Slotted-in Steel Plates Research Articles

Cyclic Behavior of Bolted Glued-Laminated Timber Brace Connections with Slotted-In Steel Plates

Cyclic Behavior of Bolted Glued-Laminated Timber Brace Connections with Slotted-In Steel Plates

Mechanical properties of multi-bolted Glulam connection with slotted-in steel plates

The Bolted Glulam Connection with Slotted-in Steel Plates (BGCSSP) is widely employed in modern timber structures due to its advantages of convenient installation and reliable force transmission. However, the current design methods lack rigorous mechanical derivation and fail to consider various influencing factors comprehensively. Furthermore, designing multiple dowel connections based on the behavior of individual dowels impedes optimization and limits the applicability of design rules. To systematically investigate the failure modes and mechanical characteristics of Multi-bolted Glulam Connection with Slotted-in Steel Plates (MGCSSP), specimens from 12 groups (6 specimens per group) were subjected to parallel grain tensile tests, considering four key influencing factors: bolt quantity, bolt arrangement, bolt diameter, and base material thickness. The experimental results indicate that as the number of bolts increases, the failure transitions from double-hinge failure to single-hinge failure. Additionally, there is an observable upward trend in both initial stiffness and peak load for the same type of specimen as the quantity of bolts increases, accompanied by a decreasing trend in the ductility coefficient. The analysis of experimental results reveals that both the quantity and diameter of bolts impact the initial stiffness and peak load of MGCSSP specimens. Based on experimental observations, dual-parameter calculation models for the initial stiffness and peak load of MGCSSP are proposed. The calculated results of the models align well with experimental data, providing references and convenience for the design of MGCSSP.

Cyclic behavior of laminated bio-based connections with slotted-in steel plates: Genetic algorithm, deterministic neural network-based model parameter identification, and uncertainty quantification

To support more sustainable construction, this paper experimentally investigates the cyclic behavior of laminated timber (Laminated Veneer Lumber (LVL)) and glubam (Glue Laminated Bamboo) connections with slotted-in steel plates in terms of experimental test, numerical simulations and parameter identification. Experimental tests included eight different configurations: two materials (LVL and glubam), two bolt diameters (8 and 10 mm), and one or two bolts. Two different cyclic-loading protocols were applied for each type of connection: only tension and tension/compression. The observed behavior is then compared to a finite element model developed in OpenSeesPy, which takes into account factors such as sliding, contact, pinching, cyclic stiffness, and strength degradation. To identify the best set of parameters for the model, three different approaches are considered: genetic algorithm, fast deterministic neural network, and probabilistic Bayesian method. First, the model identification is carried out by means of a genetic algorithm-based optimization. The parameter-identification results are evaluated in terms of elastic stiffness, yielding point, and ductility. Next, a sensitivity analysis is performed to determine the significance of the parameters, and an innovative approach combining neural network and sensitivity analysis is proposed for fast and preliminary parameter identification. Then, probabilistic Bayesian identification is employed to calculate the posterior distribution of the model parameters identified and the confidence bounds of the estimated response. Finally, different model identification parameters are compared and suggestions for algorithm selection are provided.

Behaviour of small-scale glulam timber connections with slotted-in steel plates and dowel-type fasteners reinforced with self-tapping screws

Braced frames are a common lateral force-resisting system in mass timber structures. In timber braced frames, timber-steel dowel connections are relied upon to provide ductility and energy dissipation capacity under earthquake loads. However, the ductility and energy dissipation capacity of these connections can be limited by the onset of a brittle failure mechanism (e.g., row-shear or group tear-out) prior to significant dowel yielding. This paper presents an experimental campaign investigating the structural performance of timber-steel dowelled connections reinforced with self-tapping screws. Twelve connections were tested; with 8 tested under monotonic loading and 4 tested under a cyclic loading regime. The tested connections included two different fastener diameters of 11 mm and 16 mm, with one or two internal steel plates, both with and without reinforcing screws designed to prevent brittle shear failure. The results demonstrate that the reinforcing screws are most effective for improving the ductility and energy dissipation for connections with similar design values of dowel yield and row shear capacities. In addition, the increases in ductility and energy dissipation with reinforcement were greatest for connections with high slenderness (defined as the ratio of dowel diameter to timber thickness) dowels. There was little improvement in the ductility of connections whose design capacity was dominated by row shear, although there was improvement in the energy dissipation of the connections. Overall, results of this study demonstrate the potential for using self-tapping screws to reinforce steel dowel connections and improve the seismic performance of mass timber braced frames.

