PEMB distortion

[djbse]

A pre-engineered metal building has been damaged by an accidental explosion/fire event. The main rigid frame located directly adjacent to the blast forces is also the building's endwall. This endwall main rigid frame also has two endwall columns. The main steel rigid frame rafter exhibits distortion in the top flange element where the endwall column is attached to the web of the main steel rigid frame rafter web element. The distortion resembles a cup shape and is localized to only a small area....approximately 6" in length. The web in this area is also slightly distorted. My thoughts are to reinforce the top flange of the rafter using a new flat steel plate of sufficient thickness and width to bridge across the distorted area. This new plate would be welded to the top flange. Also, my thoughts are to reinforce the web with new steel plate stiffeners welded to the existing web element.
Has anyone encountered this type of situation? If so, can you give some guidance. I would welcome any and all input. Does this approach sound reasonable? Thanks in advance for your input.

 

[ishvaaag]

After having experienced explosion/fire you seem concerned by a local corner detail. It this goes with that the general geometry of the frame itself remains as projected, that approach can be adequate.

But the kind of the deformation seems to indicate that the frame has undergone out of plane -may be permanent- deformation that maybe still present; if such is the case then complementarily the actual geometry needs to be input in a model for the wanted use and see if things remain within normative range after such deformations.

 

[djbse]

A little more background. Observation of the exisitng main frame indicates that the original, overall geometry of the main frame was not affected by the explosion/fire event. ishvaaag, thank you for your input.

 

[msquared48]

Unless there was a provision in the original design for expansion at the location of this end wall frame, it is probably not a true mainframe. More than likely it is an endwall with two wind columns.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[BAretired]

I'm curious about the "cup shape" failure. Can you provide a photo or sketch?

BA

 

[djbse]

As you know, a picture is worth a thousand words. Unfortunately, the client does not allow for photographs to be taken (or shared). I apologize for this.
mssquared48.....there is provision in the original design that the endwall frame be identical to the other interior frames. The reason being that an overhead crane runs the full length of the building is also part of the PEMB building.
BAretired.....I was thinking last night that the shape resembles more of a "spoon" shape. I have attempted to attach a sketch of the deformation.

 

[msquared48]

I am confused by the sketch a little.

I see what appear to be existing web stiffeners, and a cover plate over the dip in the top flange. Is all this existing?

If so, then the dip could have been original erection damage and the stiffeners and cover plate a subsequent repair of the mainframe.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[BAretired]

Is the column fastened to the web of the rafter? Usually the column would terminate at the underside of the rafter.

My guess is that the spoon shaped failure was caused by pressure from the blast tending to push the rafter out and up. This would create compression in the top flange. In normal usage, the top flange would be in tension in this region.

I would suggest you check the member for expected snow and wind loads because any warranty from the fabricator will likely be void now. Depending on what you find, you may want to add plates to the damaged section of flange and web. Alternatively, you may want to beef up the entire rafter with a channel full length.

BA

 

[djbse]

msquared48 - The web stiffeners seen in the sketch will be new to provide stiffening for the slight distortion in the web element. The cover plate will be new....all else is existing.

BAretired - the column is fastened to the web of the rafter! The wall girts in the endwall are flush with the endwall columns, but bypass the rigid frames. I agree that the spoon shaped damaged is the result of the endwall column pushing/kicking the rafter out. I agree that this would create compression in the top flange.

Thank you both for your input and suggestions.