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Theory of timber connections
... The monotonic load-carrying capacity of timber connections subjected to common loading scenarios have been extensively studied [110,111,112,113,114,115,116,117,118,119,120,121,122]. One of the most common connection typologies is a timber connection comprising laterally loaded dowel-type fasteners with slotted-in steel plates. ...
... One of the most common connection typologies is a timber connection comprising laterally loaded dowel-type fasteners with slotted-in steel plates. The resistance models for such connections are well established and is also reflected in design standards, such as the EN 1995-1-1:2004 [83,110,123]. However, most design standards usually use empirical formulas for the monotonic stiffness of such fasteners [124,83] and are not able to accurately predict the resistance curve including failure [119]. ...
... As a simplification, it is assumed that the elastic limit F v,y,i , δ y,i and ultimate capacity F v,u,i , δ u,i can be determined using the European yield model for a single slotted-in steel plate [83,110]: Based on recommendations by Ottenhaus et al. [108], the yield moment of the fastener M y = π f y d 3 /32 was used and the ultimate moment of the fastener M u = 0.3 f u d 2.6 according to EN 1995-1-1:2004 [83]. The mean yield stress f y = f y,k exp (1.5 · 0.07) − 20 (N/mm 2 ) and mean ultimate stress f u = 1.4 f u,k were determined in accordance with the probabilistic description recommended by the Joint Committee on Structural Safety [208]. ...
The primary function of buildings is to provide safety and shelter from the environment and a functional space for human activities. To ensure their safety, design standards provide guidance on the minimum requirements and how they can be fulfilled. In the vast majority of cases, this approach is successful and we as a society witness relatively few failures and collapses of buildings. Nevertheless, some buildings may fail to provide safety and shelter and instead become a hazard to their occupants.
Current design standards consider plausible loading scenarios from the intended usage, environmental loads, and accidental loads. However, abnormal loading scenarios from human errors and malicious actions are not considered directly. Because of the increasing frequency of malicious actions and abnormal environmental loads, the societal losses are likely to increase in concurrence with the amount of collapses.
To account for abnormal loading scenarios, design standards use threat-independent robustness measures. Robustness refers to the ability to maintain a function after sustaining damage, or the insensitivity to initial damage. The insensitivity can be interpreted that the final consequences should not be disproportionately large to the initial damage. In buildings, it means that an initial damage should not lead to a disproportionately large collapse. However, most robustness measures in design standards were developed for reinforced concrete and steel buildings and may be detrimental if directly applied to buildings comprising other materials, such as timber. Because of the immaturity compared to buildings comprising traditional building materials, their robustness properties are largely unknown. In combination with the recent increase of modern timber buildings, this poses a large risk potential. Therefore, research on timber-specific robustness and implementing results into design standards is time critical. However, this requires the analysis of progressive collapse, which may not be trivial.
Progressive collapse can be defined as the spreading of failures in a chain reaction and often requires complex and computationally expensive models. For instance, collapse is associated with phenomena like large deformations and the inelastic behaviour of materials. It is also a highly dynamic process and may involve hysteresis, changing damping properties, and impact loading from falling debris. Despite the challenges, a model capable of analysing progressive collapse can be used to make risk-informed decisions about robustness measures in design standards to maintain and increase the safety of buildings.
To this end, a modelling framework for the progressive collapse of timber buildings was developed. It uses a combination of finite element analysis, analytical equations, and results from impact loading tests. The modelling framework can simulate the progressive collapse of timber buildings with members following an orthogonal grid subjected to arbitrary initial damage scenarios and includes features, such as element erosion, debris impact loading, connection hysteresis, and incremental equivalent viscous damping. With some adjustments, the modelling framework can be extended to include other materials.
The modelling capabilities were demonstrated on a multi-storey timber building subjected to various column-loss scenarios in Switzerland. For the column-loss scenarios, the corresponding final consequences associated with the loss of materials and life were quantified. They showed that the material losses were inconsequential compared to the loss of life. The consequences were used to assess the risk of the building when considering human errors and malicious actions. Based on this, most of the available resources should be used to reduce human errors. Besides these applications, risk and damage-based methods to quantify the robustness were compared and their practical implications were discussed.
... The handbooks are used in conjunction with existing structural design standards for timber structures such as Eurocode 5 (EC5) [5] in Europe. According to EC5 and the European Yield Model (EYM) [6] that is applied for the design of timber connections, embedment strength is one of the factors that influences the shear capacity of laterally loaded timber connections. According to EN 383 [7], the embedment strength is defined as the maximum force the fastener exerts on the projected area of the fastener in the timber matrix, when displaced up to 5 mm. ...
... The study [13] showed that in addition to the CLT layer build-up, the dowel diameter, characteristic density of the timber, and the outer layer's grain direction in relation to the load direction, influence CLT embedment strength. The dependence of the embedment strength of wood on the load angle in relation to the grain orientation is well researched [6,11,12,[16][17][18][19][20][21]. However, the dependence of CLT embedment strength on the CLT outer layer's grain orientation is less investigated. ...
... The first batch consisted of 5 boards (TB3, 8,13,16,17 ) each 47 mm thick by 150 mm wide by 4800 mm long. The second batch consisted of 12 boards (TB1, 2,4,5,6,7,9,10,11,12,14,15), each 25 mm thick by 100 mm wide by 4800 mm long. The timber boards were placed in a climate chamber for six months, at a relative humidity of 65% and a temperature of 20 • C, for conditioning to an equilibrium moisture content of about 12% according to EN 383 [7]. ...
Cross-laminated timber (CLT) has become popular as a construction material and the design of CLT connections is typically based on empirical equations with an average embedment strength of the wood-based product. The experimental study presented herein aims at enhancing the understanding of the relationship between the CLT embedment behaviour and the single layers it is composed of. Non-linear embedment stress–displacement relationships were measured in 244 full-hole and half-hole embedment tests on structural timber boards as well as on CLT produced of parts of the same boards. Three different fasteners, namely a steel dowel with a diameter of 12 mm and the threaded part of screws with a nominal diameter of 6.5 mm and 10 mm, were studied. The design of the experiments allowed to validate a simple mechanical model with parallel springs for the CLT, which showed good agreement with experiments. In addition to a validation of the non-linear spring model, this unique experimental data-set is further exploited in a comparison with empirical equations and for the derivation of a non-linear embedment ratio, between parallel and perpendicular to the grain embedment stresses, over the displacement. Knowledge of the relationship between the non-linear embedment behaviour of the single layers and the CLT element can be further exploited in the engineering design and numerical modelling of CLT connections with dowel-type fasteners.
