The Ashgrove Avenue Bridge is a reinforced concrete bridge constructed circa 1925. The five span beam-and-slab superstructure is continuous over the internal concrete wall piers and simply supported on phosphor-bronze plate bearings located at each abutment. The most recent Level 2 bridge inspection discovered the bearings to be severely corroded. Consequently BCC appointed HDR to perform a Level 3 inspection of the bridge to confirm the previous inspection findings and determine the residual life of the bridge with the view of identifying and optimising future repair strategies.

The HDR Level 3 inspection revealed that the top and bottom cast iron bearing restraint plates have severely corroded, potentially allowing the restrained phorphor-zinc bearing plates from dislodging and severely damaging the structure. The residual life of the bearing components on the western abutment was assessed as only being between 3 to 5 years.

HDR’s appointment was further extended to develop a bearing replacement design in order to extend the service life of this critical asset. The original bridge design did not allow for bridge jacking, a situation that is further complicated by the abutments being founded on slender driven timber piles which precluded the bridge from being eccentrically jacked from the front face of the abutment. Hydraulic flat jacks positioned along the centroid of the deck end diaphragm beam and abutment was identified as the only practical and safe means of lifting the bridge to executing the required bearing replacement. The concrete end diaphragms are sparsely reinforced and having large irregular penetrations requiring the use of finite element analysis (FEA) techniques to aid the development and verification of the complex bridge jacking and bearing replacement design.