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Old 23rd January 2011, 12:09 PM   #1
Tony Bryer
Join Date: Apr 2008
Location: Melbourne, Australia
Posts: 909
Default Eurocode EC3 Blue Book bolt resistance tables

Whilst working on adding beam splice calculations to EuroBeam I struggled to reconcile the bolt bearing capacity I calculated manually using the formulae in Eurocode 3-1-8 with the figures quoted in the 'Blue Book' table on page C-303. My figures for M16 bolts were around 9.5% higher than those in the table. I then repeated the process with M20 bolts and got exactly the same figures as shown in the table. Then I had a Eureka moment:

The explanation for this is given in the notes on page A-42. The tabulated bolt bearing capacities have been calculated using an end distance e1 of 2d whilst the table shows this distance rounded up to the next 5mm. So for M16 bolts and S275 connected members, the bearing capacities have been calculated using e1=32mm, though the table shows e1=35mm. For M20 bolts the rounded figure is the same as the actual, thus the calculated figure agreeing with the table.

It's worth noting that in places the Eurocode uses the bolt hole diameter, d, rather than the bolt diameter, d0, for example minimum end clearances of 1.25d in BS5950 become 1.2d0 in EC3. The difference is minimal (25mm/26.4mm for M20 bolts) and if bearing is a factor then it will generally be desirable to use end and edge clearances that are significantly greater than the minimum - in the example above, going from 32mm to35mm increases the bearing capacity by 35/32, 9.4%. Above 54mm (3d0) there is no further increase. Of course this will not matter if the bolt capacity is limited by its shear capacity - you need to look at all connection calculations to see what limits the capacity.

All rather esoteric, I know, but perhaps this may help someone.
Tony Bryer, Greentram Software Pty Ltd
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blue book, bolts, connections, ec3

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