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Large spans structures should ideally be designed so that they work primarily in tension and/or
compression. In fact, minimizing bending moments leads in general to an optimum utilisation of the
structure, regardless what material is chosen. This often results in slender and elegant shapes.
Timber is a structural material which has excellent streng...
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... there is a fundamental discrepancy between the axial force generated in the suspension system and that generated in the arch, being tension in the former and compression in the latter. Therefore, the possibility of premature buckling failure -i.e. a failure which occurs before the ultimate strength of the material has been reached -makes arches less efficient than suspension systems, see Figure 7. ...
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... In historical construction practices, timber was employed as a rudimentary material, often as logs supporting roofs or functioning as two-force members in large-span timber structures (Crocetti 2016). Contemporary engineering practices have shifted towards the utilization of advanced timber elements such as laminated timber (Fleming and Ramage 2020), reinforced timber (Dietsch and Brandner 2015), poststrengthened (retrofitted) timber (Schober and Rautenstrauch 2007), prestressed timber (De Luca and Marano 2012), and post-tensioned timber elements (Wanninger and Frangi 2014;Mei et al. 2023). ...
The paper presents a fully Lagrangian mesh-free solver to simulate the dynamic behavior of post-tensioned timber structures. Weakly Compressible Smoothed Particle Hydrodynamics (SPH) is employed to model both the timber and the tendon. An efficient and simple coupling method between the timber and the tendon is proposed by considering the numerical stability. Besides, the same coupling algorithm is used to model the interaction between column and beam elements. Although the column is treated as rigid in the simulations, the coupling algorithm accounts for the initial compression of the column resulting from post-tensioning. For the verification of the code for solids and material nonlinearity of timber, benchmark problems available in the literature are used. Finally, the solver's capability is demonstrated through dynamic analysis of post-tensioned timber structures. The solutions obtained for all the cases are in good agreement with the experimental and theoretical data, which indicates the applicability and accuracy of the solver.
... Figure 2 shows the veneer-based products in timber connections [10,11]. However, in high-rise timber buildings as well as long-span timber applications, slotted-in steel plates are today the dominant connection technique [12]. For instance, such connections were used in the 18-story timber building ''Mjøstårnet'', located in Brumunddal, Norway, which is one of the world's tallest timber buildings with a height of around 85 m. ...
... where = cos ( ); = sin ( ); is the angle between the load direction and the face grain; 1 , 2 , and 12 are the off-axis stresses in the 1-2 system; and , , and are the on-axis stresses in the x-y system. 1 , 2 , , and are defined as positive in tension and negative in compression while 12 and are positive with the direction shown in Figure 6b and 6c. There is only 1 ( 2 = 12 = 0) in tensile and compressive tests and only 12 ( 1 = 2 = 0) in panel shear tests. ...
Birch (Betula spp.) is a hardwood species with a wide natural distribution on the Eurasian continent, especially in northern Europe. Compared with conventional plywood made from softwood, birch plywood has favorable mechanical properties that could be used in new types of efficient connections for timber structures, and thus enable a substitution of current systems using slotted-in steel plates. Such new connections could result in significant advantages in terms of environmental impact and economy as well as ease of prefabrication and assembly. However, birch plywood has rarely been utilized in connections, and therefore, there is a lack of knowledge necessary to design safe timber structures applying such connection systems. In particular, there is a need for increased knowledge of the mechanical properties of birch plywood and its structural performance under various loading conditions. Current connections in timber structures usually also involve mechanical fasteners, e.g., steel screws and dowels, but there is limited use of adhesively bonded (glued) connections.
The aim of this thesis is to gain new knowledge required for the development of adhesively bonded connections using birch plywood as gusset plates in structural applications. Examples of such structural applications are timber trusses and portal frames. In this context it is necessary, first, to characterize the in-plane mechanical properties of birch plywood, and second, to investigate its performance in adhesively bonded connections.
