Nondestructive Assessment of Hardwood Cross-Laminated Timber

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Abstract

This study investigated the use of longitudinal vibration technique to evaluate the mechanical properties of cross-laminated timber (CLT) of four species of lumber—red oak (Quercus rubra), sweetgum (Liquidambar spp.), yellow poplar (Liriodendron spp.), and southern pine (SYP; Pinus spp.). The hardwood CLTs for this study were made from low-grade lumber; SYP CLT was industrially manufactured. The dynamic modulus of elasticity (dMOE) was assessed using the Fakopp device. After nondestructive testing (NDT) evaluation, samples were then destructively tested and correlations between various properties were developed. These properties included bending modulus of elasticity (MOE), modulus of rupture (MOR), density, and dMOE. There was moderate correlation between MOE and dMOE for three of the species tested—red oak, sweet gum, and SYP; however, a weaker relationship was observed between MOR and dMOE for all species tested. The coefficient of correlation for MOE against density showed that 30 to 64 percent of tested samples fit into the linear relationship. The coefficient of correlation result suggests that NDT could be reliable for predicting the bending MOE of CLT. The NDT result for hardwood samples also showed that CLT from low-value hardwood lumber could be used for construction purposes, with 95 of 96 hardwood samples exceeding 8,300 MPa, the minimum allowable strength value specified in American National Standards Institute/The Engineered Wood Association for softwood CLT. This research shows that NDT techniques can be used for estimation of mechanical properties of hardwood CLT and are able to improve the grading of mass timber products.

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