Abstract
Due to the increasing number of people and activities within the cities, tall buildings are exploited worldwide to address the need for new living and commercial spaces, while limiting the amount of used land. In recent decades, the design of tall buildings has undergone a remarkable improvement, thanks to the development of new computational tools and technological solutions. This has led to the realization of innovative structural systems, like diagrids, which allow the achievement of high structural performances and remarkable architectural effects. In this paper, a thorough and updated review of diagrid structural systems is provided. Simplified methodologies for the preliminary design and structural analysis are reported. Special attention is also paid to the optimization of the structural response based on the geometrical pattern. A discussion of the effect of local deformability, stability and shear-lag phenomenon is carried out. Results from nonlinear and dynamic analyses for the seismic assessment of diagrid systems are reported, and attention is also paid to the recent research on diagrid nodes. Eventually, an overview of twisted, tapered, tilted and freeform diagrid towers is carried out, with a final mention of hexagrids, another recent evolution of tubular systems for tall buildings.
Highlights
The evolution of tall buildings has undergone remarkable developments in the last century.The first buildings reaching a few tens of stories were first built in the United States in the late 19th century, mostly in the cities of New York and Chicago
The fundamental characteristics of diagrid tubes, which rely on the axial-dominated mechanism of the external mega-bracing, have been shown in the beginning of the paper, together with an overview of the structural solutions that have brought about the realization and success of diagrids in recent years
Some of the recent simplified methodologies for the structural analysis of diagrids, which do not rely on the common FE calculations, have been described
Summary
The evolution of tall buildings has undergone remarkable developments in the last century. The adoption of mega-diagonals on the external surface offered higher lateral stiffness, while reducing some detrimental phenomena of the framed tube, such as the shear-lag effect With this new solution, a greater number of stories and an overall enhanced structural performance could be achieved, leading to important advantages from a material consumption perspective. Re Tower, obtained through an external free-form diagrid envelope, allowed the reduction of wind action on the building, and led to column-free flexible internal spaces [5] These two examples already showed the valuable features of diagrids for tall buildings: enhanced structural performance, saving of material consumption compared to traditional solutions, and significant aesthetic potential.
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