Shear Flow Calculation on Vertical Cut 1

[ChiEngr]

Hello,

I am working on a project in which we are to be adding a jib crane to an existing wide flange column. The attached sketch indicates that it will be oriented about the weak axis of the column. The existing column requires reinforcement to support the new loading, and it is already resisting strong-axis moments. Per the attachment, I plan to design (2) side plates, (1) per side, to reinforce the column.

My question comes when performing the weld design for the plate to existing column connection. For the case where you are to calculate the shear flow about a horizontal plane or cut, as for a flange cover plate added on to a wide flange beam, this is simple. But, in my case, I am getting confused as to how to determine the shear flow into the page at a vertical plane or cut.

Any feedback would be greatly appreciated. Thank you!

 

[KootK]

1) You'll likely want to deal with all of your axial load pretty close to where it's introduced into the column.

2) With regard to flexure, shear flow, it's still just VQ/It. Work out your shear diagram and go to town as you would with a beam. You're going to have significant shear between the two column attachment points which is the area likely to govern your design. This makes sense since this will be the area where the moment induced by the crane will get delivered to the column.

3) If the crane will see enough use that it represents a fatigue issue, ensure that you follow whatever provisions you normally would for welds used in fatigue situations.

That's all pretty vague, I know. It's a place to start though.

 

[dhengr]

ChiEngr:
Your sketch is pretty sketchy. I’ll bet you have a hinging system on the crane boom end near the stl. col., like Koot’s photo shows. My cover pls. would be 1.5" wider than the total col. section depth, and they would just be fillet welded to the col. flg. tips on the outside, 4 corners. Save the pl. beveling and CJP welds, you probably don’t need that much weld. You have to know more about the jib crane before you do your final design. The end structure on the jib boom will have some depth greater than the boom depth, most likely. That depth is what imparts the jib moment into the col., with two reaction vectors = M/d. At these two vectors I would want a horiz. stiff. pl. (or small stiff. bracket structure) welded btwn. the flgs. and into the web, with clipped corners at the col. web/flg. fillet. I want to get those two load vectors into the col. most efficiently, not through pl. bending as your sketch shows. At each of those vector elevations there will be bearings or bushings which allow the hinging, and at the top or bot. there will be a thrust bearing which imparts the jib’s vert. load to the col. The trust bearing and swing bearing location is what probably dictates some sort of a (small stiff. bracket structure). Then, I’d just infill with my col. flg. tip cover pl. btwn. these horiz. stiffeners. In any case it is these two horiz. stiff. structures which dictates exactly how the new loads are put into the stl. col. The added vert. load will be somewhat eccentric to the col. and you know the Mx and My on the col. I would then just combine VQ/I, the shear flow, in each direction to size my fillet welds in the connection region.

 

[le99]

I guess you intend to add two stiffener plates to assist the column to pick up the additional load from the jib crane. If this is the case, the plates need to be fully composite with the existing column, also, the composite column will be subject to the dynamic/repetitive loading conditions, so, I think it is imperative to have a full depth penetration weld that ensures the full plate strength can be achieved. This is a conservative approach but could free you from the headaches.

 

[HTURKAK]

Did you make calculation or just estimation?

I would try first without any reinforcement and plan to add if necessary and with a similar set -up Mr DHENGR suggested. CJP groove weld is not a good idea which excessive welding may cause distortion of the column. Intermittent fillet weld should be satisfactory.

The jib crane load will have axial load and moment effect and essentially shear only btw . column attachments .

If reinforcement is necessary, the column base and anchores should also be checked .