Long-span cross-laminated timber (CLT) floors are typically an assembly of prefabricated CLT panels connected together on the site. The actual connections are commonly neglected in design calculations. Hence, a CLT floor is modelled either as a monolith slab or more frequently as a set of CLT panels with no connections at all. This paper presents a numerical study designed to examine the influence of two most common inter-panel connections, i.e. single surface spline and half-lapped joint, on vibration modes and vibration responses of a range of different CLT floors due to pedestrian-induced loading. Although the inter-panel connections are relatively complex in reality, they are modelled here as an equivalent 2D elastic strip between the CLT panels. This relatively simple yet robust model can be used with ease in design practice, regardless finite element (FE) software used to extract vibration modes of a CLT floor. The corresponding monolith floors and floors without inter-panel connections are studied for the comparison of the results. Vertical vibration responses are simulated for low-frequency and high-frequency floors using the corresponding walking force models given in a popular design guideline for footfall induced vibrations of civil engineering structures. Vibration responses were calculated for single pedestrian occupants and their walking paths parallel and perpendicular to the line of connection. The results showed that including the inter-panel connections in a FE model resulted in up to 2.5 higher RMS acceleration levels. Hence, the common practice of modelling CLT floors as monolith slabs or as a set of panels without connections should be left behind.
Four kinds of glued laminated timber were produced (i.e., one with a glued edge-joint and the other three with nonglued edge joints) in the lamina at different positions toward the depth direction. Shear tests using an asymmetric four-point bending method were then conducted for these glued laminated timber specimens. The results showed that although the glued edge-joint specimens had the highest shear strength in all groups, the shear strength decreased as the distance from the adjacent nonglued edge-joint plane decreased. Furthermore, the shear strength of all specimens exceeded the standard shear design strength value (2.1 N/mm2) set by the Ministry of Land, Infrastructure, Transport and Tourism, Japan. Next, the shear strength of the nonglued edge-joint specimens was estimated based on that of the glued edge-joint specimens. Although the mean-estimated shear strength was lower than the mean-measured shear strength, the possibility of the shear strength changing based on the position of the nonglued edge-joint plane specimens from that of the glued edge-joint specimens was still estimated.
In this paper the load-bearing behaviour of traditional and newly developed timber-timber connections, multi-step and free formed, are analysed within an extensive investigation focusing on joint failure. DIC measurements allowed for an assessment of the initial behaviour of the systems and their specific failure modes. By comparing the stiffness and various load levels to those of typical joint designs the improved load-bearing behaviour of the proposed joints was demonstrated while defining the range of the obtained linear-elastic phase. The results show that the onset of failure, based on the ultimate load, strongly depends on the geometry of the joint.
Inaccuracies within timber step joints are a perennial problem of the wood construction industry. Even perfectly constructed carpentry step joints can become imperfect due to a change in moisture content. The predominant question when looking at step joints with gaps is to what extent the load-bearing behaviour is influenced by these inaccuracies. The authors look beyond this question and investigate if intentionally manufactured gaps could have a positive influence on the load-bearing behaviour and the failure mode of regular and newly designed carpentry joints.
Dowel-type joints are widely used in timber structures given their ease of construction, strength, and capacity to deform before failure. The embedment strength of timber and the bending moment capacity of dowels are considered key properties in the design. On the other hand, these properties have an inherent variability that increases the uncertainties related to the connection’s strength and associated failure modes. This study proposes to quantify the uncertainty related to the statistical correlation behavior between the timber embedment strength and dowel bending moment capacity while comparing analytical solutions to the results of double shear single doweled timber joints. Traditional distribution fitting procedures, as well as copula functions, are implemented to capture their marginal and dependence behavior. Since their source of mutual correlation is known, the effectiveness of the different approaches in describing the statistical dependence structure can be assessed. This is done by investigating how equivalent are the descriptions of dependence by copula functions and directly from the correlation origin. Results obtained here indicate that, for single dowel-type connections in double shear, the impact of the copulas on the results is small, which means that improving their joint characterization represents a minor improvement in the reliability results. Besides the minor differences, the results show that copula functions are a viable tool capable of capturing the nuances of the joint behavior between random variables.
