HBM – Railroad Tanana River Bridge-Alaska

Railroad Tanana River Bridge, Alaska

The Tanana River Bridge was designed in 2011 for a future Cooper-E80 loading on one track. The structure was also designed to carry HS25 trucks before the ties and rails are attached. The 164′-8″ long structure consists of four 11′ -3 1/2″ deep plate girders spaced at 4 feet centers and supporting a 3/4″ thick ballast plate. The web consists of a 7/8″ thick by 131″ deep plate. The flanges consist of 26″ wide by 2 1/4″ thick plates. The unsupported transverse length of the 3/4″ ballast plate is 22″. The plate girders are stiffened by intermediate stiffener plates and diaphragm stiffener plates connected to W36x135 diaphragms.

Description of Scope of Work:

HBM was retained by Hanson to perform a detailed linearly elastic structural analysis for the steel ballast plate supported by four deck girders as shown in the drawings dated June 17, 2011 provided by Hanson for the Tanana River Bridge on the Northern Rail Extension Phase 1A in Alaska.The analysis was limited to the plate spanning transverse to the girders and was accomplished using linear elastic finite element models using SAP2000.

Construction sequencing loads due to differential elevations limited to 1/2″ maximum on the top flanges of adjacent girders were considered. Additional load consisting of 9″ of well graded gravel with 20 kip tire load (AASHTO HS25) and 30% impact were included as recommended by Hanson.

The purpose of this analysis was to investigate the effects on the ballast plate caused by vertical offsets up to 1/2″. The effects considered included lasting residual stresses and capacity reduction of the plate. The controlling bending and shear stresses in the plate under normal loads were determined and the potential for failure of the plate under normal use was assessed.

Project Prime Consultant: Hanson Professional Services
Project Subconsultant: HBM Engineering Group, LLC