Rigger12
Structural
- Nov 28, 2018
- 9
I am currently making a spreadsheet to determine the capacity of lifting lugs using the processes laid out by David T. Ricker in his article "Design and Construction of Lifting Beams" published by AISC in 1991. In the article he states the 4 failure modes to check are: 1. Tension Failure at the sides of the holes, 2. Crushing Above the pin with tension tearing, 3. Shear failure in the lug plate as the pin attempts to plow to the edge, and 4. Dishing.
When going through the example for the top lug design(step 12) given at the end of the article he checks modes 1 & 2 and set the minimum thickness so dishing isn't an issue, but he never checks the lug for Shear failure (failure mode #3), is there a reason why? To me if you check shear failure using his equation of Pu=2*(0.4)*Fy*e*t and then apply a factor of safety of 5 as he recommends this becomes the controlling case with a Pu=100K so Pa=20K, he is designing the lug for a tension load of 20.4K so that would mean the lug doesn't pass. I've also seen calculations by other engineers of lifting beams and they haven't checked shear failure as outlines by Ricker either, and when I have it again becomes the controlling case, is there something I am not understanding correctly here. Why wouldn't this be checked, and why would Ricker outline it in his process and then not do it in his example?
When going through the example for the top lug design(step 12) given at the end of the article he checks modes 1 & 2 and set the minimum thickness so dishing isn't an issue, but he never checks the lug for Shear failure (failure mode #3), is there a reason why? To me if you check shear failure using his equation of Pu=2*(0.4)*Fy*e*t and then apply a factor of safety of 5 as he recommends this becomes the controlling case with a Pu=100K so Pa=20K, he is designing the lug for a tension load of 20.4K so that would mean the lug doesn't pass. I've also seen calculations by other engineers of lifting beams and they haven't checked shear failure as outlines by Ricker either, and when I have it again becomes the controlling case, is there something I am not understanding correctly here. Why wouldn't this be checked, and why would Ricker outline it in his process and then not do it in his example?
