Timber Connections Research Articles

Effects of bolt diameter and loading direction on bearing and withdrawal resistance of half-threaded bolts in glued laminated timber

Timber connections were prepared using glulam from tropical plantation species, focusing on key properties for dowel-type joints with half threaded bolts without nuts: Bolt bearing strength and bolt withdrawal capacity. Tests were performed according to ASTM standards. Three half-threaded bolt diameters (12 mm, 16 mm, and 20 mm) were tested in two loading directions, parallel and perpendicular to the grain, with 12 replicates for each configuration. Response Surface Methodology (RSM) using Design Expert Software was applied to optimize bolt diameter for both loading directions. Results showed that bolt bearing strength was higher in perpendicular loading, with the 12 mm bolt achieving 16.6 N/mm², compared to 6.01 N/mm² in parallel loading. Withdrawal capacities varied, with the 16 mm bolt showing the highest capacity in perpendicular loading at 54.2 kN. The study demonstrates that the 16 mm bolt exhibited the optimal diameter-to-embedment length ratio compared to 12 mm and 20 mm bolts, resulting in the highest withdrawal capacity. Consequently, the 16 mm bolt represented the best balance for achieving maximum withdrawal capacity. The optimization suggests using a 16 mm bolt for parallel loading to the grain and a 14 mm bolt for perpendicular loading.

Sensibility Analysis of Traditional Span Frame

ABSTRACT Traditional timber frames may have a complex mechanical behavior regarding to today engineer skills and design standards. For an identical rebuilding as required for the Notre-Dame de Paris Cathedral, accurate modeling must be performed to assess modern reliability. Identical rebuilt means same green oak material, same geometry and timber connections. In the context of the rebuilt of the Notre-Dame carpentry, a part of the timber frame based on the original schemes of the nave extracted from historical graphic document was reproduced. A full-scale replica was erected in order to perform mechanical tests. Through an in-situ monitoring, this structure represents a case study in order to provide data relative to the kinetics of displacements. This investigation allows to evaluate the global behavior of the structure. Based on the finite element method (F.E.M), a dedicated model is used to analyze the sensitivity of the material properties, the beam geometry and the wood-to-wood connections in order to design the testing carried out on the wooden structure. From these full-scale tests, we determine the real stiffness of the carpentry. Then, a retro-analysis was proposed to evaluate the axial stiffness of connections according to the corresponding finite element model, by fitting data to reproduce the real displacements. The study reveals that this property is substantial to describe the global behavior. Furthermore, we carried out in the laboratory an experimental campaign consisting in characterizing traditional joints. The goal was to estimate their stiffness and their specific failure modes by using image correlation. Concomitantly, numerical simulations were developed in order to investigate the dependence of the stiffness according to moisture content variation of oak species. The global research supplies useful tools and results, which may be able to improve the understanding of the mechanical performance of traditional structures and provide valuable information for design purposes.

Experimental investigation on lateral performance of southern pine nailed connections under monotonic and cyclic loading

Connections are responsible for maintaining the integrity and safety of wood structures when subjected to lateral force induced by wind or seismic event. The aim of this study is to provide a better understanding of monotonic and cyclic response of timber-to-timber nailed connections. A total of 48 groups of double-shear nailed connections were tested to investigate the effect of different variables on the lateral resistance performance of connections. Representative parameters derived from practical nailed timber connections were considered, including nail diameter, nail type, and load-to-grain angle. It is found that the failure modes of the specimens loaded monotonically are attributed to bending yield of nails. Conversely, under cyclic loading, the majority of nail failures occur as a result of fatigue fracture, which is caused by the repetitive bending stress. A reduction in ductility ranging from 76.9 % to 92.7 % is observed in specimens subjected to cyclic loading, as compared to those under monotonic loading. Utilizing larger-diameter nails as connectors can markedly improve the load-bearing capacity, ductility, and energy-dissipation capabilities of connections subjected to cyclic loading. Helically threaded nails (HTN) have a 29.4 % higher lateral capacity than smooth shank nails (SSN), but a 29.9 % lower stiffness and 22.9 % lower ductility. Experimental load capacities were compared with existing calculation models, and Eurocode 5 was identified as the most suitable design code for predicting the lateral performance of nailed timber joints. Two analytical models were proposed to better simulate the load-slip behavior of nailed connections under monotonic and cyclic loading conditions, respectively.

