Building Design and Construction Handbook - Merritt - Ventech!

7.22 SECTION SEVEN
than all forms of masonry, is capable of sustaining far greater load in a given space,
thus obstructing less of the floor area in performing its function.
With columns properly spaced to provide support for the beams spanning between
them, there is no limit to the floor and roof area that can be constructed with
this type of framing, merely by duplicating the details for a single bay. Erected tier
upon tier, this type of framing can be built to any desired height. Fabricators refer
to this type of construction as ‘‘beam and column.’’ A typical arrangement is illustrated
in Fig. 7.8.
The spandrel beams, marked B1 in Fig. 7.8, are located in or under the wall so
as to reduce eccentricity caused by wall loads. Figure 7.9 shows two methods for
connecting to the spandrel beam the shelf angle that supports the outer course of
masonry over window openings 6 ft or more in width. In order that the masonry
contractor may proceed expeditiously with the work, these shelf angles must be in
alignment with the face of the building and at the proper elevation to match a
masonry joint. The connection of the angles to the spandrel beams is made by
bolting; shims are provided to make the adjustments for line and elevation.
Figure 7.9a illustrates a typical connection arrangement when the outstanding
leg of the shelf angle is about 3 in or less below the bottom flange of the spandrel
beam; Fig. 7.9b illustrates the corresponding arrangement when the outstanding leg
of the shelf angle is more than about 3 in below the bottom flange of the spandrel
beam. In the cases represented by Fig. 7.9b, the shelf angles are usually shipped
attached to the spandrel beam. If the distance from the bottom flange to the horizontal
leg of the shelf angle is greater than 10 in, a hanger may be required.
In some cases, as over door openings, the accurate adjustment features provided
by Fig. 7.9a and b may not be needed. It may then be more economical to simplify
the detail, as shown in Fig. 7.9c. The elevation and alignment will then conform
to the permissible tolerances associated with the steel framework.
(E. H. Gaylord, Jr., et al., ‘‘Design of Steel Structures,’’ 3rd ed.; R. L. Brockenbrough
and F. S. Merritt, ‘‘Structural Steel Designers Handbook,’’ 2d ed.,
McGraw-Hill Publishing Company, New York.)
7.8 LONG-SPAN FRAMING
Large industrial buildings, auditoriums, gymnasiums, theaters, hangars, and exposition
buildings require much greater clear distance between supports than can be
supplied by beam and column framing. When the clear distance is greater than can
be spanned with rolled beams, several alternatives are available. These may be
classified as girders, simple trusses, arches, rigid frames, cantilever-suspension
spans, and various types of space frames, such as folded plates, curvilinear grids,
thin-shell domes, two-way trusses, and cable networks.
Girders are the usual choice where depths are limited, as over large unobstructed
areas in the lower floors of tall buildings, where column loads from floors above
must be carried across the clear area. Sometimes, when greater strength is required
than is available in rolled beams, cover plates are added to the flanges (Fig. 7.10a)
to provide the additional strength.
When depths exceed the limit for rolled beams, i.e., for spans exceeding about
67 ft (based on the assumption of a depth-span ratio of 1:22 with 36-in-deep Ws),
the girder must be built up from plates and shapes. Welded girders are used instead
of the old-type conventional riveted girds (Fig. 7.10b), composed of web plate,
angles, and cover plates.