Total Precast Office

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Credit: Original article published here.

A total Precast solution provides a great alternative to the  standard steel office building designs we see.  In this blog I am going to cover some of the basics when considering a Precast office building design.

  • Bay spacing – (Figure 1)
    • 30′ wide typical – 10′ wide tees
    • Outside bays 42′-50′
    • Center bay 20′-30′
  • Floor to Floor Heights – (Figure 2)
    • 14′-0 typical
  • Structure Depth Including Topping
    • Precast – 2’6
      • 24″ tees – outside bay – 6″ Daps
      • 18″ tees – center bay
      • 30″ deep IT-beams
    • Topping thickness
      • 3″ minimum at mid-span of tee – 2 hr fire rating
      • Figure 5″ at DT bearing
  • Ceiling Heights
    • 11′-1 at underside of beam
    • 9′-0 ceiling leaves 2′-1 for MEP space
    • May need drop down near core to get under beam
      • Use cazaly hanger to eliminate beam soffit at this location
  • Cores – Provide lateral resistance
    • Precast cores up to 8 stories
      • Columns & spandrels at perimeter
    • Higher than 8 stories
      • Precast cores if punched window walls at the permiter
        Exterior walls help share lateral loading – (Photos 1 & 1A)
      • Cast-in-place cores if columns & spandrels at perimeter – (Photo 2)
      • Weld-on haunches for DT & beam bearing need fire proofing – (Photo 3)
    • Mechanical shafts adjacent to cores – typically
    • Locate cores on grids for framing efficiency
    • Front of elevator core
      • Precast header with CMU infill
  • Loading
    • Live loads
      • 65 psf + 15 psf partitions = 80 psf
        • 10DT24 can span up to 50′-0 bay with 100 psf LL
      • Storage 125 psf to 150 psf
        • Usually locate in the center bay – short span
  • Site Logistics Considerations
    • General Contractor to provide access for crane & delivery equipment
      • Solid, level, compacted soil for crane placement & movement
        • Crane inside footprint
          • Start at one end, tower up & back out
        • Crane outside footprint
          • Floor by floor if possible
      • Do you need traffic control into and out of site?
  • Benefits
    • For General Contractor
      • Speed of construction
        • Finish trades in earlier
      • Core & shell – under one trade – usually 7-10 men can erect the entire building
      • No staging required – product off of truck onto building
      • Less site congestion
    • For Design Team
      • Exterior skin flexibility
        • Architectural precast spandrels can provide any desired aesthetic and will support the precast tees – (Photo 4)
      • Prestressing – longer spans & less structure height
        • Better interior space planning
    • For Owner
      • Speed to market – generate revenue sooner
      • Less general conditions

Dan Parker
Director of Client Services

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