Pin-connected Plates 1

[grobin]

In section D3.2 of AISC 9th, how should one interpret the first paragraph?

"The minimum net area beyond the pin hole, parallel to the axis of the member, shall not be less than 2/3 of the net area across the pin hole."

I read this as saying (assuming a uniform member thickness) the distance from the edge of the pin hole to the edge of the pinned member (in the direction of the axial load) must be at least 2/3 of the width of the pinned member minus the pin diameter (orthogonal to the axial load).

Is my paraphrased interpretation correct?

 

[miecz]

Yes. The provisions were originally developed in ASCE Transaction Paper No. 2023 by Bruce B. Johnston, published in 1938. The design approach is to size a lug for fracture at the side of the pin hole, and then provide a higher factor of safety for the two other potential failure modes: failure beyond the pin hole, and dishing of the entire plate. The requirement "edge of the member or element shall not exceed 4 times the thickness" prevents dishing. Curiously, the dishing criteria seems to have been left out of the latest AISC LRFD manual.

 

[miecz]

Oops, that was Bruce G. Johnston, who later headed up the Structural Stability Research Council for many years. The dishing phenomenon is a buckling failure mode. I'm very curious as to why it is no longer an AISC requirement.