Performance of Beam-Column Connections with Mass Ply Lam and Steel Dowels under Cyclic Loads

A mass timber lateral force resisting system (LFRS) is proposed using a mass timber buckling restrained brace (TBRB) to improve the seismic resilience of mass timber buildings. To develop a resilient braced frame, it is essential to understand and quantify the behavior of the connections, including the possible failure modes and moment-rotation capacities. Cyclic and monotonic tests were conducted on six mass timber beam-column connections to study the response of a mass timber joint connected with slotted-in steel plates and mild steel dowels. The primary goal of the subassembly tests was to measure the maximum rotation, stiffness, ductility, and failure modes of such connections for both monotonic and cyclic loads. The tests showed that the connections with three steel dowel details reached a maximum rotation of 0.11 radians (6.3 degrees) with no loss of strength. In addition, a numerical model was developed to represent the moment-rotation relationship of the mass timber beam-column connections.

Influence Factors on the Load-Carrying Capacity of Bolted Timber Connections with Slotted-In Steel Plates

Influence Factors on the Load-Carrying Capacity of Bolted Timber Connections with Slotted-In Steel Plates

Glulam Beam-to-Column Connection with Coupled Steel Rods with Screwheads: Concept and Experimental Verifications

The bolted connections with slotted-in steel plates are basic beam-to-column connections of modern post-and-beam timber building structures. However, due to significantly pinched rotational behaviors, the moment resistance of such connections are usually ignored in design. In this study, the connection-level moment resistance is enabled for modern glulam frame structures with an innovative connection design. A pair of long steel rods with screwheads is designed to generate a force couple at the sides of the connection. The proposed connection could be considered as the key lateral force resisting component, indicating a significant reduction of lateral braces and shear walls. Specimens of the target connection were carefully designed and tested in the lab to obtain their mechanical properties and failure modes. Finite element models were established and calibrated according to the tested data. The moment-rotation curves of the new connection could be easily estimated through a fitted formula. Moreover, the suggestions to improve the proposed connection is also discussed based on the observed damage modes. Results show that the new connection could be treated as rigid moment-resisting connections while the ductility could be further improved.

Bolted steel to laminated timber and glubam connections: Axial behavior and finite-element modeling

This study aims to characterize the axial monotonic and cyclic tensile behavior of bolted steel connections to laminated timber and bamboo, using slotted-in steel plates, and to provide a high-fidelity simulation using finite-element modeling. Forty-eight experimental tests were conducted, including eight different configurations, varying in material (Laminated Veneer Lumber (LVL) and Glued Laminated Bamboo (glubam)), number of bolts, and diameter of bolts, under tension, both monotonic and cyclic (three repetitions). The force and displacement were recorded, and used to define the initial stiffness, yielding strength, ultimate strength, ductility, viscous damping, and energy dissipation. The failure modes of the connections were monitored using Digital Image Correlation (DIC) techniques. A novel high-fidelity finite-element model integrating Hill’s yielding and element removal criteria was proposed to predict the mechanical performance and fracture behavior of the examined connections. The numerical simulation was validated by comparing the experimental load–displacement curves and the strain field measurements obtained with DIC. Finally, theoretical formulas for predicting the stiffness of bolted connections were proposed based on the FEM simulations.

Experimental investigation and calculation method for the bearing capability of bolt steel-to-laminated bamboo connections under the coupling of bending moment and shear force

To solve the design and calculation method of the connections in modern bamboo structure, experimental investigation and calculation method for the bearing capability of bolt steel-to-laminated bamboo connections under the coupling of bending moment and shear force are presented in this article. Firstly, the bearing capability of laminated bamboo beam-column bolt connections with slotted-in steel plates was investigated by the experiment. Secondly, the analysis of the influence of different beam-column gap, bolt arrangement, built-in filler and CFRP reinforcement on the stiffness and strength of the connections are analyzed and discussed. In particular, when beam-column gap is 20 mm, there is an obvious secondary rising segment on the moment-rotation curve. Thirdly, the typical yield modes and failure characteristics of beam-column connections under the coupling of bending moment and shear force were obtained. Finally, the calculation method for the bearing capability and the theoretical prediction model of moment-rotation curves of the connections were established. The average of the lower and upper bounds was used to predict the bearing capability of the connections. The relative error was less than 10% and the calculated results were accurate. The research results could provide the reliable basis for the design and calculation of beam-column bolt connections with slotted-in steel plates in modern bamboo structure.