... The analysis concerns the shear capacity per shear plane per fastener. As mentioned earlier in Section 2.3, according to the recommendations by Eurocode 5, the shear capacity is divided into the dowel (Johansen) part and the rope effect part [25,39]. ...
... According to the recommendations by Eurocode 5, the first term of Equations 7 and 8 is the so-called dowel part or the Johansen part [25,39], which is calculated considering the embedment failure of fasteners in timber and the yielding pattern of fasteners. ...
... The second term Fax,R 4 in Equations 7 and 8 is the contribution from the screw withdrawal capacity due to the rope effect [25,39]. ...
This study investigates frame corner joints built of birch plywood plates and glulam elements connected via self-tapping screws. Analytical calculations based on the fastener group's torsional moment resistance, the proposed fastener group's elastic and post-elastic load-bearing criteria, and the design formulas in Eurocode 5 were performed to predict the connection capacity in both elastic and post-elastic stages. A combined action check formula was adopted to predict the capacity of birch plywood plates and glulam elements. Frame corner specimens constructed with three different plywood thicknesses were planned to study the influence on global behavior and rotational stiffness. The specimens were intentionally designed so that failure occurred either in plywood or in glulam, in order to examine the robustness and validity of analytical calculation models. Another supplementary test group with 21 mm plywood and fewer fasteners was also designed and tested, in which the plastic yield of fasteners was expected. The test results of this supplementary group served to calibrate the analytical model that predicts the elastic and post-elastic capacity of the connection group. As a result of the comparison, the analytical calculations gave reasonable predictions on the failure of plywood, glulam, and the capacity of the fastener group. Only when the exposed moment exceeded the post-elastic limit of the fastener group did the plastic yielding of fasteners become observable. Moreover, numerical finite element models adopting the foundation zone-modeling scheme were constructed, which were proven to capture all test configurations' linear loading stiffness satisfactorily.
... Several studies have pointed out that low connection stiffness produces excess deformation, especially in large-span structures [12,13]. However, the current research on engineered bamboo bolted connections primarily focused on load-carrying capacity calculation methods based on European Yield Modes (EYM) [14][15][16][17][18][19][20], the performance of beam-column connections [21][22][23][24], and influencing factors on connection properties [25][26][27], while there is a lack of specialized research on the stiffness of engineering bamboo dowel-type connections. In addition, among national standards such as CSA [28], Eurocode 5 [29], NDS [30], and GB 50005 [31], only Eurocode 5 provides an empirical stiffness estimation method for dowel-type connections based on a large number of test results with the consideration of the wood density and dowel diameter, which does not account for the embedment stiffness of wood and the bending stiffness of dowels. ...
... This paper aims to develop a model for the elastic stiffness of bolted steel-bamboo scrimber-steel (SBSS) connections, which consist of a bamboo scrimber member, two steel plates, and a bolt, in bamboo scrimber structures, based on the simplified BEFT [34] and the double-shear yield mode, which is included by EYM [20]. Specifically, the method focuses on calculating the contact stiffness between the bolt and the pre-drilled hole wall, as well as the shear load applied to the bolt end by the steel plate. ...
... According to the EYM [20], the SBSS shear connections with bolts can fail by either yielding of the bamboo embedment or the bolt, while the failure of the steel plate embedment is neglected since the yield strength of the steel plate is much greater than that of the bamboo scrimber and the flexural strength of the bolt. As shown in Fig. 2, based on this assumption, the bolted SBSS connections can fail in three different ways under in-plane force: mode I, mode III, and mode IV. ...
... Estruturas de madeira, conexões e método de elementos finitos Fonte: Do Autor. No entanto, a teoria de Johansen (1949) não contemplava a elaboração de ligações com peças de madeira que apresentavam diferentes resistências ao embutimento. Tendo em vista essas limitações Möller (1951apud Meyer, 1957 ampliou a abrangência do método, tornando possível a utilização de peças de madeira com diferentes resistências ao embutimento para compor a ligação. ...
... Durante a revisão de literatura com a temática estimativa de força última e fratura em estruturas de madeira verifica-se a existência de vários modos de fratura (JOHANSEN, 1949;MÖLLER, 1951APUD MEYER 1957BLASS et al , 1999;MILCH et al , 2017;BLASS E LASKEWITZ, 2023). Para cada tipo de fratura é apresentado um modelo desenvolvido utilizando pesquisas experimentais e numéricas. ...
The use of wooden structures is widespread in countries located in the Northern Hemisphere. The wide use of wood is justified by its high strength and weight ratio, low energy consumption and reliability in structural applications. In Brazil, despite the extensive number of species in the territory, its use is restricted to lattice roof structures. However, the combination of wood with current technologies allows the use of this material in large structures. Large structures, in height and/or in span, require structural elements with large cross-sections and connections between elements. Therefore, connections have become an important and common element in these structures. With the aim of improving the structural behavior of wooden parts, several studies use composite materials reinforced with fibers, the main ones being: Fiberglass (GFRP) and Carbon Fiber (CFRP). The use of these materials increases the resistance of structural components. These materials used for reinforcement are available in different shapes and sizes, such as: sheets, fabrics, plates and bars. This article aims to present a Systematic Literature Review, produced in recent years, with research related to the areas of connections in wooden structures and the use of composite materials. The searches for works on this topic included international literature, considering the years 2010 to 2023. The Systematic Literature Review process was carried out with the help of the StArt software. After the Systematic Literature Review found that connections are the points that present the greatest conditions for collapse of the structure, much of the research analyzes the mechanical behavior of connections using numerical simulation. The use of composite materials stands out as reinforcement of structures, being little used as reinforcement in connections.
... The yielding load of the fastener F 0,f can be predicted starting from the knowledge of the maximum force F max,f determined according to EN 1995EN :2004 and Johansen's theory for timber-to-timber joints [46], assuming a fastener sufficiently slender to develop two plastic hinges. Then, F 0,f can be estimated as F max,f /8 for screws, and 0.4F max,f for nails, in agreement with prior experimental tests [7,13,32]. ...
