Total Precast Office
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
- Precast – 2’6
- 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)
- Precast cores if punched window walls at the permiter
- Mechanical shafts adjacent to cores – typically
- Locate cores on grids for framing efficiency
- Front of elevator core
- Precast header with CMU infill
- Precast cores up to 8 stories
- 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
- 65 psf + 15 psf partitions = 80 psf
- Live loads
- 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
- Crane inside footprint
- Do you need traffic control into and out of site?
- Solid, level, compacted soil for crane placement & movement
- General Contractor to provide access for crane & delivery equipment
- 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
- Speed of construction
- 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
- Exterior skin flexibility
- For Owner
- Speed to market – generate revenue sooner
- Less general conditions
- For General Contractor
Dan Parker
Director of Client Services