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
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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.