... In Eqs. 2 and 3, u max,f is the slip of the fastener at F max,f ; this can be estimated as u max,f = (b 1 +b 2 )tanα [32], with (b 1 +b 2 ) distance between the two plastic hinges of the fastener in the two members of the joint according to Johansen's theory [46], and α angle at which the yield moment of the fastener is evaluated, according to EN 409:2009 [47]. ...
The application of timber-based strengthening solutions to existing wooden and masonry structures, combines several benefits, such as reversibility, compatibility, lightness, sustainability, affordability, and effectiveness. With reference to existing timber floors, an efficient method to enhance their seismic response is the fastening of an overlay of plywood panels to the existing sheathing, an intervention that greatly improves in-plane strength, stiffness, and energy dissipation. In order to promote the use of this retrofitting solution in practice, this work presents a set of calculation tools supporting the design and advanced numerical modelling of timber diaphragms strengthened with plywood panels. The suite of tools allows to first estimate the full nonlinear, cyclic in-plane response of the strengthened diaphragms starting from the geometrical and material properties of the existing sheathing and the plywood overlay, as well as the mechanical characteristics of the fasteners. As second step, such estimated in-plane response can be transformed into a constitutive law for performing nonlinear numerical simulations, by means of a user-supplied subroutine developed for finite element software DIANA FEA. The presented calculation examples and the performed validation against reference studies from literature, show that the developed tools can provide an accurate estimate of the in-plane response of the diaphragms, and enable an efficient numerical simulation of their seismic behaviour. The implemented tools can be used to both obtain preliminary indication for plywood-based seismic retrofitting design, and to calibrate the interventions on existing diaphragms based on the specific characteristics and needs of a building, relying on the adaptability and versatility of this strengthening method.
... Estruturas de madeira, conexões e método de elementos finitos Fonte: Do Autor. No entanto, a teoria de Johansen (1949) não contemplava a elaboração de ligações com peças de madeira que apresentavam diferentes resistências ao embutimento. Tendo em vista essas limitações Möller (1951apud Meyer, 1957 ampliou a abrangência do método, tornando possível a utilização de peças de madeira com diferentes resistências ao embutimento para compor a ligação. ...
... Durante a revisão de literatura com a temática estimativa de força última e fratura em estruturas de madeira verifica-se a existência de vários modos de fratura (JOHANSEN, 1949;MÖLLER, 1951APUD MEYER 1957BLASS et al , 1999;MILCH et al , 2017;BLASS E LASKEWITZ, 2023). Para cada tipo de fratura é apresentado um modelo desenvolvido utilizando pesquisas experimentais e numéricas. ...
O uso de estruturas de madeira é amplamente difundido em países localizados no Hemisfério Norte. A grande utilização da madeira é justificada por apresentar alta relação resistência e peso, baixo consumo de energia e confiabilidade em aplicações estruturais. No Brasil, apesar da extensa quantidade de espécies no território o uso se restringe em estruturas treliçadas de telhados. No entanto, a combinação da madeira com as tecnologias atuais permite a utilização desse material em estruturas de grandes dimensões. Grandes estruturas, em altura e/ou em vão, requerem elementos estruturais com grandes seções transversais e conexões entre os elementos. Portanto, as conexões se tornaram um importante e usual elemento nessas estruturas. Com o objetivo de melhorar o comportamento estrutural das peças de madeira, diversas pesquisas utilizam materiais compósitos reforçados com fibras, sendo os principais: Fibra de vidro (GFRP) e Fibra de Carbono (CFRP). A utilização desses materiais provoca o aumento de resistência dos componentes estruturais. Esses materiais utilizados para reforços são disponibilizados em formatos e tamanhos diversos, como: lâminas, tecidos, chapas e barras. Este artigo tem como finalidade apresentar uma Revisão Sistemática de Literatura (RSL), produzida nos últimos anos, com pesquisas relacionadas às áreas de ligações em estruturas de madeira e o uso de materiais compósitos. As pesquisas por trabalhos nesta temática compreenderam literatura internacional, considerando os anos de 2010 a 2023. O processo de RSL foi realizado com o auxílio do software StArt. Após a realização da RSL verificou que as conexões são os pontos que apresentam a maiores condições para colapso da estrutura, grande parte das pesquisas analisam o comportamento mecânico de ligações utilizando se simulação numérica. O uso de materiais compósitos se destaca como reforços de estruturas, sendo pouco utilizado como reforço nas conexões.
... When designing dowel-type connections loaded parallel to the grain, brittle failure modes as those illustrated in Figure 2 must be taken into account. In EC5 [3], the design is based on the Johansen yield theory [8], which assumes ductile failure modes by plastic deformations of the dowel and/or the timber. In addition, minimum edge and end distances are given in the code, together with a reduction factor of the effective number of dowels in a row. ...
... This study has focused on acetylated wood and the increased brittleness obtained due to the acetylation. However, it should be emphasised that the conclusions drawn in regard to the influence of material brittleness on the mechanical behaviour of dowel-type joints can be generalised (see Equation (8) and the related discussion in Section 2.3.3). Consequently, the results and the below discussion are relevant for situations that involve altered material brittleness in general, not only for acetylated wood. ...
This paper presents an experimental study where the mechanical behaviour of single-dowel timber connections made of acetylated Scots pine is compared with the behaviour of connections made from untreated Scots pine. The main aim was to evaluate the influence of the acetylation on the connection brittleness and also to compare the experimental results to the design provisions of the current European structural timber code, Eurocode 5 (EC5). The experiments included embedment tests and tests with connections loaded parallel and perpendicular to the grain, and, for the latter tests, applying different end and edge distances. The acetylated wood showed a 2% increase in density and a 31% increase in embedment strength compared to the untreated wood. For tests on connections loaded parallel to the grain, all specimens made from acetylated wood failed in a brittle manner, while the connections made from untreated wood and complying with minimum end distance of the EC5 design provisions failed due to embedment failure followed by splitting involving cracking along the grain. The connections made of acetylated wood showed a 13–15% higher capacity than the corresponding specimens made from untreated wood. Thus, to fully utilize the potential of the increased embedment strength parallel to the grain, it is concluded that reinforcement of the joint, e.g., by self-tapping screws or externally applied sheet reinforcement would be necessary if the minimum end distances of EC5 are applied. The current design provisions for loading perpendicular to the grain overestimated the capacities severely with predicted characteristic values being 20–50% higher than mean values from tests for the recommended minimum edge distances. Finally, it was found that the splitting capacity in loading perpendicular to the grain was 10–18% lower for the specimens made from acetylated wood compared to the untreated wood.
