CEMP-E
TI 809-02
1 September 1999
Corrosion
b. Camber. Camber is especially important in truss type structures such as those typically
used over rolling doors in aircraft hangars. In general, however, the use of camber to offset
dead load deflections in long span beams, girders, and joists has limited benefits with respect
to building serviceability. Camber however can improve the appearance of structures where
the support systems are exposed to view.
c. Expansion and Contraction. Expansion joints should be provided when necessary to
minimize detrimental effects resulting from the lateral movement of long structures due to
thermal expansion and contraction. In general, for non-rectangular steel-framed buildings, the
maximum allowable building length without an expansion joint (or maximum length between
expansion joints) is 90 meters (300 feet) for moderate climates (temperature change less than
0o C (30o F)). This decreases to 60 meters (200 feet) for extreme climates (temperature
change greater than 20o C (70O F)). These distances may be increased for rectangular
buildings, however, they should be decreased if the building is unheated, if the building is air
conditioned, or if the building has fixed-base columns. Additional information on expansion
joints in buildings can be found in Technical Report No. 65, "Expansion Joints in Buildings,"
National Academy of Sciences, 1974. A double column arrangement is the preferred method
of establishing an expansion joint. Additional joints may be required at the junctures of T-, L-,
U-shaped and other irregularly shaped buildings, or when foundation conditions create a
potential for differential settlement.
d. Deflection, Vibration and Drift. Displacements of structural framing system under
service load conditions must be controlled to prevent damage to various architectural features
such as interior walls, partitions, ceilings, and exterior cladding. Deflection limits, expressed as
a function of span length are provided in Table 1-4 and in various codes (AISC, AISI, MBMA,
etc.). Drift limits for earthquake loadings are provided in FEMA 302. Designers should verify
the deflection and drift limits imposed by code are suitable. Drift limits more stringent than
those imposed by FEMA 302 may be warranted for those conditions where non-ductile
cladding is used.
e. Connection Slip. When connection slip can cause a significant displacement increase
in the framing system and thereby raise concerns about building serviceability, the use of slip-
critical connections should be considered. Other reasons for using slip-critical connections are
provided in Paragraph 5d.
f. Corrosion. Corrosion can reduce structural capacity as well as cause serviceability
problems. Painting of structural steel will comply with the requirements contained in either
AISC-LRFD or AISC-ASD. Except where fabricated of approved corrosion resistant steel or of
steel having a corrosion resistant or other approved coating, individual structural members and
assembled panels of cold-formed steel construction must be protected against corrosion with
an approved coat of paint. Requirements for the protection of steel in corrosive environments
are provided in Chapter 12.
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