3D ﬁnite element analysis and experimental investigations of a new type of timber beam-to-beam connection Tomas Gec ˇys a,⇑ , Alfonsas Dani  unas a , Thomas K. Bader b , Leopold Wagner b , Josef Eberhardsteiner b a Department of Steel and Timber Structures, Faculty of Civil Engineering, Vilnius Gediminas Technical University, Sauletekio av. 11, LT-10223 Vilnius, Lithuania b Institute for Mechanics of Materials and Structures, Vienna University of Technology, Karlsplatz 13/202, 1040 Vienna, Austria article info Article history: Received 19 April 2014 Revised 12 December 2014 Accepted 22 December 2014 Keywords: Timber connections Beam-to-beam connections Hill potential function Surface based cohesive contact Semi-rigid connections abstract A new type of semi-rigid timber beam-to-beam connection and its behavior under bending is presented. This connection consists of four identical steel parts, which are inserted into the timber beams in the tension and compression zone of the connection. These steel parts are easily connected by mounting bolts on the construction site. In order to avoid initial slip, gaps between the timber and the steel parts are ﬁlled using two different types of ﬁller materials, namely cement based (CEM) or polyurethane based (PUR) ﬁller. In this study, the connection is modeled by means of the Finite Element (FE) Method and the modeling results are compared to the results of an experimental assessment of the proposed connection under bending. The material model for timber encompasses a Hill criterion in combination with cohesive surface contact in order to depict both, yielding in compression and brittle failure in shear and tension perpendicular to the grain. The experimentally observed decisive failure mode, i.e. shear block failure, could be reproduced by the model. Subsequently, the FE model was used to investigate the effect of using different ﬁller materials, or not considering the ﬁller in the analysis at all. In addition, a particular inﬂu- ence of clamping bolts in the timber on the strength of the connection was revealed. The FE analysis excluding these bolts showed good agreement with the experiments in terms of the strength of the con- nection, while considering these bolts led to an overestimation of the strength. This is a consequence of the considerable inﬂuence of the clamping bolts on stresses perpendicular to the grain in the timber in the block-shear area, and therefore, on shear failure initiation. Using the CEM ﬁller hardly changed the overall behavior of the connection as compared to the analyses without ﬁller material, while the PUR ﬁl- ler leads to a less ductile overall behavior. This is well in line with experimental observations. The appli- cation of modeling approaches for timber has proven suitable for the analysis of such a type of timber beam-to-beam connection and, consequently, might be used for further optimization of this connection. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The most complex and challenging process during the design and analysis of timber structures is the proper design and analysis of timber connections. Particular attention is generally paid to the design of mounting connections for timber elements that exceed the maximum transport or production length. In this case, the con- nection is often designed to bear bending moments, but should also be easy to mount on site. As regards the mechanical behavior of timber connections, they can be idealized as moment rigid or pinned connections in engineering models. Furthermore, several types of fasteners cause relative deformations of adjacent structural elements during load transfer. Consequently, moment-resisting connections of such type of fasteners have to be treated to act semi-rigid. Their mechanical behavior, e.g. bending stiffness or tensile stiffness, is characterized by moment–rotation angle or force–deﬂection curves, respectively [1–4]. According to the cur- rent European design standard [5], the stiffness of connections must be considered in the structural analysis, since it inﬂuences the distribution of internal forces within and the corresponding deformation of a timber structure. The corresponding moment– relative rotation behavior of a new type of timber beam-to-beam connection is investigated in this study. Herein, numerical investigations of this new type of mounting connection are presented. During the design of the connection, special emphasis was given to an easy production and simple assembly at the construction site, in addition to the aim of design- ing a moment-stiff connection. For this purpose, a steel-to-timber connection with steel parts embedded into the timber beam was designed, which will be connected by means of mounting bolts on site. The initial contact between the timber beams and the steel http://dx.doi.org/10.1016/j.engstruct.2014.12.037 0141-0296/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +370 67370775. E-mail address: tomas.gecys@vgtu.lt (T. Gec ˇys). Engineering Structures 86 (2015) 134–145 Contents lists available at ScienceDirect Engineering Structures journal homepage: www.elsevier.com/locate/engstruct