wire-wound vs tendon concrete tanks 1

[mike80]

We are preparing plans for a project which requires a 3 million gallon flow equalization tank. We have been looking at information on wire-wound and tendon prestressed concrete tanks. Each seem to have advantages and disadvantages. I would like to know from others who have experience with these two types of tanks which type is favored. Or do they perform equally well?

Thanks

 

[Ingenuity]

mike80,

Wire wrapped tanks have suffered from durability problems over the years. The corrosion protection of the wire or strand wrap is dependent on the shotcrete application. And since the shotcrete is applied AFTER the tank is prestressed, the shotcrete does no have any P/A axial compression in it. Shrinkage cracks can develop, water/moisture/oxygen enters the cracks, corrosion begins.

Current wrapped tanks typically now go for galvanized strand or wire, which is basically recognizing that there was/is a problem with the shoctrete protective layer - often not providing the durability it was intended for.

I know of several tanks that have been drained and the wire wrapping removed due to corrosion - big bucks to repair these type of issues.

Re internall PT tanks - there has been a few durability issue with them too but most problems have been poor grouting practices. HPDE is a preferred duct these days for superior corrosion protection and a pre-manufactured thixotroic grout results in excellant corrosion protection, again, provided the grouting crew is experienced. Site grouting mockups are sometime a good idea.

There is a web site of a US consulting engineerng company that has an "open letter" on this issue.
Good reading.

http://www.t-jhc.com/open.htm

Steve Close, the author of this letter, is on one of the ACI tank committees I believe.

HTH

 

[mike80]

Ingenuity,

Thanks for your quick reply. We had found the website for t-jhc when we started researching wire wound tanks. Reading the letter led us into considering the tendon tanks as Mr. Close makes some very good points.

Subsequently, in asking wire-wound tank reps about some of the perceived negatives of wire-wound and positives of tendons, they have suggested some detrimental aspects of the tanks and Mr. Close's company. This is why I am asking for the forum's opinions, to find out if the reps comments are just due to fear of competition, or valid concerns.

Thanks again.

Mike

 

[CraigFreas]

Mike: There are pros and cons of both tank types and to some extent it is a matter of regional knowledge and availability. There are many wire wrapped tanks that have performed quite well and there are others that have not. Like many projects, a lot depends on the skill and reputation of the contractor and the tradesman doing the work. I have designed several internally tensioned tanks up to about 5.0 million gallons in size. All of the tanks I have done have been precast concrete, which you may want to consider. Precast tanks up to 20 million gallons have been constructed in western Canada and the Pacific Northwest. I do not know where you are located. I personally know Steve Close. He is very knowledgeable about tanks. I personally prefer internal tendon tanks but if a client wanted a wire wound tank I would be willing help him with the technical aspects of that type of structure. I am a member of ACI Committee 373, Liquid Retaining Structures with Internal Tendons, and have been associated with the committe for over 15 years. I would be happy to send you copies of papers I have written on precast concrete internal tendon tanks or answer any specific questions you may have.

 

[JedClampett]

I am not familiar with the tendon wound tank. However, in the southwest, DYK makes wire wound prestressed concrete tanks and has a very good reputation.

 

[Ingenuity]

mike80,

CraigFreas makes some good points...where I am from (Australia) precast tanks with 8" wet joints are the most common..but it is going to depend on your location.

Re the wire/strand wrapping companies are very competitive mainly because that is all they do - wrap tanks, whilst PT contractors do PT to building, bridges, tanks, etc.

I am aware of one wrapping company's senior management who used to work for a PT company - 5 years ago he used to criticize wrapping, now he criticizes internally PT on tanks.

Our expereince with some wire wrap companies in going out for competitive bids is that some projects incorporate a very very closed form spec (identical to one that is actually freely available from one companies web site) - the engineer is strongly encouraged to use it because the wrapping company basically does the design for the engineer, and it basically excludes all other systems, even other wire wrapping companies - that is very anti competitive and the owner usually pays the price for that.


Jed, I think you will find that DYK uses strand NOT wire in their wrapping.

HTH

 

[mike80]

Thanks for all the viewpoints. I appreciate your offer Craig, if I come up with additional questions as we get further in the project, I will contact you.

The types of tanks we are looking at all use precast concrete panels, with or without a steel diaphragm. The tank is to be built in southwest Ohio, USA, and there are many wire-wound tanks in the area, a few of which we have visited. The wire-wound seem to hold up well in general, but to me it seems the prestressing in the tendon tanks is better protected for the long term by being grouted in the conduits and covered by concrete. Unfortunately, I only know of one tendon tank in the area and it was constructed within the last 5 years, so no long term exposure.

We are considering allowing either tank to be bid by the contractors, writing the specs such that both are equal. The one drawback to this approach seems to be the past experience of the contractor. The wire-wound tank companies provide their own supervisory personnel and wire-wrappers, so they can show many previous tanks in their experience listing. However, as I understand it, the tendon tank is designed by a consultant, then a separate contractor builds it, who may not be able to show a lot of experience if he is a local concrete contractor. This makes the clients a little nervous. We know of one case in Ohio where the project was bid this way, the tendon tank came in about $1 million lower than the wire wound, but when pressed for proof of experience, they couldn't show sufficient evidence. As a result, the wire-wound tanks were built instead.

Any thoughts on bidding the project and allowing alternatives?


Thanks,

Mike

 

[krd]

Mike80, prequalify the contractors who are allowed to bid. This may reduce competition and increase prices, but as you note, you may not want the cheapest price you could get with open bidding.

 

[hannis]

mike80

In the UK we use tendon post tensioned tanks, generally segmental walls and then post tensioned. We find them far more economical and reliable. Wire would tank were indtroduced in to the Uk in the 60's and 70's but not with any great success. Unfortuantly numerous tanks have suffered from corrosion typically hydrogen imbritlement caused by lack of shotcrete cover. Also with wire wrapped tanks there are often problems with wire breakages in service, the East Bay Authority in L.A have experience with this during seismic events.

Regards

Hannis

 

[NCTANK]

Mike,

From what I understand, there are three companies who build wirewound concrete tanks in Ohio. They can be found at:

http://www.preload.com,

http://www.natgun.com

and

http://www.concretetank.com.

You should be able to find details of construction on those sites. I don't know much about tendon tanks.

Good Luck