Materials & Construction
Materials
A Diagrid system is a complex frame system, which has been implemented in construction of buildings for aesthetical and structural reasons. As such, diagrids have a limited number of materials that can be used in their construction. They are mostly constructed form structural steel, wood, or reinforced concrete. Structural steel is used for tall buildings (40 stories or more), reinforced concrete can be also used for tall buildings, but it does not have strength of steel. Application of wooden diagrid systems can be found in interior design, ceilings and canopies. However, using wood and timber is not advisable when we are talking about high buildings, such as skyscrapers. Wood does not have enough strength to support dead load. In current standard high rise buildings, diagrid systems use an exterior frame comprised exclusively of diagonal members as the primary means of support. When we are comparing diagrids with other structural building systems we can see that the amount of steel used for a diagrid is much smaller, which makes them more efficient. However, that does not mean the price of the construction of a diagrid system is cheaper. Using a diagrid frame system, engineers and architects can produce column free interiors, which would eliminate columns between the exterior structure and the core (same structural stability, more interior space).
One of the most interesting engineering achievements is with construction of diagrids with reinforced concrete. In this manner they are constructed as X-shaped joints, which are formed with four crossed inclined columns and horizontally positioned girders. These joints provide large stiffness and high load-bearing capacity. Furthermore, they are effective in transmitting the inner force from four crossed columns to other parts of the frame. While this is great application of usage of concrete in construction of diagrids, there is one issue. Concrete increases dead load on the foundation which could produce big problems and heighten the price of the building.
Following the architecture and design of buildings for the last 100 years, we can conclude that with development of technology, ways of construction has greatly changed. New materials and new ideas have emerged and so have advancements in diagrid structures.
Figure MC1: Steel, Wood and Concrete Diagrid
Construction
In construction of a diagrid system, engineers have to perform a series of precise calculations in order to decide which type of steel they will use, what angle is needed between beams or members they will apply, what kind of connections or nodes they will use, etc. Because of its complexity, diagrid systems are assembled in parts. Different elements are prefabricated in the factory and then transported to the construction site to be assembled. Each diagrid building is constructed with different angles in between its members. For diagrid structures which do not have vertical columns, bending is carried by the axial forces in the diagonals. For maximal bending rigidity, the optimal angle of columns is 90 degrees, and for maximum shear rigidity is around 35 degrees. The difference between angles in short and tall buildings is that short buildings with low aspect ratio (height/width) behave like shear beams. Tall buildings have a high aspect ratio and they behave like bending beams.
As we can see, the geometry of a diagrid structure is customized in order to satisfy specific requirements of a building. With diagrid frame systems there are more possibilities in developing complex shaped buildings. In order to have a unique, weird looking building, sometimes it is essential to introduce other elements in construction (support tower, cables). Crystalline applications of the diagrid have been used to create larger aggregated volumes, which is often very complicated and it demands supporting equipment during the construction such as a support tower or cable stays before the concrete floor of system has been built.