design of portal frame eaves connection where additional holes drilled into column flange

[Josha456]

Hi,

I have an existing portal frame structure i have to check where there appears to have been a mistake in the fabrication of the column / rafter connection, the column flange holes for the bolts were misaligned and new ones were drilled to match the haunch endplate. Many of these additional holes are very close to ones with bolts in, one is right next to it forming a sort of slot hole.

The major design criteria of the flanges is the bending resistance against bolt tension, which is designed by calculating the yield line pattern of failure. These patterns are standardised in Eurocode and I have found that these yield line patterns will clash with the holes closest to the bolts. Can i simply adjust the yield line to miss out the hole, or would assuming a free edge at the edge of the hole be more reasonable?

I have thought of using plug welds to reform the flange - there is no clause for the design of plug welds in bending but i would have thought it would be similar to a butt weld in bending? Though this solution would mean the connections would have to be disassembled in order to no weld the endplate to the flange though so it is not a great option.

Alternatively stiffeners could be installed across the hole, would this be a reasonable solution?

Thanks

 

[Enable]

Plug welds would be dubious here (plug welds are not to be used for tension and all that).

You can add stiffeners, but but there is no way to really determine how much that deals with the pull-through of the bolts. Doesn't matter how much you stiffen the column flange, if the bolts can pull through whatever material remains across the section, it'll fail.

My immediate thought is you need to get a backing plate behind the bolts on the column side. Of course doing that while this thing is in service either means shoring for the load or perhaps backing off one bolt at a time and slipping in individual plates that you butt-weld together. I'd still stiffen that after it was in place.

As an alternative, can you create a seat underneath that you weld to the column flange / beam underside and add vertical stiffeners to the web and weld to the top flange? Perhaps combined with a plate overtop the column / beam to be welded. Basically create yourself an in-situ welded moment connection. You'd have to check for how the added rigidity places into the overall structure though.

CWB (W47.1) Div 1 Fabricator
Temporary Works Design

https://www.enable-inc.com/

 

[Josha456]

thanks for the reply,

i had same thought with plug and tension, problem with the backing plates is that they will only help with the failure mode for double bending in the plate, not the more critical failure of single bending and bolt failure.

the seat and top plate is an interesting idea, rigidity should not be a problem as the connection is meant to be rigid.

 

[human909]

It isn't entirely clear to me that the fabricator was even the on who made the mistake. Maybe the haunch was meant to sit lower. It seems like during erection they also moved the cleat for the eave purlin by the same distance. Notice the lack of paint and rust on the cleat and the tail of where the old weld seems to have been cut off.