Behaviour of gang-nail plated timber joints in tension perpendicular to the grain

According to the American Wood Association, a tension perpendicular to the grain failure is the evil of all wood connections. However there are very limited studies conducted to address this issue. This project aims to investigate the behaviour of timber joints using Gang-Nail Plates. A failure of a joint in a prefabricated timber roof truss as a result of tension perpendicular to the grain has the potential to be a catastrophic accident. The current method of analysing timber joints subject to a tensile force perpendicular to the grain is based on a professional engineers’ theoretical analysis without the physical test data. AS1720.1 Section 4 suggests a procedure to calculate the design capacity of timber joints using screws, bolts and nails but not for gang-nail plates. Through physical testing, the strength of timber joints with gang-nail plates was determined and the results were analysed to propose a new method of design. By this, destructive testing in accordance with AS1649-2001 has been conducted to find the failure mechanism and ultimate failure force. This was then analysed to find the relationship between the force, timber properties and plate geometry. It was found that the failure load of the timber joint increases with increasing bite depth. Similarly the joints with a 125mm plate exhibited a higher failure load compared to 75mm and plates at 45 degrees for a similar bite depth. Failure in tension perpendicular to the grain occurred just below the bottom row of teeth. All failures of the tested samples were observed to be along the grain in a similar location. From the analysis, it was found that the relationship between the bite per mm depth and the bite (or plate) width produced the equation for the design force of: ( ) This equation produced more consistent results when compared to the current MiTek method, however, as only one species and grade of timber was used during this investigation, the equation is only a fit for this material. Further investigation will now be required to confirm this equation’s fit with other materials by conducting a similar testing regime with other species, grades and engineered wood products