Question on PCI handbook example

[DanAndrews]

Does anyone know why the eccentricity is taken as joint plus plate width when checking the rebar capacity in PCI handbook wall-wall shear connection example?

Shouldn't e be joint only?

 

[ProgrammingPE]

This check is for the combined shear and moment in the rebar. The shear gets transferred from the rebar to the concrete likely through a bearing mechanism. The tension or compression in the rebar gets transferred to the concrete through bonding along its entire development length, so you have something that looks like this:

Based on this free body diagram, the maximum moment would occur at the right edge of the plate (like they've shown in their calculations).

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Structural Engineering Videos:

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[DanAndrews]

Thank you for your help
I still don't fully understand.
Lets ignore the combined check for shear and focus on moment only for now.
I would consider the e from V* to the start point of weld to get the tension and compression. And then check the weld to the tension & compression as well as the bar capacity to tension and compression separately.
If e is from taken to the plate edge when checking the bar capacity, then if I increase the plate width, the moment will be increase and thus the capacity will reduce. That doesn't make much sense to me?

 

[ProgrammingPE]

Their example didn't include the check for the weld between the plate and the rebar. It's probably easier to understand if you look at the reactions from that.

The eccentricity of the weld group is always to the centroid of the weld group. If you make the plate wider, then the eccentricity increases. You'll end up with more capacity for the weld, though, since the welds get longer.

For the rebar, the assumption they are using is that the tension/compression does not start to leave the bar until there is concrete all around it, which does not occur until it gets beyond the edge of the plate (at the plate concrete is on one side and the weld and plate are on the other side). This means that the tension/compression in the rebar is increasing (see the weld reaction) until it reaches its maximum value at the edge of the plate where it then begins to decrease as it gets transferred to the concrete.

Structural Engineering Software:

http://www.structuralcentral.com

Structural Engineering Videos:

http://www.youtube.com/channel/UCOj2mXXf3ZbZtgxTc6BtkGg

 

[DanAndrews]

Thank you very much