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A bolted end plate splice in a strut is designed to transmit compression by direct bearing of connecting cross-sections. If, after accounting for the bending moment due to strut action and additional moment due to moment amplification effects, the bolts themselves still experience no tension due to the large compressive force, is it possible to design the bolts to take only vertical shear?

How would the size of bolts affect the intended stiffness (underlined clause in red below) in the strut, assuming I provide the bare minimum to counter shear due to self-weight?

clause 6.1.8.2

If you are answering with an example, you may use a 25m laced strut comprising of two numbers of UB914x305x287kg/m, taking a compression load of say 6000kN being spliced at a quarter span from each end support with 4 numbers of M20 bolts.

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  • $\begingroup$ I don't see how the size of the bolts will matter. They are either designed for a load or not. $\endgroup$ – hazzey Sep 19 '15 at 20:03
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You may already be aware of this, but BS 5950:2000 has been withdrawn and replaced by Eurocode 3 (BS EN 1993). The part you want is BS EN 1993-1-8: Design of joints.

Note that EC3 also requires splice material be provided (and bolts to connect it) to carry at least 25% of the maximum compressive force in the column. So your bolts may need to carry more than just shear due to self weight. Also, depending on the purpose of this element you may need to consider possible tension in the structural integrity load case.

In terms of the clause you highlighted. I believe it is referring to situations like the splice below. Note the locations of the bolts could easily result in a considerable reduction in bending stiffness in comparison to the sections themselves. See National Annex BS EN 1993-1-8 section 6.3 for guidance on calculating the rotational stiffness of a connection.

You may find the following document helpful as it provides design guidance for connections (including splices) together with worked examples.

SCI P358 Joints in steel construction: Simple joints to Eurocode 3 (2014 reprint)

Also note that there are standard splice details available which, if your situation allows it, are very much worth using.

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  • $\begingroup$ Yes, I am fully aware that BS 5950 is being superceded. There are countries which have yet to fully implement the new code. Indeed, the sketch you shown is the situation I am referring to. I don't understand how you intend to provision the bolts to carry 25% maximum compression under EC3 with this type of connection. Also, you did not explain how to provision the bolts to maintain member stiffness under BS 5950. $\endgroup$ – Question Overflow Sep 24 '15 at 9:02
  • $\begingroup$ The bolts themselves do not need to carry 25% of the maximum compression, the splice material does. The bolts (or welds, etc) need to make sure that this is transferred to the splice material. I would say in the sketch, assuming only compression exists, then 100% of the compression goes through the splice material. $\endgroup$ – atom44 Sep 24 '15 at 10:19
  • $\begingroup$ I'm not as familiar with BS 5950, hence my answer using Eurocodes. National Annex BS EN 1993-1-8 contains a section (6.3) explaining how to calculate the rotational stiffness of a connection. I'm not sure if there is similar guidance in BS 5950. I'm sure you could make a case for using Eurocode guidance to compare the stiffness. Or use a standard detail where this has been considered already. Hope that helps! $\endgroup$ – atom44 Sep 24 '15 at 10:29
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I think by intended member stiffness this refers back to your structural analysis that you undertook to determine the forces in the member. The member in that analysis would have had a certain stiffness and the bolts need to ensure that the same stiffness is maintained across the joint.

If your bolts are not in tension in any design case (and are not pretensioned) because of the magnitude of the axial load then the bolts will not contribute to the stiffness of the joint. I think this however unusual for all necessary load cases to result in no load combination that results in bolt tension at a joint like this.

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