Light-frame wood structures are the most common type of construction for residential and low-rise buildings in North America. The 2015 edition of the National Building Code of Canada has increased the height limit for light-frame wood construction from 4 to 6 stories. With the increase in building height, it was noticed that light-frame wood structures may be governed by inter-story drift under wind and seismic loads. To reduce the inter-story drift, a hybrid system, consisting of CLT cores and light-frame structures, is proposed. The efficiency of this hybrid system is dependent on the performance of the connections between the two sub-systems. In this project, self-tapping screws (STSs) were used to connect the CLT core and light-frame wood structures on the floor level. Monotonic and reversed-cyclic tests were carried out on CLT-wood frame connections connected with STSs inserted at 45°, 90°, and mixed angles (45° and 90°). The connection performance was evaluated in terms of strength, stiffness, ultimate displacement, ductility, and energy dissipation capacity. Results show that a joint with STSs inserted at 45° had high stiffness and ductility but low energy dissipation, while connections with STSs installed at 90° had high ductility and energy dissipation but low stiffness. Connections with STSs inserted at mixed angles (45° and 90°) achieved the advantages of both configurations when the STSs were inserted at 45° or 90° individually, i.e., high stiffness, ductility, and energy dissipation. The ductility and energy dissipation were significantly improved compared with connections with STSs only inserted at 45° or 90°. This mixed angle connection can be an ideal design for connecting light-frame wood structures to a CLT core to resist wind and seismic load.
According to Eurocode 8 moderate to high dissipative behaviour of timber structures requires sufficient ductility of the critical regions. Earlier experiments on timber connections with slotted-in steel plates and laterally loaded common steel dowels rarely achieved high ductility values. Connections consisting of LVL-C members, dowel-type fasteners with different post-elastic steel properties, full confinement of the timber member and measures to restrain the notch effect were investigated by means of monotonic and cyclic tests with regards to the displacement ductility. The measures taken proved to be effective in enhancing the plastic deformation capacity of the steel dowels to a large extent. However, a new aspect was observed: the constriction of the dowels in the contact area with the plate. The research results provided a better understanding of the factors influencing the behaviour of slotted-in steel plate connection.
Sustainability issues are driving the civil construction industry to adopt and study more environmentally friendly technologies as an alternative to traditional masonry/concrete construction. In this context, plantation wood especially stands out as a constituent of the cross-laminated timber (CLT) system, laminated wood glued in perpendicular layers forming a solid-wood structural panel. CLT panels are commonly connected by screws or nails, and several authors have investigated the behavior of these connections. Glass-fiber-reinforced polymer (GFRP) dowels have been used to connect wooden structures, and have presented excellent performance results; however, they have not yet been tested in CLT. Therefore, the objective of this study is to analyze the glass-fiber-reinforced polymer (GFRP)-doweled connections between CLT panels. The specimens were submitted to monotonic shear loading, following the test protocol described in EN 26891-1991. Two configurations of adjacent five-layer panels were tested: flat-butt connections with 45° dowels (x, y, and z axes), and half-lap connections with 90° dowels. The results were evaluated according to the mechanical connection properties of strength, stiffness, and ductility ratio. The results showed higher stiffness for butt-end connections. In terms of strength, the half-lap connections were stronger than the butt-end connections.
The performance of structural timber connections is of utmost importance since they control the global response of the building. A ductile failure mechanism on the global scale is desirable, especially in the design of structures in seismic areas, where dissipative components in which ductile failure modes need to be ensured are considered. Therefore, the knowledge of possible brittle failure modes of connections is crucial. The paper investigates the brittle failures of laterally loaded dowel-type connections in cross-laminated timber subjected to tensile load in a lap joint configuration through experimental investigations and analytical estimations. A set of 13 different test series has been performed with fully threaded self-tapping screws of 8 mm diameter and different lengths (40 to 100 mm) in cross-laminated timber composed of 3 or 5 layers (layer thickness range from 20 to 40 mm), giving rise to the activation of different brittle failure modes at different depths. Plug shear was among the most typically observed failure modes. A previously proposed model for the brittle capacity was applied to the tested connections at the characteristic level. As shown by the performed statistical analysis, the existing model is not reliable and mainly unconservative. A very low performance is observed (CCC = 0.299), but with a good correlation (c = 0.750) for the tests in the parallel direction. Further research work is required to improve the current model predictions and to gain a better understanding of the underlying resisting mechanisms.
