Steel mezzanine design inside a working restaurant

The worst case secondary beam spans 4100 mm and works as a 260x90x35 parallel flange channel. Rather than trim every other member down to its own minimum, the same section was specified for all of the secondary beams. The design carries more steel than it strictly needs as a result, and it is much harder to build the wrong beam into the wrong bay on site.

The primary and outer edge members are 300x100x46 parallel flange channels, governed by the beam at the entrance where the point loads from the incoming secondary beams land closest together.

The deck is 50x250 C16 joists at 400 mm centres over a maximum span of 1600 mm, carrying 1.0 kN/m² dead and 2.5 kN/m² imposed. Any plant or machinery going onto the mezzanine was required to have its own bearing points welded down to the channel beams rather than sitting on the joists, so that a later equipment change does not quietly load a member that was never designed for it.

Steel to steel connections use a minimum of two M16 grade 8.8 bolts, giving 117.8 kN of shear resistance against a largest beam reaction of 19.7 kN. That is a wide margin and it is deliberate. Connections in a fit-out get made by people working around finished surfaces, and a detail with no slack in it is the one that gets improvised on site.