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 steel used in a building is in the form of single pieces, or combinations of one or more pieces, to which the general term "shapes" is applied. All shapes are made by rolling out the rectangular prisms or ingots that come from the blast furnace. The following comprise nearly all the shapes rolled: Bars or
Flats, Rounds, Half Rounds, Ovals, Flat Ovals, Plates, Angles, Tees, Zees, I Beams, Deck Beams, Channels, Trough Plates, Corrugated Plates, Buckled Plates. Illustrations of some of these are given in Figs. 25 to 35.
Method of Rolling. The processes of manufacture are practically identical in all mills; and the sizes of the different shapes are identical in all mills for nearly all sizes. Certain sizes are known as "standard," because they are rolled constantly by all mills. Certain other sizes not so commonly used are known as "special," and vary somewhat in the different mills. These distinctions will be explained in greater detail later on.
The process of rolling an I beam is in general as follows: The ingots are put into what are called "soaking pits" below ground, which are heated by natural gas. When white hot or at just the right temperature, they are taken out and passed several times through the first set of shaping rolls. These rolls are at first spread nearly the depth of the ingot. They are automatically lowered, however, as the ingot is passed through, and so reduce the thickness sufficiently to enable the piece to pass through the next set of rolls, which give it the general shape of the letter I, though it still retains much thickness, and is only partly formed. After being shaped sufficiently by these rolls, the piece is passed to the third or finishing set of rolls, where the final shaping takes place. The piece, still very hot, is then passed on by movable tables to circular saws, where it is cut into certain lengths. Each size and weight of beam or other shape requires a distinct set of rolls in order that the pieces may be given exactly the required thickness and dimensions. Therefore, only one size and weight is rolled at a time, and all orders that have accumulated since the last rolling of this size are then rolled at once.
Fig. 28 Unequal Leg Angle.
Fig. 29. Equal Leg Angle.
Fig. 30 DECK BEAM.
Fig. 31 TEE BAR.
Fig. 32 SECTION OF CORRUGATED PLATE5 FOR FLOORS.
The intervals of time that elapse between rollings of a given size vary considerably, being in some cases perhaps six weeks, and in other cases several months. Generally the larger sizes are rolled at one mill and the smaller sizes at another.
Fig. 33. SECTION OF TROUGH PLATES FOR FLOORS.
Fig. 34. SECTION OF BUCKLED PLATES FOR FLOORS.
Characteristics of Shapes. Having seen in general how shapes are formed, the student should now become thoroughly familiar with the features of each. Beams and channels consist of a thin plate-like portion, called the "web," and, outstanding at each end of the web and at right angles to it, what are called "flanges." A beam has the shape of a letter I and is therefore called an I beam. A channel is like a letter I with the flanges on one side of the web omitted. The connection of flange to web is curved, and this curve is called the "fillet"; also, the inner side of a flange is beveled, and this bevel is in all sizes the same, viz., 16| per cent with the outer side of the flange. A curve of varying radius connects the outer edge with the inner side of a flange. The distribution of metal in the heavier sections of a given shape is shown by the portion not cross hatched in Figs. 25 to 29. It will be seen therefore that for a given depth, the only difference in the different weights is in the thickness of webs and width of flanges.
The accompanying cuts, Fig. 36, shows the relations, radii of curvature, and other data which are standard for all beams.
c = .60 minimum web
C= minimum web + 1/10 inch s = thickness of web = t minimum
Note. This applies for all channels and beams except 20-inch I and 24-inch I.
Fig. 35 PLAIN ANCLE.
For 20-inch standard I, S
For 24-inch I, S
For 20-inch special I, S
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 1/16 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. 3T, 38 and 39. Their uses, however, are limited to special classes of work.