A new timber frame structural system consisting of continuous columns, prefabricated hollow box timber decks and beam-to-column moment-resisting connections is investigated. The hollow box timber decks allow long spans with competitive floor height and efficient material consumption. To achieve long spans, semi-rigid connections at the corners of deck elements are used to join the columns to the deck elements. In the present paper, experimental investigations of a semi-rigid moment-resisting connection and a mock-up frame assembly are presented. The semi-rigid connection consists of inclined screwed-in threaded rods and steel coupling parts, connected with friction bolts. Full-scale moment-resisting timber connections were tested under monotonic and cyclic loading to quantify rotational stiffness, energy dissipation and moment resistance. The mock-up frame assembly was tested under cyclic lateral loading and with experimental modal analysis. The lateral stiffness, energy dissipation, rotational stiffness of the connections and the eigen frequencies of the mock-up frame assembly were quantified based on the experimental tests in combination with a Finite Element model, i.e., the model was validated with experimental results from the rotational stiffness tests of the beam-to-column connections. Finally, the structural damping measured with experimental modal analysis was evaluated and compared with FE model using the material damping of timber parts and equivalent viscous damping of the moment-resisting connections.
The use of moment-resisting frames with semi-rigid connections as a lateral load-carrying system in timber buildings can reduce the need for bracing with diagonal members or walls and allow for more open and flexible architecture. The overall performance of moment-resisting frames depends largely on the properties of their connections. Screwed-in threaded rods with wood screw thread feature high axial stiffness and capacity and they may be used as fasteners in beam-to-column, moment-resisting timber connections. In the present paper, a structural concept for a beam–to-column, moment-resisting timber connection based on threaded rods is presented and explained. Analytical expressions for the estimation of the rotational stiffness and the forces in the rods were derived based on a component-method approach. The analytical predictions for stiffness were compared to experimental results from full scale tests and the agreement was good.
The aim of the study was to create and verify a theoretical model for single-shear steel to bamboo nailed connections in natural bamboo. To this end, existing timber strength and fracture theories were used to model the brittle and ductile failure strength of the studied bamboo connection. Experimental tests of steel to bamboo nailed connection subjected to short-term loading in single shear parallel to fibre direction in Moso bamboo confirmed the suitability of the timber models to predict the connection behaviour. The findings constitute a basis for development of theory for screws, which is the advocated connector type by the authors. It is anticipated that the predictability of bamboo dowelled connection behaviour, along with the latest developments in bamboo design standardization, will enhance the designers confidence to implement dowelled bamboo connections in practice.
Inaccuracies within timber step joints are a perennial problem of the wood construction industry. Even perfectly constructed carpentry step joints can become imperfect due to a change in moisture content. The predominant question when looking at step joints with gaps is to what extent the load-bearing behaviour is influenced by these inaccuracies. The authors look beyond this question and investigate if intentionally manufactured gaps could have a positive influence on the load-bearing behaviour and the failure mode of regular and newly designed carpentry joints.
The use of timber in construction in medium–high rise construction has increased in recent years largely due to the significant innovation in engineered wood products and connection technology coupled with a desire to utilise more environmentally sustainable construction materials. While engineered wood products offer a low-carbon solution to the construction industry, the widespread use of adhesive and metallic fasteners often limits the recyclability of the structural components at the end of life of the structure and it may be beneficial to reduce this where possible.
To establish the possibility of an all-wood connection solution, this preliminary study examines a series of beam-column connections designs to evaluate the relative performance of the different designs, which are connected with modified or compressed wood (CW) connectors. The connection designs are formed between glued-laminated beam and column members in the first instance and later examined when connecting dowel-laminated timber (DLT) members.
The results show that significant moment capacity and rotational stiffness can be achieved for connections solely connected using CW fasteners. Furthermore, the all-wood solution utilising CW fasteners to connect DLT members has also demonstrated significant moment capacity and rotational stiffness capacity without the use of adhesive and metallic components.
