The Tiwai Road bridge, built in 1969 and the only access for employees and maintenance services to the New Zealand Aluminium Smelter (NZAS), has been upgraded with a new superstructure and new guardrail from CSP Pacific to cope with more than 800 light and heavy duty vehicles using the bridge on a daily basis. A 2005 engineering review of the bridge showed considerable deterioration and corrosion of the beams at midspan which meant speed and weight restrictions were imposed, severely impacting the daily operation of the NZAS.
“The review showed that structural cracking of the beams was allowing sea water into the beams and causing corrosion to the bottom reinforcing and prestressing strand, weakening the beams,” said Grant Ballinger, Project Engineer for Fulton Hogan Civil South. “Several options were considered including various degrees of repair and a total bridge replacement. Due to the fact that the piles still had plenty of life left in them, a deck replacement was tendered by Invercargill City Council and we were the successful contractor.”
Repair of the 500m long two-lane bridge began in January 2009 and has seen one lane remain open throughout the works, with only short closures for beams to be installed, allowing operations at NZAS to continue unhindered. Along with remedial repairs to the top of the pile caps and nine new Double Hollow Core (DHC) beams, which form the deck, the bridge has received new guardrail and will receive a chip seal surface once complete.
|“As we worked our way along one side of the bridge we installed new TL-3 Bridge Guardrail from CSP Pacific,” added Grant. “Work was carried out on one side of the bridge at a time with temporary guardrail installed in the middle of the bridge. As we completed the second side of the bridge we were able to reinstall this rail to the outside of that lane. 1,000m of TL-3 Bridge Guardrail was installed in total.”|
The approaches on either side of the bridge also required replacement. In total Fulton Hogan Southland, as an internal subcontractor, have installed 1,530m of TL-3 Highway Guardrail and End Terminals on timber posts for the approaches.
“The supply of guardrail to this project was pretty straight forward for us,” said Ian Rowland Area Sales Manager for CSP Pacific. “It was just a very large order and a big job for Fulton Hogan.”
Completion is on track for mid November. “Dealing with CSP Pacific for all the road safety requirements has been easy. Everything has gone smoothly and efficiently,” said Grant.
With work all but complete on the bridge Grant says the location and project was interesting and challenging. “You can’t get much further south than this and when the weather is bad, it is pretty rough.”
The Tiwai Road bridge upgrade will significantly extend the life of the bridge providing a crucial link between Invercargill and NZAS, which is a major contributor to Southland’s prosperity, providing hundreds of jobs and injecting millions of dollars into the region’s and nation’s economy.