Precast concrete Fully composed double wall

[h-badawy]

I am verifying a precast concrete doable wall designed and detailed by vendor , because i received a comment from the client engineer that “how the doable wall will be worked fully composed together by the horizontal studs/stirrups”
My question is “is there any condition or equations in the code for such a type of wall” ?
The wall thickness is 100mm external wall+50mm insulation+100mm internal wall

Thank you

 

[jayrod12]

This would be a insulated concrete sandwich panel. There should be many examples available online.

To get specific answers, you should probably indicate which code you are designing to.

These are quite similar to cavity wall construction in masonry where you have two whythes of brick separated by a space(now insulation).

 

[r13]

I think the question shall be answered by the vendor. But you can familiarize yourself by obtain a copy of PCI publication "State of the Art of Precast Prestressed Concrete Sandwich Wall Panels (JR-500), 2nd Edition (free download)", Link

 

[Brad805]

These walls can be designed fully composite, partially composite, or non-composite. Your description sounds like it could be fully or partially composite. The level of composite action depends on the type of connectors. Do you know what they are using between the wythes? They could be carbon fiber, steel, or solid concrete. The amount of detail you will find related to the connectors will depend on the supplier of the connectors. Some have sponsored many Phd research projects that are openly available, others require you to sign a confidentiality agreement before they release you any information. There are not a lot of specific rules related to the specific connectors since there are many different types. The code expects the supplier to ensure the overall wall performance meets the code req'ts.

 

[h-badawy]

I am using ACI/PCI code and there are steel studs @400mm vertical and horizontal, the thing is that vendor take all his money and he is vr reluctant to do any help so i have to prove this by myself that the wall is fully composed not even partially or non .

Thank you

 

[Brad805]

A steel connector rod in a vertical direction only is a pretty low tech solution that negates one of the benefits of double wall precast construction. The straight up/down connectors make the panels easier to construct on the floor, but as the insulation thickness increases you will find a bending action in the rods reduces your composite action. To achieve near fully composite, you need a truss, solid concrete, or something like the thinwall carbon fiber system that has been tested by a few different PHd students sponsored by Thinwall. I digress. Is the vendor PCI certified? They should help if you are at the approval stage, but most of us have experienced how that results in an endless email discussion. To determine your composite action you can model these as a vierendeel truss. Two skins connected with rods at 400 o/c. At each web you use a rod or bar equal to the total width of the rods at that level. You can model this as a beam, apply a load and compare that to how a solid beam of equal thickness will perform. Crack v. uncracked becomes a challenge. From that, you can estimate your composite action and and proceed with the methods in the PCI state of the art (not really state of art) manual. This general design is a popular research topic for carbon fiber rods since it leads to simple construction on the shop floor. You can find studies on those and simply swap out the easier design for a steel rod. You will find push off tests for rods that will help you gain comfort with the shallow embedment, and you can likely find complete studies on sandwich panels using steel rods. I have never really looked into the use of steel rods since those I work with prefer other connectors.

I am sure you will wonder why no mention of the insulation in the analysis. While it does increase the panel stiffness, testing has shown it does not significantly increase the global panel stiffness since the insulation is has a very very low stiffness compared to the concrete. I would start by neglecting it and see where you are at. Maybe you can satisfy your concerns with that. If not, you may need to search for other tests. Researchers have done tests to compare the stiffness with or without an insulation bond if you are interested. They tested with normal bond, and then re-tested using a bond breaker (poly).

If this manufacturer does not have a tilt deck or does not use cradles for shipping, it is very common that those load cases govern. Most strip the next day when you are dealing with 50% - 75% concrete strength. In situ load cases will govern for tall walls or if heavily loaded, but that is not all that common for a lot of warehouse construction unless you are dealing with long spanning double tees.

Did the owner require any protection for the rods inside the panel? I included an example connector that is common from Meadow Burke, and you can see they do offer that in a galvanized option. I believe some offer stainless as well, but you have to spec that as it drives up cost and delivery times.

 

[JLNJ]

I'm guessing that panels with studs @ 400 mm is minimally composite. The more non-cooperative the vendor the more likely he can't validate his own numbers.

There are not very many experts in this field and much of the testing information is proprietary, so you may have a hard time doing your own calculations.

 

[HTURKAK]

The conditions are unknown for us.. please provide some info ( design temperatures for winter and summer, wind, seismic..) and some descriptive sketch showing the connection of structural wythe to main FRS , non structural wythe to structural wythe , reinforcement provided, how composite the sandwich panel ? ..) to get more valuable responds..


This should be a contractual matter rather than technical .. Look to the items of contract with vendor ..May be the Vendor is not responsible to disclose their inhouse calculation report.

The reinforcement provided @400mm vertical and horizontal seems just ties which are effective in tension and compression to transfer the wind forces..There must be some shear connectors to transfer the wt of non structural wythe and their location shall be chosen to allow the free expansion of exterior panel.

Almost thirty years ago , i performed similar calculations with hand. Nowadays there are softwares specific for this job. One of them ,

https://www.tekla.com/solutions/precast-fabricators/detailing.

 

[inge911]

There's no general accepted guidance on the design of concrete sandwich wall panels regardless of the type (precast or tilt-up). PCI Handbook doesn't even have a real guide on this topic, either. I'd recommend you contacting the vendor/designer to request information on the ties. They can be made of FRP (or only plastic), steel, or by connecting the concrete walls (often called wythes), so each design can be different and yield a % composite action that isn't close to fully-composite. Bear in mind that the steel and concrete connectors ruin the thermal efficiency of the sandwich wall (so much that most states are shifting away from them). I saw it at an ASCE conference.

When you get that data, you can use different models to verify the capacity of the panel in flexure, for example:
1- Simplified model for partially-composite precast concrete insulated wall panels subjected to lateral loading.

https://www.sciencedirect.com/science/article/abs/pii/S0141029616312366?via=ihub

2- A Generalized beam–spring model for predicting elastic behavior of partially composite concrete sandwich wall panels. Use the reduced moment inertia that your engineering judgment tells you.

https://www.sciencedirect.com/science/article/abs/pii/S0141029618331341

3- Use other approaches, which are not codified either.

Other than those methods, I haven't seen many methods with a clear path for designing sandwich wall panels.