My first Magazine dsi-info-23-en | Page 58

Construction—APAC—Singapore—Commercial Buildings The DUO Project in Singapore: DYWIDAG Post-Tensioning Tendons keep huge cantilevered Building Elements in Balance The 26,700m² DUO project in Singapore, a joint venture development by the governments of Malaysia and Singapore, is located on Ophir Road in the historical districts of Bugis and Kampong Glam. The main part of this project includes the construction of two high-rise buildings: The 186m high, 50 story tall Residences Tower and the 170m high, 39 story tall Duo Tower. These two asymmetrical towers have concave shapes and include very large cantilevering elements causing a permanent imbalance in the towers. Therefore, the executing companies and engineers had to make sure that both buildings remained stable during every stage of construction. In order to maintain the permanent balance of the two buildings, the vertical walls of both towers were tensioned to counter the out of balance forces. For this purpose, the engineers had to introduce active prestressing forces at different stages of construction. In the Residential Tower, the wall had a thickness of 110cm and was therefore wide enough to place large DYWIDAG Strand Tendons into the wall that served as an active anchorage. As the walls in the second tower were only 50cm thick, 75mm Ø DYWIDAG Bar Tendons were used instead. The Residential Tower: Smooth Construction Progress with 140m long DYWIDAG Strand Tendons In order to support the overhanging block, large cantilever steel trusses were 58 placed in the two prestressed walls from levels 30 to 32. These trusses hold both 9 floor slabs below and support 20 floor slabs above. The large steel trusses were anchored in the prestressed wall using 19 75mm Ø DYWIDAG Bar Tendons. Each wall is prestressed using 6 Type 37-0.6" DYWIDAG Strand Tendons with MA Anchorages, with one additional tendon per wall installed to act as a spare tendon. The DYWIDAG Tendons were installed from basement level 3 up to the 32 nd floor, thus reaching a total length of 140m. Each tendon has a stressing anchorage at level 32 and a fixed anchorage at basement level 3. During wall construction, empty ducts were installed for the tendons. The DYWIDAG Strand Tendons were later threaded into the ducts in a single operation when construction progress had reached level 32. During strand installation, the strands were prevented from being drawn down freely by their own weight by temporarily looping the strands around the adjacent walls when feeding them into the ducts. Timing and the total amount of tensioning forces applied to the tendons at each stage of the stressing operation were crucial as these factors controlled the vertical sway of the tower. Based on a detailed design analysis and on site survey readings, it was determined that 40% of the stressing force had to be applied on reaching level 32, the tendon stress had to be increased to 70% on reaching level 40 and 100% of the load applied when reaching level 50. Once all DYWIDAG Tendons had been stressed, they were completely grouted in a continuous operation. Due to the length of the tendons, a detailed grouting method statement was prepared by Utracon, with grouting equipment being stationed at strategic locations to ensure that grouting proceed smoothly. The Office and Hotel Tower: Stability through 80m long DYWIDAG Bar Tendons Duo Tower, which will include both offices and a hotel, experienced a smaller out of balance load resulting from the overhanging block, as the main building core was designed to hang “only” 11 floor slabs from level 15 to level 25.