Diagrid structures for tall buildings: case studies and design considerations Elena Mele, Maurizio Toreno * ,† , Giuseppe Brandonisio and Antonello De Luca University of Naples Fedrico II, Faculty of Engineering, Department of Structural Engineering (DIST), Naples, Italy SUMMARY The originality of form is one of the new trends that can be identified in the current design of tall buildings. In this design trend, the so-called diagrid structures, which represent the latest mutation of tubular structures, play a major role due to their inherent esthetic quality, structural efficiency and geometrical versatility. In this paper, an overview on application of such typology to high-rise buildings is carried out; in particular, in the first part of the paper, the peculiarities of diagrid systems are described: starting from the analysis of the internal forces arising in the single diagrid module due to vertical and horizontal loads, the resisting mechanism of diagrid buildings under gravity and wind loads is described, and recent researches and studies dealing with the effect of geometry on the structural behavior are discussed. In the second part of the paper, a comparative analysis of the structural performance of some recent diagrid tall buildings, characterized by different number of stories and different geometries, namely the Swiss Re building in London, the Hearst Headquarters in New York and the West Tower in Guangzhou, is carried out, and some general design remarks are derived. Copyright © 2012 John Wiley & Sons, Ltd. Received 22 December 2011; Revised 26 April 2012; Accepted 28 May 2012 KEY WORDS: diagrid; steel Structures; optimal diagrid inclination; FEM analysis 1. INTRODUCTION Diagrids, or exodiagonal systems, are perimeter structural configurations characterized by a narrow grid of diagonal members that 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: earlier examples of diagrid in medium-rise buildings are dated back to the 1960s, with the sketch proposed by Torroja (Figure 1(a)) in his seminal book (Torroja, 1960) and, in the practice, with the 13-story IBM Pittsburgh building (Figure 1(b)), where the ‘exterior load bearing truss frame wall of welded steel in a diamond pattern grid was a radical break from post-and-beam construction’ and ‘gives an unusual liveliness to the façade, after so many years of rectangular curtain-walling.’ (Hirschmann, 1965). After this pioneering application of diagrid, the structural designers of tall buildings mainly shifted their attention to another variation of diagonalized systems, the braced or trussed tube, employing mega-diagonal members instead of the narrow grid of diagonal members characteristic of diagrids. On the contrary, 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 Seattle Library (Such, 2005), the London City Hall, the One Shelley Street in Sydney (Wilkinson, 2010) and more recently by several outstanding pavilions realized at the Shanghai 2010 Expo (e.g. France, *Correspondence to: Maurizio Toreno, University of Naples Fedrico II, Faculty of Engineering, Department of structural engineering, Naples, Italy. † E-mail: maurizio.toreno@unina.it THE STRUCTURAL DESIGN OF TALL AND SPECIAL BUILDINGS Struct. Design Tall Spec. Build. 23, 124–145 (2014) Published online 23 July 2012 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/tal.1029 Copyright © 2012 John Wiley & Sons, Ltd.