Estimating Lifetime of Damaged Concrete 1

[briancpotter]

We've been tasked with evaluating the structure of an aging residential dock made of precast concrete, sitting on precast concrete piles. The structure is around 50 years old, and has experienced extreme corrosion damage (see attached pics). We suspect it was built with surplus precast that had insufficient cover distances.

What I need to know is, do there exist any methods or companies that can evaluate the remaining lifetime of the structure? Something beyond a visual examination (which of course says the structure needs to be replaced/repaired immediately)?

https://dl.dropboxusercontent.com/u/430270/IMG_2764.jpg

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[Ron]

Brian...there are many tests that can be done that will help lead you to a conclusion of reliability or remaining useful life; however, in the final assessment, it is risk management tempered by engineering judgment.

For a 50-year old structure in the observed condition, it is probably at or very near the end of its useful life and user safety could be compromised.

Take a look at the attached paper...it might provide a little insight.

 

[TXStructural]

I'm going to step out on a limb here, but I'd say it has reached the end of its useful life, unless all reinforcement is mild (non-prestressed) and significant rehab is undertaken. And maybe not even then. And rehab would be very expensive, maybe more than replacement. The biggest concern is that with compromised reinforcement, it is no longer ductile and failure will be soon, sudden, and catastrophic.

 

[briancpotter]

Preaching to the choir. The main purpose here is due diligence, to make sure we're not missing an available option for the owner.

Ron, thanks for the paper. This quote from ACI 437 seems particularly appropriate:

"There is no such thing as an absolute measurement of structural safety in an existing concrete building, particularly in buildings that are deteriorated due to prolonged exposure to the environment or that have been damaged in a physical event, such as a fire. Similarly, there are no generally recognized criteria for evaluating serviceability of an existing concrete building. Engineering judgment and close consultation with the owner regarding the intended use of the building and expected level of performance are required in this type of evaluation."

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[SlideRuleEra]

Brian - There may be a compromise option to offer your client. I agree that the structure's life is ending. However if mild steel reinforcement is used, as TXStructural has mentioned, perhaps a simple investigation can give you more data to make an informed recommendation to the client. In the photo, I don't see an spalled concrete, except on the bottoms of some of the deck tees. On the tees it looks like reinforcing steel is visible - admittedly in poor condition. I'm suggesting to chip off some of the damaged concrete cover on the side of cap and see what is there. If it's prestressed strands, end of story. If it is rebar, and there is some steel present, there is some time left - here what I would suggest to do with that time:

1. Don't waste a dime trying to "save" the existing structure.
2. Limit use of the structure to foot traffic - since it looks like a short dock doubt if there are any vehicles using it. However, you never know - perhaps someone backs a car out on it, say to unload fishing tackle.
3. Tell the Owner that they need to start an orderly program to design, obtain permits, bid, and demolish / construct a replacement structure (if that is appropriate), over the next year, or so. Or, if the Owner doesn't want to have a replacement, at least remove the deck and abandon the piles and caps in place.

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