According to the harmonized European design code for timber structures, Eurocode 5, all pitched timber trusses are designed as an in-plane structure, meaning that the bracing systems used are assumed to prevent the out-of-plane failure of the truss if sufficient strength and stiffness are provided. The present paper studies how the stiffness of a wooden bracing system contributes to the out-of-plane stability of a trussed roof structure. Results from numerical simulations indicate that significant bracing forces may occur in compressed structural members for long-span timber structures. As well, the values obtained from the calculations according to Eurocode 5 are occasionally far from the results obtained by numerical simulations.

Plastic design methods can be used for determining the load-carrying capacity of partially anchored shear walls. For such walls, the leading stud is not fully anchored against uplift and tying down forces are developed in the sheathing-to-framing joints and the bottom rail will be subjected to crosswise bending, leading to possible splitting failure of the rail. In order to use these plastic design methods, a ductile behaviour of the sheathing-to-framing joints must be ensured. In two earlier experimental programmes, the splitting failure capacity of the bottom rail has been studied. Two brittle failure modes occurred during testing: (1) a crack opening from the bottom surface of the bottom rail and (2) a crack opening from the side surface of the bottom rail. In this article, a fracture mechanics approach for the two failure modes is used to evaluate the experimental results. The comparison shows a good agreement between the experimental and analytical results. The failure mode is largely dependent on the distance between the edge of the washer and the loaded edge of the bottom rail. The fracture mechanics models seem to capture the essential behaviour of the splitting modes and to include the decisive parameters.

Light-frame timber buildings are often stabilized against lateral loads by using diaphragm action of roofs, floors and walls. The mechanical behavior of the sheathing-to-framing joints has a significant impact on the structural performance of shear walls. Most sheathing-to-framing joints show nonlinear load-displacement characteristics with plastic behavior. This paper is focused on the finite element modeling of shear walls. The purpose is to present a new shear connector element based on the theory of continuum plasticity. The incremental load-displacement relationship is derived based on the elastic-plastic stiffness tensor including the elastic stiffness tensor, the plastic modulus, a function representing the yield criterion and a hardening rule, and function representing the plastic potential. The plastic properties are determined from experimental results obtained from testing actual connections. Load-displacement curves for shear walls are calculated using the shear connector model and they are compared with experimental and other computational results. Also, the ultimate horizontal load-carrying capacity is compared to results obtained by an analytical plastic design method. Good agreements are found.

A stiffness model for inclined screws in timber joints, or as shear connectors in composite timber-to timber members, is presented. Elastic conditions applicable to the initial or linearized part of the load deformation response in the serviceability limit state are assumed. The model for the stiffness or slip modulus is general in nature; it includes both the dowel (or shearing) action and withdrawal action of the screw, the friction between the members and it takes into account possible dissimilar properties and geometries of the different parts of the joint configuration. The model is simplified in the sense that the screw is assumed rigid and the withdrawal stresses along the length of the screw are assumed evenly distributed. However, the effects of flexibility and extensibility of the screw are taken into account by applying a theoretically derived correction factor for the embedment and withdrawal stiffness modulus, respectively. The proposed model is illustrated showing the total stiffness versus the inclination, as well as the relative contributing effect from the shearing and withdrawal stiffness, respectively, the influence of the friction coefficient. Also, the effect of dissimilar properties and geometries between the two parts of the joint is illustrated. Experimental verification of the proposed model is also given. Comparisons with other stiffness models are also made. (C) 2017 Elsevier Ltd. All rights reserved.

Theauthors present an experimental and analytical study of slotted-in connections for joining walls in the Masonite flexible building (MFB) system. These connections are used for splicing wall elements and for tying down uplifting forces and resisting horizontal shear forces in stabilizing walls. The connection plates are inserted in a perimeter slot in the PlyBoard (TM) panel (a composite laminated wood panel) and fixed mechanically with screw fasteners. The load-bearing capacity of the slotted-in connection is determined experimentally and derived analytically for different failure modes. The test results show ductile postpeak load-slip characteristics, indicating that a plastic design method can be applied to calculate the horizontal load-bearing capacity of this type of shear walls.

