It is not always possible to have a plate symmetrical. When a plate is symmetrical, the templet work, and, therefore, the cost, is much reduced. If they cannot be made symmetrical, the next best thing is to have as many as possible alike or of the same width. With a little thought along these lines a draftsman can save his week's wages for his company many a day.
For economy's sake the plate should be in an even number of inches in width. Plates are not rolled in fractions of an inch except below 6 inches. If a plate is so detailed as to require a fraction of an inch in width, the next wider plate must be ordered and cut down to the required size, this causing expense due to metal wasted and to labor required to get it cut to size. The length may be any dimen sion, but it is best to have it in even eighths of an inch, thus 2'-81" or etc. As mentioned before, the width of the plate must be stated in inches, not feet and inches. A plate is noted thus 1-Pl. 1S"Kg-"X2'-58" or 1-Pl. If the stress in a member is great, the number of rivets will necessarily be large. In such eases the thickness of the plate may be made thicker than ;1 inch in railroad, or ,A inch in highway or building work, and the member so arranged as to bring the rivets in double shear. Unless the rivets can be brought in double shear it is unnecessary to increase the thickness of the plate, for shear governs in ease of a 8-inch plate, and in case of a plate the change to a plate does not reduce the number of rivets suf ficiently to warrant it.
A plate must also be of sufficient section to transmit the stress from one member to the other. Since the area between the rivets is greater than that bearing upon. the rivet, this is automatically attended to. In the case of shear along planes between members a different condition obtains. Here the computations are more or less involved, but the draftsman need not consider this phase of the design since in such cases the experienced designer will design the plate and it will come to him with the correct thickness marked upon it.
The rectangular detailing of plates is, of course, simple. The rivets are, except in such cases as in the webs of plate girders, spaced after the manner of the spacing in angles, the same conditions gov erning. The lines on which the rivets are placed are in such cases
parallel to one of the sides of the plate and the spacing is readily laid off.
When a diagonal row of rivets is on a plate, it may be detailed in two ways: (1) By rectangular co-ordinates; and (2) by spacing along a line located by a bevel. Only in exceptional cases is the first method, shown in Fig. 54a, to be used.
The better way, and indeed it might be said the standard way, is shown in Fig. 54b. This way is easier for all concerned, and, in ease of diagonals, lends itself especially well, since the distance between working points of the plates at the ends can be computed, and the rivet spacing being measured along this line gives the distance between the last holes on the plates by snnple subtraction.
A plate should be detailed from one edge (the working edge) and the working point. The various distances to the rivet holes are measured from these places of reference. The distance from the last rivet hole to the far or side edges is not given. The plate of course being originally laid out to a large scale—a layout—care is taken that if the distances measured out from the working edge or point are used, the last rivet will not come closer to or farther from the far side of the plate than is allowed by specifications. In the case of the -I-inch rivet, these limits are q inches for the smaller and 2 inches for the greater. Specifications govern this distance by making it a function of the thickness of the plate or of the diameter of the rivet; one specification requires 2 diameters of the rivet for the least and S times the thickness of the plate for the maximum, but not to exceed 6 inches. As a usual thing, engineers desire the distance to be 14 inches for 4-inch rivets, both limits being the same, and 11 inches for 1-inch rivets.
The working point may or may not be on the plate. In many cases it is not. However, the distances must be measured from the working point. A familiar example of this is seen in the connection plates of the lateral systems of plate girders, see Fig. 54c.