DETERMINATION OF SHEARING VALUE OF RIVETS.
The resistance of a rivet to shearing along one plane is the area of the rivet multiplied by the shearing strength of the metal per unit of area.
• If d = the diameter in inches of the rivet S = the ultimate shearing strength in pounds per sq. in. then V = the ultimate shearing value in pounds.
= .7854 & S.
For the working value of the rivet a certain proportion of S is used and this varies with the factor of safety required. The safe value of the shearing strength per square inch of power-driven rivets which is generally used for buildings, is 9,000 pounds, which gives a factor of safety of about six. With rivets three-quarters of an inch in diameter, which is the usual size in building work, the safe shear ing value is therefore .7S54 XiXIX 9000 = 3976 pounds.
For rivets driven by hand as is done in many cases in assembling the parts in the erection of a building, the safe shearing strength per square inch is reduced to 7,500 pounds. One of the connections
illustrated in Fig. 191 is a case of double shear for the rivets through the angles and the web of the beam, as there are two planes along which shearing must occur, since the load is distributed by the web of the beam equally between the two angles. The above value of 3,976 must be multiplied by two to give the total resistance of each of these rivets against shearing.
The rivets, however, which go through the outstanding leg of these angles, and through the web of the girder which carries this beam are only in single shear, as here there is only one plane between the angles which transmit the load and the web which receives it. The value for these rivets would therefore be 3,976 lb. if power driven, and 3,313 lb. if hand driven.