## Design of Cranked Steel Beam

## Design of Cranked Steel Beam

(OP)

Hello,

Does anyone know where I can find the design of a cranked steel beam along with some examples?

Thank you.

Does anyone know where I can find the design of a cranked steel beam along with some examples?

Thank you.

## RE: Design of Cranked Steel Beam

Michael.

Timing has a lot to do with the outcome of a rain dance.

## RE: Design of Cranked Steel Beam

the bending moment does not change but the deflection will increase.

Be careful of overall stability at the crank as well as the strees transfer at the actual crank.

## RE: Design of Cranked Steel Beam

## RE: Design of Cranked Steel Beam

Yes - the beam is 31'-6" long with a 135 degree bend 8' from one end and a factored point load of 5,800 lbs. located 5' from the opposite end of the crank.

## RE: Design of Cranked Steel Beam

Can you explain why the deflection would increase? Won't a cranked beam peaking upward have less deflections? Would it not behave as an truss of some sorts?

We are Virginia Tech

Go HOKIES

## RE: Design of Cranked Steel Beam

My intuition was that the deflections would be lower but I checked them using FEA.

I'd be interested in what ConnectEngr has to say about the splice location.

## RE: Design of Cranked Steel Beam

## RE: Design of Cranked Steel Beam

## RE: Design of Cranked Steel Beam

You know where in Blodgett? (I'm being lazy)

## RE: Design of Cranked Steel Beam

We are Virginia Tech

Go HOKIES

## RE: Design of Cranked Steel Beam

## RE: Design of Cranked Steel Beam

Slick- Other than Moby Dick, Blodgett's Design of Welded Structures is the greatest book of all time.

## RE: Design of Cranked Steel Beam

If it is like most beams of this type then it is effectively on roller supports and therefore cannot have axial loads. You would therefore have the same bending moment as this is based on the distance between supports whereas deflection is more dictated by the actual length. You can verify this using first principles and force vectors.

As per the detail at the ridge, there has been several different controvertial discussions on this. My personal opinion if that you need a gusset plate between the flanges to equalise the out of plane force vectors in the flanges. I have been through this several times and will not be convinced otherwise.

If this is of the roller type then you also need to limit the horizontal spread of the rafter under vertical loads.

## RE: Design of Cranked Steel Beam

can you describe further what you mean about "a gusset plate between the flanges"?

## RE: Design of Cranked Steel Beam

## RE: Design of Cranked Steel Beam

I started off thinking that a "cranked beam" was actually a cranked beam, horizontal to vertical to horizontal again, a very different animal.

I don't have Kleinlogel anymore, but I found that I still have a copy of Crosby Lockwood's "The Steel Designer's Manual", this case is in there.

Michael.

Timing has a lot to do with the outcome of a rain dance.

## RE: Design of Cranked Steel Beam

No I mean a vertical stiffener at the point where you weld the two sections together. The problem with the two solutions you have suggested is that they do not restrain the top flange against buckling at the tips where it all of a sudden changes direction.

## RE: Design of Cranked Steel Beam

I have done a few beams like this that were lightly loaded and due to the availability of materials the beams were way over capacity. In this case I did not use a stiffener where csd suggests, but I do like the idea.

## RE: Design of Cranked Steel Beam

Yes I think that why this is not a common failure point is because most cranked beams are dictated by deflection and therefore over capacity for strength.

I always look at these things like a truss with the flanges/stiffeners able to take compression or tension and the webs only able to take diagonal tension. If you sketch that apex force diagram you will see what my issue is with it.

## RE: Design of Cranked Steel Beam

I sketched it out very quickly and what seems to result is:

Compression in the top flanges due to moment result in a vertically upward shear force

Tension in the bottom flanges due to moment result in a vertically downward shear force.

These two would combine to put the web of the beam at the join in tension, right?

The shear forces on the beam would want to put the same point in compression, correct?

## RE: Design of Cranked Steel Beam

## RE: Design of Cranked Steel Beam

That is why I would rather put a tee under the bottom flanges to reduce the flange forces.

Michael.

Timing has a lot to do with the outcome of a rain dance.

## RE: Design of Cranked Steel Beam