Releasing of temporary bracing to marine piles

[ozziz]

In a project, it is specficed that all 1200mm dia marine steel tubular piles in 18m deep of water had to be temporary braced and can only be released before installation of the steel roadway frames. All the steel piles are directly socketed into rock and grouted with 40 MPa concrete. There is no other overburden.
The contractor wanted to release the temporary brace to the piles after 3 days when the concrete grout achives 25 MPa.

What do the designer has to check for if the contractor wanted to release the brace at earlier date? Base on the environment loads and strength of the piles, there is no problem as the 1 in 20 years ARI loads are significantly less than 1 in 100 years condition.

 

[hokie66]

Waiting for the concrete to achieve 40 MPa seems overly restrictive to me.

 

[ozziz]

hokie66

But if the temp brace is allowed to be release early, what will be the consequences and why in the first place the specs call for bracing?

What are the design to be checked if allow early release?

 

[hokie66]

I don't really know, but it is a rare occurrence in structural engineering when a construction operation must wait for full concrete strength of the preceding step. You stated that the requirement is that the braces "can only be released before installation of the steel roadway frames." That doesn't say to me that the concrete has to have achieved 40 MPa.

 

[ozziz]

hokie66,

The pile can be unbraced is equivalent to being capable of taking full loaded after it has achieved its full strength. Otherwise could the grout be damaged under unbraced condition?
A truss frame is sitting on top of the piles and it can be acceptable if the brace can be released just prior to the installation of the truss which is a pernament brace.

So could the grout (actually is concrete as the annular between the pile OD and the socket is about 75mm (3 inches) be damaged if it is not properly set under 28 days?

 

[hokie66]

I suggest you need to check with the designer to determine at what stage the piles can be unbraced. My comments were only general in nature, that 25 MPa is normally, in most structural conditions, strong enough for other operations to proceed.

 

[ozziz]

actually the contractor wanted to unbrace early to save the numbers of props and in the specs and the designer do not know what is the criteria for unbracing as he is not the person who wrote the work spec.

 

[hokie66]

Well, if I were the contractor, I would be mad as hell if no one could give me an answer. If the designer can't make a simple decision like this, your project is in trouble.

 

[ozziz]

Hokkie

It is problem with early loads on young concrete instead of loadings at 28 days? I wonder where can I get infomation on this subject?

 

[PEinc]

If you drive marine piles with temporary bracing (guide frame), the piles will probably shift laterally when the temporary bracing (guide frame) is removed. If you are then making framed and bolted connections to the unbraced piles, the pile spacings may be off. Of course, the pipe spacings may be off also even if the frame remains in place.

That's why it is called heavy construction.

 

[LCruiser]

Is there earthquake loading? If so, forget that during construction.

 

[escrowe]

What are the odds of storm surge or ship impacts on the piles before design strength is acheived?
If the piles are 'just standing there,' then 3 days sounds sufficient,
depending somewhat on the grout mix design.
Do you know the curing (strength gain) characteristics?
For example, if the grout has a retarder (doubt it), then more time might be required.
Ask the QA/QC lab for early breaks to verify the grout strength.

 

[PilebuckEngineer]

I'm guessing that these are batter pile since they are braced. The probably need a brace to keep any movement or load from occurring while the mud cures. Most specs allow forms, falsework, or bracing to be removed at 70-80% of design strength. I'm a piledriving contractor and engineer and in my experience if the designer calls for bracing on pile it really isn't needed. The exception would be concrete batters, but it depends on the batter, length, etc. Let them remove the bracing. It'll make the contractor happy and keep the job moving in the right direction.