Clearances to permit tightening bolts and welding are discussed in Art. 7.3.7. In addition, designers also must provide sufficient field clearance for all members so as to permit erection without interference with members previously erected. The shop drafter should always arrange the details so that the members can be swung into their final position with shifting the members to which they connect from their final positions. The following examples illustrate the conditions most frequently encountered in building work:
In framed beam connections (Fig. 7.58), the slightly shorter distance outto- out of connection angles (B—1⁄8 in), as compared with the face-to-face distance between supporting members, is usually sufficient to allow forcing the beam into position. Occasionally, however, because the beam is relatively short, or because heavy connection angles with wide outstanding legs are required, the diagonal distance A may exceed the clearance distance B. If so, the connection for one end must be shipped bolted to the framed beam to permit its removal during erection.
An alternative solution is to permanently fasten on connection angle of each pair to the web of the supporting beam, temporarily bolting the other angle to the same web for shipment, as shown in Fig. 6.59. The beam should be investigated for the clearance in swinging past permanently bolted connection angles.
Attention must also be paid to possible interference of stiffeners in swinging the beam into place when the supporting member is a plate girder.
Another example is that of a beam seated on column-web connections (Fig. 7.60). The first step is to remove the top angles and shims temporarily. Then, while hanging from the derrick sling, the beam is tilted until its ends clear the edges of the column flanges, after which it is rotated back into a horizontal position and landed on the seats. The greatest diagonal length G of the beam should be about 1⁄8 in less than the face-to-face distance F between column webs. It must also be such as to clear any obstruction above; e.g., G must be equal to or less than C, or the obstructing detail must be shipped bolted for temporary removal. To allow for possible overrun, the ordered length L of the beam should be less than the detailing length E by at least the amount of the permitted cutting tolerance.
Frequently, the obstruction above the beam connection may be the details of a column splice. As stated in Art. 7.37, it may be necessary to attach the splice material on the lower end of the upper shaft, if erection of the beam precedes erection of the column in the tier above.