Stiffness and slip in multi-dowel timber connections with slotted-in steel plates

Large multi-dowel connections can provide the strength and ductility required for large, highly-loaded timber structures, but their slip under load is not well understood. This is an important gap in knowledge, because accumulated local displacements at connections represent a large part of the deformation of a timber structure. The empirical relationships used in design codes commonly scale a single-dowel stiffness by the number of dowels, so do not capture the dowel interaction effects of the multi-dowel connections used in larger structures. We present the results of an experimental test series, elastic model and probabilistic numerical analysis investigating the development of stiffness in multi-dowel timber connections with slotted-in steel plates. Novel test methods record the development of stiffness due to each individual connector to show that the stiffness of the complete connection is not proportional to the number of dowels. An elastic stress-function model shows that this is partly due to interaction of the stress field around the dowels. For the first time, this work quantitatively considers the influence of misalignment of dowels due to manufacturing tolerances, and it is shown that this may greatly reduce the overall stiffness of a multi-dowel connection. The test series is used to validate a probabilistic model of this misalignment for the stiffness of such a connection. The model incorporates the nonlinear stiffness and hole opening observed in single-dowel connections to predict the behaviour of the group. The study shows that the random misalignment of dowels in multi-dowel connections reduces the range of displacements over which the connection displays zero stiffness slightly, but that this zone is not eliminated as a result of irreversible hole opening under load, even for a connection with 35 dowels and three steel plates. We conclude that two parameters are important for the design of these connections: the unload-reload stiffness and the zero-stiffness region measured between the zero load intercept of the unload-reload linear fit. With these, a reasonable estimate can be made of the displacement at any serviceability load level in either tension or compression.

Experimental study and theoretical analysis on the rotational performance of large-size glulam bolted joints with slotted-in steel plates

This paper presents a systematic study of the rotational performance of large-size glulam bolted joints (section height of at least 600 mm). The mechanical properties were investigated experimentally considering both the section height and bolt arrangement. All specimens failed with the splitting of the lowest row of bolts, and the numerical model considering splitting failure was validated by experimental results. According to the first position of crack initiation, crack modes were classified as tensile and compressive, and theoretical derivations of the crack moment were proposed. Moment-rotation curves were accurately obtained using the proposed equations of stiffness and moment.

Reduced and test-data correlated FE-models of a large timber truss with dowel-type connections aimed for dynamic analyses at serviceability level

The rise of wood buildings in the skylines of cities forces structural dynamic and timber experts to team up to solve one of the new civil-engineering challenges, namely comfort at the higher levels, in light weight buildings, with respect to wind-induced vibrations. Large laminated timber structures with mechanical joints are exposed to turbulent horizontal excitation with most of the wind energy blowing around the lowest resonance frequencies of 50 to 150 m tall buildings. Good knowledge of the spatial distribution of mass, stiffness and damping is needed to predict and mitigate the sway in lighter, flexible buildings. This paper presents vibration tests and reductions of a detailed FE-model of a truss with dowel-type connections leading to models that will be useful for structural engineers. The models also enable further investigations about the parameters of the slotted-in steel plates and dowels connections governing the dynamical response of timber trusses.

Load-Carrying Capacity of Double-Shear Bolted Connections with Slotted-In Steel Plates in Squared and Round Timber Based on the Experimental Testing, European Yield Model, and Linear Elastic Fracture Mechanics

Nowadays, the use of timber as a building material is gaining more prominence. When designing timber structures, it is necessary to pay increased attention to the design of their connections. The commonly used connections are dowel-type connections, which are often used in combination with steel plates slotted into cut-outs in timber members. The presented paper deals with the behavior of double-shear bolted connections of squared timber and round timber with slotted-in steel plates. Several variants of connections with different distances between the fastener and the loaded end were selected for the experimental testing. A total of six types of test specimens were made from spruce timber, for which their selected physical properties were determined and evaluated before the experimental testing. Test specimens of bolted connections were first tested in tension parallel to the grain until failure under quasi-static loading. The connections were broken by splitting. Ductile failure preceded brittle failure. The actual load-carrying capacities were lowest for the lowest end distance. The load-carrying capacities for the middle and the longest end distances were comparable. The results of the experiments were then used for comparison with calculation procedures according to the standard for the design of timber structures and with calculations according to the theory of linear elastic fracture mechanics. The experiments and the analytical models were supported by a simple numerical analysis based on the finite element method.

