Composite steel beam shear stud design

[Enhineyero]

Hi All, I started a thread last year about shear stud design for composite steel beams (thread507-485849). It didn't get a lot of response and wish to revisit it.

Based on engineering principles when two or more sections are joined together to act as one, the connection joining the sections shall be checked for horizontal shear force (VQ/Ib).

Curious to know why for composite steel beams the design of shear stud is dependent on flange axial force due to bending (F = Ac x 0.4fuc) instead of horizontal shear force.

 

[BridgeSmith]

I think your confusion stems from 2 issues.

1) The "Q" in the VQ/Ib equation is the first moment of the area (sometimes called the statical moment), while the the "Qp" in the spec equation shown is the design strength of the shear studs.

2) I think the spec equation shown requires the strength of the shear studs to meet the smallest axial capacity of the components on either side of the shear stud connection to the flange. I can't tell for sure, since I'm not familiar with the other terms (Apy, Be, Fcu, Ds).

For fatigue design of shear studs on bridge girders, we use VQ/I, where V is the range of Live load vertical shear in the beam. We also check the shear strength of total number studs against the compression capacity of the slab or the tension capacity of the entire steel girder, whichever is smaller.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[dik]

A'x y_bar...

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-Dik

 

[Enhineyero]

I think your confusion stems from 2 issues.

1) The "Q" in the VQ/Ib equation is the first moment of the area (sometimes called the statical moment), while the the "Qp" in the spec equation shown is the design strength of the shear studs.

2) I think the spec equation shown requires the strength of the shear studs to meet the smallest axial capacity of the components on either side of the shear stud connection to the flange. I can't tell for sure, since I'm not familiar with the other terms (Apy, Be, Fcu, Ds).

I do understand "Q" and "Qp" are different. Here is the definition of the various variables. A = structural steel cross-sectional area, py = yield strength of steel, Be = effective flange width, Fcu = concrete strength, Ds = depth of slab.

Based on the composite code, number of stud = flange axial force due to bending / stud shear capacity. stud spacing = half the span (for simply supported) / no. of stud

If I was to calculate this I would take horizontal shear at the junction of the concrete slab and structural steel. stud spacing = V x (first moment of area) / I / b / shear capacity per stud. I'm confused why doesn't the composite code dont approach the design of shear studs in this manner.

 

[BridgeSmith]

If I was to calculate this I would take horizontal shear at the junction of the concrete slab and structural steel. stud spacing = V x (first moment of area) / I / b / shear capacity per stud. I'm confused why doesn't the composite code dont approach the design of shear studs in this manner.

That would seem to be the correct way to calculate the shear demand on the studs. However, it appears that your code, like the AASHTO bridge design code, requires you to design for the maximum shear that could be applied to the studs, which is the lesser of the tension capacity of the steel beam, or the compression capacity of the slab, or the portion of the slab on the compression side of the neutral axis.

As I said, under AASHTO, the applied shear (shear demand) is only used to calculate the required spacing for the studs for each section of the beam (range of shear at the fatigue load level). We usually calculate the required spacing at the tenth points of each span. It's similar to the way stirrup spacings in a concrete beam are handled, basing the stirrup spacing on the required shear capacity for the section under consideration.

Rod Smith, P.E., The artist formerly known as HotRod10