LDG provided planning and design services for the replacement of both the north- and south-bound bridges carrying 30,000 vehicles per day on the Pennsylvania Turnpike Commission’s Northeast Extension (Interstate 476) at mile post A57.66, over Crackersport Road, near Allentown, Pennsylvania.

Time Sensitive Challenge

The contractor only had 55 hours to demolish the two existing bridges and replace them with the new bridges to avoid substantial penalties. LDG worked with the contractor to develop and design an innovative, Accelerated Bridge Construction (ABC) lateral slide method to replace the 60-year-old bridges. The ABC method involved building the replacement superstructures adjacent to the existing structures, and then sliding the new superstructures into place as soon as the demolition of the old structures was complete, with the entire operation being completed in a single weekend.

Innovative Design & Construction Phasing

LDG reviewed demolition and erection plans, designed temporary support structures to hold the replacement bridges; designed the lateral slide process including calculation of forces and jack sizes; and designed a concrete jacking block to withstand the forces of pulling. The temporary support structure included steel pile bents at 13-foot intervals driven to absolute refusal at a depth of 60 to 70 feet. The bents were connected via a lateral slide beam and a steel jacking beam. The support structure was designed to hold each 131-foot, 1 million-pound steel-girder replacement bridge superstructure during construction and the rolling slide procedure.

Both bridges were in place in four hours and the entire bridge placement process was completed with several hours of the 55-hour window to spare. For successful design and construction efforts, the project was recognized with the following awards:

• Diamond Award, ACEC-PA
• 2018 Transportation and Infrastructure Award, Lehigh Valley Planning Commission
• 2018 Outstanding New Medium Span Bridge, ABCD Susquehanna Chapter
• 2018 TQI Partnering Award, APC