... with a steel plate thickness, , between the radius, , and the diameter, , of the dowel i.e. < < , EC5 proposes a linear interpolation using Eqs. (8) and (9). This method was used to determine the shear capacity of the connection and yielded an interpolated shear capacity of 14 by 19%. ...
... The thick steel plate causes clamping of the steel fastener at the steel plate, thereby allowing for the development of a plastic hinge, see failure modes 2.2 and 2.3 in Eq. (9). Conversely, no clamping occurs when a thin steel plate is used in the connection and the fastener can rotate freely at the steel plate, see failure modes 1.1 and 1.2 in Eq. (8). In this parameter study, the relationship between dowel diameter and steel plate thickness on the shear capacity and slip modulus of the connection was studied. ...
In this study, a numerical model that aimed to predict the strength and stiffness, of a single laterally loaded mechanical fastener in steel-to-cross laminated timber (CLT) connections using a Beam-on-Foundation (BoF) model, is presented. The BoF model was used to predict the ductile failure modes of steel-to-CLT connections and considered the layered structure of CLT. When compared to the European Yield Model (EYM), the BoF model was found to be advantageous as it not only predicted the strength but also the stiffness of the connections. A comparison of the slip modulus and strength from BoF model simulations of experimental tests carried out on steel-to-CLT connections showed good agreement with the experimental results. Using the BoF model, the influence of; (i) density, (ii) deck layer orientation, (iii) embedment behaviour, (iv) dowel diameter, (v) steel plate thickness, and (vi) embedment length, on steel-to-CLT connections was investigated in a parameter study. The results presented herein highlight the benefit of the BoF model that considers CLT layer specific embedment behaviour in determining the shear capacity and stiffness of steel-to-CLT connections.
... A more elementary model that assumes the screw to behave as a rigid body is presented in [23]. For predicting the capacity of doweltype fasteners, the Johansenn model [24] and its extensions [5,[25][26][27] are currently adopted. However, due to the interaction between the axial and transversal behavior of the screw, existing models might not be accurate for inclined screw connections [19]. ...
... (21)). According to Johansen theory [24], the transversal strength of a dowel-type fastener is given by Eqs. (21). ...
Timber structures are susceptible to sound propagation problems. The issue can be mitigated by decoupling structural components at connections level by means of polyurethane soundproofing interlayers. These layers are much softer than timber but, at the same time, they are characterized by higher friction coefficients. In this paper, an experimental investigation is carried out to characterize the mechanical behavior of insulated screw connections assessing the implications of the soundproofing layer use. Different interlayers, screw inclination angles and setups are considered. The load–slip behavior is studied, and a proper empirical model, suitable for performing push-over analysis of buildings involving soundproofed connections, is derived. The essential design parameters, namely the slip modulus, the strength and ductility, are determined and compared with existing models predictions, thus testing their accuracy. Substantial reductions in terms of stiffness, load-carrying capacity and ductility are observed in soundproofed connections.
... In the case of seismic-resistant structures, screw connections must fulfil two main requirements: (i) adequate capacity and (ii) high ductility (Eurocode-5 2004). Based on the European Yield Model derived from Johansen's work (Johansen 1949), the capacity estimation was thoroughly studied in the last decades through experimental, finite element (Stamatopoulos and Malo 2016) and analytical investigations . ...
... The connections exhibit a ductile behaviour with the formation of two plastic hinges, except for the interlayer configuration with three hinges. This failure mode is the most ductile among those predicted by the European Yield Model derived from Johansen's work (Johansen 1949). Figure 11 plots the relative and absolute wood deformation energy vs. maximum displacement. ...
Inclined screws represent a typical connection solution for timber structures. They can provide higher capacity and stiffness due to the combined axial-shear interaction. This paper investigates the effect of engineering wood products choice (glued-laminated timber and cross-laminated timber), fibre inclination, friction, and interlayers on the capacity and deformation energy of timber-to-timber screwed connection with inclined screws. First, the authors carried out thirty push-out tests with inclined screws considering six structural configurations. Then, through X-ray computed tomography (CT) and threshold-based image segmentation, they assessed the deformed configuration of the screws to isolate the screw and timber contributions to the total deformation energy. The deformed shape of the connectors, fitted by a six-order polynomial, provides an estimate of the connection bending deformation assuming an elasto-plastic stress–strain constitutive for steel. By subtraction, the authors separately evaluated the role of timber embedment and steel deformation in the overall energy deformation in all the tested configurations. The experimental results revealed that most deformation energy comes from the screwed connection without interlayer, while the remaining can be attributed to timber plasticization. Conversely, the presence of the interlayer significantly unbalances such contribution, considerably reducing the role of timber plasticization.
... Strength means the longitudinal shear force capacity of the connection in the TCC structure. In EC5 part 1-1, the strength of the connection is based on Johansen's (1949) theory. But the strength model is restricted for the screwdriven vertically. ...
... The predictive strength model proposed by Symons et al. [46] was derived based on Johansen's [13] theory. The innovation in the model was to take into account the inclination angle of the screw within the timber. ...
This paper reviews the type of engineered timbers and connection systems used in timber concrete composite structures. The literature references were selected and reviewed carefully to get a detailed overview of the use of timber and connections systems in timber-concrete composite structures. The list of connection systems used in the timber-concrete composite structures was reviewed from the previous works to perceive its advantages and disadvantages. It was found that the glued joint is the stiffest connection but low in ductility. Mechanical fasteners such as screw connections have moderate stiffness and ductility compared to the hardwood studs which have the lowest stiffness and the highest ductility. The design models of connection strength and stiffness of the screw connections were assembled and discussed to recognise their limitations to the design of timber-concrete composite structures.
... Basing on Johansen's yield theory (European Yield Model, EYM) [17], the Eurocode 5 design method for dowel-type timber connections calculates load capacity for single connectors per shear plane under vertical loading. This model uses material properties, connection geometry, and assumes rigid-plastic behavior to streamline the analysis. ...
