and methodology for predicting the force in reinforcement

This paper deals with the estimation of the design force in self-tapping screws used as a reinforcement ofnotched cross laminated timber plates (CLT). With the reinforcement, apart from an increased load-carrying capacity, amore ductile behaviour of this detail can be achieved. An analytical model based on the Timoshenko Beam Theory wasdeveloped, enabling the estimation of the axial force in the reinforcement. A parametric numerical analysis was conductedto verify the model and to provide possible ways for the calibration. The results show a good matching of the model withthe numerical results. The load-bearing capacity is analysed using a simple fracture mechanics model taking intoconsideration the effect of the reinforcement to correctly depict the increase in performance. Theoretical and numericalresults are compared with experimental findings and show acceptable correlations encouraging a further development anda subsequent implementation in EN 1995-1-1

Experimental tests on annular ringed shank nails for seismic resistant Cross-Laminated Timber (CLT) structures

This paper presents an experimental programme on Simpson Strong-Tie annular ringed shank nails, conducted at the Institute of Timber Engineering and Wood Technology, Graz University of Technology. The fastener under investigation is commonly used in cross-laminated timber (CLT) buildings to anchor typical metal connectors to the timber panels, and the understanding of its performances is of particular interest for the design of earthquake resistant timber structures. Shear tests in parallel and perpendicular direction to the face lamination of a CLT panel, and withdrawal tests, investigated the bearing capacity of a nail driven in the plane side of a CLT element. Furthermore, uniaxial tension tests and bending tests were performed on single fasteners to determine the ultimate tensile strength and the yielding moment, respectively. Mean and characteristic values of the mechanical properties were assessed in terms of strength, stiffness and ductility, and compared with the simplified calculation methods provided by the standards. Finally, a numerical model of the connection, considered as a non-linear spring with three degrees of freedom, is presented and calibrated on the experimental results. As an applicative example, the numerical model is used to simulate a shear and a tension test of a Simpson Strong-Tie AE116 angle bracket