Coralie Avez

Timber Joints with Multiple Glued-in Steel Rods

Timber joints with glued-in rods constitute a viable solution for numerous applications as they exhibit advantages, e.g., the formation of very stiff connections, high fire resistance, and improved aesthetics. Most previous research has focused on testing single rod joints to evaluate the influence of parameters on structural performance; in practice, however, multiple steel rods are required to transfer the loads from one structural component to the next. The lack of design guidance related to the performance of multiple glued-in rods hinders the widespread application of this joint type. This paper describes experimental investigations on joints composed of glued-in steel rods in glue-laminated timber. The influence of the anchorage length was studied to establish performance benchmarks; then joints with multiple rods (two, three, and four rods with the spacing between rods varied) were manufactured and tested under uniaxial quasi-static tension loading. The results showed that for joints using multiple mild steel 12.7 mm glued-in rods, a ductile failure can consistently be attained if: i) the anchorage length of the rod is longer than 10 times the diameter; and ii) the spacing between rods is five times the rod diameter. The results contribute toward a better understanding of the performance on timber joints with multiple glued-in rods.

Load-Bearing Capacity of Traditional Dovetail Carpentry Joints with and Without Dowels: Comparison of Experimental and Analytical Results

Post-disaster field studies widely suggest that historical timber structures are seismically resistant, and a growing number of experimental studies support this observation. The joints between structural members, which are the major energy dissipation mechanism within the structure, play a crucial role in the overall robustness and the way that a structure handles the seismic demand. Joints mostly fail when the timber members are still in the elastic range, therefore a thorough understanding of their behaviour under various loading schemes is of utmost importance to gain deeper insight about the overall structural performance of timber structures. This paper summarizes the findings from a series of testing carried out on dovetail joints, which is one of the most common traditional carpentry joints, during the 5th COST FP 1101 Training School, held in University of Minho, Portugal. Within this framework, a dovetail joint (with and without dowel) was tested under compression and tension. The experimentally obtained load-bearing capacity of the joints was then compared to the capacity values calculated using analytical models, and the failure modes were further discussed. The results showed that the experimentally obtained capacity values can be successfully reproduced by analytical models for dovetail joints without dowel. On the other hand, the capacity of a dovetail joint with dowel under compression or tension is always underestimated by analytical models.

Finite element modelling of inclined screwed timber to timber connections with a large gap between the elements

Since the 80’s, Johanssen’s Yield Theory has been adapted to fit new design practices: fastening of timber elements with a layer of insulation (or gap) between the elements or fastening with inclined fasteners. However no rules exist for connections with large gaps (up to 500 mm) and inclined fasteners. The behaviour of screwed connections (timber/large gap/timber) is modelled using an orthotropic material, cohesive surface, Hill criterion and a fictitious material that wraps the screw and models a complex medium where steel and wood interact. The calibrated FE model is finally compared to experimental results.

Experimental and Analytical Assessment of the Capacity of Traditional Single Notch Joints and Impact of Retrofitting by Self-tapping Screws

The joints are the most crucial parts of a timber building and determine the overall structural behaviour, load-bearing capacity and failure mechanisms. Therefore, keeping the joints fully functional is of utmost importance to ensure a desired structural performance of timber buildings under various actions. Since replacement of damaged parts of an existing structure is expensive and in many cases very difficult to perform in situ, retrofitting to avoid failure becomes an increasingly widespread strategy. In this paper, the capacity and failure mechanisms of single notch joints before and after a simple retrofitting intervention by means of self-tapping screws were investigated. To this end, a series of tests were carried out during the 5th COST FP 1101 Training School, held in University of Minho, Portugal. The joints were first tested under compression, and the load-bearing capacity values obtained at the end of tests were compared to the capacity values calculated using theoretical models proposed in a variety of national codes. Then, tested joints were retrofitted using self-tapping screws. The retrofitting strategy aimed to prevent failure mechanism that was shown to dominate joints’ behaviour in the unreinforced state, rather than to increase the load-bearing capacity or stiffness. The impact of retrofitting on the joints’ performance was discussed and the success of the proposed intervention was further debated.

Large-diameter single dowel joint: finite element modelling of a reinforced joint

Finding new efficient connectors or improving existing ones are important issues in timber construction. This research investigates an innovative large-diameter dowel-type connection by using a finite elements model calibrated with experimental results. This connection is made of a large-diameter single dowel reinforced by means of a steel plate with a vulcanised rubber layer. The steel plate shape, thickness and dimensions, the rubber stiffness, the steel mechanical properties, etc., are parameters that may influence the critical load of the plate. The joint load-bearing capacity is also highly depending on the load direction to the grain. Those parameters are investigated using FE modelling and discussed in order to propose design recommendations.

Stiffness of prosthetic repairs for historic timber beams

Glued connections are often used as reinforcements or repairs of decayed parts in historic timber frames. Those timber frames are most of the time statically indeterminate structures, meaning that the ratios of stiffness between different members and joints of the structure are related to distribution of stresses within the structure. Hence, a poor repair, i.e. a too stiff or at the contrary a too flexible intervention may change dangerously the distribution of stresses within the structure, induce cracks and damage the whole structure. However, there are still no guidelines on how to evaluate the stiffness of glued connections and therefore, on how to predict the impact of these interventions on the force distribution in the timber frame. This paper focuses on glued-in rods, and uses finite element models to predict and compare the stiffness of glued-in rods in different configurations of repairing connections. This study shows sensitively different axial stiffness between those configurations: they may indeed vary in the ratio of one to two for the same strength. This highlights the importance of predicting the stiffness of glued-in rod connections to be able to make recommendations for the configuration which best respects the original structure.