Diagrid

Definition:

Design and construction of artificial infrastructure on the lines of  biomimicking principles requires the development of highly advanced structural systems which has the qualities of aesthetic expression, structural efficiency and most importantly geometric versatility. Diagrids, the latest mutation of tubular structures, have an optimum combination of the above qualities.

The Diagrids are perimeter structural configurations characterized by a narrow grid of diagonal members which are involved both in gravity and in lateral load resistance. Diagonalized applications of structural steel members for providing efficient solutions both in terms of strength and stiffness are not  new ,however nowadays a renewed interest in and a widespread application of diagrid is registered with reference to large span and high rise buildings, particularly when they are characterized by complex geometries and curved shapes, sometimes by completely free forms.

Module Geometry:

Diagrid structures, like all the tubular configurations, utilize the overall building plan dimension for counteracting overturning moment and providing flexural rigidity through axial action in the diagonals, which acts as inclined columns; however, this potential bending efficiency of tubular configuration is never fully achievable, due to shear deformations that arise in the building "webs"; with this regard, diagrid systems, which provide shear resistance and rigidity by means of axial action in the diagonal members, rather than bending moment in beams and columns, allows for a nearly full exploitation of the theoretical bending resistance. 

Being the diagrid a triangulated configuration of structural members, the geometry of the single module plays a major role in the internal axial force distribution, as well as in conferring global shear and bending rigidity to the building structure.  While a module angle equal to 35° ensures the maximum shear rigidity to the diagrid system, the maximum engagement of diagonal members for bending stiffness corresponds to an angle value of 90°, i.e. vertical columns. Thus in diagrid systems, where vertical columns are completely eliminated and both shear and bending stiffness must be provided by diagonals, a balance between this two conflicting requirements should be searched for defining the optimal angle of the diagrid module.   Usually Isosceles triangular geometry is used.

Optimal Angle:

As in the diagrids, diagonals carry both   shear and moment. Thus, the optimal angle of diagonals   is highly dependent upon the building height.  Since the   optimal angle of the columns for maximum bendingrigidity is 90 degrees and that of the diagonals for   maximum shear rigidity is about 35 degrees, it isexpected that the optimal angle of diagonal members for   diagrid structures will fall between these angles and as   the building height increases, the optimal angle also   increases. Usually adopted range is 60 -70 degree.