The procedures and formulations suggested in literature for the design of diagrid structures start from the assumption that diagonal sizing process is governed by the stiffness requirements, as usually occurs for other, less efficient, structural types, and that member strength demand is automatically satisfied by the cross section resulting from the stiffness requirements. However, thanks to the high rigidity of the diagonalized façade, strength requirements can be of paramount importance and even be the governing design criterion. In this paper, stiffness and strength design criteria for diagrid structures are examined and translated in simplified formulae for quick member sizing. The application of the two approaches for the design of a 100-storey building model, carried out for different diagrid geometrical patterns, gives the opportunity of discussing the relative influence of stiffness and strength on the design outcomes, in terms of resulting diagonal cross sections and steel weight, as well as on the structural performance

SUMMARYThis paper provides a first insight on tube configurations based on the hexagonal shape (hexagrid) for tall buildings. The idea is to investigate the mechanical properties of hexagrid to assess their applicability in tall buildings and to compare their potential efficiency to the more popular diagrid systems.For the above purposes, a general homogenization approach has been established for dealing with any structural patterns, and a methodology for characterizing the structural patterns from the mechanical point of view has been developed and specified for hexagrids and diagrids. Then on the basis of a simple stiffness criterion, a design procedure has been proposed and applied to a tall building case study, and several structural solutions (both hexagrids and diagrids) have been designed and assessed by varying the major geometrical parameters of the patterns.

Stability of isolation rubber bearings is a topic widely studied and concerns (1) the critical load capacity in the undeformed configuration, under long-term load (gravity) effects; and (2) the stability condition under short-term vertical pressure (due to gravity plus seismic loads) at large lateral deformations. In this paper the problem of elastomeric bearing stability under large lateral displacements is addressed through FEM parametric analysis; rubber bearings typical of current design practice, characterized by S 1 = 20 are considered, with the value of the secondary shape factor S 2 being varied between 1.5 and 6.2 in order to assess the effect of slenderness on the mechanical behavior, failure mode, and interaction vertical pressure-shear deformation. The analysis results show that the sensitivity of the shear response to the applied vertical pressure is directly related to the value of S 2 and that S 2 has an overwhelming effect on the stability behavior and shear response of the bearing, as compared to the effect of the primary shape factor and of the rubber shear modulus. Finally, S 2 is the parameter which governs the failure mode of the bearing in the seismic condition (vertical pressure-shear deformation). On the basis of these results, design implications are discussed.

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