Reinforced concrete bridges - Computational Analysis and Design of Bridge Structures - page 99

Reinforced concrete bridges
4.1 IntRoductIon
Reinforced concrete (RC) was first introduced into bridge engineering in
the late nineteenth century, and it has become a major material for bridges
ever since then for its versatility, flexibility, and durability. RC bridges were
widely used during the reconstruction of Europe after World War II. In
general, a bridge that mainly uses RC for its major structural components
can be categorized as an RC bridge. For example, RC arch bridges, RC
beam-slab bridges, and RC rigid frame bridges are all considered as RC
bridges. Because of cracking, only partial of a concrete section is intact and
functional, the RC sectional strength to resist moment, shear, and tensile
is much lower than that of a prestressed concrete (PC). The cracking in
the tensile area, which is allowed in RC and actually does exist in services
state, poses potential corrosion risk on reinforce steels and thus deteriora-
tion of a cross section as a whole. The spanning capacity of an RC bridge
is limited to short to middle spans, and its application also depends on the
site environment.
Due to RC's special material behavior and the existence of cracking,
several distinctive issues arise in both the structural analysis and the com-
ponent design of an RC bridge. For example, how to count for the variation
of sectional modulus from location to location when conducting structural
analyses, as effective area of a cross section is related to moment it resisted,
and when behaviors of concrete and steel have to be considered in separa-
tion are common questions an engineer may ask when modeling or design-
ing an RC bridge. To be more practical, cracking and steel reinforcement
to cross sections can be simply ignored in most generic structural analyses
for obtaining component design forces. Sectional modulus variation due to
cracking loss and steel reinforcement is minor with regard to global load
distributions. Having obtained design forces, special principles and codes
should be strictly followed when coming to component design phase. When
the ultimate capacity of an RC bridge is of interest, which is more often
the case for short- to medium-span RC bridges than medium- to long-span
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