The Indigo Icon Office Tower in Dubai, UAE by Atkins Architects creates a variation of the X bracing system. The bracing frame is set outside the exterior cladding of the tower to exaggerate its expression. There are issues related to climate and temperature swing associated with the choice to set such a structural element outside the environmental/thermal envelope, as the exterior steel will experience thermal expansion differently than the interior structure. This sort of solution is only applicable in climates where thermal bridging is also not a significant issue.
The idea of exterior bracing as a means of both structural and architectural expression is widely used. This differs from genuine diagrid construction as here the diagonal bracing is simply used as an addition to fairly standard framing and as a means to give additional rigidity to the building and is not used as the primary structural system. Left: The Quantam Nano Engineering Building at the University of Waterloo, ON, Canada, designed by KPMB Architects, uses multiple means of diagonal bracing on both the exterior and interior of the laboratory building. The extra resistance on this 5-story structure was required due to the nature of the labs and the processes contained. Right: The AESS steel bracing of the Quantam Nano Building sits outside the curtain wall system. Different finishing is required for this steel in contrast to the painted steel structure on the interior.
Left: This residential tower structure in Dubai uses truss band bracing. Here two floors of truss structure are used with standard vertical columns supporting the four floors between. In this instance, the diagonals of the trusses will be incorporated into the cladding design and the spaces will be used as occupied floors. The trusses here are less obtrusive, as the design allows for a clear, column-free span from the core to the outside wall. Right: The mechanical floor of the Bloomberg Tower in New York, NY, USA, designed by Cesar Pelli. This bracing floor is constructed of trusses, with the structural steel spray-fireproofed.
TRUSS BAND SYSTEMS The truss band system is a variation of other tubular systems. Bracing can also be provided to a framed structure by conceiving a number of floors of the tower as large truss structures. On the exterior of the building this is typically seen as a truss band. These floors are often planned for use as mechanical service floors, as the space is substandard for use as office space due to the interference of the many diagonal web members of the trusses that can exist within the plate area of the usable floor space. The frequency of the occurrence of these floors, and the depth of the trusses, are a function of the height-to-width ratio of the building, combined with local wind and seismic issues. Mechanical service needs will also impact the requirements.
– ADVANCED FRAMING SYSTEMS: DIAGRIDS