MOMENT RESISTANCE PERFORMANCE OF LARCH LAMINATED TIMBER BEAM-COLUMN JOINTS REINFORCED WITH CFRP

This study evaluates the moment resisting capacity of the drift pin larch beam-column joint with slotted-in steel plates of larch laminated timber. It is reinforced with carbon fiber reinforced plastic (CFRP) to suppress the brittle fracture of the beam-column joint and improve the joint capacity using larch laminated timber, a wood material manufactured by multi-layering of timber as a structural member of heavy timber.The average maximum moment capacity of the control specimen was 16.9 kN·m and the average maximum moments of the Type-A (volume ratio of joint reinforced with CFRP: 3.6%) and Type-B (volume ratio of joint reinforced with CFRP: 5.4%) were increased by 46% and 62%, respectively, compared to that of the control specimen. The capacity of the joint, such as the average yield capacity, ultimate moment capacity, and ductility ratio, of the control, Type-A, and Type-B specimens increased as the reinforcement ratio of the CFRP increased. For the failure mode of the control specimen, splitting failure occurred in both the column and beam members in the end distance direction. However, the splitting failure did not occur in the beam member due to the improvement of the joint and ductility of the specimens reinforced with the CFRP. The Type-A specimen had improved joint capacity and ductility compared to the control specimen; however, brittle failure occurred owing to the external force exceeding the joint capacity. However, in some of the Type-B specimens, the splitting failure did not occur in the column and beam members due to the CFRP reinforcement. Particularly, the Type-B3 specimen exhibited ductility.

Investigations of connection detailing and steel properties for high ductility doweled timber connections

According to Eurocode 8 moderate to high dissipative behaviour of timber structures requires sufficient ductility of the critical regions. Earlier experiments on timber connections with slotted-in steel plates and laterally loaded common steel dowels rarely achieved high ductility values. Connections consisting of LVL-C members, dowel-type fasteners with different post-elastic steel properties, full confinement of the timber member and measures to restrain the notch effect were investigated by means of monotonic and cyclic tests with regards to the displacement ductility. The measures taken proved to be effective in enhancing the plastic deformation capacity of the steel dowels to a large extent. However, a new aspect was observed: the constriction of the dowels in the contact area with the plate. The research results provided a better understanding of the factors influencing the behaviour of slotted-in steel plate connection.

Splitting load-carrying capacity of steel-to-laminated bamboo dowel connections with slotted-in steel plates

For engineered bamboo and timber structures, beam to column connections with slotted-in steel plates are prone to splitting failure. The splitting load-carrying capacity and failure mechanism of laminated bamboo dowel connections with slotted-in steel plates loaded perpendicular to grain were studied. The fracture parameters of laminated bamboo and yield moment of dowel needed to estimate the splitting capacity were determined by tests. A total of 24 connections in 8 groups were conducted to evaluate the effect of loaded edge distance and end distance of the dowels. The load-displacement curves of the connections and dowels were studied revealing the splitting failure mechanism of laminated bamboo dowel connections. Brittleness, low ductility and moderate ductility forms of the connections with different degrees of dowel bending were observed. Furthermore, the experimental results were compared with predictions from Van der Put and Jensen. The best prediction agreements were obtained from Van der Put model. Finally, a more accurate calculated equation for these connections has been developed.

Force\u2013displacement relations of bolted timber joints with slotted-in steel plates parallel to the grain

To study the force–displacement relations of bolted timber joints with slotted-in steel plates, we performed a monotonic loading test parallel to the grain on 24 specimens. The influences of the bolt diameter, timber thickness, and their ratio were considered. As shown by the test results, the joints had a high deformation capacity and experienced a linear stage, a stiffness degradation stage, a yield plateau stage, and a failure stage during loading. Based on the curve fitting and parameter identification, the force–displacement relations of the joints were summarized in a mechanical model with two parameters, i.e., the bearing capacity and the elastic stiffness. Based on theoretical analysis, we proposed a theoretical calculation formula for the bearing capacity and elastic stiffness of the joints. Finally, we calculated the force–displacement relation curves of bolted timber joints with slotted-in steel plates using the mechanical model and the theoretical formula. The calculated curves fitted well with the experimental curves.