EXPERIMENTAL TESTS OF RED MERANTI (SHOREA SPP.) DOWEL BEARING STRENGTH AT AN ANGLE TO THE GRAIN

The angle to the grain has a significant influence on timber bearing strength. As the grain angle increases the bearing strength decreases. The aim of this research was to obtain the dowel bearing strength of the red meranti (Shorea spp.) timber at an angle to the grain. The scope of this research was as follows the specimens were made according to ASTM D143, the grain angle ranged from 0° to 12°, and the dowel bearing tests were displacement controlled in accordance with ASTM D5764. Results of this research was an empirical equation of dowel bearing strength (in MPa) in terms of an angle to grain θ (in degrees) namely Fe = 32.74 - 4.701θ + 0.2064θ2. The importance of studying the influence of the grain angle to the dowel bearing strength for timber connection design is because the direction of the timber grain is not perfectly 0°.

Behaviour Analysis of Beam-Type Timber and Timber-Concrete Composite Panels

This study addresses the enhancement of material efficiency and reduction in brittleness in timber-to-concrete adhesive connections for beam-type timber and timber-concrete composite panels. The research explores the potential benefits of adding longitudinal timber ribs to cross-laminated timber (CLT) beam-type panels. Three groups of flexure-tested specimens were analysed as follows: (1) timber panels (1400 mm × 400 mm) with two 100 mm thick CLT panels and two 60 mm thick CLT panels reinforced with 150 × 80 mm timber ribs; (2) eight specimens (600 mm × 100 mm × 150 mm) with CLT members (600 mm × 100 mm × 100 mm) connected to a 50 mm concrete layer using granite chips and Sikadur-31 (AB) epoxy adhesive; (3) six CLT panels (1400 mm × 400 mm × 50 mm) bonded to a 50 mm concrete layer, with two panels containing polypropylene microfibres and two panels incorporating polyethene dowels for mechanical connection. Specimens were subjected to three-point bending tests and analysed using the transformed section method, γ-method, and finite element method with ANSYS 2023R2 software. Results indicated a 53% increase in load-carrying capacity for ribbed CLT panels with no additional material consumption, a 24.8–41.1% increase for CLT panels strengthened with a concrete layer, and improved ductility and prevention of disintegration in timber-concrete composites with polypropylene microfibres.

Glued-in steel plate and screwed connections in Timber–Concrete Composites systems: Mechanical performance and design implications

This paper presents a comparative study between Timber–Concrete Composite (TCC) systems with glued-in steel plates and screwed connections. The research focuses on evaluating the structural performance of these connections, with a particular focus on the innovative glued-in steel plate through full-scale four-point bending tests on floor subassemblies with a 7.5 m span, complemented by push-out tests for assessing the behaviour of the slab-beam connection. The study aims to determine if the glued-in steel plate, a more economical option, can replace screws without significantly compromising the TCC system’s stiffness or strength. The findings reveal that while the glued-in steel plate connections exhibited lower stiffness and ductility compared to screwed connections, they demonstrated a significantly higher load-bearing capacity. Specifically, the glued-in connections achieved capacities ranging from 670-720 kN, markedly exceeding the 300-350 kN and 480-520 kN capacities of specimens with fewer and more screws, respectively. These results suggest that glued-in steel plate connections can effectively replace screws in TCC systems, offering a cost-effective alternative without significantly reducing structural integrity. Moreover, the paper evaluates how to design TCC floors by estimating the effective number of connectors and the effective length of the glued-in steel plate using an iterative γ-method. This is done to account for changes in stiffness, as determined from push-out tests and observed in bending tests. The iterative γ-method’s findings have been validated against the predictions of a Finite Element model.

Enhancing Deep Line Segment Detection and Performance Evaluation for Wood: A Deep Learning Approach with Experiment-Based, Domain-Specific Implementations

In recent decades, wood structures have gained significant attention for their ecological benefits and architectural versatility. The performance of wood, a popular construction material, often depends on the integrity of its connections. This study focuses on bolted glulam timber connections, which are strong but prone to cracks that pose structural health challenges. Traditional crack evaluation methods are manual, time-consuming, and error-prone. To address these issues, this research proposes a two-stage performance evaluation method. In the first stage, an innovative approach called ‘Enhanced Deep Line Segment Detection’ (Deep LSD), a non-supervised machine learning technique, is used for crack detection without relying on large, annotated datasets, thus enhancing efficiency and adaptability. In the second stage, cyclic loading assays simulate varying damage stages to collect data and establish a correlation between crack states and connection damage. The Park and Ang damage model is employed within this framework to assess the extent of damage. The efficacy of enhanced deep LSD is confirmed by comparing detected crack areas with ground truth measurements, yielding a high R-squared value of 0.98 and a minimal error margin of 1.41. Additionally, a damage index based on the Chinese standard (GB/T 24335-2009) is used to classify damage across different connection groups, ensuring robustness and alignment with established practices.

