slip critical vs bolt strength, single plt conn

[rnorth]

when designing a bolted single plate shear connection, beam to column, is it appropriate to use manual table 7-1 for shear strength of bolts or should table 7-3 be used for slip as a serviceability limit state?

the examples given in the manual companion use different methods for this connection from example II.B-1 (7-1) and then II.A-17 which uses table 10-9.

the question stems from a connection with vertical reaction that is satisfied when using table 7-1 but slightly overstressed when using the lower value of bolt shear given by table 7-3. thanks in advance!

 

[ajh1]

Normally a single plate shear connection would be designed without using a slip-critical method. The intent of a shear connection is that it takes shear only, not moment. If you pretension the bolts to achieve the slip-critical aspect, you are then forcing moment through the joint which it hasn't been designed for. Installation of a member on a single plate shear connection will generally have the bolts bottomed out on the holes anyway due to the dead weight of the member, and hence slip-critical doesn't provide any benefit since the member can't slip anyway having already started at the limit of the hole.

 

[connectegr]

Slip critical bolts can be used for single plate connections. But that is a much larger discussion. For a standard single plate connection the plate typically has horizontal short slots and uses bearing bolt values. These capacities are tabulated in the AISC manual, as straight shear connections with no eccentricity in the bolts.

Note that AISC uses bearing bolts in all design examples.

http://www.FerrellEngineering.com

 

[structuresguy]

connectegr is correct. Use slotted holes and bearing bolts. This allows for slight rotation of the joint, and can relieve any moment which may generate in the connection. Single plate shear connections have no inherent flexibility, unlike angle connections, so if you clamp the bolts down tight in a slip critical connection, you will generate unintended (and undesired) moment in the connection.