Screw withdrawal : a means to evaluate densities of in-situ wood members

Abstract

Dynamic modulus of elasticity (MOE) of a wood member is defined as the product of its density and square of stress wave speed. The dynamic MOE, which is highly correlated to the static MOE, is commonly used to estimate the load carrying capacity and serviceability of in-situ wood members. The stress wave speed can be estimated using ultrasonic, impact, or vibration techniques. However, nondestructive evaluation of density in place is more difficult than under laboratory conditions. Screw withdrawal resistance, one of the techniques that could be used to estimate the density, was examined on wood samples salvaged from old buildings. The results show that there is a good correlation relationship between screw withdrawal strength and the density. The result of screw withdrawal test on salvaged joists indicates that there is a good relationship between the static MOE and the dynamic MOE which is calculated based on the estimated density.

Citation

Cai, Zhiyong; Hunt, Michael O.; Ross, Robert J.; Soltis, Lawrence A. 2003. Screw withdrawal : a means to evaluate densities of in-situ wood members. Proceedings of the 13th International Symposium on Nondestructive Testing of Wood : August 19-21, 2002, University of California, Berkeley Campus California, USA. Madison, WI : Forest Products Society, 2003: Pages 277-281