Experimental study and analytical model of bolted connections under monotonic loading

Dowel-type connections are essential components of safe, economical timber buildings. This study analyzes the mechanical properties of different configurations of bolted connections with slotted-in steel plates. The test results indicate that the parallel-to-the-grain connections exhibited three typical failure modes, whereas wood cracking was the predominant failure mode of the connections perpendicular-to-the-grain. The mechanical properties, such as initial stiffness, yielding load, maximum load capacity and ductility, are obtained from load-displacement curves and compared with a design code. The relationship among the mechanical properties, bolt diameter and the thickness of glulam timber is investigated. Based on the experimental load-displacement curves, a two-parameter analytical model related to the initial stiffness and load-carrying capacity is proposed for the prediction of nonlinear load-displacement behavior, and the curves generated using the analytical model are consistent with the test curves. The two physical parameters can also be calculated using the design formulas, rendering the analytical model more useful in practice. This work is beneficial by contributing mechanical knowledge and providing a database for improved connection designs in timber engineering.

Influence of steel properties on the ductility of doweled timber connections

In the seismic design of structures according to the dissipative structural behaviour, the connection ductility is crucial in order to ensure the desired level of energy dissipation of the overall structure. Therefore, in case of ductile zones composed of dowel-type fasteners arranged in series, it is important to ensure that all the fasteners can fully develop their energy dissipation capacity by plastic deformations. However, when different types of connections made of two symmetrical and serially arranged assemblies of dowel-type fasteners are tested, it often appears that only few fasteners fully work in the plastic region while most of the remaining ones exhibit very low yielding.Looking at the causes of this dysfunction, a possible explanation is due to the fact that the rules for the seismic design of dissipative zones in timber structures given in international codes and used in common practice often make reference only to the steel quality of the dowel-type fasteners specifying a minimum tensile strength or sometime, like is the case of the current version of Eurocode 8, only to maximum values of the dowel-type fastener diameter and of the thickness of the connected timber or wood-based members. Also, the research conducted so far about the ductile behaviour of serially arranged connections was not focused on the post-elastic properties of steel. However, for the seismic design of ductile zones of other materials, such as for example is the case of reinforced concrete walls, post-elastic characteristics of steel are required for the reinforcing bars, in order to achieve the desired dissipative behaviour.Inspired by this fact, timber connections composed of serially arranged dowels made of steel grades with different hardening ratio and elongation at maximum tensile stress were fabricated and tested. The purpose of this work is to understand if the use of steel with significant post-elastic properties may help to solve the problem of limited yielding in serially arranged dowel-type connections.The tested specimens were composed of two symmetrical timber members made of Glulam and LVL connected to two 6 mm thick slotted-in steel plates by means of 9 steel dowels with a diameter of 6.0 mm, which were subjected to monotonic and cyclic tests carried out by implementing dowels made of steel with favourable post-elastic properties.The results showed that the simultaneous yielding of two serially arranged dowelled assemblies is possible, although not fully. Moreover, assuming as reference the steel grade with the lowest post-elastic properties, the connection ductility and strength measured through monotonic and cyclic tests increased by about 30% for the steel grades with the highest hardening ratio and elongation at maximum tensile stress, whereas the displacement at maximum strength was about five times higher.In addition, it was found that confinement of the timber members and shaping of holes were crucial in order to avoid undesired and premature brittle failures and to increase the connection strength and ductility.The results obtained may be useful in order to bring a reassessment of the code requirements regarding the steel properties of ductile connections as well as of certain principles of dimensioning and detailing.

Analysis and optimization of the bearing capacity of connecting wooden structures with application of dowel type self-drilling

The multiple shear connection with slotted-in steel plates and dowel-type self-drilling is a very efficient timber connections for frame and truss. It is used in practice, due to its high capacity and faster construction method. However, when the complex connection and many parameters affect the bearing capacity, instead of a ductile mechanism, brittle failure may govern its capacity. To achieve the desired working connection, the relationship between the connection configuration parameters is established but no standard specifically with this kind of connection. A series of parameters changes affecting the bearing capacity of the connection are given. Calculate and compare with many previous research methods in ductile failure modes to assess their prediction accuracy and optimal connection. A model for the optimization of the ductile failure mode for the multiple shear connections with slotted-in steel plates and dowel-type self-drilling is then proposed.