Estimation of withdrawal strength of different nail diameters in coconut (Cocos nucifera) lumber subjected to accelerated aging cycles using ultrasonic tests and multiple linear regression analysis

Outside urban areas, people often live in non-engineered structures; however, these structures are more vulnerable to natural hazards such as typhoons. Past studies show that pull-out (withdrawal) risk is significantly higher than pull-over risk on these structures in the Philippines. However, one of the limitations of destructive withdrawal tests is that specimens cannot be used once the testing is performed. To address this limitation, non-destructive tests (NDT) such as ultrasonic testing are performed. To date, there is no study for estimation of nail withdrawal strength of different nail diameters in wood using ultrasonic tests. Therefore, this study pioneers the use of ultrasonic test parameters as predictors for nail withdrawal strength of coconut lumber through multiple linear regression analysis. The prepared samples were subjected to different number of accelerated aging cycles. Ultrasonic and withdrawal tests were then implemented. Based on several performance indicators and adequacy tests, an overall best model was selected. The best model achieved an R2 value of 0.6381. The results also revealed that the lower-prediction bound of the developed model (i.e., best model) in this study may supplement existing structural codes, namely National Structural Code of the Philippines 2015 (NSCP 2015) and National Design Specification for Wood Construction 2024 (NDS 2024) and be used to conservatively estimate withdrawal strength of coconut lumber in non-engineered structures. This work contributes a novel, practical approach to improving structural safety in vulnerable communities in the Philippines.