Empirical Investigation of Withdrawal Capacity of Staple for Experimental Design of Irish Timber

Sitka spruce is the main tree species grown in Ireland, covering over 50% of the forest area. Despite this, Ireland imported €1.8 billion worth of wood products in 2020 mostly from UK, China, US and Sweden. One of the factors that currently limits the specifying of Irish grown timber in construction applications is the lack of data relating to its structural performance. Expanding the use of this locally available material in construction will add economic and environmental benefits, creating new opportunities for employment. In order to effectively use Irish timber for structural purposes, a comprehensive analysis of its inherent properties is essential. However, much of this data is limited, outdated or entirely lacking in the public realm. Timber element design is influenced by the connection stiffness which is in turn effected by the connection withdrawal capacity. Staples are a conventional fastener, providing a strong and stiff timber connection compared to alternatives. However, few works have focused on proving the characteristics of staple fastener connections. To thoroughly analyse the withdrawal capacity of staples in Irish Sitka spruce timber, it is crucial to understand the behaviour of staples in various grades of timber and the impact of various parameters on the withdrawal strength. This study focuses on providing an empirical equation for withdrawal load of staples in timber for varying densities and developing an empirical equation using gene expression programming by incorporating the most influential parameters affecting withdrawal load. Furthermore, sensitivity analysis shows the influence of each parameter on the withdrawal load