Integral bridges - Computational Analysis and Design of Bridge Structures - page 491

Integral bridges
16.1 BasIcs of Integral BrIdges
16.1.1 Introduction
An integral bridge is a jointless bridge with no bearing at the connection
point where the superstructure and substructure are framed together.
Therefore, integral bridges are categorized as rigid-frame structures
because they eliminate expansion joints. Integral bridges include integral
abutment bridges (IABs) as well as integral piers. As most discussions
focus on IABs, this section will briefly mention integral piers before mov-
ing onto IABs.
One type of integral bridge is the integral pier, which involves build-
ing a monolithic or framing-in joint at the pier. There are a number of
ways to form an integral pier (Sisman and Fu 2004). A common method
in concrete construction is a frame-type structural system, namely, cast-in-
place concrete box girder bridges and was also carried over to steel I-girders
framing into a concrete pier cap or diaphragm. More recently, a number
of versions of integral piers have been developed, which involve steel plate
girder construction to improve substructure layouts, eliminate detrimen-
tal effects of a skewed substructure, or enhance bridge performance under
seismic loads. Some of the new concepts use steel framing-in caps, which
integrate with the concrete columns (Figure 16.1); others are various ver-
sions of traditional concrete caps with varying structural boundary condi-
tions. Whichever method, integral piers concealed within the boundaries
of superstructure lines are definite enhancements to the aesthetic value of a
bridge, whether it is in an urban setting or on a country road.
The main type of integral bridges is the IAB. An integral abutment is
a stub abutment on a single row of flexible piles and constructed without
joints. These bridges allow for expansion and contraction through move-
ment at the abutments. In the conventional design of the superstructure,
bridges are idealized as a continuous beam with simply supported ends.
Figure 16.2 shows possible configurations for a typical four-span highway
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