Suspended slabs and parking garages: what the engineer needs before the crane rolls on.

1. Why the garage is different

On grade, the support design depends on the slab, ground, and underlying conditions. On an elevated deck, loads pass through the slab, deck, beams, and columns. A uniform floor load rating does not authorize a concentrated crane reaction at one location. The engineer must assess the proposed concentrated loads and their path through the structure separately.

2. What actually gets checked

• Local bearing and punching shear: can the slab take the pad load without the pad pushing through? Thickness, reinforcement, and pad size govern.
• Slab flexure and one-way shear: the slab spanning between beams or deck flutes under a point load.
• Metal deck: on concrete-over-deck floors, the deck's concentrated-load capacity and flute direction.
• Beams, joists, girders: where the pad load goes next. A pad mid-span between joists is a different case from one over a beam.
• Columns and existing loads: what the framing is already carrying from the levels above.
• Edges, joints, openings, drains: a pad near any of these loses the support on one side.

3. Pick the lightest machine that does the job

On a deck, the crane weight and maximum pad reactions are early screening inputs. Compare the exact configurations using their manufacturer documentation, including fitted attachments, counterweights, and transport condition. No model is automatically a garage machine: a smaller machine still needs review, and a larger machine is not approved by a broad class comparison. Check weight and reaction alongside access, reach, and the proposed support locations.

4. Place the pads where the structure is

Get the framing plan and have the engineer identify acceptable support locations and exclusion zones. Locate beams, girders, column lines, slab edges, openings, and joints, then confirm whether the required crane geometry can fit the approved positions. Do not choose an edge clearance from a generic pad-width rule. The Outrigger Spatial Planner can help document the geometry; it does not approve structural support.Outrigger Spatial Planner

5. When shoring is the answer

If the engineer's check fails at a beam or a deck span, the fix is often temporary shoring on the level below, under the pad locations, down to a level that can take it. That is an engineered item with its own drawings; the crane plan has to be locked before the shoring is designed, because moving a pad moves the post. Alternatives are a lighter machine, a shorter radius so the reaction drops, or a different setup position over stronger framing.

6. The submittal package

• Machine make, model, and weight, with the spec sheet
• Maximum pad reaction and the conditions that produce it, from the manufacturer
• Pad size, material, and rating; stack details if any
• Plan view of the setup with pad positions dimensioned to the column grid
• Lift geometry: load, radius, boom length, slew sector
• Travel route on the deck and track mats if used
• The engineer's markup: approved, approved with shoring, or relocate

The Outrigger Reaction Simulator can support a preliminary reaction-and-pressure review for supported machines. Supply its assumptions alongside the manufacturer information and site drawings. Elevated-slab and metal-deck checks require the engineer of record; a planning-tool report is not structural approval.Outrigger Reaction Simulator