sustainability Article Analysis of Rotational Stiffness of the Timber Frame Connection Marek Johanides 1, * , Lenka Kubíncová 1 , David Mikolášek 1 , Antonín Lokaj 1 , Oldˇ rich Sucharda 2 and Petr Mynarˇ cík 3   Citation: Johanides, M.; Kubíncová, L.; Mikolášek, D.; Lokaj, A.; Sucharda, O.; Mynarˇ cík, P. Analysis of Rotational Stiffness of the Timber Frame Connection. Sustainability 2021, 13, 156. https://dx.doi.org/10.3390/ su13010156 Received: 24 October 2020 Accepted: 13 December 2020 Published: 25 December 2020 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: © 2020 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/ licenses/by/4.0/). 1 Department of Structures, Faculty of Civil Engineering, VSB—Technical University of Ostrava, 708 00 Ostrava-Poruba, Czech Republic; lenka.kubincova@vsb.cz (L.K.); david.mikolasek@vsb.cz (D.M.); antonin.lokaj@vsb.cz (A.L.) 2 Department of Building Materials and Diagnostics of Structures, Faculty of Civil Engineering, VSB—Technical University of Ostrava, 708 00 Ostrava-Poruba, Czech Republic; oldrich.sucharda@vsb.cz 3 Department Centre of Building Experiments, Faculty of Civil Engineering, VSB—Technical University of Ostrava, 708 00 Ostrava-Poruba, Czech Republic; petr.mynarcik@vsb.cz * Correspondence: marek.johanides@vsb.cz Abstract: Initially, timber was considered only as an easily accessible and processable material in nature; however, its excellent properties have since become better understood. During the discovery of new building materials and thanks to new technological development processes, industrial process- ing technologies and gradually drastically decreasing forest areas, wood has become an increasingly neglected material. Load-bearing structures are made mostly of reinforced concrete or steel elements. However, ecological changes, the obvious problems associated with environmental pollution and climate change, are drawing increasing attention to the importance of environmental awareness. These factors are attracting increased attention to wood as a building material. The increased demand for timber as a building material offers the possibility of improving its mechanical and physical properties, and so new wood-based composite materials or new joints of timber structures are being developed to ensure a better load capacity and stiffness of the structure. Therefore, this article deals with the improvement of the frame connection of the timber frame column and a diaphragm beam using mechanical fasteners. In common practice, bolts or a combination of bolts and pins are used for this type of connection. The subject of the research and its motivation was to replace these commonly used fasteners with more modern ones to shorten and simplify the assembly time and to improve the load capacity and rigidity of this type of frame connection. Keywords: rotational stiffness; frame connection; screws; glued laminated timber; numerical model; FEM 1. Introduction Wood is a material with highly variable properties [1] and is the only renewable material that is born in nature and disappears without negative consequences for the environment; furthermore, it can be used in construction for the implementation of all load-bearing structures. Among the most influential factors that cause this dispersion of properties is the species of timber and the location in which the timber grew. The soil, climate, altitude, the time of the year in which the tree was cut and, last but not least, the subsequent method and quality of processing have a major impact on the characteristics of timber. In the case of wood as a structural material, either grown wood, which is obtained by cutting from a trunk of coniferous or broadleaved timber [2], or wood-based material such as glued laminated timber [3], which is made by gluing timber laminations to the required size and shape, are considered. The timber exhibits different physical and mechanical properties in mutually perpendicular directions. This means that the characteristics observed parallel to the fibers are different from the properties observed perpendicular to the fibers. Timber has the greatest strength and stiffness and the least deformation due to moisture and temperature in the direction parallel to fibers. The mechanical properties of timber reduce its ability to withstand external loads. In this Sustainability 2021, 13, 156. https://dx.doi.org/10.3390/su13010156 https://www.mdpi.com/journal/sustainability