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Site Cast "Precast" Beams and Planks

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BadgerPE

Structural
Jan 27, 2010
500
I have a project that is somewhat of a training facility for university-level construction students. The facility will be constructed/deconstructed twice annually. I have been asked to design concrete beams and planks that will be "precast" by the students on site and then lifted into place. Spans are less than 14' and standard grade 60 reinforcing will be used.

It seems like a pretty simple task, but are there any nuances to designing a "precast" member vs. true CIP?
 
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Lifting stresses would be the only one for me off the top of my head.
 
Lifting stresses and adequate attachment to the resulting structure are probably the biggest. Type III cement could be used and shrinkage concerns are less critical. You could argue that clear cover requirements could be based on the precast requirements rather than CIP, though obviously this depends on the quality control of your "plant".

Interesting project.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
 
Locate rebar equally on each face since they might install the planks and beams upside down.
Embed angles at the bearing locations to prevent spalling due to repetitive construction/deconstruction.
 
I suggest using Meadow Burke or Dayton Superior Hardware for lifting and bracing. It may be worth asking them about the durability of the lifting hardware. Typical elements from a precast plant are lifted or moved maybe 4 times, and they will probably want to use these for many many years.
 
Thanks all!

I spoke with my usual PC supplier and we discussed some of the lifting concerns. All should be good now. It is going to be a cool project if it gets off the ground!
 
I wrote the paragraph below, then reread the initial post ... I think my post would relate more to structural engineering students, not necessarily university level construction students, however, whatever their specialty, I think the idea conveyed below, with some twists and turns appropriate for the syllabus would be appropriate and a good teaching tool.

I would NOT locate the rebar equally on each face. In fact, I would go out of my way to design it so that the students would need to think and figure out which orientation would be best. There would need to be some identification on the beams, or perhaps tapered beams that would go along with some form of summary of how they are reinforced. Or mark the faces of a rectangular beam 1, 2 , 3, 4. Mark the upper and lower surfaces of the slabs A and B and reinforce them differently. Make it so that they could physically be installed in both the proper orientation and the improper orientation, put lifting lugs on all sides, then grade them on how they thought it through and assembled. Could be quite a fun design exercise to consider all the load cases to make sure all the correct orientations work structurally and the incorrect ones do not work structurally (while having adequate capacity not to collapse .... although unlikely if no live loads applied). Heck, throw in some variations, i.e. if they need 20 beams, have 30 made, make sure 10 of them have some mistakes, i.e. enough area of reinforcement, but bars spaced too close together ... the possibilities are endless.
 
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