NEVADA SHOPPING MALL.

The new steel roof for the Nevada shopping mall in Armilla (Granada), built on a pre-existing concrete structure, takes up an area of 32,000 m2 and presents volumes of different heights, geometric complexity and columns layout and distances; features dictated by the uses to which each building is intended.

The roof is composed of conventional flat light structures, with spans between 16 and 24 m, and more special roofs, sometimes curved, with internal spans and cantilevers of up to 40 m and 25 m respectively. The first ones are composed of laminated profiles, while for the main beams of the second ones, built-up box sections or trusses composed of built-up profiles are used.

The structure is strongly conditioned by the architectural requirement to minimize vertical crossings, which should brace the structure horizontally, against wind pressure and seismic action. The latter is characterized in this area by an elastic response spectrum whose acceleration is 0.32 g. The structural arrangement that can properly adapt to these restrictions is that of rigid frame, in which the dissipation of much of the energy is carried out in a controlled manner, in the steel supports lower part, where hinges are provided, capable of developing significant plastification without experiencing appreciable loss of strength.

To allow the full formation of these plastic hinges, it is necessary to avoid non-ductile failure mechanisms, such as flexural-torsional instability, local buckling and brittle fracture, phenomena taken into account in the push-over analysis through the Mazzolani-Piluso semi-empirical method, which assumes a moment-curvature diagram of type “elastic-plastic flow-strain hardening”. The diagram “basal shear-column leaning” is determined and the over-resistance is calculated so as to be considered in the verifications of the non-ductile elements.