NOTE. This applies for all channels and beams except 20-inch I and 24-inch I. For 20-inch standard I, S = .55 inch For 24-inch I, S = .60 " For 20-inch special I, S = .65 " The slope of flanges for all beams and channels is 2 inches per foot.
In tables V and VI, the weights printed in heavy type are those that are standard. The other weights are rolled by spreading the rolls of the standard size so as to give the required increase, and are known as special weights. These are not rolled so regularly, and are therefore in general more subject to delay in delivery.
The two parts of an angle are called "legs." These are in one class of equal length, and in another class of unequal length. Notice also the fillet and curve at outer edge. The method of increasing the weight is shown by the full lines. It will be seen, therefore, that for an angle with certain size of legs the effect of increasing weight is to change slightly the length of legs, and to increase the thickness.
In case of angles, the distinction between " standard" and "special" applies, not to different weights and thicknesses of a given size as in the case of beams and channels, but to all weights of a given size as a whole, as will be seen from the tables on pages 36-7. Angles vary in all cases by inch in thickness between maximum and minimum thicknesses given in the tables. In the addition to the above special sizes of angles, there are certain special shaped angles known as square root angles, cover angles, obtuse angles, and safe angles. These shapes are illustrated in Figs. 37, 38 and 39. Their uses, however, are limited to special classes of work.
The square root angles are used where it is necessary to eliminate the fillet. The cover angles are for use in splicing so that the covers will fit the fillets of the angles spliced. As the demand for such is limited in any particular piece of work, it is customary to plane off a regular angle. The other shapes are for special uses, as will be readily understood.
Bent plates are very commonly used in place of obtuse angles. None of the above can be obtained easily at the Dallis, and would be used only when it is not possible to adopt the regular shapes.
With the above explanation the student should be able to understand readily the features of the other shapes by carefully studying the cuts.
Plates are of two classes known as "sheared" plates and " universal mill" or " edged " plates. Plates up to 48 inches in width are in general universal mill plates. This term applies to plates whose edges as well as surfaces are rolled, thus insuring uniform width. Plates above 48 inches in width have their edges sheared, and are known as sheared plates.
As already stated, there are various meanings of the terms " beam " and "girder," and it is very important to understand fully the distinctions. The definitions previously given are applied to the manner of loading.
" Beam" is also the term applied to the shape rolled in the form of the letter I, in distinction from the channel, as noted in the preceding paragraphs. An I beam may be used in a position which, from the definition given, fixes it as a girder in distinction from a beam ; and in speaking of such a case, one should say that the girder consists of an I beam. In ordering the material, however, the shape should be referred to as an I beam and not as an I girder.
Similarly, a channel may be used in a position which, from the definition, would fix it as a beam. In referring to it, one should say that the beam consists of a channel; and in ordering material, it should be referred to as a channel and not as a beam.
The beam may in sonic cases be made of sections riveted together, and, in such cases, would be referred to, in ordering, as a riveted girder. Frequently, also, two beams bolted together are used, and are then called beam girders. It will be seen, therefore, that there are two distinct uses of these terms, beams and girders — the first depending on the manner of loading, and the second on the particular form of section of the member used. These two uses should never be confounded, as serious results might follow, especially in ordering material.