The authors have developed a new plastic design method for light-framed timber shear walls, which is capable of analysing the load-bearing capacity of partially anchored shear walls. For proper application of the plastic method it is necessary to ensure ductile behaviour of the sheathing-to-framing joints and to avoid brittle failure of the bottom rail. In a partially anchored shear wall, the tying down forces are developed in the sheathing-to-framing joints along the bottom rail, which may introduce a brittle type of failure of the bottom rail that needs to be eliminated in order for the plastic method to be applicable. This paper deals with design of anchor bolts needed to tie down the bottom rail properly and it describes experimental results for proper design of washers for anchor bolts to avoid these splitting failures of the bottom rail. The effect of different washer sizes and location of the anchor bolts on the failure load when splitting of the bottom rail occurs is presented. The tests indicate that the failure load depends on the distance from the edge of the washer to the loaded edge of the bottom rail. An explicit design equation for the capacity of the bottom rail is presented.

The authors have developed a plastic design method for sheathed timber frame shear walls. It has been presented and discussed for inclusion in Eurocode 5 and a Swedish handbook has been presented. In the plastic method, you can choose to transfer the anchoring force via the leading stud to the substrate, corresponding to a fully anchored shear wall (no uplift of studs), but you can also choose to utilize the sheathings to transfer the tensile force via the sheathing-to-framing joints to the substrate by anchoring the bottom rail, corresponding to a partially anchored shear wall (studs experience uplift). By the plastic method several alternatives for anchoring the wall are possible and they can also be combined in such a way that each of them take a portion of the uplifting force, e.g. through a simple tying down device, through the sheathing-to-framing joints and through anchoring of the shear wall to the transverse wall. The method also makes it possible to include the load-bearing capacity of wall segments including openings. The handbook treats primarily shear walls, but for the sake of completeness some aspects of the roof and floor diaphragms are also discussed. The interior force distribution in sheathed timber frame walls weak in shear is discussed, as are the fundamental difference between the effect of vertical loads on the stabilisation of walls which are rigid or weak in shear, and how the plastic design method is applied to multi-storey timber buildings. (C) 2016 The Authors. Published by Elsevier Ltd.

In this part 2, the practical design and strength of a number of different joints is described: (1) Sheathing-to-framing joints the plastic design method is based on the premise that the load-displacement relationship of the sheathing-to-framing joints has sufficiently large plastic deformation capacity; the sheathing-to-framing joints have great influence on the load-carrying capacity of the wall; (2) Stud-to-rail joints by utilizing the shear capacity of the stud-to-rail joints, the plastic design method can be simplified and the load-carrying capacity can be increased; (3) Hold down devices for the (leading) stud - the capacity of the tying down force of the hold down determines whether the shear wall will act as fully or partially anchored; tying down the shear walls by connecting them to the transverse walls leads to a 3-dimensioonal behaviour that is a very favourable for the load-carrying capacity and the stiffness of the shear wall; through transverse walls the anchoring of the leading stud can be reduced or eliminated (those types of transverse wall connections are not discussed in detail in this paper); and (4) Anchoring devices for the bottom rail in - partially anchored shear walls it is necessary that the bottom rail is anchored to the substrate against uplift. Characteristic values for the different types of joints are given. Also, joints between the panels in the walls, roofs and floors are described briefly. (C) 2016 The Authors. Published by Elsevier Ltd.

Design of shear walls has been a topic of major discussions to develop a common European code for design of timber structures. The main problem has been that shear walls are fastened to the substrate in different ways in different countries and that this fact must be reflected in the code. In this part the requirements are given that must be met for the ductile characteristics of the sheathing to-framing joints in order for the plastic design method to be applicable. The method is based on the plastic lower bound theory. The fundamental prerequisites for the method are that the static equilibrium for the structure is fulfilled and that the sheathing-to framing joints are ductile. What requirements that should be made on the mechanical properties of the joints for the plastic design methods to be applicable and the precaution measures to take to avoid brittle behaviour are discussed. The two main principles for anchoring of sheathed timber frame shear walls, fully and partially anchored, are illustrated showing the static behaviour of the walls and the force distribution in the framing members and the sheathings. In addition, a general description of the design in the serviceability limit state is given. For medium-rise and taller buildings the serviceability limit state needs to be taken into account. There are no specified criteria for deformations in the present code. (C) 2016 The Authors. Published by Elsevier Ltd.