A new connection concept for joining cross-laminated timber (CLT) plates in their secondary direction is presented. The connection consists of two laminated veneer lumber (LVL) gusset plates with finger-joint-like profiles milled on one side which are glued onto the outermost layers of the CLT. It is demonstrated that the joint represents a stiff moment resistant connection, enabling the activation of the normally underutilized biaxiality of CLT plates and expanding the design freedom of architects and engineers. The concept was analyzed by means of analytical and finite element (FE) models for two geometry alternatives, differing in either a 2D or 3D tapered finger profile. The 3D tapered finger profile produced a stress reduction of around 5% in the region of stress concentration and a more even shear stress distribution on the bonded surface. Thereafter, four specimens were manufactured – two of each geometry alternative – and then tested in four- and three-point bending setups in order to assess the behavior at pure bending as well as at combined moment and shear loading, respectively. At pure bending, the studied connection delivered bending capacities of 100% of the characteristic value of the unjointed CLT material. For the case of moment and shear loading, the global capacity was determined by a bending failure in the CLT region subjected to maximum moment, while the joints remained unbroken. Measured deformations and strains during the tests validated the FE model, which can be used to further develop the connection concept, which allows for a full activation of the biaxial behavior of large-span CLT floors.
Cross-laminated timber panels offer an effective option for timber structures; they allow biaxial load transfer and have good dimensional stability. However, practical transportation and handling limits size of the panel and a stiff connection between the panels is required to effectively utilise biaxial properties. In this paper, a dovetail splice joint for timber panels is presented using cross-banded LVL with cast concrete grout interlayer. The interlayer allows a tight fit, which is important for stiffness, but also avoiding installation problems due to manufacturing tolerances and moisture-induced dimensional changes. The mechanical behaviour of the dovetail joint was investigated experimentally for various geometries. Furthermore, a numerical model was developed that shows a wide agreement with the experiments, especially in the cases with governing failure in the LVL. Using the numerical model, a parameter study was performed where the influence of the connection length (number of dovetails) and the joint geometry on the strength and stiffness properties was investigated. Besides the optimal geometrical configurations of the dovetail joint, also a significant increase of the strength and stiffness properties with increasing connection length was identified.
This paper presents an experimental evaluation of the fire resistance of glued-in rod timber joints using epoxy resin, with and without modification. A heat-resistant modified resin was designed by adding inorganic additives into the epoxy resin, aiming to improve the heat resistance. Joints that were made using the modified epoxy resin at room temperature showed a bearing capacity comparable to those with commercial epoxy resin. Twenty-one joint specimens with the modified epoxy resin and six with a commercial epoxy resin were tested in a fire furnace to evaluate the fire resistance. The main failure mode was the pull-out of the rod, which is typical in fire tests of this type of joints. As to the effects of the test parameters, this study considered the effects of adhesive types, sectional sizes, stress levels, and fireproof coatings. The test results showed that the fire resistance period of a joint can be evidently improved by modifying the resin and using the fireproof coating, as the improvements reached 73% and 35%, respectively, compared with the joint specimens with commercial epoxy resin. It was also found that, for all specimens, the fire resistance period decreased with an increase in the stress level and increased with an increase in the sectional sizes.
Stress-laminated timber (SLT) decks in bridges are popular structural systems in bridge engineering. SLT decks are made from parallel timber beams placed side by side and pre-stressed together by means of steel rods. SLT decks can be in any length by just using displaced butt joints. The paper presents results from friction experiments performed in both grain and transverse direction with different levels of pre-stress. Numerical simulations of these experiments in addition to comparisons to full-scale experiments of SLT decks presented in literature verified the numerical model approach. Furthermore, several alternative SLT deck configurations with different amounts of butt joints and pre-stressing rod locations were modelled to study their influence on the structural properties of SLT decks. Finally, some recommendations on design of SLT bridge decks are given.
Until today, all known timber building systems allow only slabs with a uniaxial load bearing action. In the framework of a large research project a new timber slab system has been developed and already tested in first real applications. The developed slab system is designed for housing, commercial and industrial buildings. The slab system works as a flat slab carrying vertical loads biaxial and consists of timber slab elements like CLT glued together on site with a high performing butt-joint bonding technology. This technology was called Timber structures 3.0 (TS3). Several research and tests about the performance of the different slab elements and the butt-joint bonding have been performed. First structures have been built and proof the system.