Bolt bearing in cold formed steel

[sdz]

I’m designing a lap shear connection in a cold formed corrugated steel tank to AS/NZS 4600. Shear is horizontal as shown in the drawing.

Calculating bearing capacity to AS/NZS 4600 - 5.3.4.2 the washers don’t make full contact with the plate so I designed it for “Single shear and outside sheets of double shear connection without washers under both head and nut, or with one washer only.” giving a modification factor of C=0.75.

My understanding is that the washers prevent local buckling around the hole, but because the wall plates are strongly curved at the joint I think this will prevent buckling and it will act more as a bolt through a CHS, and the modification factor could be taken as C=1.0.

Can anyone advise me on this or direct me to a design guide for through bolts to CHS? I’ve looked in my somewhat old AISC Design of Structural Steel Hollow Section Connections and at Cidect design guide 9 and neither cover this situation.

 

[Agent666]

I would have expected the provisions to only apply to scenarios where the fasteners are in the snug tight condition. The only way you're going to achieve that is some shaped washers/packers which clamp the curved surface. Which doesn't seem too practical to achieve.

I can't see that arrangement performing without significant deformation of the corrugated metal due to the large air gap between the bolt head and washer. This obviously would have implications for retaining whatever liquid is in your tank I would have thought in addition to making the shear capacity from normal provisions not really applicable.

 

[human909]

I haven't performed the calculations myself but I could dig some up....

Often hard rubber gromment are used in such circumstances which provide a seal and allow sufficient 'snug' tightening. The calculations I've see are generally simple sheet bearing and tearout checks.

This arrangement is used quite commonly on imported sheet metal silos.