The results of the mechanical testing show that birch plywood possesses the highest and lowest tensile, compressive, and bending strength and elastic modulus at 0° (parallel) and 45°, respectively, to the face grain (the fiber direction of the face veneers). The opposite findings were noticed for the shear strength and the shear modulus. All these strength values are similar to or higher than the corresponding strength values of common softwood structural timber in its longitudinal direction. Moreover, a size effect on the in-plane bending strength property was observed at 0° and 90° to the face grain but not at other angles, which is attributed to different failure mechanisms. Based on the experimental work, both analytical and numerical models to predict the in-plane mechanical properties of birch plywood are proposed.
Three different adhesives systems were used in the studies: melamine-urea-formaldehyde (MUF), phenol-resorcinol-formaldehyde (PRF), and a two-component polyurethane (2C PUR). All adhesives used show adequate bonding strength between birch plywood and spruce glulam. However, the use of the adhesive systems should be further investigated in the future. The different manual pressing methods investigated show no significant influence on the bonding strength. Moreover, the bonding strength changes within a relatively small range when the loading direction is varied from 0° to 90°, which is beneficial for the design of birch plywood in adhesively bonded connections. A clear correlation exists between the bonding strength and the shear strength of the weakest wood adherend.
In addition, the moment capacity and bending stiffness of adhesively bonded connections using birch plywood were determined experimentally as well as by analytical and numerical models with a satisfactory agreement.
In timber connections, especially those that are prevalently loaded in tension and/or compression (e.g., in timber trusses), the contribution of the plywood width on the load-bearing capacity needs to be quantified. The results show that the tensile strength of birch plywood within the bonded area shows very low angle-dependence. This is possibly due to the restricted crack propagation at 22.5° and 45° when the gap between the bonded regions is small. The tensile capacity of birch plywood loaded at 0°, 22.5°, and 45° reaches a plateau at certain widths of the gusset plate, which can be well predicted and explained by the spreading angle theories proposed in this study.
In the future, more studies are required for the further development of the adhesively bonded connections with birch plywood. Some preliminary studies serving this purpose have been presented in the thesis as on-going work.
... Previous research indicates that wood is a building material with a specific strength. In comparison to metal or concrete, wood is of low density but contains very good mechanical qualities (Crocetti 2016). Michael Foster (1983) noted in his seminal book on the principles of style, structure, and composition that most contemporary buildings erected from any material can be copied identically when replaced with a wooden structure. ...
... The relevance of joints and their impact on timber structures is particularly important when dealing with modern and complex timber structures, such as large-span structures, tall timber buildings, and statically indeterminate timber structures [4,5]. These modern timber structures are typically made from engineered wood products, such as gluedlaminated timber (glulam), laminated veneer lumber (LVL), or cross-laminated timber (CLT). ...
... Joints with laterally loaded metal dowels are, for example, used in combination with slotted-in or outer steel plates in trusses [4], medium-to high-rise buildings [5], and in bridges [21]. In the design, the rotational stiffness of closely spaced small groups of dowels is often neglected even if they are subjected to moment action due to eccentricities [20]. ...
... Axially loaded STS provide high resistance and stiffness; therefore, shear joints with inclined STS are used for high-performance joints, e.g., in moment-resisting joints in domes [4] and grid-shells [25], or in large structures, such as arches as interior joints to restore the continuity of the arch [26], and in beam-column joints [4]. Ductile behaviour of STS joints can be obtained if the screws are mostly laterally loaded or if the screws are placed in a combined arrangement, i.e., inclined and perpendicular to the shear plane [27]. ...
