Classes of Tension Members 50

The small plate in between the web and the outer plate, is used only to fill in, since it is only as great in width as the diameter of the pin.

The net area of the other two plates is: 2 Plates, 2x11x1 in 11.00 square inches Out for pin, 2xix6 6.00 square inches Total 5.00 square inches This is less than the 7.91 extra square inches required on the condition that the section through the pinhole shall be times that required for the body of the bar. The plates will have to be made thicker. Each added will add (11-6) X square inch to the net area; and since 7.91-5.00=2.91 square inches extra is required, it will be necessary to increase the thickness sixteenths, making the total thickness of both plates 19/16 inches. The inner plate will be made inch, and the outer one inch.

The distance from the pin to the end shall be such that the area will be 15.00 square inches, the same as in the body of the member. The thickness is that of a web and the two pin-plates. This is and the distance must then be inches. The distance from the center of the pin to the end is then inches.

The web is or inch; the outer plate is inch; and the inner plate is or inch, making a total of 31 sixteenths. The stress dis tributes itself over the pin evenly, and each plate takes a stress in proportion to its thickness. The stresses in the pin-plates on one side of the member only are considered, those on the other side being the same.

240,000 2 plate= 240,000 -in. plate= 2 As both of these plates get their stress from the web, there must be sufficient rivets in bearing in the web to transfer this. The required number (see second table, C 195), is: 50,300+4,920=11 46,450+4,920=10 Now each plate has a tendency to slide along the web. This will tend to shear the rivets off, and therefore there will be required (see same table): For in. plate, 50,300:4,510=12 For plate, 46,450÷4,510=11 This makes a total of 21 for bearing, and 23 for shear. The distribution of the rivets is as shown, remembering that one rivet is in double shear but cannot take 2 x 4,510, but only 4,920, since it is in bearing in a web.

52. Connections. The connection of mem bers by means of pins has been discussed. The connection of plate and angle members by means of rivets should by this time be easy of computation for the reader. The total stress

is divided by either the shearing or bearing of a rivet, whichever is the smaller; and the result will be the number of rivets required.

Standard Connections. The connection of beams to girders and girders to columns has been discussed. The method given was a gen eral one, and is applicable to all cases. How ever, for cases such as usually occur in building work, standard connections may be used. These are standard for any given beam, and are so designed that, if the beam will be safe for bend ing, the standard connection is safe. They are given on (C 177-188). They should not be made use of at random. First, the number of rivets required should be computed; and if this is the same as or less than those in the standard con nection, then the standard connection should be used.

On (C 189-190) are given beam connections to Z-bar columns. They may also be used on channel columns or on columns built up of shapes. The range of values for reactions of beams is from 4.4 to 26.5 tons, and this is usually as great as is required. In case the reaction is greater than that there given, the number of rivets may be increased proportionately, or connection angles may be put on the beam as shown in Fig. 82, the additional rivets being put in the connection angles. The field rivets are used with the top angle, in order that, should the beam be a little greater in depth than that given in the handbook, the adjustment can be made in the small angle and not in the beam or by cutting off the angle, which would be the way if field rivets were not used.

Entering connections, of which Fig. 83 is an example, should be avoided. The distance a is either made equal to the thickness of the web of the beam which is to join at that point, or it is made larger. In the first case, the web is more than likely to be thicker than the value given in the handbooks; and one of the angles must be cut off in order to get the beam in. On the other hand, if the opening is too great, there is the danger of a loose fit; but this can be done away with to a certain extent by putting in pieces of shiming sheets. Taking into consideration all conditions, it should be a fixed rule that they should never be employed.