Rack supported warehouses with reduced-section diagonals for improved dissipative seismic behaviour

Rack supported warehouses are structures proven to be vulnerable to seismic action as currently designed, being prone to quasi-brittle failures that mainly involve key components. This paper presents a dedicated design approach for the transversal frames of these warehouses, with the main objective of exploiting potential sources of ductility (yielding of diagonals under tensile force) while protecting the non-dissipative components and maintaining the structural configuration and technological components typical of these structures. To this end, the diagonal's cross-section is reduced in specific areas, allowing for yielding and seismic dissipation, while ensuring the overstrength of the connection. Specific guidelines are also provided to design the reduced section portions to achieve the necessary ductility level, both locally and globally, and to limit the slenderness of the profile. The potential of the approach is evaluated by designing and numerically assessing the seismic vulnerability of a case study and comparing the obtained behaviour to that of the same structure designed using the current approach. The results show that the new approach allows for the protection of diagonal connections and non-dissipative elements for seismic intensities higher than the design level. An experimental campaign on the reduced-section braces is an ongoing activity necessary to assess the effective behaviour and to provide general design criteria that also account for geometrical and material imperfections arising from fabrication and assembly processes.