St=12,500X0.6013 = 7,510 pounds which is less than the amount required to strain its head up to the maximum allowable.

Fig. 45. Drawing of Standard Rivet.

## Table X. Rivet Spacing Multiplication Table

On account of the fact that riveted heads are not driven symmetrically the value of the rivet in tension is not certain, and their use in tension is not to be advised. Use turned bolts.

The bearing and shearing values of rivets may be found in the handbooks of the various manufacturers. The values for all values of allowable stresses are not usually given, but by a little trouble almost any values may be obtained by dividing those values there given, or by taking a multiple of them. For example, the bearing value of a 7/8-inch rivet in a 7/16-inch plate, unit allowable bearing stress 18,000 pounds, may be obtained by taking 1 1/2 times the value given in the 12,000-pound table, giving 6,885 pounds.

In cases of the webs of channels or I-beams, or other thicknesses of metal which are not in even sixteenths of an inch, but are given in decimal fractions, the values may, with the help of the slide rule, be obtained from the tables. For example, let it be required to find the value of a 7/8-inch rivet in bearing in the web of a 15"X33# channel, the unit-bearing stress allowed being 15,000 pounds. From Cambria, the thickness is seen to be 0.4, and the bearing of a 7/8-inch rivet in a 1/2-inch plate is found to be 6,563 pounds. Therefore, the value sought will be

6,563 V = 0.5 X 0.4= 5,250 pounds

For convenience in rivet spacing, Table X will be found convenient, the value of any number of spaces of a given length being determined at a glance.

Bolts, Nuts, and Washers. Bolts are made by forming a head on one end and cutting a thread on the other end of an iron rod. In such cases the body of the bolt does not represent the strength, but the area at the root of the threads. In the handbooks is given the diameter of the screw thread for any bar or bolt of given diameter, and from this the strength of a bolt may be calculated, once the allowable unit tensile stress is determined. The diameter given for the rod or bolt is the diameter of the upset screw end. The strength of the bolt is then obtained by multiplying the diameter of the screw at root of thread by itself, by 0.7854,* and by the allowable unit stress, thus

Strength of Bolt=0.7854 d12X S

*In some books the area at root of thread is given direct.

## Table XI. Standard Cast O. G. Washers

 DIMENSIONS a = 4d + 1/4" b = 2d + 1/4" t = d c = d + 1/8" DIAMETER OF BOLT d 1/2 5/8 3/4 7/8 1 1 1/8 1 1/4 1 3/8 1 1/2 1 3/4 2 DIAMETER a 2 1/4 2 3/4 3 1/4 3 3/4 4 1/4 4 3/4 5 1/4 5 3/4 6 1/4 7 8 1/4 Wt. Of 100 WASHERS IN Lbs. 21 43 70 113 175 256 332 455 610 865 1115 All dimensions in inches

For example, let it be required to determine the strength of a 1 1/2-inch bolt, the unit allowable stress in tension being 18,000 pounds per square inch. It is

Strength of Bolt=0.7854 X 1.2842 X 18,000 = 23,350 pounds while if the area of the body of the bolt was used the strength would be 31,800, from which it is seen that in determining the strength of bolts care must be taken to use the diameter at the root of the thread.

Information regarding bolts and nuts in general is given in the handbooks. Here the exact dimensions of the heads and nuts are given. In detailing it will be sufficiently accurate to assume the side of a square head or nut or the short diameter of a hexagonal head or nut as twice the diameter of the bolt, the thickness of each being equal to the diameter of the bolt.

When the nut is screwed up, the bolt should extend from 1/8 inch to 1/4 inch above the nut.

Washers are of two kinds, cast and cut. The former are designated as O. G. (pronounced Oh Gee) washers on account of the curve given to their side. The sizes and weights of O. G. washers are given in Table XI.

Cut washers are made by stamping them out of sheet metal, and are principally used as separators where two angles are bolted together, or under the heads and nuts of small bolts which bolt timber in place. General information regarding them is given in Table XII.

## Table XII. Standard Cut Washers

(In 200-pound kegs)

 a = 2d + 1/2" c = d + 1/16" upto d = 1" = d + 1/8" when d is greater than 1" SIZE OF BOLT OR UPSET = d DIAMETER DIAMETER orHOLE c THICKNE5S NO IN 100 POUNDS a t 3/16 9/16 1/4 3/64 36 200 1/4 3/4 5/16 1/16 4 900 5/16 7/8 3/8 ,, 11 100 3/8 1 7/16 5/64 6 700 7/16 1 1/4 1/2 ,, 4 100 1/2 1 3/8 9/16 7/64 2 6oo 9/16 1 1/2 5/8 ,, 2 700 5/8 1 3/4 11/15 9/64 1 300 3/4 2 13/16 ,, 1 000 7/8 2 1/4 15/16 5/32 728 1 2 1/2 1 1/16 5/32 595 1 1/8 2 3/4 1 1/4 ,, 507 1 1/4 3 1 3/8 ,, 428 1 3/8 3 1/4 1 1/2 11/64 328 1 1/2 3 1/2 1 5/8 ,, 284 1 5/8 3 3/4 1 3/4 11/64 248 1 3/4 4 1 7/8 ,, 2/8 1 7/8 4 1/4 2 ,, 194 2 4 1/2 2 1/8 ,, 173 All dimensions in inches

Tension Members. These may consist of square, round, or rectangular bars, or they may be of shapes riveted together. The latter class will be considered under the detailing of tension members.

When the bar is square or circular in section, it may be formed into loops at its ends, or upset and nuts put on, in order to attach it to other parts of the structure in which it is used. In the former case it is called a loop bar. In case it is rectangular in section it may be formed into a loop bar, or may have its ends forged out into a somewhat circular shape, see Fig. 46, and a hole bored in them in order to connect them to the rest of the structure. In this case it is called an eve bar.

In order to be assured that the eye bar will not break in the head, the distances a are made such that 2a is greater than w, usually between l.3w and l.4w. If not required by the specifications, it is usually left to the manufacturers with the stipulation that the eye bars must break in the body of the bar, not in the head.

Fig. 46. Dimensions Required in Eye-Bar Design.

The dimensions of eye bars are given in the handbooks. In Cambria the excess through the pin hole for the 2-inch bar is (4 1/2 - 1 7/8) ÷2= 1 15/16 an excess of 33 per cent.

Care should be taken to note that the values here given are the minimum thicknesses. Bars thinner than these are liable to upset so imperfectly as to be unsafe in the heads. An eye bar should not, as a rule, be less in thickness than one-sixth of the depth. The pins given in the tables in the handbooks are maximum pins. The