Shear reinforcing for anchors in concrete pedestal

[McSEpllc]

Hi All,

I am working on the foundations for a pre-engineered metal building.
The forces on the anchor bolts only work, assuming anchor reinforcement for shear.

Referencing ACI 318-14, Fig. R17.5.2.9b:

Question 1:
Are the bars not effective for anchor reinforcing per the figure required?

Question 2:
Shouldn't the hook of the anchor reinforcement extend beyond (below) the 35 degree shear line?
Intuitively, it seems the hook should extend by the development length beyond this shear line.

Thanks

 

[GC_Hopi]

Q1: Not effective as anchor reinforcing, see the highlighted "Bars effective as anchor reinforcement" in the figure you provided. Not required as anchor reinforcing but other requirements will drive the addition of the reinforcing (flexure, temp and shrinkage, etc).
Q2: You need a development length pass the shear line. See the highlighted "Ldh" in the figure you provided.

 

[JedClampett]

What's you folks' opinion of hairpins in this situation? ACI doesn't address them, but they seem pretty effective.

 

[driftLimiter]

We use hairpins for this situation routinely. AISC Design Guide 1 includes examples that use the Hairpins as well. When using them take care to complete the rest of the load path. If resolving the shear as a friction between the floor slab and subgrade, take steps to ensure that this portion of slab is structural and remains in place as such.

I like to extend my hairpin out wide enough to engage enough slab bars to transmit the total tension, or wide enough to engage the calculated width of slab required to resist the shear in friction. Sometimes this controls the length of the hairpin.

To the OP.

The diagram indicates that you can count on any bars that are fully developed (Ldh) beyond the shear failure breakout surface of the concrete. For the purposes of anchor reinforcement the other bars (shown in grey) are not required.

The goal is to get the full development of the anchor reinforcement so that the shear V can be transferred from the anchor to the concrete then into the reinforcement. You are restraining the breakout of the entire cone by developing this tensile strength at the slab level. Follow the tension load path all the way until it resolves into the soil !

 

[McSEpllc]

Thanks guys for your thoughts.