04.06 Panels and units
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Introduction
Panels and units are proprietary products fabricated under factory conditions, delivered to site and then lifted directly onto their secondary structural frames or directly to the main building structure as the situation warrants. Units tend to be storey height components spanning 1.2m – 1.8m between structural mullion sections which in turn are secured directly to the main building structure. Panels move up in scale and tend towards full story height components spanning the main structural bay width up to 6m – 8m in some cases.
Design
The basic structural design of panels and units follows the same lines as outlined in Section 04.05 Stick Systems, taking due account of the load transfer within and between components. Differences lie simply in determining appropriate load paths as overall component size increases and more load is accumulated within facade components prior to being transferred back to the structural frame. These increased loads and the larger span ranges involved might require the use of structural forms such as trussed strongbacks to provide the necessary stiffness and strength. The higher stresses might also suggest the use of steel rather than aluminium, and if trusses are used steel allows more straightforward industry standardised connection details.
Structural steel design within buildings is covered by BS5950, which follows the same general philosophy as the aluminium code BS8118. Both are limit state codes and follow broadly similar lines. BS5950 allows the use of plastic design but as noted elsewhere the serviceability condition normally provides the limiting condition for façade components and so elastic design is the normal approach.