Timber bond performance

Subsequent work was, therefore, directed to substitution of resorcinol, a much more expensive phenol, in cold-setting, waterproof adhesives (38). Formulations based on 30 to 60% of extract mixed with a resorcinol-formaldehyde condensate and additional formaldehyde met pot-life and assembly time requirements for timber lamination. Test bonds passed requirements of the major performance standards in the United States, but competition from lower cost, phenol-modified resorcinol resins and the lack of longterm commercial perfor-... 

This article discusses briefly the use of adhesives on the construction site in the context of structural repair and reinforcement the requirements and practical dilficulties in the work on site with regtirds to the strength and durability of the rehabilitated timber structure and the consequent need for queility control. It also highlights the characteristics and requirements that must be fidfilled by structural adhesives and reinforcing materials factors affecting performance and durability of bonded joints tmd ways to improve adhesion and durability. Finally, it points out some research needs and future developments identified by the authors. 

Wood is a porous, permeable, hygroscopic, and orthotropic material of extreme chemical diversity and physical complexity. Because of this, its properties vary between species, between trees within a species, and even within a tree. This variability can result in an adhesive to produce bonded joints that will perform inconsistently and with different levels of performance among the several types of timber species. 

Nevertheless, more research work is needed to develop appropriate test methods for the accrual of accurate property performance data that consider realistic loading and environmental conditions to overcome the lack of information about extreme service temperature and fire resistance of bonded connections to develop realistic predictive tools for the long-term behaviour of bonded timber joints and connections. These are required in order to promote their wider use through the increased confidence of architects, designers and owners alike. 

Key words on-site bonded composite systems, repair, reinforcement and seismic retrofit, timber and concrete structures, limitations and requirements, performance and durability. 

Structural analysis showed the need to reinforce a number of joints in the top chord of one of the truss arches (Fig. 22.8) to enhance their resistance to wood splitting perpendicularly to the hbres. The perpendicular to wood grain reinforcement of the timber member, in the connection, was performed by internal bonding of threaded rods. These rods were inserted perpendicularly to the existing metallic fasteners close to the beam end (Fig. 22.9). Three rods were used per joint, located just after the beam joint fasteners (Fig. 22.10). The threaded rods, having a diameter of 16 mm, were bonded into... 

Temperature is an important factor in the durability of structural adhesive joints, since it can affect the creep, fatigue and fire performance of adhesive bonded joints. Well-designed and well-made joints with any of the normally structural adhesives should retain their mechanical properties indefinitely if the substrate moisture content is kept low (e.g., if timber moisture content stays below approximately 15%) and if the temperature remains within the range of human comfort. However, when adhesives are exposed either... 

---