Joints in timber structures are today typically designed in a simplistic manner, i.e., by assuming linear elastic behaviour or neglecting their real stiffness by assuming ideal pinned or fixed conditions. While such assumptions may be acceptable for simple structures, they do not reflect the real behaviour of joints in complex structures, and could, in some cases, lead either to an over-conservative or even unsafe design. Therefore, a more accurate and realistic representation of the nonlinear behaviour of joints with mechanical fasteners is needed. The most common modern timber joints with mechanical fasteners are realized with dowels, bolts, glued-in rods, or self-tapping screws. In this paper, an overview of the impact of the most influential parameters on the shape of the load-displacement curves of these joints under common static loading is given. The joints were differentiated according to the characteristics of their nonlinear load-displacement behaviour. Different analytical models from the literature for the description of the load-displacement curves of timber joints were reviewed. The performance and suitability of these models for describing the variety of nonlinear load-displacement behaviours of joints were evaluated and the advantages and limitations of each model were identified. It was found that the Richard–Abbott model is the most suitable to parametrize a variety of timber joints and to capture the variability of the test data by its parameters. Such an analytical model can be used to incorporate a parametrized, more realistic, nonlinear load-displacement representation of the behaviour of joints in reliability analyses, structural design software, and design guidance for modern timber structures.
... It submitted that until roof is in place on a structure, it cannot be completely called building. Truss is an assemblage of long slender structural elements that are connected at their ends [27,28]. There are several types of roof truss in practice but an acceptable roof truss must be able to fulfill certain conditions; aesthetic (beautiful shape and configuration), economy (relatively cheap), safety (satisfactory in deflection) and stable (all the joints must be balanced, remain in position and not fail under load). ...
The trends of researches in the built industry are exploration of the available alternatives; either as raw materials or finished products construction materials, to most construction materials that have been playing dominant roles in construction industry for decades. Aside that the cost of using them in construction keep rising, the associated health hazards in their production and usage are huge and costly to rectify. The usage of locally available construction materials is being hindered by the lack of useful engineering data of the materials for structural design. Wood is an alternative local, green and sustainable material to steel in roof truss design and construction. Its usage has been limited to short span roof trusses based on inherited knowledge especially in Africa. There is need to know the actual capacity and potential of various wood species in relation to roof design. This work studied the properties of; Gmelina arborea, Tectona grandis (Teak), Terminalia superba (Afara), Ayin (Anogeissus leiocarpus), and Acacia (Robinia pseudoacacia). The values obtained from the laboratory experiments conducted on them were used to design rafter and tie beam of king post roof truss spanned to 12 m and 8 m using timber section 0f 50 mm x 150 mm of all the species. Then section sizes of 150 mm x 250 mm and 250 mm x 350 mm of Acacia were then designed separately. It was found that the five species were not suitable for long span roofing using the chosen three section sizes because the tie beams failed in deflection, which is most critical to deliver a safe, durable and serviceable roof. However, all the species, except Afara, are satisfactory for rafter whose span is not more than 7.5 m. It was also discovered that the higher the section size of timber used in the design the lower the deflection.
... The design of timber connections is of great significance since their performance is decisive for timber structures. In high-rise timber buildings as well as long-span timber applications, slotted-in steel plates are widely used in joints [1]. Nevertheless, plywood plates could be an alternative to slotted-in steel plates. ...
... See Figure 2 for the illustration of plywood applications in timber connections [12,13]. However, in high-rise timber buildings as well as long-span timber applications, slotted-in steel plates are dominant [14]. For instance, the 14story timber building 'Treet', located in Bergen, Norway, is one of the tallest timber buildings worldwide with a height of around 49 m. ...
... In order to study the size effect on the edgewise bending properties, birch plywood beams with the nominal depths of 20 mm and 50 mm (test series No. 01-05 and No. [10][11][12][13][14] were firstly tested in the time sequence. It is found that the size effect on the edgewise bending strength is noticeable on the specimens at 0° and 90° but nearly negligible at 22.5°, 45°, and 67.5° (see Figure 16). ...
... As noticed in Table 5, birch plywood beams were tested at three MC levels, i.e., 7.2%, 11.9% and 21.8%, with the constant nominal depth of 20 mm (test series No. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. See Figure 18 for the test results. ...
