This section is from the book "Safe Building", by Louis De Coppet Berg. Also available from Amazon: Code Check: An Illustrated Guide to Building a Safe House.
In pieced work where angles are attached to beams, etc., if it is punched and fitted together at the mill with bolts the whole will be charged at a standard rate per pound ; if, however, the pieces are riveted together, there will be an extra charge on the whole, even if only one rivet were used.
If pieces are required to be cut to exact lengths there is usually an extra charge on the whole. If pieces are required to be drilled or punched, there is an extra charge on the whole, even if there is only one hole in each piece.
For these reasons it is usual where there is much fitting, drilling, etc., to be done to have it done at the mill for the standard rate per pound. Where, however, there is only a little to be done, as is usually the case in building construction, it is cheaper to do it at the building, using portable hydraulic punches or other similar contrivances to facilitate the labor.
A saving can also be made by doing all painting of heavy work at the building, as the mills charge a standard price per pound of metal for each coat; but where this is done, the architect cannot be too careful in having all rust removed.
In building up plate-girders, plates as wide as eight feet can be rolled, and of thickness and Length in one piece not to exceed in finished weight two tons or four thou-sand pounds, this weight being about the Limit for single pieces of rolled-work within reasonably economical limits.
Avoid great length.
Cost of Fitting.
Practicable Plate sizes.
Thus, for instance, we could get plates five feet wide, one inch thick and twenty feet long, or eight feet wide, one-half inch thick and twenty-five feet long. If we require wider plates (usually for deep webs) we must take an eight-foot wide plate and shear it off, splicing the pieces. Thus if we required a ten-foot deep web, we would shear the eight-foot plate in ten-foot lengths, would place them side by side vertically, connecting them by covering plates of some kind, and our web would thus be composed of a series of panels each ten feet high and eight feet wide. Plates should not be over one inch thick on account of the difficulty of punching, nor less than one-quarter inch thick for fear of loss by rusting and failure by buckling. In steel plates, Carnegie, Phipps & Co., of Pittsburgh will roll plates up to 9'.6" wide and 14'.2" long, if about 1/2" thick, or 9'.2" long by above width, if 11 /4" thick. See Table, p. 51, in their hand-book of 1889.
In round, square and flat bars almost any sizes can be made, but, here too, unusually light or heavy ones are charged at extra rates.
The sizes of these vary with different mills, but are about as follows : The ordinary sizes for rounds and squares, are 3/4" to 2" diameter, and for flats from 1" to 4"x3/8" to 11 /2" and 4 1/8" to 6" x 3/8" to 1," these are made at regular rates.
But the mills will make, at additional rates, rounds from wire sizes up to 3/4" diameter and from 2" to 7" diameter; half rounds from 3/8" to 1 1/4" diameter; squares from 5/16" up to 5" ; flats from 11/32" x 3/32 up to 12"x2".
In designing flats the best rule to follow is to make the thickness between one-fourth and one-third of the width, except for very wide bars, when it can be between one-eighth and one-quarter.
Where long bars are in tension, and one or both ends are held by nuts and screws, it is often economical to "up-set" the screw-ends, that is, enough material is added where the screw is cut. that is the diameter is enlarged enough at ends, to make the diameter at the root or thinnest part of the screw (that is between the threads), equal to the diameter of the whole bar. The screw itself is thus "upset," that is set upon the bar. The cost of upsetting screw-ends is more of course, than cutting screws upon ordinary bars, on account of the extra welding necessary, but in long bars, or very heavy bars, the material saved by not having to increase the diameter of the bar its whole length
Sizes of Rounds, Squares and Flats.
(to allow for cutting away at the ends), more than offsets the extra cost of up-setting. In light bars and short bars, as a rule, it is more economical to add enough to the diameter for the whole length to allow for cutting the thread at the end. In such a case the strength of the bar, in tension is, of course, only equal to the section at the root of the thread. It is a curious fact that threads cut with old dies are stronger than those cut with new dies; the old ones apparently crushing and thus leaving more material in the threads, while the new ones cut the material right out.
Different mills have different standards for threads, nuts, heads, etc. Practically, however, they all closely resemble the standards adopted by the Franklin Institute (of Philadelphia), February 17, 1866, and which are here reproduced by their permission as Table XXXIII.
In forming eye-bars the practice of different mills again varies.
It should be remembered that they are all welded, and therefore, if of wrought-iron, only some 80 per cent in strength of the metal in the bar. All parts should therefore be designed for some 25 per cent more strength than required with the usual faetors-of-safety.
For ordinary sizes of flat iron the mills have dies on which these eyes are "die-forged," that is, formed by machinery. The Phoenix Co., for instance, have some fifty-six sizes of dies for flats varying from 2" x 5/8" up to 6" x 2 1/2". The New Jersey Steel and Iron Works have some forty seven sizes of dies for flats from 2 1/2" up to 6". Their standards for pins are 1/16" less than even quarter-inches, as 2 3/16" diameter, 2 7/16", 2 11/16", 2 15/16", etc. All pin-holes in eye-bars should invariably be drilled, and should always be made (not over) 1/50 inch larger in diameter than the pin, to allow for slipping same in.
The practice of the latter company where eye-liars are of same thickness as the flat-bar, is to make the diameter of pin (if not governed by other circumstances) four-fifths of the width of bar (or d=4/5.b). In such a case the width of metal beyond the eye (at end of bar) is made equal to the width of bar (or a = b) and the width each side of eye equal to three-quarters of the width of bar (or c= 3/4.b), Bee Figure 162. Where larger pins are used the proportion must be even more increased on account of the greater amount of weakening by welding.
The above sizes are good averages. In some cases the metal around the eye forms a concentric circle with the eye. In such cases (if not required to be larger) the radius of the eye is from three-eighths to one-half of the width of flat, and the radius of the surrounding circle is from four-fifths to nine-tenths (of the width of flat) larger than the radius of eye. The thickness of eye is, usually, but not necessarily, the same as that of the flat.
Threads, nuts, etc.
Eye-bars and pins.
For further information as to sizes, etc., the reader should consult the hand-books issued by the different rolling-mills, taking care to get the latest issues, as they are constantly changing their rolls and stock sizes.
These books will also give the practice of each mill for locating holes in flanges of beams, channels, etc., sizes and weights of separators, manner of connecting beams by framing, etc.
Table XXXIV gives in condensed form the results of the most recently published tests on irons and steels.