Rebar Cage Guying/Bracing

[JackHandy]

Does anyone know how to check the strength of a rebar cage when it is braced or guyed? I am not counting on the horizintal bars for strength (no horizontal shear flow), so I am summing the bar properties about a guy location. I am applying the wind load specified by the CalTrans Spec for rebar cages, but they do not provide any guidance on how to analyze the cage.

 

[LSPSCAT]

Check into rebar cages for slurry walls. I did have a technical paper on this subject, however, I cannot find it at this time. It was mainly dealing with large rectangular cages for slurry wall panels. Dangerous business picking up a 60' - 80' cage.

 

[JackHandy]

A technical paper would be great. These cages, especially in seismic zones, can become very dense and tall. They are like supporting a slinky. Thanks

 

[TXStructural]

There is no universal way to know how stiff a cage will be, however they will generally only be as stiff as the individual members. Tie wires cannot be relied upon to create a Vierendeel or similar structure. Long cages routinely fall due to inadequate bracing.

Cages which are shop fabricated and welded may be stiffer and stronger, but the forces on the welds can be excessive when the cage acts as a truss.

Cages may be subject to large wind loads. Un-guyed cages can displace laterally far enough that gravity will force them down

That is my long-winded way of saying that bracing/guying must be based on the flexibility of individual longitudinal bars.
--

US OSHA says:
1926.703(d)
Reinforcing steel.

1926.703(d)(1)
Reinforcing steel for walls, piers, columns, and similar vertical structures shall be adequately supported to prevent overturning and to prevent collapse.



John Turner CSP PE
CRSI Greater Southwestern Regional Manager

 

[JackHandy]

TXStructural

Thank you.
I am familiar with the OSHA guidelines. They are very vague and give no help from a structural stand point. Believe me, I want to keep the steel vertical. Does CRSI have a committee on the guying of rebar cages? I would be interested in learning more.

Due to the complexity of analyzing the cage my preferred method is to set up half the form, fly in the cage and then set the second half of the form. This takes the strength of the cage out of the problem and is adequate for most small columns. I am finding some projects where the workers like this approach, and other projects they don’t. I also prefer to keep workers off the cage. Stay off the thing and use a manlift if needed!