Behavior of Steel Plate–Reinforced Cross-Laminated Timber Panels under Out-of-Plane Loading

Abstract

The use of steel plate reinforcement to improve the stiffness and strength of cross-laminated timber (CLT) was examined in this study. Double-shear lap tests were conducted to study the bond between wood and steel, and epoxy was determined to be suitable to bond steel to wood. Bond strength equations that limit plate thickness to prevent bond failure were proposed for use in panel design. Unreinforced, singly reinforced, and doubly reinforced panels were fabricated, with hybrid layers consisting of thin wood tie layers bonded to each side of each steel plate using epoxy, fabricated prior to panel assembly and used in a conventional panel manufacturing process. Panels were tested to failure under four-point bending in the out-of-plane direction. Steel plates in the test panels were 1.59 mm thick, and the measured secant stiffness at initial peak load was 2.26 times larger for the singly reinforced panel and 3.46 times larger for the doubly reinforced panel relative to that of the 175-mm-thick unreinforced panel. Test results were compared with analytical results from the shear analogy method. For the reinforced panels, an improved fit between model and test data was found when neglecting shear deformation. A parametric study was conducted using the shear analogy method with shear deformation neglected, and the use of steel plate reinforcement for a practical range of parameters was shown to provide a significant increase in out-of-plane panel stiffness. In the parametric study, the decrease in stiffness for a singly reinforced panel relative to a doubly reinforced panel with the same total plate thickness was less than 6%. This modest decrease suggests that use of singly reinforced panels may be favorable in some instances because the singly reinforced panel offers the benefit of simplified construction.