Macalloy 460 System delivers stress relief on Phoenix High School - 28/04/11
Thu, 28 April 2011
This gravity-defying propped cantilever was made possible thanks to an ingenious hybrid structural system, devised by structural engineers SKM Anthony Hunt and Bowmer & Kirkland, which combines a super-reinforced concrete frame with deep foundation piles, two structural steel columns, and the Macalloy 460 tension bar system.
The pairs of Macalloy tension rods are embedded into concrete at roof level on either side of the cantilever’s central corridor and span diagonally out to the base of the cantilever walls on the external facade.
Each bar is fitted with Macalloy's patented TechnoTensioner system. Once the bars had been tensioned and propping has been removed from under the cantilever, the bars help prevent short- and long-term vertical deflections.
Before tensioning could begin, structural engineer SKM Anthony Hunt had to calculate the as-constructed total load on the building, including any secondary steelwork, fittings and finishes, and construction live load. Based on this the engineer determined target stresses for each bar.
Then, as propping was gradually struck, and under SKM Anthony Hunt’s supervision, concrete subcontractor John Doyle Construction individually tensioned each of the four bars, which allowed for fine adjustment and easier measurement of forces within the system. Once the falsework was removed the system was able to achieve target tension values of 1,080kN per bar, or 2,160kN per pair.