Arch bridges - Computational Analysis and Design of Bridge Structures - page 265

Arch bridges
9.1 IntroductIon
The arch bridge is one of the oldest types of brides and has been in existence
in the world since more than 2000 years (Brown 2005). The Romans were
the first to take the advantages of the arch in building bridges. There are
more than 900 ancient Roman bridges found in Europe; most of them are
arch bridges. Applying arch into bridges and buildings has a long history also
in the East. The Anji Bridge, the oldest open-spandrel segmental stone arch
bridge with a central span of 37 m, was built in AD 605 in Hebei, China
(Figure 9.1). The use of cast iron as dovetails to interlock stone segments and
open spandrels so as to reduce structural weight and to increase water flow
during flooding made it a milestone in the long history of arch bridges. Its sur-
vival of at least eight wars, ten major floods, and numerous earthquakes, espe-
cially the 7.2-richter-magnitude earthquake in 1966, Xingtai (40 km away
from the site) demonstrates the strength and advantage of the arch bridge.
Arch is sometimes defined as a curved structural member spanning an
opening and serving as a support for the loads above the opening. This
definition omits a description of what type of structural element; a bending
and/or an axial force element makes up the arch. Nomenclatures used to
describe the arch bridges are outlined in Figure 9.2. A true or perfect arch,
theoretically, is one in which only a compressive force acts at the centroid of
each element of the arch. The shape of the true arch can be thought of as the
inverse of a hanging chain between abutments. It is practically impossible
to have a true arch bridge, except for one loading condition. However, an
arch is usually subjected to multiple loadings, which will produce bending
stresses in the arch rib that are generally small compared with the axial
compressive stress.
Arch bridges have great natural strength. In addition to pushing straight
down, the weight of an arch bridge is carried outward along the curve of
the arch to the supports at each end. These supports carry the load and
keep the ends of the bridge from spreading out. When supporting its own
weight and the weight of crossing traffic, every part of the arch is under
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