Wood Block Tear-Out Resistance and Failure Modes of Timber Rivet Connections: A Stiffness-Based Approach Pouyan Zarnani 1 and Pierre Quenneville, M.ASCE 2 Abstract: Existing prediction models for parallel to grain wood failure in timber connections using dowel-type fasteners consider the mini- mum, maximum, or summation of the tensile and shear capacities of the failed wood block planes. This results in disagreements between the experimental values and the predictions because the stiffness of the tensile and shear planes differs, which leads to uneven load distribution among the resisting planes. The present study focuses on timber rivet connections. A closed-form analytical method is proposed to determine the load-carrying capacity of wood under longitudinal loading in rivet connections in timber products. For the wood strength, the stiffness and strength of the planes subjected to nonuniform shear and tension stresses are taken into account. Furthermore, an algorithm is presented that allows the designer to predict the possible brittle, ductile, and mixed failure modes. The results of tests on New Zealand Radiata Pine Lami- nated Veneer Lumber (LVL) and glulam, and data available from the literature, confirm the validity of this new method and show that this predictive method can be used advantageously in comparison with other existing models. DOI: 10.1061/(ASCE)ST.1943-541X.0000840. © 2013 American Society of Civil Engineers. Author keywords: Wood block tear-out; Connection capacity; Stiffness; Timber rivet; Failure modes; Wood structures. Introduction Connections are often the most critical components of any type of structure. The evaluation of timber buildings damaged after extreme wind and earthquake events has shown that weak con- nections are one of the major causes of problems (Smith and Foliente 2002). From, small diameter fasteners having a significant advantage in timber connection technology, the timber rivet is a well-established example (Williams 2006). Timber rivets are tightly fit fasteners of 40, 65, or 90 mm in length and 3.2 by 6.4 mm in oval-rectangular cross sections used in high capacity steel-timber connections (Begel et al. 2004). Dowel-type timber connections can fail in four different failure modes in loading parallel to the grain (Quenneville and Mohammad 2000), such as row shear, block tear-out, bearing, and splitting failure. The only ductile failure mode is the bearing or embedment failure mode, in which the dowel compresses the wood up to yield- ing, which results in localized wood crushing. Because rivets are small in diameter and installed in small spacing, they do not exhibit row shear or splitting failure modes, which can occur for larger dowel-type fasteners such as bolts. Therefore, for riveted connec- tions, there are two major mechanisms of failure: the brittle tear-out of a block of wood defined by the perimeter of the rivets cluster and the ductile yielding of rivets with wood embedment. The brittle failure mode should be avoided because it results in a sudden collapse of the structure. In addition, as observed in this study, a mixed failure mode (a mixture of brittle and ductile behavior) is also possible and is presented in this paper. Motivation Existing wood strength prediction models for parallel to grain failure in timber connections using dowel-type fasteners consider the minimum, maximum, or summation of the tensile and shear capacities of the failed wood block planes [Eqs. (1)–(3)]. This results in disagreements between the experimental values and the predictions. It is postulated that these methods are not appropriate because the stiffness of the tensile and shear planes differs, which leads to uneven load distribution among the resisting planes (Johnsson and Stehn 2004; Zarnani and Quenneville 2012a). For instance, in a block tear-out failure (Fig. 1), the contribution of the bottom or lateral shear planes to the wood resistance cannot simply be considered as a function of their respective areas because the connection load is not shared uniformly among the resisting planes as a result of the unequal stiffness of the adjacent wood vol- umes loading the fasteners. In the proposed analysis, this short- coming of the existing predictive models is taken into account. Rivets are part of the structural wood design standards of the United States and Canada. However, in the current standards, there is no closed-form solution for the wood strength prediction of this type of connection (Stahl et al. 2004). Also, the standards restrict the use of rivets to specific configurations and for glulam and sawn timber of some limited species. Thus, a closed-form analyti- cal method is desirable to determine the load-carrying capacity of wood under parallel to grain loading in rivet connections for vari- ous timber products. To determine the wood strength of the con- nection, the stiffness of the adjacent loading volumes and the strength of the failure planes subjected to nonuniform shear and tension stresses are considered. The effective wood thickness for the brittle failure mode is derived and related to the elastic defor- mation of the rivets. For the mixed failure mode, the connection strength depends on the governing ductile failure mode of the rivets. To assist the designer, an algorithm is presented that allows 1 Ph.D. Candidate in Structural Timber Engineering, Dept. of Civil and Environmental Engineering, Faculty of Engineering, Univ. of Auckland, 20 Symonds St., CBD, Private Bag 92019, Auckland 1142, New Zealand (corresponding author). E-mail: pzar004@aucklanduni.ac.nz 2 Professor of Timber Design, Dept. of Civil and Environmental Engineering, Faculty of Engineering, Univ. of Auckland, 20 Symonds St., CBD, Private Bag 92019, Auckland 1142, New Zealand. E-mail: p.quenneville@auckland.ac.nz Note. This manuscript was submitted on August 13, 2012; approved on March 15, 2013; published online on March 18, 2013. Discussion period open until March 11, 2014; separate discussions must be submitted for in- dividual papers. This paper is part of the Journal of Structural Engineer- ing, © ASCE, ISSN 0733-9445/04013055(11)/$25.00. © ASCE 04013055-1 J. Struct. Eng. J. Struct. Eng. 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