Design and Construction of Modern Glued Timbers

In Douglas-fir it has been found that the best economy and quickest delivery are obtained by using combinations of lumber grades which have bending stress levels at or below 2,600 psi. The best practice is for the designer to specify stress levels rather than grades. Working stresses for glued timbers are higher than those of sawn timbers of the same grade. Grading of laminations is performed to the standard and dressing rules of the lumber associations. Two-inch laminations are the most economical of glue, lumber, and labor. End joints in laminations occur in nearly all work, since lumber lengths are seldom long enough to avoid splices. The construction and location of end joints are of great importance to the strength and appearance of the timber. The types of joints include plain scarf, stepped scarf, butt joints, pegged scarf joints, double-bevel plain scarf joints, and pre-glued joints. Fire-resistance of glued timbers is excellent because they are large size and have fewer connections.

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