Nondestructive Prediction of Load-Deflection Relations for Lumber
Keywords:
Lumber strength, acoustic emissions, proportional limit, ultimate deflectionAbstract
Three machine-stress-rated grades of Douglas-fir lumber were pretested to the proportional limit (PL) under an accelerated deflection rate with a microcomputer-controlled testing machine. The same specimens were then tested to failure. Load, deflection, and acoustic emissions (AE) were monitored continuously throughout the testing. The observations from nondestructive testing were used as independent variables in regression models to predict the destructive parameters.
Computer-detected PL was highly correlated with PL determined from destructive testing (r = 0.92). The correlation of the computer-detected PL with modulus of elasticity was a good estimator of lumber strength (r = 0.83) but a poor predictor of ultimate deflection (r = 0.54). A combination of AE variables below the PL and physical properties was strongly correlated with PL (r = 0.76), strength (r = 0.93), and ultimate deflection (r = 0.83).
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