A Duo in Downtown Singapore

David Wood
Technical Director
Beca Group, Wellington

A pair of 50-story towers is nearing completion at Bugis Junction in downtown Singapore. The towers are carved into sweeping concave shapes, evoking the kinetic movements of a dancing couple. The residential tower required the top 25 stories to cantilever nine meters out from the face of the tower, from one of two structural cores. The detailing of the cantilevered truss structures, and in particular the connections directly to the slender walls of the concrete core, required special attention. With a tendency to lean over due to the significant building projections, control of long-term creep-and-shrinkage-induced lateral deflections was a key consideration in the design of the buildings. The need for co-ordination with vertical transportation requirements is discussed. The cantilevered section of the commercial tower provides a 20-meter overhang of 10 stories around the mid-levels of the tower. Vertical deflection and ongoing creep was limited at the front edge support by composite columns, with the whole cantilever truss tied back to the tower core to control rotation. Manual calculation of relative shortening of cores and perimeter columns over time was used to confirm staged computer model predictions. Correlation of creep coefficients with concrete testing is discussed, together with co-ordination of pre-set and surveyed building position during construction. Critical interactions with the construction team early in the project planning are summarized.