Custom Stone Look for Concrete Arches of Coton Bridge

This article describes the design and construction of the Coton Bridge in Virginia, which is a nine-span arch-box precast concrete structure that spans a creek. The bridge combines state-of-the-art engineering while fulfilling ecological and aesthetic considerations. The bridge was built with private funding, and turned over to the Virginia Department of Transportation (DOT) for maintenance. A stone facing for the precast bridge was originally preferred, but due to maintenance concerns, a simulated stonework appearance was created by using historic stones as patterns to make molds that would appear in elastomeric form liners for the cast-in-place parapet walls. The concrete was stained to given the appearance of stone and to provide weather resistance. Each of the nine arches contains 21 precast units to make up the total 82 ft transverse width of the bridge. Sloping from east to west, the bridge was designed to meet DOT road elevations and slopes. Only three central spans are over the creek waters, and the other spans maintain the vertical curve of the road alignment. The elevation of the precast arches above the stream is established with cast-in-place piers, with pier walls providing direct support for the precast bridge components. The entire bridge (except the end abutments) is in a flood plain, with the underside of the arches as much as 35 ft above normal water level. This job differed from typical precast installations in terms of the foundations across a highly variable site with rock, shale and clay. Installers also had to work in water while minimizing environmental impact.