Building Design and Construction Handbook - Merritt - Ventech!

STRUCTURAL STEEL CONSTRUCTION 7.127
pings fall into the space and form bridges over which water may pass, to attack
the steel. The net effect is premature failure of both wall and steel. Walls have been
shattered—sheared through the brick—by the powerful expansion of rust formations.
The preventatives are: (1) coating the steel with suitable paint and (2) good
wall construction.
A typical building code reads: ‘‘Special precautions shall be taken to protect the
outer surfaces of steel columns located in exterior walls against corrosion, by painting
such surfaces with waterproof paints, by the use of mastic, or by other methods
of waterproofing approved by the building inspector.’’
FIGURE 7.63 Flashing at spandrel and lintels.
In most structures an asphalt-type
paint is used for column-flange protection.
The proviso is sometimes extended
to include lintels and spandrels, since
the danger of corrosion is similar, depending
on the closeness and contact
with the wall. However, with the latter
members, it is often judicious to supplement
the paint with flashing, either metallic
or fabric. A typical illustration,
taken from an actual apartment-building
design, is shown in Fig. 7.63.
In general, building codes differ on
field paint; either paint is stipulated or
the code is silent. From a practical viewpoint,
the question of field painting cannot
be properly resolved with a single
broad rule. For an enclosed building in
which the structural members are enveloped,
for example, a field coat is sheer
wastage, except for exterior steel members
in contact with walls. On the other
hand, exposed steel subject to highhumidity
atmospheres and to exceptionally
corrosive gases and contaminants
may need two or three field coats.
Manufactured buildings should always
be closely scrutinized, bearing in
mind that original conditions are not always permanent. As manufacturing processes
change, so do the corrosive environments stimulated by new methods. It is well to
prepare for the most adverse eventuality.
Special attention should be given to steel surfaces that become inaccessible, e.g.,
tops of purlins in contact with roof surfaces. A three-coat job of particularly suitable
paint may pay off in the long run, even though it delays placement of the roof
covering.
7.48 STEEL IN CONTACT WITH CONCRETE
According to the ‘‘Steel Structures Painting Manual,’’ Vol. I, ‘‘Good Painting Practice’’
(Steel Structures Painting Council, 40 24th Street, Suite 600, Pittsburgh, PA
15213):