Timber-concrete composite (TCC) structures are gaining attention in sustainable construction for their complementary material properties and potential to reduce carbon emissions. This study investigates the load-carrying capacity and failure mechanisms of an innovative X-shaped headed connector with rectangular notches for TCC beams. To evaluate load-slip behavior and failure modes, experimental push-out tests were conducted on two series of specimens with different concrete strengths to evaluate load-slip behavior and failure modes under increasing loads. Results indicate that specimens with higher concrete strength (Series B) demonstrated significantly improved load-carrying capacity and stiffness, achieving a maximum load of 60 kN compared to 42.5 kN for Series A. Both series shows similar failure mechanisms due to timber's shear failure and bending failure of the connectors. A new load-carrying capacity equation for the X-shaped connectors is developed which aligns with Eurocode 5 design guidelines. The proposed equation is validated through comparison with experimental results, and it achieves an average theoretical to experimental ratio of 0.99. These findings provide a deeper understanding of shear connector behavior in TCC systems and support the development of more resilient and efficient TCC structures.
... The load-carrying capacity of the connections can be described by the European Yield Model based on a plastic limit state analysis. The first researcher working in this area assumes this model has an ideal rigid-plastic behavior of the timber and steel dowel, [1]. This method predicts the strength of a two or three-member dowel type connection, [2]. ...
The main objective of this manuscript is to present an analytical procedure of steel-to-timber and timber-to-timber connections in simple shear, related to the calculated number of dowels needed. These types of connections need to be assembled by dowel–type fasteners, such as nails, screws, bolts, and dowels. In this work, the connections are fixed with steel dowels. Timber connections made with dowels are a good choice, they look great when compared to screw connections and are rigid because have a tight fit while screws have a loose fit in the hole. Different simplified equations were used to calculate the characteristic load-carrying capacity in simple shear per fastener. These equations are useful in designing connections in simple shear when loaded in tensile and allow calculating the number of dowels needed. To obtain the results for discussion, different parameters were considered: three steel dowel diameters, three applied tensile loads, and three species in homogeneous glued laminated timber, each one with different densities. The discussion of the results shows that the number of dowels increases when the diameter decreases, and the material properties have a lesser dependence on this calculation. Using these simplified equations provides a better and easier understanding of the factors that can affect the behavior of steel-to-timber and timber-to-timber connections in simple shear. The key connection point is the shear capacity and ductility behavior of the screw and or dowel element, as presented in this work.
... Theoretical models for the evaluation of the resistance of timber-totimber and steel-to-timber connections given in European standard prEN 1995-1-1 [33] are based on yield theory (also note as European Yield Model, EYM) firstly introduced by Johansen [37]. In particular, prescriptions for the evaluation of the shear resistance of plywood and OSB panel-to-steel sheet connections depend on the ratio between steel sheet thickness (t s ) and screw diameter (d). ...
... The study proposes a test protocol involving separate lateral and axial displacement phases and provides a tri-linear approximation of the experimental load-displacement curves. Analytical predictions using Johansen's model [52] were reliable for uniaxial tension conditions, however, the study emphasizes the need for revised design procedures and numerical models to account for axial-shear interaction, especially for large lateral displacements to ensure safe and effective CLT shear wall designs. Additionally, Shahnewaz et al. [53] studied the hysteretic behavior of single-story single-and coupled-panel CLT shear walls with nailed connections, focusing on factors such as panel aspect ratio, nail spacing, presence of washers, and the number of shear brackets. ...
Cross-laminated timber (CLT) is one of the most sustainable, robust, and green building materials nowadays and is normally used for walls, floors, or roofs. The number of studies on CLT has increased significantly since 2010, which shows the acceptance and needs of CLT. Connection systems, rolling shear performance, and sustainability are the popular and main research topics within CLT, including wooden connections, metallic connections, adhesive and rod connections, aspect ratio, bonding performance, life cycle assessment, carbon emission, and environmental impact. Based on these three branches, the current study conducts a literature review on CLT. This review article aims to provide a valuable view and better understanding of CLT, which are linked to (1) promoting the usage of CLT and (2) summarizing the weaknesses of the CLT's research. This article presents a full background of the CLT research and gives potential research directions for CLT as a structural material. It revealed that the design and analytical methodologies for novel timber and steel connections are the main trends. As for the CLT's rolling shear performance, standardized testing protocol, environmental impact, and bonding quality need further development. Furthermore, the data collection, selection, and influence of different policies are important for the CLT's sustainability assessment.
... Their findings indicated that in group bolt tests, the failure mode transitioned from longitudinal splitting in a single row of bolts to longitudinal cracking at the bolts on the sides as the number of bolt rows and bolts per row increased. Additionally, the load capacity of single-bolt connections can be calculated using Johansen's yield model [8]. ...
Wood as a sustainable building material demonstrates significant advantages in terms of environmental protection, economy and functionality. Studies showed that adding 1.0m3 of wood could absorb 1.0kg of carbon dioxide, produce 730kg of oxygen, and fix 270kg of carbon, which plays an important role in ecological environment protection. In addition, in addition, wood has good thermal insulation performance, can adjust indoor humidity, beneficial to human health.China's wooden structure architecture has a long history. As an important technology in China's traditional architecture, mortise and tenon connection technology constitutes an important part of Chinese traditional architectural heritage through the insertion of wood components. As a prefabricated building form, modern wood structure has a history of more than 100 years in developed countries. The main forms include heavy wood structure, light wood structure, square wood wood structure and wood mixed structure. In recent years, wood structure architecture has attracted wide attention in scientific research and application in China. Whether for new construction or large-scale reconstruction projects, wood structure buildings are widely adopted because of their design flexibility, high strength and aesthetics, as shown in Figure 1.1. Modern wood structure buildings show the advantages of energy conservation and environmental protection, good earthquake resistance, convenient construction and safety and comfort, and its development is fully in line with the national sustainable development strategy.
... As a first stage to generate reliable designs/models of CLT connections, it is necessary to account for an accurate estimation of their elastic stiffness and strength capacity. Several predictive analytical models exist in the literature (Johansen 1949, Uibel & Blaß 2013, Blaß & Uibel 2007, Ottenhaus et al. 2018, Ou et al. 2023) and timber codes (EC8 2013, EC5 2014, CSA 2014, NDS 2018. Moreover, it is also important to characterize the hysteretic parameters of connections potentially subjected to large deformations to enable nonlinear modeling. ...
