Precast Double-T flange failures using C-Grid carbon FRP 1

[Ingenuity]

I came across this "local collapse" recently to precast DT's using C-Grid carbon FRP to the top flange, in a parking garage:

Link

More than 100 parking garages (majority in the east coast area?) have been constructed with the precast DT's using the C-Grid FRP and three, to date, have had local failures.

In case you cannot access the subscription-based article, here is a sample photo:

EDIT:

The collapses on Feb. 19, 2015, and April 15, 2016, involved two ramps—the first in the six-level, 1,200-space hotel garage and the second in the eight-level, nearly 2,400-space casino garage. Completed in 2010, the structures are owned by the Tribal Casino Gaming Enterprise.

It was reported that there was a third failure [Link] in a separate parking garage structure, however I am not aware of where or when.

 

[hokie66]

So what is the stuff supposed to do? Top reinforcement for flange cantilevers? Just another reason I don't intentionally enter precast parking structures.

 

[Ingenuity]

So what is the stuff supposed to do? Top reinforcement for flange cantilevers?

Exactly.

There are 'legal statements' that the FRP tensile capacity was overestimated by a magnitude of 4, and its placement depth in the top flange was 'variable'.

I recall when C-GRID was first released/marketed (mid 2000's?), and its 'target' market was concrete counter-tops. Seems it got oversold to "real world" applications with some bad consequences.

 

[hokie66]

So how thin are those flanges? I assume they are so thin because of the FRP.

 

[cooperDBM]

I believe garages generally use pretopped DTs with a 4" top flange. A regular DT usually has a 2" top flange and would probably need a cast-in-place topping for a garage. Since the grid would be in the precast it would be lower down with a 2" flange + topping.

I'm curious about the black staining. It looks like the crack had been there for a while leaching the black waterproofing though with the water leakage.

 

[dik]

Interesting that parkades are designed typically for 50 psf, but, a realistic sort of loading would be approx 15-20 psf... and it failed. A lot of fixing to be done, and not an easy fix if the flanges were improperly reinforced... maybe new carbon fibre job...

Dik

 

[ImminentCollapse]

At least the conduit did it's job.............

Agree with dik, garages rarely see full LL, that's a big miss somewhere. Easy fix though, "Install conduit at 1/2" O.C."

IC

 

[ATSE]

For this local fail, seems like uniform loading magnitudes are less important. Maximum wheel load and effective wheel area govern the maximum moment demand on the flange (3,000 lb point load over 4.5"x4.5").
Carbon fiber for reinforcing will for sure grow in market share in the coming years. I like A615 a lot more.

 

[dik]

...another issue... with a recent parkade fire in the UK, it appears that newer cars have a lot of combustible plastic. It used to be that an automobile was relatively flame resistant. FRP's don't fare so well with fire. Wonder when the codes will change to reflect this.

Dik

 

[TehMightyEngineer]

Dik: Eh, doubt it will change much IMO. I remember reading a while back when I looked heavily into FRPs and vehicle fires that the heat affected zone wasn't too large. You're obviously going to destroy a few double tees and possibly have a localized collapse but what I saw was that it wasn't too much worse than normally reinforced concrete. The parkade fire was an extreme in my mind; I don't know if we should be realistically designing for an entire parking garage to go up in flames.

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[Sparweb]

Blaze destroys hundreds of cars, melts floors of Liverpool parking garage

The steel reinforcing grid is the only thing keeping the floor together after that fire.

STF

 

[dik]

I dunno... from the land of the Grenfell fire, and, from the BBC, "The blaze engulfed Liverpool Waterfront car park, at the Arena and Convention Centre (ACC) Liverpool, destroying about 1,300 vehicles on Sunday.

Joe Anderson warned people desperate for belongings from the site to "steer clear" while it is made safe.

He said one car had collapsed through to the floor below after the "inferno"."

Dik

 

[Mjkkb2]

...just a side comment about the LL in garages. In the East Coast they only needed 40 LL per code and due to unclear LL reduction criteria and its interpretation by precast TT manufacturers a lot of them were designed to 35 PSF. It was a common thing until newer ASCE7 code clarified the garage LL reduction criteria. It is still unbelivable that a parking garage floor can be designed to loads equal a typical wood framed floor of a house.....
I have to say that I have never heard of TT's reinforced with FRP util now.

 

[Ingenuity]

The parking garage was constructed sometime in 2008/09.

In a North Carolina District Court filing, dated 02/10/2016, it states:

On or about April 4, 2013, an ENGINEER were retained by the OWNER to perform a site visit to review the conditions at the Parking Deck, and to give the OWNER a condition assessment report on how the Parking Deck was performing. Following its site visit, the ENGINEER noted numerous deficiencies, including:

a) 'tee to tee' welds broken and failed,
b) widespread sealant failure & sealant had failed to set and solidify;
c) elastomeric membrane failure at the roof;
d) full-depth cracking in tees throughout the garage, and
e) half the light fixtures had failed, likely from leaking water.​

The first collapse (2015) occurred about 2 years after the above assessment.

The contractor undertook "failed remediation attempts in 2014" and "conditions at the Parking Deck continued to deteriorate".

I believe garages generally use pretopped DTs with a 4" top flange. A regular DT usually has a 2" top flange and would probably need a cast-in-place topping for a garage. Since the grid would be in the precast it would be lower down with a 2" flange + topping.

According to the legal filing "the DTs were factory-topped by Metromont using a precast topping slab manufactured by Metromont, which used carbon fiber C-GRID® as an alternative to traditional steel mesh.'.

I think Metromont used 3-1/4" thick pre-topped flanges, based upon this older STRUCTURE Magazine article, authored by a Metromont engineer in 2006: Link

I'm curious about the black staining. It looks like the crack had been there for a while leaching the black waterproofing though with the water leakage.

Indeed troublesome. The black staining may be the 'sealant that had failed to set and solidify' - and given the failure of the elastomeric membrane (at least to the roof), coupled with DT flange welded connection failure/s and cracking, no wonder the ramps suffered distress/failure.

 

[cooperDBM]

Thanks Ingenuity, The welded connections are intended to resist long. shear and tension in order to provide diaphragm action. They may have failed in tension/flexure through deflection of the soft flanges with weak cantilever strength.