Effectiveness of Studs in Tension

[slickdeals]

Folks,
How do you typically calculate the number of effective studs and plate thickness for conditions as shown in the sketch? It appears that the plate thickness will need to increase considerably before the studs on either side of the flange become effective.

Your thoughts?

 

[ishvaaag]

I some years ago did some worksheets dealing with anchors to concrete. Here is a printout of one of the most complex I did that applies moment, axial force and shear to the plate, purportedly following ACI 349-2R-89 / 1994, the code that I used as guide and where (or in its substitute, if any) you may find useful information for your problem. I think have no cases with more than two studs horizontally, but the code surely will be more general in scope.

This Mathcad worksheet is in an optimization setup that may be a bit more complicated to follow than a mere check.

 

[cntw1953]

Yes, it is a complicate issue as pointed out above.

Prior to powerful computer programs, we usually layout the bolt rows in a symmetrical manner with respect to beam flange connections, so the top and bottom connections each has two bolt rows to resist tension, and assume the middle row of bolts takes shear only to simplify the analysis. But nowadays I think you can use FEM method with the plate supported by tension only springs (representing concrete) and pins (studs) to derive more relistic results.

Watchout for prying action on top & bottom plate edges.

 

[cntw1953]

Correction: "compression only springs" in place of "tension only springs".

 

[Ron]

How can you assume no moment in this connection? Even if resolved into a couple, you will have tension in the studs and shear. Prying action as cntw1953 noted will be an issue. A thicker plate is irrelevant if pullout occurs.

 

[slickdeals]

Yes, there will be tension in the studs. My question was in trying to understand how many studs will be effective in carrying the tension? The pull-out is being prevented by using U bars developed on either side of the concrete cone.

 

[Ron]

Pullout will be mitigated to some extent, by the U-bars; however, it will not be prevented unless there are sufficient anchors (obviously). If the plate is sufficiently rigid, then pullout can be calculated in lines of fasteners, considering the fasteners to be reactions in a continuous beam (the plate).

FEA analysis will be more accurate, but you can get close with the beam approximation.

 

[cntw1953]

Yes, plate thickness affects the number of studs engaged when loaded in tension. With thin plate, the studs in nearest vicinity of the flanges would be stressed the most, while the studs further away may feel little stress or none. The other factor affecting the force in stud is stud arrangement, an efficient layout usually carry the load in an effective, economical manner.

Have you checked PCI design manual, it shall have something on concrete embedment like this.