This study examines experimentally and numerically the in-plane behavior of a steel-spline Cross-Laminated Timber (CLT) connection with self-tapping screws. Although this connection is a strong, rapid, and cost-effective alternative suitable for CLT diaphragms of tall timber-concrete buildings, no previous cyclic/monotonic testing has been documented. Two specimens were tested under axial and in-plane shear loads, where a ductile failure mode was observed due to bending and withdrawal of screws, and deformation and buckling of the strap. Mechanic properties, such as strength capacity, stiffness, ductility, energy dissipation, equivalent viscous damping, stiffness/strength degradation, and damage index characterize the joint. Furthermore, the yield point and ductility were calculated with
the EEEP, CEN, and Yasumura–Kawai methods, the last approach most accurate, with a mean ductility of 7.25 and 5.50 for the axial and in-plane shear tests, respectively. Overstrength factors of about 2.6 and 1.9 were also estimated for respective tests by comparing analytical expressions from timber codes and literature. Finally, three numerical models (SAWS, DowelType, and ASPID) were assessed to measure their epistemic uncertainty, showing an adequate force and dissipated energy history simulation, with a normalized root mean square less than 8.8% and 4.5%, and R2 over 87% and 97%, respectively.
... The damage modes serve as a way to visualize the effect of each factor on the performance of the connection. According to European Yield Model (EYM) of Johanson [48], Table 3 shows three types of steel clamp plate-engineered timber bolted connection damage modes(European Committee for Standardization 2016) [49]. I: When the bamboo thickness is thin, the damage form is only dowelbearing damage. ...
Bamboo is a great building material due to its low carbon and environmental friendless. The connection performance of beam-column joints had an impact on the seismic performance of the whole structure. The beam-column connection performance is critical in earthquakes. Steel-engineered timber connections have good seismic properties, and the properties of bamboo and timber are very similar. Therefore, the form of wood structure connection can be used in bamboo structures. The type of member materials used and the connection forms applied determine the structure elastic behavior. Common engineered bamboo has been introduced, and the current connection form of engineered timber has been summarized in this paper. Secondly, research on the indicators of connection performance under cyclic loads has been introduced, including damage forms, strength, ductility, and energy dissipation capacity. Thirdly, the traits of various types of connections are presented, and this paper could be taken as a reference for future studies on connections in steel-engineered bamboo structures.
... The reliability of connections is the key to the overall safety performance of a structural system, due to their stable mechanical performance, bolted connections are widely used in wood or bamboo structures (Hong et al. 2020). Johansen (1949) believed that the mechanical performance of bolted joints mainly depended on the bending properties of bolts and the dowel-bearing properties of timber, and proposed the European Yield Model (EYM) for predicting the capacity of bolted connections. Later researchers (McLain and Thangjitham 1983;Soltis et al. 1986) also verified the applicability of EYM. ...
The dowel-bearing properties of a newly laminated flattened-bamboo (LFB) composite for engineering use was studied in this research by using the 5% bolt diameter offset method. The effects of specimen dimensions, bolt diameter, density, and bolt placed direction were included. Computed tomography (CT) and scanning electron microscope (SEM) were used to identify the failure type. The test results indicate that the parallel-to-grain dowel-bearing strength of LFB generally increased with an increasing density. When the bolt was placed along the LFB’s radial direction, the parallel-to-grain dowel-bearing strength approximately remained a constant (52 MPa) with the change of specimen dimensions and bolt diameter, while when the bolt was along the tangential direction, the dowel-bearing strength increased with the raising ratio of specimen thickness and bolt diameter. The first failure type was a crushing failure of bamboo fiber underneath the bolt, it happened when bolt diameter was small (12 mm and 14 mm) and placed along LFB’s radial direction. The second type was a splitting failure due to the lateral force generated by the bolt embedded into specimen, bamboo fiber splitting failure dominated for specimens with bolt along radial direction, while when bolt along tangential direction, glue layer splitting happened. The measured dowel-bearing strength was compared to the predictions obtained from equations in current wood specifications and articles. The results indicated that, except for the predicted values from the NDS equation (max error = 36%), which showed relatively reasonable agreement with the test values, the remaining predicted values exhibited discrepancies with the test values. To obtain proper predicted values, equations include density and ratio of specimen thickness and bolt diameter were proposed for calculation of LFB’s parallel-to-grain dowel-bearing strength.
... The minimum distance between two crossing screws is set as 20 mm. The shear capacity of the connection is the minimum between the values associated with six different failure mechanisms, labelled from (a) to (f) and illustrated in Fig. 5 [46]: ...
The most common and practical connection between CLT walls can be realized with inclined screws. This choice avoids the realization of more elaborated half-lap or spline joints. The failure mechanism of CLT-to-CLT screwed connections is highly ductile. However, the epistemic and aleatoric uncertainties associated with the capacity estimation of the connection might lead to an undesired overstrength, compromising the expected hierarchy between failure mechanisms. This paper presents the results of an extended experimental campaign to estimate the overstrength of CLT-to-CLT screwed connections. However, the overstrength directly obtained from the experimental tests could be underestimated. In the experimental campaign, the same wood and screw stock is used, which might not represent the actual scatter of the material properties and construction uncertainties of the as-built connection (e.g., the screw inclination). Therefore, this paper attempts to provide a model-driven assessment of the overstrength factor, assuming more realistic values for the parameter uncertainties. The authors propose a method for removing the contribution of epistemic uncertainty to the model-driven estimation of the overstrength based on experimental tests with two Montecarlo simulations. Following the proposed method, the paper compares the overstrength estimations from the experimental tests to the predictions of analytical and nonlinear finite element models. This study has proven that an overstrength factor between 1.8 and 2 can represent the actual uncertainties in as-built CLT-to-CLT screwed connections.
... Common to all of these is that the force is transferred from the timber to the fastener through the interface between the timber and the fastener. Professor K W Johansen first applied the yield theory to timber fasteners [7] and the failure modes are summarized in Table 1. Mode I and II only involves the collapse of members with the fastener remaining rigid, while Modes III and Ⅳ involve one and two plastic hinges of the fastener respectively. ...
