Structural Engineering Award of Excellence: Raffles City Chongqing Complex, Chongqing
Chit Phee Tan
Deputy Director, Design Management
CapitaLand Limited, Chongqing
An Outrigger System Protected by a Seismic Fuse
Tall buildings and long-span structures have existed for a long time, but designing a combination of the two required a unique approach to ensure structural and economic feasibility. Raffles City Chongqing is a mega-scale development that also serves as an important transportation hub. The most noticeable component is the Conservatory—a 300-meter-long glass-clad structure that sits astride four tall, curved towers. The articulation of the Conservatory in relation to its four supporting towers, two with a slenderness ratio of 9.4:1, required a very strong structural frame for lateral stability. A hybrid outrigger system using concrete walls adjacent to cores, steel diagonals, and structural fuses was developed.
A “seismic fuse” connects the outrigger wall to the mega column to control load paths in major seismic events. This fuse component can dissipate the seismic energy in case of severe shaking, protect other components of the outrigger system, and ensure the safety of the whole complex. Force patterns, deformations, and failure sequences were studied, and finite element analyses were carried out on the separate elements and on the outrigger system as a whole. Under Level-1 earthquakes and normal wind loads, the fuse will remain fully elastic. However, under Level-2 and Level-3 earthquake events, the fuse shear component will yield and deform, so as to dissipate the energy. This damping effect will protect the outrigger wall and core. The fuse can be readily replaced after severe earthquake events. Compared with conventional outrigger systems that are predominantly structural steel, the hybrid system uses minimal steel connecting elements, whilst achieving higher rigidity within a more compact refuge floor zone. Moreover, it shortens the construction time and achieves further cost savings.