Novel type engineered structural beams from pine lumber
CommitteeGrebner, L. Donald
Seal, Dan R.
Shi, Q. Sheldon
The intersection of decreasing resource size and increasing population and its associated demand creates a pressing need to develop products that act as alternatives to solid sawn lumber. Engineered composite lumber is one such alternative. The product described herein utilizes a modified form of sawn lumber as the raw material. The objective of this research was to manufacture, mechanically test, and evaluate a novel type of engineered lumber. Non destructive evaluation of raw materials and finished beams, and final mechanical testing to determine mean strength and stiffness values as per ASTM 5456 were used. The mechanical property data was converted into design values for fiber stress in bending (Fb) and stiffness (MOE). These design values was compared to those published by the U.S. (NDS) for wood construction. Pine logs were reduced into cants and further processed into matched symmetrical trapezoids. Symmetrical trapezoids were then non-destructively evaluated via E-computer and Director, and sorted by results. Next, the sorted trapezoids were matched into pairs and assembled into bowtie beams. Polyvinyl acetate adhesive was used throughout. Stiffness of the manufactured beams was nondestructively evaluated too. Then the beams were mechanically tested. The information from the E-computer was correlated to the strength and stiffness for each beam. The design strength and stiffness was compared to the values of sections of equivalent depth and maximum width as shown in the NDS. Also, non destructive test values were compared and correlated to those from the destructive tests. Finally, the design strength and stiffness values were respectively multiplied by the sectional area or the moment of inertia. This produced a strength efficiency factor and a stiffness efficiency factor. These factors were compared to factors derived from multiplying the design strength or design stiffness values (from the NDS) times the area or the moment of inertia of a rectangular section of equivalent depth and maximum width. It is found that the mechanically efficient bowtie section produced an increased strength and stiffness efficiency as compared to that of solid sawn material.