Horizontal Shear

[damo74]

Hi all,

I'm designing a member that is supporting vertical load. The member is to consist of 2 steel beams, one placed directly on top of the other.

I want to design them to act compositely and therefore I want to use bolts to fix the top flange of the lower beam to the bottom flange of the upper beam.

I understand that it is the horizontal shear I need to calculate in order to calculate the shear on the bolts, but I don't know how to calculate this horizontal shear.

Can anyone shed some light on this subject for me?

 

[hokie66]

It takes a lot of bolts. For full composite action, you need to provide enough bolts to develop A*Fy of the smaller beam on each side of the maximum moment.

 

[DaveAtkins]

hokie66 is correct, if you are designing with LRFD. For ASD, you could use the formula for shear flow, VQ/I. I would recommend you look in your Strength of Materials textbook--it will cover this.

DaveAtkins

 

[Einsteim]

You might also consider welding the two together if possible.

 

[kslee1000]

Horizontal shear flow = VQ/I (V is the vertical shear at location of interest).

 

[kslee1000]

DaveA: Sorry, didn't notice you have already pointed out with better info.

 

[Ron]

Compute the extreme fiber stress in bending at the top of the lower flange of the upper beam and at the underside of the top flange of the lower beam. The difference between the two is a conservative estimate of the longitudinal/horizontal shear. Do this calculation considering that full composite action occurs, then compute assuming no composite action occurs....you'll see the range,and it won't be that great (unless you have thick flanges).

If the clamping force of the bolts is sufficient to maintain full contact, the composite action will occur. I suspect, but haven't tried to prove it, that if you space fasteners such that no differential flange bending occurs, that will take care of any horizontal shear.

 

[miecz]

If you calculate the horizontal shear as A*Fy (LRFD approach), then you need to determine the shear strength of the bolt. In normal composite construction, AISC uses the tensile strength of the stud to determine the shear strength of the connection. But this is based on testing of the steel/concrete interaction (see thread507-235469). In your case, I would use the shear strength of the bolt, not the tensile strength, as there's no testing on the steel/steel interaction to back up the use of tensile strength.

 

[damo74]

Thanks guys you've confirmed what I expected. I'll take it from here.

 

[jrwhite2013]

So is the following correct for bolts and welds?:

Horz shear flow (LRFD) = A*Fy
Horz shear flow (ASD 13th) = A*Fy
Horz shear flow (ASD 9th) = VQ/I

Can someone point me to where shear flow = A*Fy is specified in the 13th edition?

- Thanks

 

[Lion06]

It's not specified anywhere in the 13th edition, but it makes simple sense. If you assume that the section develops the plastic moment then the shear to be transferred at the joint will never be more then AsFy.
It's analogous to a composite steel beam.