Load-bearing furniture modules for fast deployable and reusable systems

The urgent need to reduce carbon emissions in the construction sector has driven the exploration of circular economy practices in the built environment. Nevertheless, the implementation of circular economy principles in projects remains limited. This research contributes to bridging this gap by introducing a project proposal that establishes a typology of modular systems designed for easy assembly, disassembly, and reuse. Specifically, the proposal focuses on load-bearing wood furniture modules (FMs) as an intermediate solution between planar and volumetric modules. These FMs expand the structural wall’s volume, facilitating the integration of services, storage, and appliances. This addresses scenarios where swift building deployment is required. The proposed modular dimension enhances transportation efficiency compared to volumetric solutions and simplifies construction by eliminating the need for temporary stabilization, as seen in planar systems. Standardization and “separability” of each component within the FM allows for easy integration and maintenance. Special attention is paid to the timber connection systems within and between FMs facilitating easy assembly, and disassembly for future reuse. The adaptability of the FM concept is demonstrated through versatile compositions and layouts, facilitating space reconfiguration. While the technical feasibility of the FM-based system is demonstrated, further research is needed to address regional and cultural variations and customize the system to different contexts. The study emphasizes the potential of FMs as a solution for buildings aligned with circular economy principles and highlights the importance of continued research and development in this field.

Experimental and analytical evaluation of semi-rigid timber connection with screwed-in threaded rods and steel coupling part

A major challenge for mid and high-rise timber buildings is fulfilling serviceability requirements. Moment-resisting timber frames with semi-rigid moment-resisting connections as the primary lateral load-resisting system can be an alternative to buildings with wind bracing or shear walls, allowing for more free space, enhanced building performance, and architectural flexibility. Moreover, introducing semi-rigid timber connections can improve the performance of floors against human-induced vibrations and potentially decrease the material used. The performance of moment-resisting frames depends mainly on the properties of their beam-to-column connections. The paper presents an experimental investigation of semi-rigid moment-resisting connections with long screwed-in threaded rods and a steel coupling part. Long threaded rods (i.e., screwed-in threaded rods with wood screw threads) feature high axial stiffness and resistance and allow for immediate load transfer without initial slip. Due to these properties, threaded rods are preferred over conventional dowel-type fasteners such as bolts and dowels. Five full-scale moment-resisting timber connections were tested under cyclic and monotonic loading to investigate moment resistance, rotational stiffness, and energy dissipation. The stiffness obtained by cyclic and monotonic tests was compared with numerical and analytical methods. The beam-to-column moment-resisting connections demonstrated a high moment resistance of 92.2 kNm and rotational stiffness of 8049 kNm/rad without initial slip. The experimental results and analytical calculations of rotational stiffness differed only by 5 %, whereas the finite element model exhibited a discrepancy of approximately 35 %. The equivalent viscous damping was determined based on cyclic load tests at service load levels and was found to be in the range of 5.5 %–10.0 %. Finally, a parametric study is presented to discuss the effect of semi-rigid connections on the performance of the timber floors and material savings. The increase in rotational stiffness of the beam-to-column connections could lead to up to 13 % material savings.

Thermal response of timber connections using densified wood dowels under fire

A new type of timber connection using densified wood dowels is being developed and tested. The procedure involves inserting these densified dowels into pre-drilled holes. As this connection technique is in its early stages, a unique design approach is necessary, considering the impact of temperature variations. The primary goal is to characterize the thermal behaviour of these connections under elevated temperatures. The study employs an experimental approach, complemented by numerical analysis, innovatively applying kinetic models, commonly used for investigating heat-related biomass characteristics, to wood. The method requires the use of thermogravimetric analysis to identify the kinetic parameters. The proposed pyrolysis kinetic model has been implemented in the Abaqus/Implicit code via a user subroutine UMATHT. The study concludes that using kinetic models enhances accuracy by considering mass loss, a key factor influencing thermal properties. Simulation successfully replicates temperature distribution and charred layer thickness, crucial for designing timber structures.