The lateral resistance of dowel-type connections with CLT is related to its lay-up, species of the laminations and even the manufacture method. Treating the CLT as homogeneous material, current methods develop new equations through test results or make use of the existing equations for the embedment strength already used in design codes; thus, the lateral resistance of dowel-type connections of CLT can be calculated. This kind of approach does not take the embedment stress distribution into account, which may lead to inaccuracy in predicting the lateral resistance and yield mode of the dowel-type connections in CLT. In this study, tests of the bolted connections and the screwed connections of CLT were conducted by considering the effects of the orientation of the laminations, the thickness of the connected members, the fastener diameter and strength of the materials. The material properties including yield strength of the fasteners and embedment strength of the CLT laminations were also tested. Using analysis of the dowel-type connections of CLT by introducing the equivalent embedment stress distribution, equations for the lateral resistance of the connections based on the European Yield Model were developed. The predicted lateral resistance and yield modes were in good agreement with the test results; the correctness and the feasibility of the equations were thus validated.
This paper presents an investigation of the load-slip behaviour of aluminium-timber composite connections. Toothed plates with bolts are often used for connecting timber structural members with steel structural members. In this paper, toothed plates (C2-50/M10G, C2-50/M12G or C11-50/M12) have been used as reinforcement in aluminium-timber screwed connections for the first time. The push-out test specimens consisted of laminated veneer lumber slabs, aluminium alloy beams, and hexagon head wood screws (10 mm × 80 mm and 12 mm × 80 mm). Of the specimens, 12 additionally had toothed plates as reinforcement, while 8 had no reinforcement. The load carrying-capacity, the mode of failure and the load-slip response of the strengthened and non-strengthened screwed connections were investigated. The use of toothed plate connectors was found to be effective in increasing the strength of aluminium-timber composite connections and ineffective in improving their stiffness. The examined stiffness and strength of the connections can be used in the design and numerical modelling of aluminium-timber composite beams with reinforced screwed connections.
In this paper the load-bearing behaviour of traditional and newly developed timber-timber connections, multi-step and free formed, are analysed within an extensive investigation focusing on joint failure. DIC measurements allowed for an assessment of the initial behaviour of the systems and their specific failure modes. By comparing the stiffness and various load levels to those of typical joint designs the improved load-bearing behaviour of the proposed joints was demonstrated while defining the range of the obtained linear-elastic phase. The results show that the onset of failure, based on the ultimate load, strongly depends on the geometry of the joint.
The present study deals with the innovation and the possibilities of improving the design solution of a frame connection for two selected types of fasteners. All specimens were made of glued laminated timber. Dowel-type mechanical fasteners, a combination of bolts and dowels, and full-threaded screws were used for the connection. The main goal of this research was to replace the typical solution (common dowel-type fasteners) with a more modern, faster, and easier solution in order to improve the load-carrying capacity, ductility, and deformation capacity of this type of frame connection. This article also aimed to provide a detailed evaluation of the mechanical properties of the used glued laminated timber and fasteners in order to comprehensively evaluate the research task. For the design solution, a frame connection created from a system of two struts and a partition was chosen as the basis of the experimental program. Dowel-type mechanical fasteners, as well as combinations of bolts and dowels, were used for the connection; however, in addition to these standardly used mechanical fasteners, full-threaded screws were used. The article describes the use of static destructive testing to determine the ductility of the connection, considering different variations in the strengthening of the individual segments of the mentioned connection means. In the first variation, the individual components of the frame were not reinforced in any way. In the second, the crossbar was reinforced with two full-threaded bolts. In the third, the webs and the crossbar were reinforced with two full-threaded bolts. In the article, these ductility values were compared with each other and the procedure was set by the currently valid standard.
The cost of connections in a mass timber structure can significantly affect the overall project cost; however, because mass timber connection design must consider not only structural design but also aesthetics, fire-rating requirements, constructability, accommodations for shrinkage and swelling, and moisture protection, finding the optimal solution can be challenging. To assist designers in this effort, WoodWorks has published an easy to use index highlighting the spectrum of available structural and architectural mass timber connections. The intent is to facilitate the selection of cost-optimal connection types while balancing other important considerations. This paper focuses on the structural connections in the index, addressing each of these considerations.
This index is a compilation of connections used in mass timber construction. Mass timber elements are solid wood pieces with inherent fire resistance due to their mass, as defined in the 2021 International Building Code (IBC). Examples of mass timber include but are not limited to cross laminated timber (CLT), dowel-laminated timber (DLT), nail-laminated timber (NLT), glue-laminated timber (GLT), mass plywood panels (MPP), and structural composite lumber (SCL) products such as laminated veneer lumber (LVL) and laminated strand lumber (LSL). Mass timber can be used as structural floors, roofs, walls, columns and/or beams. The examples in this index illustrate a broad spectrum of connections for use in mass timber construction. Depending on the unique constraints of each project, the connection choice made by the designer may be influenced by aesthetics, load carrying capacity, fire-rating requirements, quality assurance requirements, cost and/or constructability. The purpose of the index is to facilitate the designer’s selection of project appropriate connections.
