Building Design and Construction Handbook - Merritt - Ventech!

STRUCTURAL STEEL CONSTRUCTION 7.123
izontal slotted (Art. 7.3.1), thus providing some built-in adjustment to accommodate
mill and shop tolerances for beams and columns.
Similarly, for beams with framed connections (Fig. 7.46 and 7.47) that will be
field bolted to columns, allowance should be made in the details for finger-type
shims, to be used where needed for column alignment.
Because of several variables, bearing of column joints is seldom in perfect contact
across the entire cross-sectional area. The AISC recommends acceptance if
gaps between the bearing surfaces do not exceed 1 ⁄16 in. Should a gap exceed 1 ⁄16
in and an engineering investigation shows need for more contact area, the gap may
be filled with mild steel shims.
Tolerance for placing machinery directly on top of several beams is another
problem occasionally encountered in the field. The elevation of beam flanges will
vary because of permissible variations for mill rolling, fabrication, and erection.
This should be anticipated and adequate shims provided for field adjustments.
7.43 ADJUSTING LINTELS
Lintels supported on the steel frame (sometimes called shelf angles) may be permanently
fastened in the shop to the supporting spandrel beam, or they may be
attached so as to allow adjustment in the field (see Fig. 7.9, p. 7.21). In the former
case, the final position is solely dependent on the alignment obtained for the spandrel
itself, whereas for the latter, lintels may be adjusted to line and grade independently
of the spandrel. Field adjustment is the general rule for all multistory
structures. Horizontal alignment is obtained by using slotted holes in the connection
clip angles. Vertical elevation (grade) is obtained with shims.
When walls are of masonry construction, a reasonable amount of variation in
the position of lintels may be absorbed without much effort by masons. So the
erector can adjust the lintels immediately following the permanent fastening of the
spandrels to the columns. This procedure is ideal for the steel erector, because it
allows him to complete his contract without costly delays and without interference
with other trades. Subsequent minor variations in the position of the lintels, because
of deflection or torsional rotation of the spandrel when subjected to deadweight of
the floor slab, are usually absorbed without necessitating further lintel adjustment.
With lightweight curtain walls, however, the position of the lintels is important,
because large paneled areas afford less latitude for variation. As a rule, the steel
erector is unable to adjust the lintels to the desired accuracy at the time the main
framework is erected. If the erector has contracted to do the adjusting, this work
must wait until the construction engineer establishes the correct lines and grades.
In the usual case, floor slabs are concreted immediately after the steelwork is inspected
and accepted. The floor grades then determined become the base to which
the lintels can be adjusted. At about the same time, the wall contractor has scaffolds
in place, and by keeping pace with wall construction, the steel erector, working
from the wall scaffolds, adjusts the lintels.
In some cases, the plans call for concrete encasement of the spandrel beams, in
which case concreting is accomplished with the floor slab. The construction engineer
should ensure that the adjustment features provided for the lintels are not
frozen in the concrete. One suggestion is to box around the details, thus avoiding
chopping out concrete. In some cases, it may be possible to avoid the condition
entirely by locating the connection below the concrete encasement, where the adjustment
is always accessible.