Q: We need to replace two arch bridges in a local park. One is a three-span structure with a 70-foot center span flanked by two 56-foot spans. The smaller bridge is a single 35-foot span. These are both masonry bridges, vintage about 1920, and the park district is concerned that the new bridges maintain some of the aesthetic qualities of the old ones. At the same time, we must find an efficient construction method. What can you suggest?
A.: The City of Grand Rapids, Michigan, recently faced a similar problem on a somewhat larger structure (Concrete Construction, May 1989, page 459). The consultant, Williams & Works, Inc., designed a bridge using precast prestressed I beams with a cast-in-place concrete deck. By integrating precast, conventionally reinforced arch-shaped fascia panels into the design, they maintained a resemblance to the old arch bridge that was replaced, and a feeling of harmony with older structures in the downtown area. Accent lighting which outlines the arches brings the structure to life after dark.
Precast prestressed I beams make up the structure of this bridge.
The addition of precast arch-shaped fascia panels makes its appearance more harmonious with older structures in the area. Using standard, readily available bridge beams saved both time and money.
A solution like this gives the owner a wide choice of finishes on the arch face panels, including a ribbed texture that could be achieved with form liners or the texture of aggregate exposed by use of chemical retarders or mechanical tooling. Application of stone masonry veneer as shown on the pedestrian bridges in our January 1990 issue (page 64) would be an appealing but more costly alternative. For the shorter arch span you might consider an inflated forming method (described in Concrete Construction, April 1988, page 385) which permits shotcreting an arch that supports H10 loading.