This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
The centers of all groups of field holes above the bottom of the beam should be given.
Where two beams are placed close together; they should be connected by "separators" to prevent lateral motion. When such is the case the holes are indicated as shown in Fig. 60. The various kinds of wall anchors are shown in the handbooks and in Fig. 20. Care should be taken to provide for their connection to the beams when required.
When beams are used in building work, it is usually required that either the upper or the lower flanges of part or all of the beams be at the same elevation. Whien the girder or main beams are deep enough, the joist top or bottom flanges may be brought to the same elevation as shown in Fig. 63 which shows a 12-inch and a 7-inch beam. The connection angles are in all cases arranged so that the rivets through the girder web and the smaller connection angles go through the connection of the larger beam also.
Fig. 64. Method of Coping a Beam Top and Bottom.
Fig. 65. Methods of Coping Beams to Fit Beams of Various Heights.
In case it is desirable to have beams so as to have all their tops or bottoms at the same elevation, it may be accomplished by an operation known as "coping" the beam. By coping is meant that the flange is cut back for a certain distance depending on the size of the beam which is to join the beam under consideration and the web is then cut down a distance X and sloped back on a. bevel of 3 inches in 12 inches, see Fig. 64.
Fig. 66. Method of Cutting Flanges When a Beam is Coped on a Bevel.
Fig. 64 shows a beam coped top and bottom to fit into another beam of its own depth. A beam may be coped on top only, Fig. 65a, or on bottom only, Fig. 65b. Other conditions of coping are shown in Fig. 65c - f, together with the ways of indicating them. Fig. 58 shows some indicated in the beam sketches.
When a beam is to be coped on a bevel, the flanges are not cut to a bevel, but are cut as in Fig. 66. The distances a and b should be given allowing a 1/4-inch clearance, and the portion of the beam coped is to be shown cross-hatched. This method of cutting to a bevel should be used whenever possible, whether the beam is coped to fit another or is simply cut to a bevel.
When a single beam or a girder formed of two beams having a cover plate riveted thereto is cut to a bevel, the cover plate should be sheared to the line of bevel and the beam should be cut as shown in Fig. 66.
Fig. 67. Method of Cutting an I-Beam or Channel to a Bevel.
When an I-beam of a channel is cut to a bevel across the depth, the cut should be made as shown in Fig. 07, and the distance "a" should be given.
Detailing of Roof Trusses. The first thing to determine in this respect is the outline of the outer line of the roof and the end, and the center depths. The chords should now be located by center lines corresponding to the gauge lines of the angles, or the center of gravity lines of the pieces, as the case may be. The above mentioned determinations may be obtained from the architect's drawing and from the stress sheet; and in many, if not most all cases, the center lines of the chords are shown on the stress sheet. The stress sheet may be an outline with the stresses and the sections on it, or it may and in fact should be as shown on Plate I. Here the designer, who is an experienced man, has shown the general details. It now remains for the draftsman to draw this up so that the shopmen can make it. After he has finished, the results will be as shown on Plates II and III, which will now be discussed in detail.
After the center lines of the chords are drawn in, the angles themselves should be drawn on by laying of the gauge lines on one side and then the other edge of the leg on the other side of the gauge line. After this the top chord should be divided into a certain number of equal parts at each of which a purlin is to be placed. This done, lines from these points should be drawn perpendicular to the top chord and their points of intersection with the bottom chord should be noted. From the intersection of the center one with the bottom chord to the apex or top, a line is now drawn, and this is the center line of the main interior tie, or tension member. The member itself should now be drawn on this gauge line. After this the other members should be drawn in as shown.
In order to proceed, the distances between the various points of intersection must be carefully computed, thus giving the remaining data necessary to compute the bevels, which should now be done.
In order to determine the length of the members and the sizes of the plates, it is now necessary to take each point of intersection where any members meet at any other than a right angle and make a layout of that joint to some large scale, say 1 1/2 to 2 inches to the foot. The customary 1/4-inch clearance should be allowed where there is any liability of pieces touching and, after the ends of the various angles are drawn in, the first rivet is set back 1 1/8, 1 1/4, or 1 1/2 inches as the sizes of the angle and of the rivet allow, and the other spacing is so arranged as to make the size and shape of the plate advantageous and economical. The distance from the first rivet to the intersection is measured off and noted. After the layout for each joint has been made and the necessary dimensions of the plates and the distance from each intersection to the first rivet has been determined, the length of each member may be computed. This is equal to the length, intersection to intersection, plus the sum of the distances from the first rivet at the ends to the end of the member, minus the sum of the distances from the first rivet to the nearest intersection. For example, in the main interior tie U4 L2, Plate I, the length, intersection to intersection, is 21'-10 1/2", the distance from each first rivet to the end of the angle is 1 1/2 inches, and the sum of the distances from each first rivet to the nearest intersection is (4 1/2+9) = 13 1/2 inches, which is 1'-1 1/2". The length of the member is: