The new Shenandoah River Bridge spans 1,400 feet over a deep river valley in the eastern panhandle of West Virginia, making it the longest span delta frame bridge in the United States. With a height of 200 feet, the bridge’s steel superstructure comprises a five-girder, four-substringer system supported by five lines of delta legs — one for each girder. Each leg covers a vertical distance of 150 feet and a horizontal distance of 150 feet, creating a girder span of 300 feet between the delta legs.

As the lead designer on the Shenandoah design-build project, HDR provided preliminary and final design as well as construction engineering. The detailed construction plan accounts for the erection heights, uniqueness of the delta leg erection when the deltas were incomplete, tall temporary works, small site footprint, fluctuating river levels and other unique site conditions. Since there were no directly applicable design codes for portions of the structure, HDR developed the appropriate design checks. HDR created a finite element analysis of the erection procedure so each step could be examined individually and so the temporary works and permanent steel framing could provide stability to the structure until completed.

HDR’s recommendation to pursue the delta frame differed from other bids, but we recognized that the required span arrangement and dimensions of the valley provided the perfect geometry for balancing the spans for the delta frame structure. We also saw that the delta frame option would be extremely cost-effective, offering $8 million in savings compared to more traditional designs.