Shoring requirements for the rehabilitation of Spruce Run Bridge in Pennsylvania posed some difficult problems. Eleven badly deteriorated cross beams beneath the deck of the concrete arch bridge were to be cut in half and replaced one half at a time so that the bridge could remain open to traffic. Since the cross beams were supported only by two outside arches, shoring was needed on both sides of the cut and would be subjected to live loads for periods up to 1 1/2 years.
To reduce the amount of shoring needed, engineers first considered using steel bents to span across from the bridge's two main supporting arches. This option was abandoned in favor of erecting shoring towers. Erecting shoring towers from the ground up offered several advantages. Potential deflection problems were avoided with the elimination of long horizontal spans required by the steel bent system. Components would be smaller, making erection and dismantling easier. And, because shoring towers were built with modular components they could be reused on other projects. The basic unit for tower construction was a 4-foot by 6-foot-high frame with a rated load of 25,000 pounds per leg or 50,000 pounds per frame. Towers were supported either on existing bridge piers or on new footings. Anchor bolts were cast in the new footings or placed in drilled holes in existing piers.