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.
In this paper, the peculiarities of the Diagrid, its structural behavior under loading and the design and construction of diagrid nodes are described. A case study of some recent diagrid tall buildings, namely the Swiss Re Building in London, the Hearst Tower in New York, and the West Guangzhou Tower in china is also presented.
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.
Among the large-span buildings some examples are represented by the Seatlle Library, the London City Hall, the One Shelley Street in Sydney, and more recently by several outstanding Pavilions realized at the Shanghai 2010 Expo, (e.g. France, UAE) as well as by some dazzling projects like the Astana National library. Among tall buildings, noteworthy examples are the Swiss Re building in London, the Hearst tower in New York, the CCTV headquarters building in Beijing, the Mode Gakuen Spiral Tower in Aichi, the Cyclone Tower in Asan, the West tower in Guangzhou, the Lotte super tower in Seoul, the Capital Gate in Abu Dhabi, the Bow project in Calgary, the Building of Qatar Ministry of Foreign Affairs in Doha.
. The diagrid systems are the evolution of braced tube structures, since the perimeter configuration still holds for preserving the maximum bending resistance and rigidity, while, with respect to the braced tube, the mega-diagonal members are diffusely spread over the façade, giving rise to closely spaced diagonal elements and allowing for the complete elimination of the conventional vertical columns. Therefore the diagonal members in diagrid structures act both as inclined columns and as bracing elements, and carry gravity loads as well as lateral forces; due to their triangulated configuration, mainly internal axial forces arise in the members, thus minimizing shear racking effects. To begin with the behavior of basic Diagrid module is discussed, followed by construction process. Then the merits and demerits of Diagrids are listed.
MATERIALS USED FOR DIAGRIDDS:
Material selection for a Diagrid construction is based on the following factors .
a) Unit weight of the material.
b) Availability of the material.
c) Lead Time.
d) Erection Time.
g) Labor cost.
h) Fire resistance.
MERITS OF DIAGRIDS:
Some major benefits of using Diagrids in structures are discussed below.
1) The Diagrid structures have mostly column free exterior and interior, hence free and clear, unique floor plans are Possible.
2) The Glass facades and dearth of interior columns allow generous amounts of day lighting into the structure.
3) The use of Diagrids results in roughly 1/5th reduction in steel as compared to Braced frame structures.
4) The construction techniques involved are simple, yet they need to be perfect.
5) The Diagrids makes maximum exploitation of the structural Material.
6) The diagrid Structures are aesthetically dominant and expressive.
7) Redundancy in the DiaGrid design is obvious. It is this redundancy then that can transfer load from a failed portion of the structure to another. Skyscraper structural failure, as it is such an important/ prominent topic, can be minimized in a DiaGrid design A DiaGrid has better ability to redistribute load than a Moment Frame skyscraper. Thus creating a deserved appeal for the DiaGrid in today’s landscape of building.
DEMERITS OF DIAGRIDS:
Some demerits of using Diagrids are mentioned below:
1) As of yet, the Diagrid Construction techniques are not thoroughly explored.
2) Lack of availability of skilled workers . Construction crews have little or no experience creating a DiaGrid skyscraper.
3) The DiaGrid can dominate aesthetically, which can be an issue depending upon design intent.
4) It is hard to design windows that create a regular language from floor to floor.
Typical Uses of the Diagrid the variety of open floor plans with a Diagrid the exterior of the floor plates are relatively static besides the service core, the floor plan is free of columns and other structural elements the service core only carries a vertical gravity load
very aesthetically pleasing for skyscaper design free of exterior columns access to generous amounts of natural sunlight reduces the amount of steel normal used by about 20%of the construction techniques are rather simple the redundancy of the diagrid transfers loads from failing portions of the building to other parts of the building, which prevents a total failure of a building
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