1-bolt connection

[I-beam]

I have a steel stair fabricator who would like to use a single 3/4" A-325SC bolt to connect a landing support beam (C4)to a header. The single bolt connection is adequate for the 1500# reaction, but do you have to use the AISC 2-bolt minimum requirement for a stair. Does anyone know of the rational behind the 2-bolt minimum, other than for redundancy?

 

[skeletron]

Good practice for rotational restraint (in- and out-of-plane) and redundancy.

 

[KootK]

1) Agree on redundancy.

2) I'd not get too excited about the two bolt thing for an application this small if bending a little would make somebody important happy.

3) Two bolts may been a horizontal row of bolts. In my opinion, that kind of neuters the redundancy anyhow. If you loose the front bolt, the rear bolt's bound to be heavily eccentric to the support reaction.

4) As skeltron alluded, if you go one bolt, make sure a connection is used that doesn't rely on the rotational restrained associated with having multiple bolts.

 

[Tomfh]

Two bolt connection absorbs the eccentricity between the bolts and the shear centre. Prevents potential double hinge forming.

But if one bolt works it works. Make sure the assembly is fully stable with a pure pin joint at that location.

 

[klaus.]

'old' engineers say....One Bolt is No Bolt

 

[cal91]

Two bolts is also nice for erection. The iron worker sticks his spud through one hole to align the pieces and then he can bolt up the other hole. With only one bolt you can't do that, so one bolt should only be used on small pieces.