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Concrete Vaults

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cher122976

cher122976

Civil/Environmental
Mar 16, 2009
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We are designing a 20' and 8' stormwater detention vault. Is it customary to allow the contractor to determine if its cast-in-place or not.
 
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Are you designing for the contractor to build, or for contractors to bid? If build, and thats what he wants, so be it. If for bid, you should explore whats best for the client, and if the contractor wants to VE it, so be it.
 
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20Lx8Wx6D........My little experience in these has been to show a plan of profile view of our vault design and then include a spec with the rebar, concrete, etc specifications for Pre-Cast. Do you think its normal to ad a cast in place spec also and let the contractor decide? Anything wrong with my method?

I have seen our company have a structural engineer design the rebar and concrete for the vault but I think this is useless as long as its spec'd out and you require a submittal in your spec.

Thoughts?
 
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Whatever you decide, the contractor is required to either just put in the other, or to whine and complain about your choice, then put in the other. Then tell you they wish they would of put it in the way you designed it in the first place.
It's the law!
 
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Right Dick, that is simple enough. The vault process is simply laid out in a spec and them approved through a contract submittal. The only design done is a plan and profile showing dimension of vault. My question is regarding letting the contractor decide wether it should be cast in place or not. Should a cast in place spec be included? Personally I have never run into a situation where the additional cost of a cast in place structure was required
 
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In my experience I have had situation when some buildings were designed in precast and as result they have been built with concrete in situ and vice versa. Ofcourse the choice how the structure will be built is determinated by designer but in agreement with contractor, and it depends of costs ( of structural conditions as well).

Designer in the side of the contractor should decide how to build. And if it is able to build with precast elements he shouldn't be afraid to use it.

 
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Cast in place is controlled by the weather and the skill of the crew doing the work. Precast is built in a factory with quality control, delivered and set in place. The joints can be sealed with a good hydrophilic grout and open cell rope.

Richard A. Cornelius, P.E.
 
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Right Dick. The issue here is not how each is performed but lets say during construction the contractor find that it is not feasible to bring a pre-cast vault to the location and the need to go with a cast-in-place vault. I am trying to find out if its normal to include both a pre-cast and cast in place spec.

Becasue of the high cost pre-cast is not a prefered options in mosst cases.
 
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its customary for the engineer to decide on one or more alternative methods up front. then if the contractor wants to initiate a change during construction, it is customary for the engineer and owner to evaluate the technical, cost and schedule impacts of the proposal. Schedule is usually the main reason for pre-cast.
 
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cvg,
i really dont think as engineers we need to decide on alternatives methods to our entire design up front. Is that what you mean?

For vaults, if they design is for pre-cast and they decided to go to cast-in-place who comes up with a rebar and concrete design?
 
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I guess what I am asking is what are peoples experience with this. In my little experience with vault design I have prepared a design of the vault with consisted of only a layout (dimensions) of the vault and then specificications for both pre-cast and cast-in-place. These specs gave the critiera to for the concrete and rebar. The contractor will then be required to sumbit the vault design to us prior to construction. Even if its cast in place the contractor will get a vault design to submit from his concrete people.

I have seen my company have our structural engineer prepare a complete vault design with rebar which I think is completely unneccessary if you just spec it out appropriately.

Any thoughts on this?
 
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just depends on the industry. On public works projects, the engineer of record is generally required to do a complete design. On industrial projects, usually only specify the criteria and let the contractor submit a design. It's usually quicker and cheaper the second way. Either way, I would only specify one method - either precast or cast in place. Why do twice the work up front specifying both when it is unnecessary? I've done it both ways and get tired of second guessing contractors who always want to do something different.
 
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VE=Value Engineering - which really means the contractor thinks he has a cheaper way to do something. it's up to the engineer to advise the owner if it is really just a way for the contractor to profit more at the expense of the owner, or if he has the owners interests in mind also...
 
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When I need to decide how option I should choice (cast in situ or with precast elements)I think about:

1. conditions (static, environmental)
2. schedule
3. cost (money which I have got or which I could get from investor in the case when I will propose solution other than the specified)
3. process technology (it's very important as well)

I'm not designer, and that's why before I'll decide to change design / choice option I ask designer. The designer - who I work with - not should but have to tell me 'You can, we can try to do it in THIS way and then we will estimate how the cost of that solution is' or 'You can't / mustn't, becouse...'

Summaring... ask vaults designer or concrete construction designer.
 
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