Applications of Spatial Timber Structures in China and Research on the Performance of Their Typical Connections

Timber, being a versatile and sustainable material, has been used for residential and public buildings throughout history. In recent years, advancements in engineering and construction technology have resulted in the development of innovative timber spatial structures that push the boundaries of traditional timber construction. Especially, numerous spatial timber structures have been constructed in China in recent years. This study aims to provide an overview of notable examples of spatial timber structures in China, including their architectural features, structure arrangement and construction method. Additionally, the configuration of some timber connections utilized in the Taiyuan Botanical Garden project are analyzed and the mechanical behavior of connections are investigated by a brief introduction of experimental tests. The research will provide a reference for engineering design of spatial timber structures in the future.

In-plane testing and hysteretic modeling of steel-spline cross-laminated timber diaphragm connection with self-tapping screws

ABSTRACT 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 R 2 over 87% and 97%, respectively.

P2PE: A finite element formulation for panel-to-panel cross-laminated timber connections

This paper presents a new multi-spring finite element formulation called P2PE that simulates the cyclic behavior of panel-to-panel Cross-Laminated Timber (CLT) connections. The formulation comprises five types of uncoupled linear/nonlinear springs representing the fasteners and contact between panels. For instance, the in-plane fastener behavior is simulated with a co-rotational spring and the Modified Richard–Abbott (MRA) model, which is adapted to account for the asymmetry, pinching, degradation, and low-cycle fatigue of timber connections. The model was implemented into ANSYS through user-element/materials, including all computer implementation steps, and can be freely downloaded. The model's response and sensitivity were studied in three demonstrative CLT diaphragms, and it was validated at the connection and assembly stage with benchmark tests. In the first stage, the fastener model was verified with four cyclic CLT connections, while in the second stage, the model was validated with three medium-to-large scale CLT assemblies. The model accurately predicts the stiffness, strength, deformation, slip, and failure mechanisms of both stages. Finally, a parametric analysis of in-plane bending CLT diaphragms was assessed by varying their panel dimensions. This analysis demonstrated that diaphragms with slender panels have larger capacities, fastener energy dissipation, and shear slips but lower ductilities than shorter ones.

Bonding strength between spruce glulam and birch plywood at different load-to-plywood face grain angles

There is growing interest recently in reducing the usage of metals in timber structures. Birch plywood possesses satisfactory mechanical properties compared to other wood-based panels and is promising to be utilized in timber connections as a substitute for the more conventional slotted-in metal plate. There are essentially two possibilities to connect plywood plates and other timber elements by means of either mechanical connections or adhesively bonded connections. Despite the more commonly adopted mechanical connections in current timber structures, the adhesively bonded connections hold the distinct advantages of being more cost-effective, stiffer, and with a lower risk of moisture penetration in the timber elements. When employing birch plywood in timber structure applications such as trusses and frame corners, stresses from different directions need to be transmitted by the plywood gusset plate. However, it is still uncertain how the bonding strength is affected by different loading angles to the face grain. This research question, specifically concerning the bonding strength between birch plywood and spruce glulam, has been addressed in this paper. It was found that the bonding strength varies within a relatively small range when the load-to-plywood face grain angle varies from 0° to 90°, which is promising for the development of adhesively bonded joints. Failure mainly occurred in glulam at 0° and 15°; while at other angles, a mixture of cohesive failure in glulam and plywood face veneer was dominant. The weak angle-dependence of the bonding strength can be explained by further checking the shear strength of the weaker wood adherends between glulam and plywood. A strong positive correlation was observed between bonding strength and the wood shear strength.

