Anchoring in prestressed T-wall panels...?

[nohandlesonme]

I'm trying to add a new facade to a t-wall panel type of wall and a normal Hilti gun shot just curls up on contact with this concrete. Is it a higher strength concrete or does the tensioning make it that hard. A small % of nails did penetrate it and more just knocked off a surface chip. What would be the best anchor system as there are several hundred required.

 

[Ron]

It is the concrete. The prestressing has little to do with it. Use drilled fasteners such as TapCon or Titen screws.

 

[concretemasonry]

Definitely the concrete.

There are two major factors that enter into the situation. Without knowing manufacturing and and curing methods are a couple of general categories.

If it was produced in a plant, the mix is usually well controlled and accelerated curing could could be stripped quickly to handle the panels and let the natural conditions add a little to meet and exceed the specified concrete strengths. Not all plants are set up for the manufacturing of Tees.

If they were produced in lesser controlled plant that uses some exterior variable curing it is common to over-load the mix to create enough to allowing stripping to get enough strength to strip the forms quickly and meet the specified strength. The further natural curing later may increase the strength to an unknown level and could be higher, but uncontrolled strength.

That is one of the problems with lab 28 day curing and testing. When Mother Nature gets involved there is addition strength and will depend on the age and conditions.

Older over designed concrete is definitely much tougher to deal with when it comes to drilling. By the time the panels are in place, the actual in-place strength could above what is specified or very much higher.

It is cheaper to add cement and possibly some additives to many concrete products than to change the process.

As everyone knows, concrete gains strength is several ways with time and conditions.

Dick

 

[hokie66]

You're going to have to drill. Buy plenty of bits. The concrete is resisting being covered. Anyway, shot fasteners shouldn't be used to support cladding.

 

[dik]

Even shooting into recently produced HC slabs can be problematic. If you require analysis, it may be possible to determine the strand/wire location and size by using a covermeter These can be pretty accurate due to the reduced cover.

By locating the strand, you can readily avoid them with the installation of anchors.