Composite wood beam and method of making same

A composite beam comprising:

• interconnected, horizontally extended upper and lower, vertically spaced apart, approximately rectangular cross-section wood chords of substantially uniform width;
• at least one horizontally elongated wood strip of approximately rectangular cross-section, fitted between and spanning the space between the chords for a portion of the beam length, the chords and wood strip each having faces and opposed edges, the wood strip upper and lower edges in contact with the respective chord lower and upper edges respectively;
• a number of metal, elongated, plate-like fasteners, each embedded in the adjacent faces of and mechanically joining together adjacent portions of the wood strip and the respective chord, so that said wood strip is joined to both of said chords;
• each of said fasteners, in their elongated direction, being acutely angled from the vertical at an upward slope toward its nearest beam end, and with the angle of each fastener being roughly aligned with the angular direction of alignment of the hypotenuse of the force vector triangle formed of the endwise directed horizontal and the vertical upwardly directed force vectors resulting from a predetermined load on the beam at the approximate location of the fastener, and wherein each fastener is angled from the vertical between about 30.degree. and 40.degree. at an upward slope toward the nearest beam end;
• and
• whereby the fasteners are each normally placed in tension under application of beam loads and tend to compress together, in tight frictional contact, the contacting wood strip and chord edges for absorption by both the strip and fasteners of part of the shear load component due to the applied beam loads.

A beam comprising:

• a normally horizontally extended, vertically spaced apart, parallel upper and lower, approximately rectangular cross-section wood chords of substantially uniform width, the chords each having edges and faces;
• a pair of normally horizontally extended wood filler strips, each of approximately rectangular cross-section and fitted within and filling the space between the chords at opposite ends of the beam and each extending from the respective free end of the beam for a predetermined, relatively short distance inwardly, toward the center of the beam, each filler strip having faces and opposed edges with the upper and lower edges of each strip being in substantially full tight, frictional contact with its adjacent chord edge;
• a center wood filler block arranged between and filling the space between the chords at the central portion of the beam and overlapping the area where the longitudinal, endwise directed, shear forces, resulting from applied beam loads, change direction, so that there are horizontal elongated gaps between the chords and the adjacent ends of the center wood filler block and the end strips, said filler block having a face and opposed edges;
• the wood strips and wood filler block being fastened to their adjacent chord portions by elongated plate-like mechanical fasteners, each fastener inserted at an acute angle from the vertical in the face of one of the chords and the faces of the adjacent filler, and wherein said mechanical fasteners are angled to approximately correspond to the angular alignment of the hypotenuse of a force vector triangle at the location of each of said fasteners, so that each fastener is under tension in response to the applied load;
• whereby a part of the longitudinal shear force components, which are due to the vertically downwardly applied loads upon the beam, are absorbed by the strips and block, and fasteners, and the fasteners are placed in tension when the loads are applied to the beam, the tension on the fasteners for maintaining frictional contact between each chord and the strips and block thus reducing the shear force on the fastener.

A method of forming a composite beam by assembling together a pair of spaced apart, elongated wood chords and interconnecting the chords with members which span the space between them, with said interconnecting members including at least one elongated wood filler strip which spans and fills a portion of the space between the two chords, the chords and interconnecting members each having faces and edges and with the filler strip edges in contact with the opposed edges of the portion of the chords which are overlapped by the filler strip, the improvement comprising the steps of:

• fastening the chords and strip together by embedding a number of plate-like mechanical fasteners edgewise into the adjacent face portions of each of the chords and the wood filler strip at approximately a pre-determined angle relative to the longitudinal direction of the chords;
• said pre-determined angle for each fastener being roughly the angle of the hypotenuse of a force equilibrium vector diagram made up of a longitudinal force vector and a normal force vector resolved from a predetermined load applied transversely upon the beam, with the orientation of said hypotenuse angle being such that each of the fasteners is placed in tension upon such applied load and thereby tends to compress the chords and strip together in proportion to the applied load;
• positioning a wood filler strip at each opposite end portion of the beam, and also at the central portion of the beam to overlap the area where the longitudinal shear force, due to such applied load, changes directions;
• and fastening each of said strips to the chords at such predetermined angles, wherein the fasteners are oppositely angled at the opposite end strips, and the fasteners in the strip located at the central portion of the beam being oppositely angled relative to said area, and wherein said predetermined angle is between about 30.degree. and 40.degree. measured from the vertical.