Mezzanine floors

What a mezzanine floor is

A mezzanine floor is an intermediate floor built inside a building, partly or fully covering the ground floor. In a pre-engineered building it is used for offices above a warehouse, storage platforms, plant and equipment decks, and production levels. The mezzanine consists of columns, main beams, joists, a floor deck, stairs and handrails. It may be tied to the main frame – using the PEB columns for support and lateral stability – or free-standing, with its own bracing. The choice must be made before the main frames are designed, because a tied mezzanine adds vertical and horizontal loads to the frames. See also mezzanine buildings.

Framing and deck options

Columns are typically hot-rolled H or hollow sections on their own base plates; main beams are hot-rolled or built-up I-sections; joists are hot-rolled beams or cold-formed C/Z sections, typically spaced 1–3 m depending on the deck.

Joist and deck types in more detail

Joist and deck choices interact: the deck span sets the joist spacing, and the joist type sets the floor depth, the services zone and the fire protection approach.

Where the mezzanine is tied to the main frames, the floor diaphragm (concrete slab or braced deck) can transfer horizontal loads into the PEB columns; a free-standing mezzanine needs its own vertical bracing or moment frames and should be separated from the building frame by a small gap so that the two structures do not interact unintentionally.

Loads and sizing rules

• Add superimposed dead loads: finishes, ceilings, partitions, services and equipment.
• Typical deflection limits: span/360 under live load and span/240 under total load (IBC Table 1604.3); tighter limits for brittle finishes.
• Check floor vibration for walking excitation, especially for offices and long-span light decks (AISC Design Guide 11 or equivalent).
• Preliminary beam depths of roughly span/18 to span/22 and joist depths of span/20 to span/25 are common starting points.
• Forklift, pallet-truck or point loads from racking can govern the deck and joists.

Stairs, handrails and fire safety

Stairs, guardrails and handrails must meet the building code of the project location. Typical requirements include guard heights of about 1,070 mm (42 in) under the IBC and NBC, 900–1,100 mm for industrial platforms under AS 1657, and 1,100 mm under EN ISO 14122-3; guards must also resist specified line and point loads. Mezzanines may count toward floor area for fire and egress purposes; codes limit the size of open mezzanines and may require fire-rated construction, sprinklers below and above, and a second escape stair. Coordinate these at concept stage. Stair geometry, ladder fall protection and floor plate options are detailed in staircases, ladders, grating and checkered plate.

Installation and WSC supply

Mezzanine columns are set on base plates anchored to the slab or to separate footings, then beams and joists are bolted using shear-tab or end-plate connections. Deck sheets are fixed to joists, followed by shear studs and slab pour for composite floors. Handrails and stairs are installed last. Tolerances follow the same standards as the main structure – see erection tolerances.

World Steel designs and fabricates complete mezzanine floor systems, including columns, beams, joists, deck, stairs and handrails, integrated with the primary frame and the design loads of the building.