Closing a bridge for rehabilitation or emergency repairs always causes costly delays and inconveniences the traveling public. A bridge system that is economical, relatively easy and quick to construct, and capable of withstanding the live loads and volume of today's traffic would alleviate some of these problems. As a possible solution to the nation's need for an emergency or" bypass" bridge, a new type of bridge-the shell bridge-has been developed. The feasibility and practicality of the shell bridge system have been verified through analytical and experimental investigations. The use of a folded-plate deck structure instead of a circular-shell deck structure in a shell bridge system was investigated. The obvious advantage of using a folded-plate cross section is that fabrication would be much simpler (ie, flat form work instead of curved form work). The folded-plate bridge system was investigated analytically using the AN SYS general-purpose finite-element program. In the experimental portion of the investigation, a 1: 24 Plexiglas scale model of a folded-plate bridge was fabricated and tested. The model was subjected to in-plane forces to simulate posttensioning forces and vertical forces to simulate live loading. In this preliminary investigation, the foldedplate deck structure, except for the higher transverse stresses caused by the lack of arch action, was determined to be an improvement over the circular-shell deck structure.

Because bridges are a vital element of any country's surface transportation system, the closing of a bridge for any reason (emergency repairs, strengthening, rehabilitation, etc.) always causes costly delays, detours, and inconvenience to the traveler. This is especially true in the cases of isolated bridges where the next available bridge is several miles away or bridges subjected to high volumes of traffic. To help alleviate some of these problems, a shell bridge system has been developed that is economical, relatively easy and quick to construct, and capable of carrying legal loads and today's volume of traffic. Although it is primarily intended to be used for" bypass" bridges, this system can be used with appropriate modification in permanent installations.