Currently, one of the largest commercial construction projects in Australia is under construction at the centrally located Collins Square in Melbourne's Western Precinct. It involves the construction of a large block of buildings that includes six towers and a renovated, historical warehouse that will accommodate offices, retail facilities and restaurants on an area of over 250,000 m².
Strand and bar post-tensioning systems were used in levels 26 and 27 of the 39 story high Tower Two at 727 Collins Street. The contractor, Form 700, together with its partner company Postenco, designed an alternative solution for the complicated structural design of both levels. In order to comply with the design of the architects, no columns could be used in the façade of level 26 on one side of the building. As there are 12 more stories above level 27, not having these columns in the façade created structural instability that was initially solved with passive reinforcement.
Active post-tensioning as light-weight alternative
As an efficient and light-weight alternative, Postenco proposed active post-tensioning using eight 57 mm Ø bar tendons and strand tendons with MA Anchorages. The large steel "triangles" on level 26 were tensioned back to the central core of the building using bar and strand post-tensioning tendons.
In total, eight Fep 1,050 N/mm² bar tendons with nuts, couplers and plates were cast into the floor and the walls of the core. The strand tendons were installed in the heavy beams on level 27, tying back the steel triangles of level 26. All 37 strands in one cable were installed parallel to prevent entangling and friction of the individual strands in each cable bundle. Due to limitations in stressing space and maximum weight restrictions, stressing was carried out using a monostrand jack. In total, 10 strand post-tensioning tendons were used.