Bridge geometry - Computational Analysis and Design of Bridge Structures - page 547

Bridge geometry
18.1 IntroductIon
Bridges are counted as a part of road facilities to serve the purpose of
transportation. Most bridges are designed and built to satisfy their roads'
requirements. To satisfy requirements of a road alignment, the axis of a
bridge may have to be curved in both horizontal and vertical directions, and
the finished grade of bridge deck must comply with the transverse slopes set
forth in road geometries. Also, a bridge has to be designed under certain
engineering aesthetic guidelines, which may force a bridge axis, profiles, or
its components in curve or complex shapes. In other words, both the bridge
axis and a bridge component are more complex than what they are usually
described in mathematics and mechanics models.
A few questions may arise when building an analysis model of a
geometrically complicated bridge, for example, how a curved girder axis
is calculated and meshed into small elements and how a haunched girder
profile is defined and simulated. In this chapter, bridge geometry-related
principles and practical methods will be introduced.
18.2 roadway curves
The design of a roadway curve is usually separated into horizontal and
vertical curves. The horizontal curve, the projection of a roadway on plane,
defines the transition from one tangent to another allowing a vehicle to turn
in a graduate horizontal rate; the vertical curve, the projection of a road-
way on elevation, defines the transition from one slope to another allow-
ing a vehicle to change grade in a graduate vertical rate. In addition to the
constraints of sight distances and drainages, the design of both curves must
provide a roadway with graduate changes of curvatures or grade, rather
than a sharp change. Due to the different requirements of horizontal turns
and vertical grade changes, characteristics of horizontal curves and vertical
curves are different.
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