Unbraced Length of a Column
Unbraced Length of a Column
(OP)
I have situation where a steel lintel (wide flange) supporting reinforced masonry is supported by a steel column in the middle due to the length of the steel lintel (steel lintel is continuous over the column). Will the column be designed with K=1 in both directions or should column be designed with K=1 in one direction and K=2 in the other?
My boss says that since the masonry is reinforced and is braced back (steel angle - 2'-0" above steel lintel) to the joists as well as designed for out of plane bending and braced at the top with the deck, K should be one in both directions.
My boss says that since the masonry is reinforced and is braced back (steel angle - 2'-0" above steel lintel) to the joists as well as designed for out of plane bending and braced at the top with the deck, K should be one in both directions.






RE: Unbraced Length of a Column
RE: Unbraced Length of a Column
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Unbraced Length of a Column
OK KootK, since I never heard of the word, "Anther", I googled it.
"the terminal part of a stamen consisting usually of two lobes each containing two sacs in which the pollen matures"
Was that a typo or do I need a better dictionary?
RE: Unbraced Length of a Column
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Unbraced Length of a Column
RE: Unbraced Length of a Column
Speaking of post instability, assuming K=1 for the post implies a lateral bracing demand at the top of the post that would need to be supplied by the supported beam. And that would be additive to any lateral torsional buckling restraint requirements at the post.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Unbraced Length of a Column
RE: Unbraced Length of a Column
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Unbraced Length of a Column
Would stiffeners plate at beam web above column provide rotational restraint? That was one of the reasons I wanted to use K=2 in one direction.
RE: Unbraced Length of a Column
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Unbraced Length of a Column
RE: Unbraced Length of a Column
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Unbraced Length of a Column
RE: Unbraced Length of a Column
What we do is weld a vertical A706 rebar to the top flange of the beam and extend it up into the block in grouted cells.
This creates a rotational resistance for the beam against twisting. KootK is correct above to suggest that any bracing supplied by the beam/wall for the column should be considered in the design of the beam/wall.
The wall will need to resist the beam twisting through bending in the wall...probably not a big deal.
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RE: Unbraced Length of a Column
I've been doing this for a long time. It's a detail that I inherited from my mentors. I've never seen one partially constructed, however, and I've always wondered about the constructibility of it. It seems to me that coordinating the bars to hit the masonry cells would be almost hopeless. And if you missed them, you'd end up having to knock out the webs of the blocks for who knows how many courses above the beam. Can anyone comment on this aspect of it?
Some more thoughts on K=2:
1) As described here, it would imply a fixed base connection.
2) Designing the column for K=2 would not, on its own, be sufficient to prevent rollover in the beam at the interior bearing. One would need to ensure that the column was also strong and stiff enough at the top to serve as bracing for the beam.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Unbraced Length of a Column
RE: Unbraced Length of a Column
This continues to make me nervous. You mean braced for LTB at all three supports, including at the interior post, but nowhere in between, right?
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Unbraced Length of a Column
RE: Unbraced Length of a Column
1) Stiffeners establishing torsional-flexural connection between beam and column and/or;
2) Studs establishing torsional-flexural connection between beam and wall?
Just want to be sure.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Unbraced Length of a Column
I would rather move the brace to the top of web of the beam but the architect is not allowing itsince it was done earlier with brace 2'-0" above top flange.
RE: Unbraced Length of a Column
LOLZ
"We shape our buildings, thereafter they shape us." -WSC
RE: Unbraced Length of a Column
The 2' offset doesn't bother me at all. The masonry ought not have any difficulty cantilevering down from the 2' from the braces.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Unbraced Length of a Column
RE: Unbraced Length of a Column
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.