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

Report on the seismic performance of three-dimensional moment-resisting timber frames with frictional damping in beam-to-column connections

The seismic performance of three-dimensional moment-resisting timber frames with frictional damping devices was investigated experimentally. This article describes a novel three-dimensional beam-to-column connection which was designed to behave rigidly up to moderate seismic intensities and to start the frictional dissipating behavior at higher intensities. The three-dimensional beam-to-column connection component was initially tested under cyclic loading, and then the connection was mounted in a three-level prototype frame and tested on a shake table. From the cyclic loading tests, the energy dissipation of the proposed beam-to-column connection was higher than the equivalent rigid connection. The frame demonstrated self-aligning capabilities without permanent drift at seismic intensities up to 1.4 g and maintained strength up to high seismic intensities of 2 g. Because wood frames allow for large elastic deflections and can exhibit excellent self-aligning capabilities (i.e., connections tolerate large rotations within safe stress levels), the proposed frictional beam-to-column connection is a promising alternative for moment-resisting timber frames that can be used to prevent structural members from reaching critical stresses