Flexural Behavior of Cross-Laminated Timber Panels with Environmentally Friendly Timber Edge Connections

As a sustainable construction material, timber is more promoted than steel, concrete, and aluminum nowadays. The building industry benefits from using timber based on several perspectives, including decarbonization, improved energy efficiency, and easier recycling and disposal processes. The cross-laminated timber (CLT) panel is one of the widely utilized engineered wood products in construction for floors, which is an ideal alternative option for replacing reinforced concrete. One single CLT panel has an outstanding flexural behavior. However, CLT cannot be extended independently without external connections, which are normally made of steel. This article proposes two innovative adhesive-free edge connections made of timber, the double surface (DS) and half-lapped (HL) connections. These connections were designed to connect two CLT panels along their weak direction. Parametric studies consisting of twenty models were conducted on the proposed edge connections to investigate the effects of different factors and the flexural behavior of CLT panels with these edge connections under a four-point bending test. Numerical simulations of all the models were done in the current study by using ABAQUS 2022. Furthermore, the employed material properties and other relevant inputs (VUSDFLD subroutines, time steps, meshes, etc.) of the numerical models were validated through existing experiments. The results demonstrated that the maximum and minimum load capacities among the studied models were 6.23 kN and 0.35 kN, respectively. The load–displacement responses, strain, stress, and defection distributions were collected and analyzed, as well as their failure modes. It was revealed that the CLT panels’ load capacity was distinctly improved due to the increment of the connectors’ number (55.05%) and horizontal length (80.81%), which also reinforced the stability. Based on the findings, it was indicated that adhesive-free timber connections could be used for CLT panels in buildings and replace traditional construction materials, having profound potential for improving buildings’ sustainability and energy efficiency.

The application of shape memory alloy technology in steel, timber and concrete connectors

The application of shape memory alloy technology in steel, timber and concrete connectors

Progress on the connection performance of steel-engineered bamboo beam-column connections under cyclic loads: a review

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.

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Recent experimental evidence has shown that wood–steel–wood dowel-type connections exhibit a semi-rigid behaviour even after 90 min of fire exposure. Because a semi-rigid behaviour influences the bending moment distribution among structural members, considering the moment–rotation relationships within frame analyses in which structural members are modelled as beam elements can enable a realistic fire response analysis that is significantly simpler than the three-dimensional finite element method. This study proposes an analytical methodology that accounts for the thermo-mechanical behaviour of timber and dowels, enabling the simulation of the non-linear moment–rotation relationships under fire conditions. The proposed analytical model divides dowels into a series of elements on an elastoplastic foundation and performs a direct stiffness method in a time-incremental procedure using an element stiffness matrix derived from beam-on-elastic-foundation theory. This study also presents the results of load-carrying tests on timber frames with dowel-type connections performed under ambient and fire conditions. The analytical results were consistent with the fire test results. Additionally, the analyses were also performed under three conditions in which the dowels were rigid, linear elastic, and elastoplastic bodies. These three results converged to the same value after 65 min of heating, which suggests that the ultimate states of beams with dowel-type connections exposed to fire can be modelled by assuming that dowels are rigid bodies.

Experimental Investigation of Cross-Laminated Timber Connections with Glued-In Rods under Monotonic and Cyclic Loading

Experimental Investigation of Cross-Laminated Timber Connections with Glued-In Rods under Monotonic and Cyclic Loading

A New Moment-Resisting Glulam Beam-End Connection Utilizing Mechanically Fastened Steel Rods—An Experimental Study

A new moment-resisting mass timber connection was designed based on the principles of force equilibrium in applied mechanics. The connection configuration utilizing two mechanically fastened threaded steel rods embedded into the end of a glulam beam section was experimentally investigated in this study. A gradually increasing transverse load was applied to the free end of a cantilevered beam, causing a bending moment on the beam-end connection until failure. Four different connection configurations were examined, each replicated twice to verify results. The beam connection parameters investigated were rod anchorage length (200 and 250 mm) and square washer size (38.1 and 50.8 mm). Test results show that increasing the washer size increased the connection bending strength by increments more significantly than those due to increasing the rod anchorage length. However, the connection configurations with the smaller-size washer, which failed mainly due to wood crushing under the washer, had higher ductility ratios than those with the larger-size washer, which failed due to steel rod yielding. In a real-life scenario, a structural element such as a glulam beam is usually loaded to approximately 50% to 70% of its design capacity, considering a reasonable margin of safety. The study estimates a maximum possible bending moment utilization factor for the strongest connection configuration that ranged between 34% and 48% compared to the maximum moment resistance of a supported glulam beam spanning an average length of 4.0 m to 6.0 m (a common span length in framed timber buildings) and has a cross-section size same as the one utilized in this study. This utilization factor is quite large for a timber connection, and thus, confirms a considerable moment-resisting capability of the new configuration developed in this study.