BTH-1 hooks below spreader bars

[rmaj14]

thread507-273125
We are checking hooks cut from plates to pick up rolls very similar to "Model 415 Spreader Beam" by Bushman (see

http://www.bushman.com/index.php/content/below_the_hook/roll_handling_equipment

). For fatigue design, should the side of the hook, which will have both bending and tensile stress, be checked for fatigue per BTH-1, Table 3-5 (AISC Table A-3.1) section 1.1 (stress category A) or section 2.4 (Stress Category E)? Section 1.1 refers to base metal "away from connections" which is vague, and Section 2.4 seems to apply to tight fitting connections. There is a large difference in allowable fatigue stresses.

 

[Bagman2524]

I would think section 1.1. Section 2.4 looks like it's concerned with stress cracks forming at the edge of the eye-hole. See Fig 2.4 in table A-3.1

 

[dhengr]

Rmaj14:
I think you should probably use Stress Category “E”, per the BTH-1 description section 2.4. Your “J” hooks, if that’s what they are, are much more like the eyebar shown in section 2.4., than a plain bar with only axial normal tensile stress. The combined stresses in your hooks and the eyebar are in the same general region of the member and are of the same nature, bending, shear and normal tensile stresses combined. And, the type of crack shown in section 2..4 is exactly what you are trying to guard against and worried about. In your application it is assumed that the hooks will be used many times per day, and there is some considerable potential of them taking some damaging abuse in the regions of the max. tensile stress; nicking, denting, scraping, abrasion and the like . You certainly don’t want a flame cut edge on the plate on the inside of the hook, you want to grind or machine that to a nice smooth surface. And, at the two corners of that edge I would grind a 3/16" radius, or some such, to minimize the chances of sharp nicks, etc. in the sharp 90̊ corners, certain stress raisers. Then, as important as the design process and allowable stress range is, a good inspection routine on those hooks, in this area, is of equally import. You also want to cut those hooks from a plate which has the rolling grain in the steel running in a favorable orientation w.r.t. the max. tensile stress region. What size and thickness are these hooks, and what loads and cycles per day are you dealing with? Since they are in a captive environment, inspection and control over their use should be better than equipment in an open rigging environment. These types of hooks might be worth studying with FEA to optimize the shape and thickness in the max. combined stress region. And, a nice snug fit btwn. the hooks and the shaft through the core of the rolls would be a design improvement too, I would think.