Reinforced concrete bridges - Computational Analysis and Design of Bridge Structures - page 100

non-RC bridges, a full material nonlinear analysis is required. In such an
analysis, material behaviors of concrete and steel are considered in great
detail. For example, a specific constitutive relationship for steel RC as a
whole may be used, special concrete elements with consideration of the
existence of reinforcing steels can be developed, or concrete and steel are
separately modeled in the structural level.
Fiber-reinforced concrete (FRC) is a kind of concrete that contains
fibrous material for reinforcement to increase the structural integrity. FRC
contains short discrete fibers that are uniformly distributed and randomly
oriented. Fibers include steel, glass, synthetic, and natural fibers, which give
different structural properties. Several ultrahigh-performance concrete
(UHPC) bridges using FRC have been built in the United States (Fu and
Graybeal 2011). The addition of fiber to concrete was aimed primarily at
enhancing the tensile strength and postcracking behavior of concrete. FRC
behaves as regular concrete but with higher strength, especially tensile
strength. For highway bridge structures, FRC can be applied to overlays
in bridge decks, seismic- and explosion-resisting structures, and recently
UHPC bridges.
On the other hand, fiber-reinforced polymer (FRP) is a composite mate-
rial made of a polymer matrix reinforced with usually glass, carbon,
basalt, or aramid. FRP bars and grids have been commercially produced
for reinforcing concrete structures for over 30 years. FRP bars have been
developed for prestressed and non-prestressed (conventional) concrete
reinforcement. FRP has been used for strengthening structural members
of RC bridges that are structurally deficient or functionally obsolete due
to changes in use or consideration of increased loadings (Kachlakev 1998).
Many researchers have found that FRP composites applied to such mem-
bers provide reliable and cost-effective rehabilitation. FRP composites
are orthotropic materials with two constituents, that is, reinforcing and
matrix phases. The reinforcing phase material is fiber, usually carbon or
glass, which is typically stiffer and stronger, whereas the matrix phase
material is generally continuous, less stiff, and weaker. The behavior of
FRP-strengthened concrete structural members can be analyzed using
finite element method (FEM).
As detailed RC cracking analysis, most early finite element models of RC
were based on a predefined crack pattern. The recently developed smeared
cracking approach overcomes these limitations of unpredicted predefined
cracks and has been widely adopted for predicting the nonlinear behav-
ior of concrete. It uses isoparametric formulations to represent the cracked
concrete as an orthotropic material. More details of this subject are dis-
cussed in Section 4.4.2—Nonlinear Modeling.
In this chapter, RC bridge behavior at the material level, especially
the coworking of concrete and steel; characteristics of skewed slabs as a
common application of RC bridges; and different modeling methods are