Section 7 - Lumber—Calculations to Select Framing and Trim Materials

Abstract

This chapter discusses how to carry out calculations to select framing and trim materials from lumber. Rift sawing at a 30-degree or greater angle to the growth rings produces narrow boards with accentuated vertical grain pattern. Rift-sawn boards are often favored for fine furniture and other applications where matching grain is important. When loads are applied, structural members bend, producing tension in the fibers along the faces farthest from the applied load and compression in the fibers along the face nearest to the applied load. Horizontal shear stresses tend to slide fibers over each other horizontally. Most predominate in short, heavily loaded deep beams. Increasing beam cross section decreases shear stresses. The internal stress induced by this kind of loading is the same across the whole cross section, and the fibers are uniformly stressed parallel to and along the full length of the piece. Lumber used in the manufacture of large laminated members should be dried to moisture content slightly less than the moisture content expected in service so that moisture absorbed from the adhesive will not cause the moisture content of the product to exceed the service value.