BENDING STIFFNESS OF STRESS-LAMINATED TIMBER DECKS WITH BUTT JOINTS

Stress-laminated timber bridge decks consist of lumber assemblies tran sversely posttensioned with high-strength steel bars. The lumber compo nents 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 regula r pattern, with one butt joint in a group of three to five laminae. Th e presence of butt joints in a bridge deck reduces its longitudinal be nding stiffness. Since stress-laminated timber bridge decks are modele d as orthotropic plates, the actual system stiffness properties are ne eded in the analysis. This paper presents an analytical-experimental s tudy to verify existing bending stiffness reduction factors for decks with regular butt-joint patterns. Forty northern red oak and hickory s tress-laminated beams with three butt joint patterns and subjected to three transverse stress levels are tested in bending, and the experime ntal responses are correlated with existing theoretical predictions us ing linear regression analysis. Design recommendations are presented.