The Performance of Bond Lines of Engineered Wood in Cone Heater Testing

Engineered wood structures are widely used in modern buildings, for example, glued laminated timber, cross-laminated timber, finger-jointed solid wood, laminated veneer lumber, and so forth. These products often contain bond lines between the lamellae and/or within the lamellae. The most common types of bond lines are face bonding, finger joints, and edge bonding. The type of bond line can impact the behaviour of engineered wood in fire. At ambient temperatures, the bond line integrity is usually maintained; however, at elevated temperatures or in fire, the bond lines can lose their integrity. The new Eurocode 5 for fire design of timber structures will contain different design scenarios and parameters depending on the behaviour of adhesives at elevated temperatures. This paper aims to support the development of the new Eurocode 5. The bond line integrity was tested with 10 adhesives using two cone heater test methods and furnace tests with glulam. All specimens were made with softwood. Loaded finger-jointed specimens and unloaded face-bonded specimens were tested under the cone heater. Unloaded glued laminated timber specimens were tested in a model-scale furnace. The results are analysed and compared. Generally, a good correlation between the different types of tests was seen. The same adhesives tested in various experiments showed similar performance levels. Adhesive families may have different performances depending on various factors. To assess the adhesives and choose the appropriate calculation method, test methods for assessing the adhesives with cone heater are analysed, compared to fire test results, and proposed in this paper.