Construction of a Precast Segmental Bridge uses Strand Post-Tensioning Tendons
In the year 2000, 28,000 vehicles per day travelling on the Pennsylvania Turnpike crossed the Susquehanna River near Harrisburg. Since local traffic projections for the region anticipated that this traffic would double by the year 2020. Strengthening and expansion or replacement of the existing 55 year old bridge became necessary.
The bridge’s owner, The Pennsylvania Turnpike Commission, decided to build a new 6-lane bridge north of the existing bridge.
The new bridge consists of twin 1,800 m long by 17 m wide concrete box girder structures with typical span lengths of 45 m. Considering the required geometry and consistent multiple spans, the project was well suited for the precast segmental construction method. One major advantage of the use of precast elements is the much shorter construction time compared to alternative construction methods. In addition, the maintenance costs for precast concrete segmental bridges are significantly lower and the hollow box girders also offer additional space for utility lines.
The precast prestressed concrete segments are supported by a total of 78 piers and two abutments. The bridge’s piers consist of two drilled concrete shafts, a solid concrete collar, a hollow concrete collar and a post-tensioned concrete pier cap.
To cast the 1,040 precast segments, each weighing up to 106 tons with a height of 2.5 m and a length of up to 4 m, the contractor set up a casting yard in close proximity to the bridge. In addition, the precast elements were prestressed in transverse direction in the casting yard. Prestressing of the precast concrete segments included installation and stressing of 4x0.6" DYWIDAG Strand Post-Tensioning Tendons anchored in the top slab. In addition, 4 m long 36 mm Ø Grade 150 DYWIDAG Post-Tensioning Bars were installed and stressed at the bottom of the individual elements.
The precast segments were trucked to the construction site for installation. Subsequently, the segments were hoisted onto an erection gantry by a crane, and each 45 m long span was pre-stressed with an average of 8 27x0.6" DYWIDAG External Strand Tendons.
Since construction work on this important project proceeded faster than scheduled, the new bridge was opened to traffic in the spring of 2007.