Abstract
This paper investigates the influence of gap size (openings/spaces between two structural members) and the presence of intumescent sealants on the development of temperature when timber ...connections are exposed to fire conditions. The experimental results of 21 samples representing a concealed steel‐to‐timber connection configuration that was exposed with a 0, 3, 6, and 10 mm gap to the ISO834 standard fire for 120 min are presented. Half of the samples in each sample group were protected with an intumescent fire protection sealant. The temperatures in the timber were measured at various locations around the gap and directly next to the steel component. The experimental results show that the presence of a gap increases the temperature of the timber more than predicted by the thermal penetration models available, with current code guidelines (e.g., Eurocode 5) possibly being non‐conservative. The use of an intumescent fire protection sealant in the gap is shown to be an effective protection method, but that the application configuration is important to ensure effective protection, especially as the gap becomes smaller. The results also show that the use of an intumescent fire protection sealant in a gap increases the predictability of the temperatures in the timber in longer duration fires. Unprotected samples and 0 mm gap samples exhibited large variability in the thermal development outcomes over time.
•Exploring the effect of screw size on the mechanical properties of the steel beam–CLT panel connection.•Investigating the effect of screw size and spacing on the vibration serviceability of the CLT ...floor by numerical simulation using OpenSees.•Reducing the screw spacing from 1400 mm to 181 mm produced a 38.3% decrease in VDV.•Proposing a theoretical model to predict the fundamental natural frequency and a design method to predict the VDV of the CLT floor.
Due to the lightweight nature of timber, vibration serviceability is a crucial issue in the design of timber floors. The purpose of this study is to investigate how beam–panel connections affect the vibration serviceability of cross-laminated timber (CLT) floors subjected to multi-person loading. Cyclic tests were carried out to determine the mechanical behaviour of steel beam–CLT panel connections with various screws sizes (diameters and lengths). A numerical model of a CLT floor was developed to determine the response to human-induced vibrations with different screw configurations (sizes and spacing). The results showed that the dynamic characteristics of the floor were slightly impacted by the screw size. However, as the spacing between screws reduced, the fundamental natural frequency increased by 4.3% and the vibration dose value (VDV) of the floor decreased by 38.3%. A theoretical model was introduced to predict the fundamental natural frequency of a CLT floor system. In addition, a design method for predicting the vibration serviceability, in terms of VDV, of low-frequency CLT floors was proposed.
Feasibility and acceptable performance of the steel-timber composite (STC) system as a sustainable alternative to conventional steel-concrete composite have been demonstrated through recent static ...push-out and bending tests. But, structural behaviour and energy dissipation capacity of the STC connections subjected to cyclic loads have not been investigated yet. This study investigates the cyclic behaviour of STC connections with mechanical shear connectors. In total, twelve STC joints were fabricated by connecting the cross-laminated timber (CLT) panels to the flanges of a steel profile and the joints were subjected to low-cycle high-amplitude loading regime. Effects of the shear connector type (i.e. screw, high strength bolt), shear connector size and the orientation of CLT panels (outer lamellas parallel and/or perpendicular) with respect to the direction of the load were considered in the experimental program. The ductility, strength impairment and equivalent viscous damping which characterise the performance of a mechanical shear connector under cyclic loading conditions in steel-timber composite connections were assessed. The results of the cyclic tests demonstrated the high ductility and energy dissipating capacity of the steel-timber composite connections. A simple hysteretic model was proposed for steel-to-CLT composite connections with bolt and screw shear connectors and the model was calibrated against the results of laboratory experiments.
•Cyclic behaviour of steel-timber composite connection is experimentally investigated.•Steel-timber composite connections have high ductility and energy dissipating capacity.•Four different modes of failure were observed in the steel-timber composite connections.•The strength deterioration in cyclic loading is much higher than that in monotonic loading.•A simple analytical hysteretic model is calibrated and developed.
The experimental results of timber bolted connection tests for the purpose of optimizing the use of current design standard are presented. The test was conducted to investigate the structural ...performance of bolted connections loaded parallel to the timber grain. Both ductile and brittle failure modes were investigated to identify the governing parameters that affect the types of failures. The Meraka hardwood was chosen because it was found to be commonly used in the construction of the structural components of floor and roof diaphragms in Malaysia unreinforced masonry (URM) buildings. From this study, a wood database can be established for assisting the design engineers in developing the retrofitting technique of the building, especially the timber diaphragm joint part of the wall-diaphragm connections. Eighteen characteristics of steel-wood-steel (SWS) with a single row bolted joints were tested in tension, whereas ten specimens were prepared for each connection group. From the results obtained, it can be observed that the current timber design code is far too conservative compared to the optimized design proposed in this paper.
•Brittle failure modes may happen in timber connections loaded parallel-to-grain.•Splitting is the main brittle failure in connections with one row of fasteners.•A new and simple model dealing with ...splitting failure is proposed.•The new approach clearly improves the accuracy of the existing proposals.
