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A common method of repairing old riveted structures is to replace any damaged rivets with new high strength bolts.

When this is done, the new bolts are typically installed like they would be on a new structure which results in a bolt pretension. My concern is that the one bolt location might be effectively slip-critical while the rest of the existing rivets are something less than slip-critical. This may concentrate stresses on the one bolt.

When new high strength bolts are installed within an array of existing rivets, is there a concern with stress concentrations resulting from the increased clamping force from the bolt?

hazzey
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  • Can you elaborate what you mean by slip-critical? I don't recognise the term. If you mean 'liable to slip and shed load before another part' I observe that a riveted connection does not slip, because the riveting process means the rivet fully fills the holes, even if the holes don't line up (that's what makes rivet-busting hard work). So a rivet and a friction-grip bolt are both non-slip-in-service-conditions elements. – achrn Mar 14 '15 at 10:09
  • @achrn It seems like you have the correct idea about [slip-critical](http://www.aisc.org/DynamicTaxonomyFAQs.aspx?id=1766) bolted connections. The rest of your comment looks like an answer... – hazzey Mar 14 '15 at 13:38

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According to AISC J1.9 rivets can be considered as sharing the load with high strength bolts, specifically in joints designed as slip-critical as per J3. The apply this section to both new work and alterations.

The commentary on this section points out that this is because the ductility of the rivets.

This means that you do not need to be concerned with the distribution of load across the various fasteners as long as your holes are appropriately sized for slip critical connections. What's not clear to me is if the faying surface requirements of RCSC for slip critical connections would apply.These would obviously be hard or impossible to verify when replacing just some fasteners in an existing connection.

The second page of this Modern Steel Construction article suggests that while the riveted connection is not slip critical, simply tightening the new bolts as if it were is enough to consider the bolts and rivets to share the load, but won't make the joint slip-critical as a whole.

The RCSC Design Guide (PDF link) for bolted and riveted connections has a more detailed explanation in section 14.2.2, which suggests that in connections that are under significant load, the AISC rule may be a simplification.

Ethan48
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