19.04: Diagrid: the renaissance of steel structures for tall buildings geometry, design, behavior

Abstract

Structural configurations best addressing the traditional requirements of strength and stiffness for tall buildings are the ones employing the tube concept, whose efficiency, however, is strictly related to the involved shear-resisting mechanism. In this perspective, diagrid structures -the latest mutation of tube structures -show an extraordinary efficiency, related to the adopted geometrical pattern: thanks to the triangle tessellation of the façades, internal axial forces are largely prevalent in the structural members, thus shear lag effects and racking deformations are minimized. Being also adaptable to whatever surface, diagrid is becoming the most used structural solution for tall buildings of complex form. In this paper some specific design issues for diagrid structures are identified, namely: the relative importance of strength and stiffness design criteria, as well as to the need of secondary bracing systems for counteracting the inter-module flexibility effects. Simplified procedure for dealing with such issues are proposed and design implications are discussed.

New Trends Towards Enhanced Structural Efficiency and Aesthetic Potential in Tall Buildings: The Case of Diagrids

“…Further investigation regarding the suitability of stiffness-and strength-based criteria for the preliminary design is subsequently developed in a broader range of diagrid structures [14,15]. In [14], Mele investigates the effect of both approaches on 90-story tall diagrid tubes, with diagonal angles of 60 • , 70 • and 80 • . The results are in line with the previous findings.…”

“…From Figure 14a,c,e, it is also evident that the insertion of the SBS does not affect the global stiffness of the building, since the top lateral deflection remains the same. The efficacy of the SBSs has also been assessed in the investigation of real diagrid buildings, i.e., the Hearst Tower (New York) and The Bow (Calgary) [14]. Since the majority of diagrids are not stand-alone systems but present central cores that provide local floor-to-floor restraints to the diagonal members, avoiding their flexural engagement, the adoption of SBS-like structures can preserve the axial-dominated behavior in the diagrid structure, thus better exploiting the extraordinary efficiency of the external tube mechanism [14].…”

Automated topology design of high‐rise diagrid buildings by genetic algorithm optimization

“…The process was applied for various top and bottom angles in order to evaluate optimum geometry for minimum weight of the structure. Furthermore, in the paper published in 2017 by Mele, [6] a 90-story steel high-rise building having various uniform diagonal angles was examined by means of strength-and stiffness-based design with and without secondary bracing system (at core perimeter), in order to evaluate whether it is needed to neutralize inter-module flexibility effects. After this research, the author also studied some different varying angle (VA) models and optimized their weights by genetic algorithm (GA) to compare weight efficiency with UA models.…”