Standing proudly and beautifully on Jalan M.H. Thamrin in Jakarta, the 33-storey City Tower is far from the conventional and traditional building. Its shape speaks of asymmetry, dynamic composition, and sleek shapes. It adopts the shape of a nautilus – a shape that suggests asymmetry yet centrality, order yet fluidity. The ‘nautilus’ plan can be seen in sweeping lines and layered surfaces of the façade.
Positioned on a triangular site, this composite construction office building is topped with a unique spiralling steel and aluminium crown reaching 30 metres high. This building also has a 5-level basement and sky-lounge on the top floor. On typical floors, 16 metres of free column office space, spanning from the core to the perimeter columns, providing great flexibility for working space.
The structural system of the City Tower is a very modern one for Indonesian standards. It uses a reinforced concrete core wall that acts as the lateral system, while the gravity system is a composite concrete-metal deck floor with partial composite steel truss, supported by “Super-Columns”. The steel trusses span 16 metres, fabricated from high-strength ASTM grade 50 steel beams, cut into two, and laced with steel pipes as diagonal chords. This type of truss does not need gusset plates, is simple to fabricate, and provides space for mechanical or electrical services.
The super-columns are composite infill steel tubes, using high strength concrete, grade 50 MPa. The steel tube gives a high confinement effect and acts together with the concrete to take the load of the building. To transfer the forces from the steel-beam to the composite column, a special connection detail has been developed. The steel beam flange is inserted into the steel pipe, and tension-compression force on the flange is transferred by bearing action to the infill concrete. This type of construction has never been used before in Indonesia.
The City Tower is designed as a seismic-resistant structure and is capable to resist a 500-year earthquake with a peak ground acceleration of 0.230mGal.
