A Queensland contractor has taken an innovative approach to constructing a bus duct riser: building it wholly offsite. The technique delivered considerable efficiency and safety benefits, as Kate Jordan reports.

Bus ducts are generally constructed onsite, presenting various difficulties such as site access, tool security and safety. For a recent tender, Fredon Queensland suggested avoiding these and other issues by constructing the bus duct riser (BDR) offsite. Another branch of the company, Fredon Air, had previously completed a similar project with prefabricated duct assemblies and air handling unit modules. Fredon Queensland calculated that the approach would also work well with bus ducts and the client, Watpac Constructions, agreed, awarding it the tender for the 248-bed private hospital in Southport, Gold Coast.

There are three bus ducts in the riser: essential, non-essential and safety services. These were constructed in four frames at the Fredon head office in Brisbane and then transported to the site. The frame is seven-stories high and weighs 12 tonnes. An in-house team manufactured and assembled the distribution boards, as well as designing and installing the mounting brackets to support the bus duct.

“We designed it with spigots, so the whole frame could slide into itself for installation of the bus duct that has 2mm tolerance. The whole bus duct was assembled in our factory before it even left for the site, to test that every piece fit,” Fredon Queensland operations/engineering manager Brenden Harris says. The BDR was then dismantled into its four frames, ready for transporting.

Transporting and installing the BDR created additional requirements. The four frames needed specialist jigs and trolleys to move them about, which were also made in-house. To install the BDR in the building, a crane needed to lift the frames from a horizontal position to a vertical one, which required further strengthening.

“The flexing when you lift anything from horizontal to vertical creates stresses within the steel and can cause it to buckle. We put in stiffeners by welding the floors into the frame itself. That eliminated a lot of the deflection that we would get, which protected the bus duct,” Brenden explains.

With only 20mm tolerance on either side of the BDR, a calm, windless day was needed for installation.

“Once it was lifted up and craned in, it wasn’t really that stressful because everything was done via laser measurements onsite and that was checked three times.”

When the fourth and final frame was in place, Watpac slid a prefabricated concrete lid into place that ensured the BDR was water tight – fortunate, as a storm rolled in a couple of hours later.

So why bother with all this? Because, Brenden explains, offsite construction offers a raft of improvements in efficiency and safety.

“Off-site construction eliminated issues with wet weather and industrial relation matters onsite. We had very tight time frames that we had to meet and the environment that our workers were in was a lot more conducive to design modifications than an onsite team.”

For installation, the time required onsite was a mere day.

“They went from having no electrical infrastructure at all to being completely down and finished within an eight hour period, so the next day they could be ready to turn the bus duct on,” Brenden says.

As the concept was very new, it was also beneficial to be able to draw upon the expertise of the whole office.

“As construction was in the head office, we were able to have an engineering team oversee the whole installation process. Any sort of technical or any risk factors that were identified in the project were eradicated and eliminated very quickly.”

In addition, with all the construction taking place in a controlled, supervised environment, quality control could be assured. Waste – such as cable drums and scrap metals – was eliminated from the site.

Vast improvements were also made in safety, which was recognised by both the client and government agencies. Watpac services manager Colin Biggs comments:

“We were audited by the Government OHS safety team, who have recommended the Gold Coast Private Hospital (GCPH) as a whole be commended highly for the approach to safety. Specifically they observed the bus duct installation and install methods adopted.”

Safety was a part of the project from the very beginning.

“Our safety manager Andrew Campbell, in conjunction with construction manager Michael Steuart, did a full safety compendium and put it to Watpac,” Brenden says.

The risk of falls was a big challenge.

“We had a safety meeting in relation to how we were going to close the floors off to stop people from falling down when we were dropping the riser in. You need to guide the frames down on different floors to make sure that no one would be harmed. That’s when we came up with the floor solution and incorporating the floors into the steel frame. So we engineered that in halfway through the project.”

Will we see more of these types of installations in the future? Brenden isn’t sure, as it’s a fairly specialised product.

“It’s not a product that will suit every single project, maybe one percent of projects going around. You’ve got to have very specific loads in certain places and a cable sized to counteract the cost of the bus duct.”

Currently, Fredon Queensland only has a couple of clients interested in the product, with others possibly balking at the apparent price rise.

“When companies price a job, they don’t look at the savings that it offers to structural elements and incorporate those things into their pricing models. A BDR typically would be 50% more expensive on the infrastructure, but they don’t look at all the other savings on site or productivity efficiencies from their workers,” Brenden says, using the example of savings in crane use, where four lifts were used instead of the usual 40.

Although perhaps not suitable for widespread use, Fredon’s BDR installation offers an insight into alternative construction techniques and could lead to other future developments – after all, it’s an idea that grew out of another innovation. Who knows where the next innovation could lead?