A data center carries a lot of heavy equipment outside the data halls: generators, switchgear, transformers, chillers, dry coolers and rooftop mechanical units. Most of it sits on steel dunnage, the framing that lifts equipment off a roof, slab or grade and carries its load into the structure.
Dunnage rarely gets the attention the building frame does, but it sits right in the critical path. It has to be on site before the equipment it carries, and on a data center that equipment often has the longest lead time on the job.
Where dunnage shows up on a data center
- Rooftop mechanical. Post-and-beam frames over the roof that carry air handlers, condensing units and exhaust fans. Posts pass through roof curbs, so the roofing contractor needs the post layout early.
- Generator yards. Frames and elevated platforms for generators and their auxiliaries, often with stairs, landings and guardrails for service access.
- Electrical yards. Support frames for switchgear, transformers and busway runs between buildings.
- Cooling equipment. Platforms for chillers, cooling towers and dry coolers, sized for operating weight and service clearance.
- Equipment screens. Screen posts and girts around rooftop or yard equipment, carrying the screen panels.
Common forms and materials
Most dunnage is built from a short list of shapes:
- Main members: W-Beams (ASTM A992) for posts and rails, or HSS (ASTM A500) where a closed section suits the loads or the look.
- Secondary framing: channels and angles (ASTM A36 or A572 Grade 50) for bracing, struts and screen girts.
- Plate parts: base plates, cap plates, clips, gussets and stiffeners, laser- or plasma-cut from plate.
- Platforms: framing for grating or checker plate decks, with stair and guardrail steel for access.
Galvanized or painted
Dunnage outdoors is usually hot-dip galvanized to ASTM A123, or shop-primed and painted to the project specification. A few things to settle before release:
- Vent and drain holes. HSS and closed sections need them for galvanizing, so they belong on the shop drawings, not drilled afterward.
- Galvanizing kettle size. Very long or wide assemblies may have to be split to fit the galvanizer’s kettle.
- Touch-up. Field cuts and welds on galvanized steel are repaired per ASTM A780. The touch-up material belongs in the erector’s scope.
Design and approvals
Dunnage carries equipment weight plus wind and, in California, seismic loads. The engineer of record or a delegated engineer designs it; in seismic regions, equipment anchorage follows ASCE 7 Chapter 13 through the building code. Dunnage and other miscellaneous steel are often handled as deferred submittals, so build approval time into the schedule.
Coordinate early with three trades:
- Roofing: curbs and flashing at every post that passes through the roof.
- Concrete: embeds and anchor bolts for yard frames and platforms.
- Equipment vendors: final weights, footprints and anchor patterns, which can change after equipment selection.
What to send for a quote
- The equipment schedule and cut sheets, with weights, footprints and anchor patterns.
- Structural and roof framing plans, plus the dunnage design or the engineer’s details.
- The finish spec: galvanized, primed or painted.
- Quantities per building or phase, and the equipment setting dates.
- Delivery addresses, site access and crane or laydown constraints.
Delivery and staging
Dunnage is best shipped in sequence with equipment setting: bundled by unit or area, tagged by piece mark, and delivered before the crane pick for the equipment it carries. On a campus, the same dunnage design often repeats from building to building, so standard frames can be released again for each phase.
How Mona Steel fits
Mona Steel supplies the steel for dunnage, equipment platforms and screens: W-Beams, HSS, channels and angles, cut to length, drilled and coped to your shop drawings. We also supply laser- and plasma-cut base plates, clips and gussets, and coordinate hot-dip galvanizing in the same order. Our detailing team can prepare shop drawings and anchor bolt plans from the engineer’s design. From our Anaheim, California headquarters we deliver across California and ship to data center projects nationwide, including Texas, Arizona and Nevada.