Prestressed Concrete Insulation Wall Design

[JohnRwals]

Hello!

I am looking at 8" think precast prestressed concrete insulation wall design ONLY with strands and shear connectors.
(No WWR or additional reinforcement except solid zone around stripping/handling anchors.)
As strand layout was decided for the wide pieces with opening in the middle of the piece,
narrow pieces can have large area with no reinforcement.
Don't you think these plain concrete areas will bring about cracks later after they are erected?
In the past, wire meshes were added as minimum reinforcement.
But, this is a new trial with the current ACI 318.

Your comments would be appreciated!

_JRW

 

[haynewp]

There should be minimum wall reinf per ACI anyway. Any legs will likely crack during lifting if there is no reinf in the solid areas. They should have submitted lifting calcs with whatever wind calcs were done.

 

[Aesur]

How are the two faces of the concrete tied together? Wouldn't that require some kind of reinforcing for unbraced lengths? Can you even design plain concrete per code this tall and thin with this type of construction? Are there horizontal tendons as well? Is 3" concrete thick enough for compression of that tall of unbraced length to prevent rupture of the concrete for the tensioning forces? How is the diaphragm/framing attached, is there some kind of solid beam sim to a masonry bond beam at the diaphragm level? I assume there is some kind of confinement reinforcing at the top and bottom that may distribute some of the loading to the rest of the panel for pre-compression, but am not familiar with pre-stressing walls. Personally I would want some kind of welded wire mesh in there assuming there is some kind of ladder reinforcing tying the two sides together.

I know this is a schematic section, but I see a lot that makes me nervous with that design as shown/described.

 

[JohnRwals]

Aesur,
I understand your questions and concerns.
I think this area is really tiny niche market, but growing industry.
PCI's committee report "State of the Art of Precast/Prestressed Concrete Sandwich Wall Panels, 2ned Ed." will provide general knowledge.
-JRW

 

[strucbells]

Are these bearing walls or shear walls or just cladding?

If bearing walls..3" may not be enough bearing length depending on your roof loads and roof framing.

I worked on prelim design of a water treatment plant a few years back where we had similar height (30-40ft) prestressed precast concrete wall panels. Our walls were bearing (precast double tees spanning ~60 ft) and shear walls. IIRC, our panels were 14" thick, 8-3-3: 8" structural wythe, 3" insulation, 3" of architectural veneer concrete at the exterior. Your dimensions seem thin.

Talk to your local precasters as they probably have standard panels that they use and can give some guidance on this, don't reinvent the wheel.

 

[haynewp]

I started to ask if they were bearing walls or not but it looks like they are not given the adjacent beam. I just had a project with 25ft sandwich panels and they all had 4x4-W4xW4 WWR in each wythe to cover T&S and any bending stresses instead of relying on plain concrete at large areas.

 

[JohnRwals]

The following info came from PCI committee's report, which I have edited as an example.
Insulation walls can be used for both load bearing and non-load bearing walls.
Composite action with shear connectors may allow this system applicable to high ceiling structures.
I guess similar problems exist in the tilt-up construction industry.

_JRW

 

[Brad805]

Precasters are far more sensitive to weight than tilts. The vast majority of tilts I see are designed as non-composite panels. Dr. Maguire has completed research into partially composite tilt panels RESEARCH, but this has not been codified yet.

PCI is about to release a new standard for the design of precast tilt up panels. Some of the connectors referred to in the current guideline are not that common.

It is very common to have solid regions or thickened zones in these panels for point loads. A 3/2/3 precast wall is quite common for those stressing their panels. The company I work for does not stress panels, so our thicknesses are greater.