Birch plywood has favorable mechanical properties that could be used in new types of connections for timber structures, and thus enable a substitution of the current system with steel plates. Such new connections could result in significant advantages in terms of environmental impact and economy as well as ease of prefabrication and mountability. However, there is a lack of data concerning some of the mechanical properties of birch plywood that would be necessary in order to perform a safe design. In particular, there is a lack of reliable data and understanding of the mechanical properties of birch plywood in directions other than along and perpendicular to the face grain. The aim of this thesis is to gain new knowledge about this anisotropy and to study the variation of the in-plane mechanical properties of birch plywood at different loading angles to the face grain, including effects of size and moisture changes. The goal is that this knowledge will serve as input for the design of birch plywood connections under various loading conditions in timber structures. Specifically, birch plywood specimens were laboratory tested in in-plane tension, compression, shear and bending. The results show that birch plywood possesses the highest tensile, compressive and bending strength and elastic modulus parallel to the face grain and the lowest ones at 45° to the face grain. The opposite findings were noticed for the shear strength and the shear modulus. Moreover, a size effect on the in-plane bending strength property was observed at 0° (parallel) and 90° (perpendicular) to the face grain but not at other angles, which is attributed to the different failure mechanisms. In addition, the increase of moisture leads to the decreased bending strength and elastic modulus in the hygroscopic range. Validated by the experimental work, both analytical and numerical models to predict the mechanical performance of birch plywood under different load conditions and various moisture contents are proposed.
... The standard practice is to locate the highest (G1) veneers in the surface layers and the lowest (G3) veneers in the core to maximise the panel-bending strength and usage of all veneer grades. All the models described in this section are stand-alone programs and have been utilised separately or in combination for training, process optimisation, and product development (Semple & Dai, 2016a, 2016b, 2018a, 2018b, 2018cWang & Dai, 2014). Further work is needed to create a fully integrated model from the process stages to the prediction of the final product mechanical properties and performance. ...
This chapter introduces the history and advantages of long-span timber structures, along with typical structural form and systems. It discusses general aspects of analysis for long-span timber structures, as well as the influence of the span on the structural design of long-span timber structures in terms of structural stability, bracing, and joints/ connections. It describes in detail the analysis and modelling of the typical structural types of long-span timber structures (i.e., trusses, portal frames, arches, suspended structures, domes, and freeform structures), with corresponding recommendations.
... The diagnostics of existing structures is related to the testing of their mechanical properties [1]. The current possibilities of timber processing also allow the design of multistory buildings [2] or long-span structures [3], where it is necessary to respect the experience gained from previous accidents and structural failures [4]. For timber and timber structures, the use of experimental tests of structural details [5,6] or structural parts, e.g., whole frames [7], is very important. ...
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 diagnostics of existing structures and the determination of mechanical properties are closely related to the testing of mechanical properties [5]. The current possibilities of wood processing technology and design of structures allow a wide range of applications from simple structures, through multi-story buildings [6] to long-span structures [7]. However, it is important to take into account the experience from previous accidents and structural failures in design and analysis [8]. ...
With the development of wooden structures and buildings, there is a need to research physical and numerical tests of wood-based structures. The presented research is focused on construction and computational approaches for new types of joints to use in wooden structures, particularly glued lamella elements made of wood and wood-based composites. This article focuses on improving the frame connection of a wooden post and a beam with the use of fasteners to ensure better load-bearing capacity and stiffness of the structure. In common practice, bolts or a combination of bolts and pins are used for this type of connection. The aim is to replace these commonly used fasteners with modern ones, namely full thread screws. The aim is also to shorten and simplify the assembly time in order to improve the load-bearing capacity and rigidity of this type of frame connection. Two variations of the experimental test were tested in this research. The first contained bolts and pins as connecting means and the second contained the connecting means of a full threaded screw. Each experiment contained a total of two tests. For a detailed study of the problem, we used a 2D or 3D computational model that models individual components, including fasteners.
