23:16 Dec 17, 2009 

The chords on your references refer to the trussed arches that support the bridges (which are lattice structures and have a bottom or lower chord and a top chord). A vertical curve is a geometrical concept used in road design that applies to the curve used to join different grade tangents, so it is an element that defines the geometry of the road surface itself). Thanks for the interest and the references.

17:40 Dec 17, 2009 

I believe Sergio's "vertical curve" is likely correct, but consider these references I came across to the terms "vertical chord" and "parabolic chord". Would they apply here?

Bayonne Bridge (NY 440 and NJ 440) - [ Traducir esta página ]The revised design of the Bayonne Bridge arch was to feature a slender, ... trussed arch in which the bottom chords form a perfect parabolic arch. .... pass under the bridge at low tide because there is not enough vertical clearance. ...
www.nycroads.com/crossings/bayonne/ - En caché - Similares
Testing and monitoring of a centenary arch bridge - - Citado por 3 - Artículos relacionados
maximum height, with a variable vertical chord thickness from 16.7 m near the supports to 7.1 m at the crown, and presenting a parabolic geometry both in ...
www.informaworld.com/index/713683562.pdf
Panther Hollow Bridge 1896 - HAER PA-489 - Bridges and Tunnels of ... The arch ribs forming the lower chord may be constructed with a ... engineer designed the parabolic lower chord to support itself, merely accepting uniformly distributed loads through vertical and diagonal web members. ...
pghbridges.com › Articles › HAER - En caché