System Comparison
The diagrid structural system has unique properties that are both modern and economical. Although the role of a structural system is the same, carrying loads to the foundation and beyond, the diagrid has components that make this role more efficient. This section will walk you through the similarities and differences between a diagrid and other structural systems. Figure SR1 shows an illustration of how typical steel-framed structural systems compare based on their typical number of floors.
Figure SR1: System Comparison
Diagrid vs Steel-Framed Braced Tube
Figure SR2: Diagrid vs Braced Tube
Almost all the conventional vertical columns are eliminated for diagrid structures. This is possible because the diagonal members in diagrid structural systems can carry gravity loads as well as lateral forces because of their triangulated configuration. On the other hand, the diagonals in conventional braced frame structures carry only lateral loads. The gravity loads in conventional braced frames are carried down to the earth by the vertical members both in the exterior and interior of the building. Diagrid structures are also much more effective in minimizing shear deformation because they carry shear by axial action of the diagonal members, while conventional framed tubular structures carry shear by the bending of the vertical columns.
Diagrid vs Steel-Framed Outrigger Structures
Although both a diagrid and an outrigger structure are effective in reducing the moment and drift of the building, the outrigger system does not provide shear rigidity. The diagrid structure provides both bending and shear rigidity. Thus, tall buildings which employ outrigger systems require cores having significant shear rigidity. Diagrid structures do not need high shear rigidity cores because shear can be carried by the diagrids located on the perimeter. Thus, buildings with outrigger trusses are typically not built taller than buildings with diagrid construction. This camparison can be seen in Figure SR1. Outrigger system also requires megacolumns around the perimeter and in the core of the building. This makes it impossible to create an open floor plan feel that a diagrid provides.
Diagrid vs Concrete-Framed Structures
There are countless reasons on choosing diagrids over concrete framing. Unlike steel, concrete has very low tensile strength. Therefore, it is not desirable to be used to create long spanning members without reinforcement. In addition, the diagrid eliminates the need for large columns, making it lightweight. This is the complete opposite of a concrete-framed structure. More concrete volume is needed to achieve the same amount of compression as a diagrid structure. Although rare, concrete is also used in diagrid systems. However, a diagrid's simple organic nature allows for a great multitude flexibility of overall design shapes allowing for a designer to easily consolidate forces into compression rather than tension.