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Old 29th July 2011, 11:12 PM   #1
Tony Bryer
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Default Bearing resistance of bolt groups

SCI have updated their guidance on how the bearing resistance of a group of bolts subject to some tension should be calculated - this situation arises when considering a group of bolts connecting an end plate or angle cleats to a supporting member.

Where you have a group of bolts, the bearing resistance of the end bolts will probably be not be the same as the bearing resistance of the other bolts in the group. The resistances are a function of the bolt end and edge clearances and pitch.

Eurocode 3 EC3-1-8 3.7(1) sets out how bolt group resistances are to be calculated. If the shear resistance of every bolt in the group is greater than its bearing resistance then the group bearing resistance is taken as the sum of the individual bearing resistances. If the shear resistance of any bolt is less than its bearing resistance then the group resistance is taken as the number of bolts multiplied by the smallest value of the individual bolt bearing resistances.

Reference to NCCI SN014 and SCI publication P364 shows the comparison being made between the 'gross' shear resistance, Fv,Rd, and the greater bearing resistance. However the shear resistance of the bolts in an end plate connection or angle cleat connection to the supporting member should be taken as 80% of that given by Table 3.4 to allow for the bolts being subject to some tension. SCI have now confirmed that this lower value should be used when making the comparison.

Consider the second end plate example in the article Simple connections to Eurocode 3 in New Steel Construction March 2009. Using the previous guidance, changing the bolt spacing increases the bearing resistance of the group from 705kN to 737kN - the end and other bolts have bearing resistances of 87.8 and 93.6kN; the shear resistance is 94.1kN. Thus the bearing resistance under the old rules is 2 x 87.8 + 6 x 93.6 = 737kN. Under the new rules, the adjusted Fv,Rd, 75.3kN, is less the larger bearing capacity so the bearing capacity of the group has to be taken as 8 x 87.8 = 702kN. In this case shear, 8 x 75.3 = 602kN would govern, but with a different bolt size and/or material thickness the change might be significant.

This change will be incorporated in EuroBeam 1.05 due to be released in early August.

Designers should note that using the minimum end and edge clearances will generally materially reduce bolt bearing resistances. This may or may not determine the optimum bolt size and spacing.
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Old 1st August 2011, 01:09 PM   #2
Tony Bryer
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Default Re: Bearing resistance of bolt groups

Release 1.05a incorporating this change is now available for download by registered users using the 'Check for Updates' facility within your current copy of EuroBeam.
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