Macdonald Bridge Foundation Retrofit
Location: Halifax, NS
Client: Halifax Harbour Bridges
Duration: 2013
Project Description
As part of the deck replacement of the Angus L. Macdonald Bridge, the existing bridge elements to remain in service were analyzed for the new loading conditions. Due to the decrease in deck weight and revised wind loads, the analyses indicated a potential overturning instability in the Halifax Cable Bent foundations. Rock anchors were selected as a means of remediating this instability.
Harbourside’s Role
Rock anchors were designed by Harbourside based on the hold down requirements indicated by the numerical analysis. Bedrock properties were obtained from previous boreholes and geotechnical studies.
A design was developed which allowed minimal modification to the existing structure, by drilling two holes through each cable bent leg baseplate and foundation into the underlying bedrock.
Anchor bars pregrouted into corrugated tubes were selected to maximize corrosion protection, and drilling methodologies were specified to prevent damage to the surrounding foundation concrete. During previous investigations, this was found to be deteriorating.
After the anchors were installed and grouted, proof testing was performed to confirm the installation. Pretensioning of the anchors was then specified to the required holddown force.
Harbourside performed the detailed design of the anchors as a subconsultant to Buckland and Taylor, Ltd.
Unique Challenges
Work on either the Angus L. Macdonald Bridge, or the Mackay bridge necessitates careful planning. As two of the busiest stretches of roadway in the province, shutdowns are costly, with huge impacts on the city. These must be kept to a minimum, and any work must be done efficiently as possible.
Social Impact
The health and maintenance of both harbour bridges are essential to keeping the city moving. When even one of the bridges is impacted, the Halifax Regional Municipality easily becomes gridlocked, affecting all aspects of city life. This necessary work ensures the continued longevity of the Macdonald Bridge, and reduces the need for further maintenance down the line.