The widespread use of energy-intensive metallic connectors and synthetic adhesives in modern timber construction has negative implications for the end-of-life disposal or re-use of the structural timber components. Therefore, it is favourable to substitute metallic connectors and synthetic adhesives with bio-based alternatives such as wood-based connectors. Recent studies have shown that densified or compressed wood (CW) with superior mechanical properties could be suitable for the manufacture of wood-based connectors in the form of CW dowels and CW plates. This study experimentally examines the moment-rotation behaviour of semi-rigid type timber-CW beam-beam connections under pure bending. The study also assesses the suitability of current design rules to predict the moment capacity of timber-CW connections. The comparative study has shown that the moment capacity of the timber-CW connection can be conservatively predicted from the characteristic load-carrying capacity of the connections calculated using the EC 5 strength equations.
This paper discusses the design principles of timber connections for ductility with focus on laterally-loaded dowel-type fasteners. Timber connections are critical components of timber structures: not only do they join members, but they also affect load capacity, stiffness, and ductility of the overall system. Moreover, due to the brittle failure behaviour of timber when loaded in tension or shear, they are often the only source of ductility and energy dissipation in the structure in case of overloading, much like a fuse in an electrical circuit.
This paper addresses current challenges in connection design for ductility, reviews selected best-practice design approaches to ensure ductility in timber connections, suggests simple performance-based design criteria to design connections for ductility, and aims to stimulate a discussion around potential solutions to implement safe design principles for ductile connections in future design codes and connection testing regimes.
This study investigates timber connections with flexible polyurethane adhesives, which prove to have the potential for timber-adhesive composite structures without mechanical connections for seismic regions. Results of conducted cyclic double lap-shear adhesive timber joints tests were compared with available experimental results on timber connections with standard mechanical dowel-type fasteners and with results of numerical finite element analysis. The study found that the shear strength, elastic stiffness and strength degradation capacity of the flexible adhesive connections were significantly higher compared to mechanical fasteners commonly used in seismic-resistant timber connections. The latter, however, manifested larger ultimate displacements but also yielded at lower displacements.
Timber has been used for building construction for centuries, until the industrial revolution, when it was often replaced by steel and concrete or confined to low-rise housings. In the last thirty years however, thanks to the development of mass timber products and new global interest in sustainability, timber has begun to make a resurgence in the building industry. As building codes and public perception continues to change, the demand for taller and higher-performance timber buildings will only grow. Thus, a need exists for new construction technology appropriate for taller mass timber construction, as well as for fabrication and deconstruction practices that respect wood’s inherent sustainable nature. With this in mind, this research program aims to develop a new hybrid shear connection for mass timber buildings that allows for easy construction, deconstruction, and reuse of the structural elements.
This report includes results of Phase 1, which focused on connections consisting of partially threaded 20M and 24M steel rods bonded into pockets formed in CLT and surrounded by thick crowns of high-strength three-component epoxy-based grout. A total of 168 specimens were designed and fabricated, and push-out shear tests carried out with a displacement-controlled monotonic loading protocol. Strength and stiffness values were assessed and effective failure modes in specimens identified. These latter, along with the recorded load-deformation curves, indicate that it is possible to develop mechanics-based design models and design formulas akin to those already used for typical dowel-type fastener timber connections. Additionally, the specimens were easily fabricated in the lab and quickly fastened to the test jig by means of nuts and washers, suggested such connections have a strong potential for prefabrication, disassembly, and reuse.
Timber connections with steel dowel-type fasteners may fail in ductile or brittle ways. The design of this joints was traditionally focused on ductile failure, assuming that brittle failure could be avoided by means of geometrical limitations. However, recent studies demonstrated that these assumptions do not always guarantee ductile failure. A new design model for timber connections with small diameter dowel-type fasteners is provided in this paper. Its improved accuracy is demonstrated by analysing an extensive database of experimental tests and comparing its prediction accuracy to that of existing models.
