Mezzanines and multi-tier structures

How does Mezzanines and multi-tier structures work, step by step?

1. 1

   Step 1: Establish the brief and the loading

   What the mezzanine is for decides everything else. Storage, picking, offices, plant support or a mixture all impose different loading and different fire requirements. The operator states the intended use, the structural engineer sets the design loading from it, and that loading is what goes on the notices. Changing the use later - offices becoming storage is the classic - is a design change and goes back to the engineer.

2. 2

   Step 2: Get the fire strategy settled before the layout is fixed

   The fire engineer assesses the effect of the new floor on the building: escape travel distances from the deck, the number and position of stairs and exits, protected routes, smoke detection and alarm coverage, sprinkler provision above and beneath the deck, and the fire resistance required of the mezzanine structure. Those requirements shape the layout, so they come before it. A mezzanine laid out first and assessed afterwards usually has to be redrawn.

3. 3

   Step 3: Investigate the existing slab and design the interface below

   The structural engineer checks what the columns will stand on. Trial holes and slab investigation establish the slab construction, its thickness, its reinforcement and the subbase beneath. Where the existing slab cannot take the concentrated column loads, pad foundations are designed and formed by breaking out locally and casting. This is decided before the mezzanine is fabricated, because column positions may have to move to suit what is found.

4. 4

   Step 4: Coordinate with services, sprinklers and the equipment below

   The deck cuts the building in two. Everything that was serving the space above now has to serve two spaces: lighting, heating, sprinklers, smoke detection, power and data. Sprinkler heads are added below the deck where required, and the head positions have to work with the racking or equipment underneath. Penetrations through the deck for services, conveyors or lifts are designed in and detailed, not cut later.

5. 5

   Step 5: Erect the structure

   Column base positions are set out from the survey grid and the bases are fixed to the slab or to the new pads. Columns are stood and plumbed, main beams and secondary beams are landed and bolted, and the frame is braced as the erection sequence requires. Work at height is managed with the designed access and fall protection arrangements, and the frame is not left partly braced overnight.

6. 6

   Step 6: Lay the decking and install edge protection

   The deck is laid and fixed to the design - boarding, steel decking or a composite arrangement as specified - with the surface finish suited to the use and to the traffic. Edge protection, handrails, kickplates and the pallet gates or loading gates at any transfer position are installed as the deck goes down rather than afterwards, because an unprotected deck edge is the most dangerous thing on the project.

7. 7

   Step 7: Install stairs, escape routes and load notices

   Stairs, landings and any protected escape routes are installed to the fire engineer's design, along with the signage, emergency lighting and door arrangements that go with them. Load notices are fixed at the stair heads and at the deck edges stating the loading the deck is designed for. Where goods are transferred up or down, the gate or lift arrangement is installed and its interlocks tested.

8. 8

   Step 8: Complete the approvals and hand over

   The deck is checked against the structural engineer's drawings and the fire engineer's requirements, the necessary approvals are completed by the client's team, and the structure is handed over with drawings, notices and the maintenance and inspection arrangements. Any later change - a new use, a new racking arrangement on the deck, an additional penetration or a heavier load - goes back to the structural engineer and the fire engineer together before it happens.