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 k inch to 4 inch above the nut.
Washers are of two kinds, cast and cut. The former are desig nated as 0. G. (pronounced Oh Gee) washers on account of the curve given to their side. The sizes and weights of 0. 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.
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 eye 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 1.3w and 1.4w. 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.
The dimensions of eye bars are given in the handbooks. In Cambria the excess through the pin hole for the 2-inch bar is (41 ÷ 2= 1H, 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 he 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 American Bridge Company practice requires the smallest pin to be not less than three-fourths the width of the cye bar.
Bars of a square or circular section could, as in the case of bolts, have a screw thread cut on their ends and by means of nuts be connected to the other part of the structure, but such an opera tion would be costly since the bars are long and much of the section would be wasted for a great length. In such cases the bars are ordered 6 inches longer than required and this 6 inches is, after heating to a welding heat, upset or pushed in 6 inches, thus increasing the diameter of the bar at the end so that the diameter at the bottom of the screw threads will be greater than the diameter of the original bar. This is done so that the bar will break in the body, and not at the joint.
The sizes of upsets for bars of various sizes are given in the handbooks. Let it be required to determine the size hole through which a 1k-inch bar with upset end would pass and the nut required. We find opposite the the value 1, showing that the upset will be 1 z 'inches. In another table opposite q is given the size and weight of a square nut, viz, 11 inches thick, 3 inches on the side, and weight 3.175 pounds. The use of square nuts is not to be encouraged, the hexagonal form being the better, on account of their lighter weight.
Instead of the rods being fitted with nuts and threads at their ends, they may, as mentioned above, be made into loop bars. Loop bars are welded, and for this reason are not to be desired since welds are never as strong as the original. However, the loop bar has 100 per cent excess through the pin, and in order to have an efficiency of 100 per cent it must have a weld with an efficiency of 50 per cent. Since such a weld is well within the limits of possibility, it is per missible to use loop bars in highway bridges or other structures where the impact is not great, and in counters, since here the pins are usually of such a diameter that they would be too great for an eye bar of the section of the counter. Table XIII gives information regarding loop bars. They must be made of wrought iron since steel does not weld well.