Where beams frame to deep girders or to columns, even if the connection is made by angles on the web of the beams, it is customary to put a shelf angle under the beam. The student should not confuse this construction with the one just described. The object of such a shelf is to facilitate erection and not to support the beam after the web connection is made. Where such an angle is used, therefore, no stiffeners should be used under the beam, as these would prevent the web connection from performing the work for which it was de signed. The draftsman must see that the connection angles are not placed so as to interfere with the fillet of the beam or of the girder. This consideration arises where the connection is raised or lowered on the beam, or where the beam does not frame flush with the girder, or where a small beam frames flush with a large one, as for instance a 5-in. beam to a 24-in. beam. Fig. 36, Part I, gives rules for deter mining the distance from outside of the flange to the commencement of the fillet. These distances are given also in the Cambria. Hand book. It is possible to encroach a little on the fillet but generally not more than in. • The standard form of connections of beams to columns is by a shelf angle with the stiffeners under it, with the required number of rivets, and with a cap angle over the top. The beam is riveted both to the cap and the shelf angles. Generally there are four rivets in each flange—sometimes only two in each flange are used. The shelf angle is usually a 6 X 6 X •÷,-in. angle and the cap angle a 6 X 6 X in. angle where four rivets in the flange are used; if only two rivets are used the outstanding leg would be 4 inches instead of 6 inches. The size of stiffener angles varies with the size necessary to conform to the rivet pitch of the column, and to keep the outstanding leg of the stiffener the required distance from the finished line of the column. As stated previously, the deflection of the beam tends to throw the load near the outer edge of the angle and therefore the stiffener should come as near this edge as is practicable. Another point to be considered in choosing the size of stiffeners is to bring the out standing leg as near as practicable under the center of the beam as this is the portion of the shelf loaded by the beam. It is not always practicable to do this, however, and sometimes two stiffeners are used coming a short distance each side of the center of the beam.
A good many designers use only one stiffener under a beam or girder, and as the load to the stiffener comes from the outstanding leg, this brings a moment on the rivets through the other leg of the stiffener. For usual sizes of beams, there is probably ample strength in the rivets to provide for this moment. It is better design, how ever, to use two stiffeners back to back, with rivets connecting the outstanding legs, as shown in Fig. 217. This avoids the strain due to the moment on the rivets and also distributes the load to the column symmetrically with regard to the axis, instead of entirely on one side. These points are of very great importance where heavy girders or unusually heavy concentrated loads are concerned. Special column connections will be taken up later on.
The connections of beams to double beam girders, involve the consideration of a number of practical points peculiar to each case. These beams are generally bolted together with only a slight space between the flanges, and if the girder rests on a column, the holes must be arranged where they are accessible. In general this would be in the outside flanges unless the end of the girder was exposed so that the inside flanges could be reached.
Where beams frame to such a girder they cannot be riveted unless it is possible to rivet all the lines of such connections to each beam comprising the girder before they are brought together and bolted up. Where there were several lines of such girders it would be difficult to do this for all of them. In many cases, therefore, these connections have to be arranged for bolts to go through both beams of the girder. Where double beam girders frame into another girder the connection can only be made by single-angles on the outside of the webs, unless the beams are spread far enough apart to allow bolts or rivets on the inside to be reached. If the girder carrying the double beams is deep enough a shelf connection can of course be used, and this would be preferable to the single-angle connection. Connections by angles on only one side of the web, as shown in Fig. 193, should always be avoided if possible, as they are subject to a bending moment on the rivets in the same way noted for single stiffeners. Where such a connection must be made sufficient extra rivets should be used to provide for this moment. The remarks in regard to double beam girders apply also to girders made up of three and four beams. In these cases, however, there must be room for connection angles on the inner beams, and if the connection cannot be made when the beams are bolted together, it must be arranged so that these beams can be erected before the outside ones. In such an arrangement it is obvious that the standard form of cast iron plate separators could not be used very readily unless rods were used through the separators instead of bolts.
In Figs. 131 to 140, Part II, are shown cases of special framing to which the student should refer again and become thoroughly familiar with.
Where different sizes of beams frame opposite to the same girder it is necessary to change the position of the framing angles on the beams in order to use standard connections in each case. These changes in position are generally made to conform to standard prac tice, which is illustrated in Part II and which in general is as follows: In all cases except where one of the beams is a 7-in. beam, the first hole is 31 in. from the flanges which are flush with each other, and standard angles are used. Where one of the beams is a 7-in. beam and the other is either a 6,8,9,10 or 12-in. beam the first hole is 24 in. from the flush flanges; for a 12-in. beam the first hole is 21 in.
Fig. 190 shows the Carnegie code of conventional signs for rivets. It is important to follow the code in use by the particular shop for which the drawings are intended, as only by the use of such signs can elaborate notes be avoided.
Illustrations of Details. Fig. 195 shows a detail of a punched beam. Note that there should always be a single overall measurement on the sketch. Groups of holes, as for instance holes for connections of other beams, as shown in the top flange and the web, are located by fixing the center of the group. The reason for this is that the beam on which is the framing connecting to the holes is located by its center, and therefore it is important to locate this exactly. If the holes are symmetrical with regard to the center it is not necessary to dimension each hole from the center, by, simply to give the distance between them, corresponding with the distance in the out standing legs of the connection angles on the beam framing to this one.