(3) Reinforced concrete framing may also swell by taking on
moisture from the air when the humidity fluctuates widely or when the
concrete is immersed in free water. This change in volume has the same basic
effects as those described for shrinkage in Paragraph (2) above. However,
this is usually not a problem since swelling tends to be counteracted by
creep deformation.
(4) Reinforced concrete framing, particularly for facilities in an
earthquake zone, must be carefully detailed for continuity between various
elements such as the floor slabs, beams, and columns to provide for
sufficient ductility to safely resist lateral loads induced on the framing.
(5) Reinforced concrete framing must also be evaluated for its
serviceability in regards to the amount of anticipated cracking which will
occur under normal dead load and live loading and the resulting affect upon
the appearance of the structure as well as the affect upon the deflection and
displacement characteristics of the structure as it changes from a noncracked
to a cracked section design criteria.
(6) Although not as likely as in the case of structural steel
framing, the corrosion of reinforcing within the concrete due to exposure to
salt air or industrial air pollutants can be of considerable importance in
the structure particularly if severe cracking of the concrete occurs or
insufficient concrete cover is provided over the reinforcing steel.
(7) In prestressed concrete members, elastic shortening of the
members and time-dependent movements inducing camber can cause additional
design problems in the support framing. Member shortening and camber affect
the performance of the structural support system and may result in
differential movements which cause additional strains in the chamber or its
components.
(8) Depending upon the
area climatology, and the degree of
exposure of concrete framing, the
thermal effects upon the framing should be
evaluated. Because of concretes'
greater mass this is not as critical as it
is for structural steel for short
term variations in temperature but can be a
factor under seasonal variations.
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