P & L Railroad Bridges J23.3 & J23.7

Located just outside the Fort Knox Army Base, the Paducah & Louisville (P&L) Railway’s steel trestle bridges J23.3 and J23.7 were originally constructed in the late 1800s, consisting of wrought iron towers and girders on spread footings.

After more than 30 years of providing inspection services on these bridges, Benesch determined that 120 years’ worth of deterioration had rendered further repairs to the existing structures impractical. A life-cycle cost analysis determined that building new bridges on an offset alignment was the most reasonable and economical way to replace the aging structures.

Designing the new structures required innovative techniques that would provide for economical and safe replacement of the existing bridges, while accommodating regular rail traffic operations in the mountainous region.

The preliminary engineering scope included developing multiple horizontal and vertical track profiles. The profiles had to tie into key existing track points between bridges and meet all railroad track design standards. Once the horizontal and vertical profiles were determined, the project team balanced blasting rock quantities with determining economic bridge lengths.

Developing multiple horizontal and vertical track profiles was key to the project’s success, as the profiles had to tie into existing track points between the bridges to meet all railroad track design standards. Because the structures would be built on an offset alignment, the design team had the freedom to use longer span lengths and consider several more innovative superstructure types.

Long-span prestressed concrete girders, in combination with multi-column concrete piers, allowed for the new structure to be built just feet away from the existing bridge, minimizing rail re-alignment and environmental impacts. This structure type was an unusual choice, as these girders are American Association of State Highway and Transportation Officals-type girders most often used on highway structures.

During the design phase, P&L decided to apply for a Tiger Grant. The project team accelerated the design plans and specifications to meet the grant requirements. Benesch also contributed to the Tiger Grant application, which P&L won.

Construction was successfully completed while maintaining regular train operations on this strategic railway route to Fort Knox.