Code requirement to label post-tensioned slab?

[Yikes]

I've seen images of concrete slabs that are stamped with an identification that they are post-tensioned.

I'm wondering if this stamp is a code requirement, or simply best practice.
I'm helping a multifamily client make their podium building ADA accessible, and it involves coring into the concrete deck for new waste lines. The edges of the slab are not visible, so I can't use that as an indicator.
Before we pay for GPR testing: Would the absence of a PT slab stamp be a relatively safe indicator that the slab is not post-tensioned?

 

[Yankee Chronicler]

No.

 

[jar546]

I've seen images of concrete slabs that are stamped with an identification that they are post-tensioned.
View attachment 11963
I'm wondering if this stamp is a code requirement, or simply best practice.
I'm helping a multifamily client make their podium building ADA accessible, and it involves coring into the concrete deck for new waste lines. The edges of the slab are not visible, so I can't use that as an indicator.
Before we pay for GPR testing: Would the absence of a PT slab stamp be a relatively safe indicator that the slab is not post-tensioned?

No but it should be

 

[TheCommish]

Where would the stamp be placed so that it always visible?

Trust but verify, if you are unsure the cost of testing is probable cheaper than the fix.

 

[Yankee Chronicler]

Where would the stamp be placed so that it always visible?

Trust but verify, if you are unsure the cost of testing is probable cheaper than the fix.

Guaranteed.

A post-tensioned slab is like a bomb waiting to go off. The result of a mishap can be catastrophic.

When I was in architecture school, there was a post-tensioned parking garage being constructed near the campus, and several of us had managed to arrange to watch from a nearby building when the tensioning operation was being performed. Something went wrong, and they "lost" one of the tendons as it was being tensioned. It was under nearly full tension when it let go. When it snapped, it tore a chunk of concrete about the size of a small car out, tossed it completely across the width of the entire parking deck, and it landed on a vehicle on the ground. Unfortunately, the vehicle belonged to a manufacturer's rep who was just leaving the site, and he was killed instantly.

Anyone remember that bridge that collapsed a couple of years ago at a Florida university? That was a post-tensioned structure. It wasn't a post-tension slab that let do, but it was a post-tensioned structure.

Don't take ANY chances with a post-tensioned structure, or the possibility of one.

 

[ICE]

Where would the stamp be placed so that it always visible?

Garage floor. I thought that it was required and I have required it... a bunch of times without complaint. I think that I will continue to require it. The few times that a tendon was cut they were dumbfounded that there wasn't some warning.

 

[ICE]

post-tensioned structure

That is something I've never seen. I have worked with pre-stressed concrete structures.

 

[Yankee Chronicler]

That is something I've never seen. I have worked with pre-stressed concrete structures.

So have I, but post-tensioned is a completely different animal, and the question is about post-tensioned.

The difference is that in a prestressed element, the strands are tensioned first, the concrete is poured around them, and the tensioning devices are removed only after the concrete has cured. This means the strands are encased in the concrete with full contact along the entire outer surface of the strands, so if a strand is cut or damaged, the two halves remain solidly embedded in the concrete and can't go flying around.

In post-tensioning, the structure is built with empty tubes across the width, and the concrete only encases the tubes. (Or the strands are placed first and then wrapped with an outer jacket that prevents any bond between the strands and the concrete. After the concrete has cured but before the forms are removed, they attach huge jacks to one end of the strands, pull them tight, and then attach a wedge thingie (excuse the technical jargon) and release the jacks to lock the wedges in place. The reason post-tensioned is so dangerous is that the strands are not bonded to the concrete at all, so if a strand is cut or broken it becomes a whip -- and it's lethal.