With the advantages of environmentally friendliness and high strength-to-weight ratio, glulam has been widely applied to modern structures. The glulam space frame structure is a representative large-span spatial structure, which can be categorized as glulam space grid structure, geodesic dome, post formed gridshell, and reciprocal structure. A comprehensive review of the main research advances of the glulam space frame structure is presented and mainly expounded from the aspects of mechanical performance of joints and overall structures. The main existing forms of joints applied in spatial structures were summarized and classified as dowel-type joint and glued-in rod joint. The behavior and innovation of the joints were systematically presented based on the latest research progress. Several issues that should be paid attention to the study of overall structures were proposed such as overall stability, seismic performance and creep characteristic. Finally, the further researches worth investigating were put forward. This paper has certain reference significance for the research and can also promote the development of relative engineering applications.
Bamboo materials are known for their excellent toughness and seismic performance, which makes them a promising option for advancing their application in the field of structural engineering to enhance the seismic resilience of engineering structures. This study focused on mechanical behavior of bolted steel‐neosinocalamus affinis‐based bamboo scrimber and steel connections, and conducted shear test research and analysis on 54 specimens divided into 18 groups, aiming to promote the application of bamboo scrimber in the field of structural engineering. The study indicates that connections with thin steel plates ( t = 0.5 d , t = 1 d ) predominantly exhibit a single‐hinge yield mode, while those with thick steel plates ( t = 2 d ) are inclined towards a double‐hinged yield mode. The yield and ultimate load‐carrying capacities of a connection are enhanced with the increase in bolt diameter. However, the influence of the steel plate's strength grade on these capacities is minimal. The yield load‐carrying capacity of connections with thick steel plates has a significant increase compared with the connection with thin steel plates. The thickness of the steel plate does not significantly affect the connection ultimate load‐carrying capacity. The initial stiffness of a connection is positively correlated with the bolt diameter, yet it remains unaffected by variations in the steel plate's thickness. The stiffness of a connection is categorized into two distinct types based on the steel plate strength grade. Connections using steel plates with a strength grade above Q235 exhibit similar stiffness levels, which are consistently higher than those using Q235‐grade steel plates. The angle between the load direction and the grain direction has an effect on the connection ductility. The ductility coefficient across various connections predominantly centers around 2.5. The research also validates that the Foschi theoretical model, traditionally applied to wood structures with bolted, nailed, and similar dowel‐type connections, accurately delineates the nonlinear load–displacement behavior of bolted steel–bamboo scrimber and steel connections for the entire duration of the process. When comparing the same configurations, connections utilizing neosinocalamus affinis‐based bamboo scrimber demonstrate a higher load‐carrying capacity than those using phyllostachys pubescens‐based bamboo scrimber, with a maximum enhancement in load‐carrying capacity of 18%. The design carrying capacity meets the test load requirements for the given end distances of 7 d . This research can provide theoretical support for the engineering application of neosinocalamus affinis‐based bamboo scrimber.
This paper reports the results of an experimental study on the fire resistance of bolted laminated bamboo beam-to-column connections exposed to an ISO 834 standard fire. Six full-scale connection specimens were fabricated. Connection types included bolted connections with slotted-in steel plates and bolted connections with T-shape steel side plates. Ratios of the applied load during fire exposure were 0.3 and 0.5 of the ultimate connection capacity. In loading tests to failure at room temperature, the steel side plate connections exhibited significantly greater rotational stiffness and ultimate bending capacity than did the slotted-in steel plate connections. Fire resistance of the steel side plate connections was 32% and 38% longer than that of slotted-in steel plate connections under load ratios of 0.3 and 0.5, respectively. Additionally, failure was pushed out of the critical connection region into the beam. The steel side plates effectively encapsulated the combustible bamboo in the connection region. The average charring rate of the four specimens was 0.87 mm/min, which is slightly lower than the nominal linear charring rate (0.90 mm/min) prescribed for engineered bamboo structures.
In recent years, the focus has shifted toward more sustainable construction methods. Cross-laminated timber (CLT) has emerged as an excellent material in terms of structural properties and environmental impact. Across Europe, C24-grade timber is primarily used for the manufacture of CLT and hence most of the research data available is for CLT of this grade. However, Ireland has an increasing supply of C16-grade Sitka spruce timber and studies have shown that C16-grade Irish timber is suitable for use in CLT. This paper reviews the commonly available connectors for wall-to-floor connections in CLT and their feasibility and functionality for a multi-storey modular building constructed using C16-grade CLT. A modular building consists of stackable and scalable prefabricated modular units which are manufactured off-site and transported and assembled on-site. The most common types of commercially available connectors have been reviewed and angle brackets have been identified as the most common type of connectors for wall-to-floor connections. Numerical modelling of these connections to predict their behaviour under shear and tension loads has also been reviewed. Future research needs for using these connections for a modular building made of C16-grade CLT have also been identified and highlighted.
This paper summarizes the results of an experimental study of fire resistance of composite concrete-topped cross-laminated timber (CT-CLT) slabs exposed to fire at their soffit. Six composite CT-CLT slabs and one untopped CLT slab were tested under ISO 834 standard fire exposure while subject to an applied load equal to 20% of the slab ultimate capacity. Test variables included the type and configuration of shear connection between the topping and CLT. Large bending deflections were observed as the slabs reached their fire resistance. Although the untopped CLT slab exhibited a fire resistance of only 16 minutes, all CT-CLT exhibited fire resistance greater than 1 hour. The improved behavior is attributed to the stiffer CT-CLT behavior. CT-CLT slabs exhibited delamination of the lowermost layer of the CLT following through-layer charring. Observed charring rates were approximately 46 mm/hour. Observed charring depths were well-predicted by existing design standard-recommended equations. Importantly, the interface between the concrete topping and CLT remained close to 30 oC and never exceeded 65 oC in any test. This is a promising result for employing adhesive systems to affect composite behavior between the topping and CLT.
This paper focused on a newly engineering use flattened-bamboo composite (FBC) and studied the effect of fiber orientation angle (0° - 90°, 15° intervals) on FBC’s embedment performance and failure modes by half hole test. The results indicated that with larger fiber orientation angle, both the embedment strength and initial stiffness gradually decreased (embedment strength: 52 ∼ 26 MPa, initial stiffness: 27062 ∼ 11149 kN/mm), and Hankinson’s formula could effectively predict FBC’s embedment strength with error less than ±7 %. Combing the experimental phenomenon and scanning electron microscope (SEM) results, the failure modes of embedment specimens were classified. For angles of 0° and 15°, the failure mode was a mix of fiber crushing failure and split failure between fibers. For angles from 30° to 60°, the phenomenon of fiber being crushed became less obvious, only small cracks were witnessed around the half-hole area. For angles of 75° and 90°, the bamboo fiber compression failure perpendicular to fiber direction dominated, and two horizonal cracks happened on both sides of the specimen. A damaged constitutive model using continuum damage mechanics was proposed for simulating FBC’s embedding failure modes, and the proposed model was verified by comparing with the experimental phenomenon.
