Bending stiffness of stress-laminated timber decks with butt joints

Stress-laminated timber bridge decks consist of lumber assemblies transversely posttensioned with high-strength steel bars. The lumber components contain end-to-end butt joints to span the length of the bridge. At any cross section of the bridge, the joints are placed in a regular pattern, with one butt joint in a group of three to five laminae. The presence of butt joints in a bridge deck reduces its longitudinal bending stiffness. Since stress-laminated timber bridge decks are modeled as orthotropic plates, the actual system stiffness properties are needed in the analysis. This paper presents an analytical-experimental study to verify existing bending stiffness reduction factors for decks with regular butt-joint patterns. Forty northern red oak and hickory stress-laminated beams with three butt joint patterns and subjected to three transverse stress levels are tested in bending, and the experimental responses are correlated with existing theoretical predictions using linear regression analysis. Design recommendations are presented.