Timber connections with one row of fasteners can fail, as the rest of timber connections, in a ductile (yielding of the fastener and embedment of the timber) or in a brittle way (wood fracture). In this latter case, one of the most common brittle failure modes is splitting, which has been traditionally assumed to be avoided in design practice by respecting a minimum spacing between fasteners. This measure reduces the possibilities, but it does not guarantee to avoid splitting. A new model dealing with splitting for connections with one row of large diameter fasteners loaded parallel-to-grain is presented in this paper. An extensive database of tests is used to compare the new approach with the existing models and to demonstrate the reached accuracy improvement.
AbstractThis paper experimentally investigates the influence of the strain rate experienced during earthquake and progressive collapse events on mechanical properties affecting the design of softwood ...laminated veneer lumber timber connections. The parallel and perpendicular to grain embedment stiffness and strength, tension strength perpendicular to grain, and Mode I and II fracture energies were examined under four levels of strain rates. Results showed that the embedment stiffness and strength increased by up to 35% from the quasi-static to dynamic strain rates, whereas the embedment ductility decreased by up to 17%. The fracture energies and tension strength perpendicular to grain were found to be mostly insensitive to the investigated range of strain rates. Furthermore, the influence of the strain rate on the behavior of timber connections is analyzed and discussed by (1) using the experimental data in the European standard design equations for single and double shear connections; and (2) quasi-statically and dynamically testing one connection type with two different fastener spacings. Results showed that for the connections investigated, the dynamic strength can be up to 30% higher than the quasi-static one, however, the dynamic ductility of the connections can be reduced substantially by up to 32.5%.
•Brittle failure modes may happen in timber connections loaded parallel-to-grain.•A new model for brittle failure in joints with large diameter fasteners is proposed.•As a design model, it aims to be ...clear and simple for designers.•The new proposal improves the accuracy of the existing models.
Timber connections may collapse in a brittle or in a ductile mode. The calculation models of timber joints are mainly focused on ductile failure mode, since it has been traditionally assumed that brittle failure was avoided by respecting a minimum spacing between fasteners. However, this assumption alone does not guarantee a ductile failure. This paper proposes a new design model dealing with brittle failure modes of timber connections with large diameter fasteners (those protruding the whole thickness of the timber member such as dowels or bolts). A comparison between the proposal and the existing models, using an extensive database of tests, is used to demonstrate the improved accuracy of the proposed design method.
This study investigates timber connections with flexible polyurethane adhesives, which prove to have the potential for timber-adhesive composite structures without mechanical connections for seismic ...regions. Results of conducted cyclic double lap-shear adhesive timber joints tests were compared with available experimental results on timber connections with standard mechanical dowel-type fasteners and with results of numerical finite element analysis. The study found that the shear strength, elastic stiffness and strength degradation capacity of the flexible adhesive connections were significantly higher compared to mechanical fasteners commonly used in seismic-resistant timber connections. The latter, however, manifested larger ultimate displacements but also yielded at lower displacements.
This work aims to present a study approach for double-shear connections of wood under fire with dowel pins and plates in steel material, using different types of glulam. The simplified Eurocode ...equations for ambient temperature were used to determine the dimensions and the number of dowel pins that each studied connection needs in order to resist an applied tensile load. Following this methodology, the finite element method was used to assess the thermal analysis of the studied connections under fire. The study aims to increase the information on these connections, where the wood material represents a complicated behavior in fire circumstances, with the addition of the steel material. The heat conducted by the dowel pin inside the connection, and the steel plate and its effect on the wood were analyzed. According to the results, it can be assumed that the temperature evolution is due to the geometry of the connection, the dowel pin or plate position, and the glulam density. Inside the wood element, the temperature remains lower, and externally a charred depth is developed when the target temperature of 300 °C is reached, and, in the vicinity of the dowel pin or the steel plate, a burned wood depth is indirectly formed. The rate of the charred layer is not constant throughout the entire fire exposure. Steel-to-timber connections with an internal steel plate with high glulam density have greater fire resistance due to the lower temperatures obtained.
•Brittle failure in multiple shear planes timber connections has been scarcely studied.•An overview of the main existing models for brittle failure is given.•A stiffness model is proposed to apply ...these models in the studied connections.•A set of experimental tests is performed to assess the ability of the models.•When the existing models are combined with the proposal, the accuracy is improved.
The multiple shear connection with slotted-in steel plates and dowel-type fasteners is a very efficient timber joint for large timber cross sections. It is used in practice, mainly due to its high capacity and its better performance under fire. However, when the number of inner plates is increased, instead of a ductile mechanism, brittle failure may govern its capacity. No standard deals explicitly with this kind of joint.
A set of tests has been performed in order to study the brittle failure of this kind of connections. The test results are then compared with the available prediction models that study both ductile and brittle failure modes to assess their prediction accuracy. An improved model for the assessment of the brittle failure mode for the multiple shear connections with slotted-in steel plates and dowel-type fasteners is then proposed.
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