Laminated bamboo lumber (LBL), a renowned engineered bamboo composite known for its outstanding performance and sustainability, is extensively used in modern bamboo structured buildings. This study focuses on examining the effects of diverse reinforcement techniques, particularly self-tapping screws and tension control bolts, on the load-bearing capacity of bolted LBL connections with steel plates. In total, 24 specimens were categorized into 8 groups and subjected to monotonic loading tests. The test results demonstrate that the non-reinforced group clearly shows longitudinal splitting failure at the bolt position, followed by a decrease in load-bearing capacity after failure. In contrast, the group with self-tapping screws (ST) and tension control bolts (BT) exhibited fiber tearing at the lower part of the midspan, accompanied by section bending and damage. The final load-bearing capacity of the groups reinforced with single-row three-bolt self-tapping screws and tension control bolts showed an increase of 67.30% and 52.95%, respectively. Likewise, the groups with single-row four-bolt configurations also demonstrated significant reinforcement effects, with increases of 40.52% and 29.66%, respectively. Furthermore, DIC-3D analysis was employed to examine the displacement of the connection bolts, and the van der Put model was utilized to estimate the load-bearing capacity of bolted LBL connections under splitting conditions. Subsequently, finite element models were established and calibrated based on the experimental data. The results confirm that self-tapping screws and tension control bolts can serve as structural enhancements in the design of bolted LBL connections, providing effective reinforcement for existing engineering structures.
The mechanical performance of timber composite floors is influenced by the degree of composite action between the components. In this study, the shear strength performance of cross-laminated timber and glued laminated timber composite floors based on the joining method was evaluated by push-out test. Eight types of timber-timber composite joints were evaluated using three different methods: lag screw joints, glued-in rod joints using fully threaded bolts and glass fiber reinforced plastic, and hybrid joints. Strength characteristics were derived to make theoretical predictions on the load-carrying capacity of the joints. The results showed that the glued-in rod joints were superior to the lag screw joints, with slip coefficients and ductility measured as 10 times and 2.5 times higher, respectively. The reliability of the strength characteristics of the glued-in rod joints was remarkably different depending on the presence or absence of anti-adhesive tape applied to the timber-to-timber joint surface. The load capacity of the hybrid joint, which combines mechanical and glued-in rod joining methods, was 47% higher than that of the lag screw joint and 38% higher than that of the glued-in bolt joint. In the European Yield Model modified to estimate the load capacity of joints, the rope effect and the yield moment of the fasteners had a remarkable impact on the predicted load capacity.
Im Kontext der nachhaltigen Tragwerksplanung wird am Lehrstuhl Tragkonstruktionen der TU Dortmund aktuell an einer Stahl‐Holz‐Verbunddecke (SHV) geforscht. Die Leistungsfähigkeit des Deckensystems hängt neben den verwendeten Materialien insbesondere von der konstruktiven Durchbildung der Verbundfuge ab. Demnach wurden zu Beginn der Forschungsarbeiten verschiedene Fugenkonfigurationen mit reversiblen mechanischen Verbindungsmitteln experimentell untersucht. Im Zuge der durchgeführten Abscherversuche konnten die Vorzüge von senkrecht zur Holzfaser eingebrachten Holzschrauben (HS) im Vergleich zu selbstbohrenden Blechbohrschrauben (BS) sowie geneigt eingebrachten Holzschrauben festgestellt werden. Die senkrecht installierten Holzschrauben wiesen eine vergleichsweise hohe Verbundsteifigkeit sowie einen ausgeprägt duktilen Versagensmechanismus bei gleichzeitig geringem Montageaufwand auf. Dementsprechend werden in zukünftigen versuchstechnischen Untersuchungen zur Erfassung des Biegetragverhaltens der Stahl‐Holz‐Verbunddecke überwiegend senkrecht eingebrachte Holzschrauben zur Sicherstellung des Verbunds vorgesehen.
In the present work, single-and double-dowel joints following different geometric configurations are experimentally and numerically investigated to derive the splitting behaviour of beech wood (Fagus sylvatica L.), one of the most widespread hardwood species in Europe for structural purposes. The influence of the spacing between dowels, their distance to the supports, and the slenderness of the beams is analysed. The correlation of the experimental failure loads with those predicted numerically by cohesive zone finite element-based models using the fracture properties of the species is discussed. The experimental results are also compared with those obtained from the normative expression included in Eurocode 5 and two other design models reported in the literature. The splitting failure loads predicted by both the analytical and numerical models were found to be conservative, the latter being closer to the experimental values.
Mixed angle screws provide a strong, stiff, and ductile hold-down solution for high-capacity Cross Laminated Timber (CLT) shear walls. Timber is an inherently brittle material and most inelastic responses in timber structures are concentrated in connections. Seismic performance of a CLT shear wall system is typically governed by connection behaviour. By combining screws installed at an inclined angle and a 90° angle to the grain, the strength and stiffness of inclined screws and the ductility of 90° screws can be superimposed for strong, stiff, and ductile connection performance. Previous research presented to NZSEE has demonstrated the performance of mixed angle screw hold-down connections under cyclic loading, and their ability to be easily repaired post seismic events. This paper extends on this research topic and presents high-capacity testing results along with a discussion on design methodology. The high-capacity testing results showed that mixed angle screw hold-down connections can achieve yield forces averaging 952 kN in Douglas fir CLT and 1029 kN in radiata pine CLT. Strength predictions from Eurocode 5 and NZS AS 1720.1:2022 are discussed, with NZS AS 1720.1:2022 being more conservative. The conservatism of current approaches is also discussed with analytical predictions underestimating the characteristic 5 th percentile yield strength from testing by a factor of 1.3. The observed overstrength factor based on analytical predictions and characteristic 95 th percentile values of maximum force averaged 2 with a maximum of 2.4. NZS AS1720.1:2022 introduces a cap on overstrength demand at the maximum action generated due to equivalent elastic seismic demand. Therefore, for structures designed with system ductility of 2 overstrength demands are likely to be governed by the equivalent elastic demands.
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