ASME Below The Hook Lifting Devices 2011: Pinned Connections

[HOWDOO]

Hi,

could anyone with experience in this standard help explain something about the the effective width limit equations:

beff ≤ 4t ≤ be (3-47)

beff ≤ be 0.6 Fu/Fy √(Dh/be ) ≤ be (3-48)

Where:
Fy = Material Yield Strength
Dh = Hole Diameter
be = Actual width of a pin-connected plate between the edge of the hole and the edge of the plate on a line perpendicular to the line of action of the applied load.
Fu = Material Ultimate Tensile Strength
t = Material Thickness
beff = Effective Width to each side of the pin hole.

The following link has an image of the notation: Link

The two equations shown above are intended to prevent out of plane buckling and are based on empirical research by (Duerr, 2006). beff is used as a component in the tensile stress area failure mode. If the plate is stiffened to prevent out of plate buckling equation (3-47) does not apply.
Please note that I don't have access to Duerr.

What I can't understand is the thoery behind the limit state (3-47) as this basically states that 4 x the material thickness must be equal or less than the width of material either side of the pin-hole. Which to me says that if I increase the thickness of the material I have to increase the width of the material either side of the pin-hole. Surely if I increase the thickness of material it would serve to reduce the chance of out of plane buckling therefore in theory it should be acceptable to reduce the width between the hole and the plate edge?

I'm willing to accept I may be missing something here, would just appreciate if someone could improve my understanding.

TIA. Alex

 

[JStephen]

I think that first line is intended to say "beff is less than or equal to 4t and is also less than or equal to be", and similarly for the second line. I don't think it's intended as a limitation on "t". You mmight forward that to the committee involved for clarification in a future edition.

 

[HOWDOO]

Thanks for the reply JStephen,

I have looked up the most up to date standard (those equations were from BTH-1 2005, my apologies). This is what BTH-1 2011 has:

The effective width shall be taken as the smaller of the values calculated below:

beff = 4t ≤ be (3-47)

beff = be 0.6 Fu/Fy √(Dh/be ) ≤ be (3-48)

Note the equals sign in place of the inequality.

To me equation 3-47 now says the effective width (beff) must equate to 4 x the material thickness which has to be less than or equal to be.

It might be clearer in what i'm asking with an example:

I have a lifting lug of thickness t = 10mm

therefore:

beff = 4t ≤ be
= 40 ≤ 40

As shown above the minum value for distance between the edge of the hole and the edge of the plate (be) has to be 40mm.

Now if I reduce the thickness of the plate to 5mm:

beff = 4t ≤ be
= 20 ≤ 20

Reducing the plate thickness essentially allows me to reduce the distance between the edge of the hole and the edge of the plate (be).

Am I missing something?

Alex.

 

[dhengr]

HOWDOO:
To help answer your own question, and to make us all the smarter for this exchange, see if you can dig up that Duerr, 2006 research, and post it here. I don’t think I’ve ever seen that, but I have a few thoughts and comments on the matter from long before any 2006 research. You’ve obviously read the commentary in ASME BTH-1 on this matter, and I don’t know how Duerr’s research leads to the exact formulas or coefficients in the formulas. Without picking their brains and seeing the Duerr research, its anyone’s guess how a committee comes up with coefficients in an empirical equation.

The admonition in eq. (3-47) is to keep it stocky (thick) so it can’t buckle out of plane, and your latest thinking t = 10mm & be = 40mm vs. 5mm & 20mm is bass-acwords because the latter condition will likely not check in tension (actually max. combined stress) at the net area, and/or it is more prone to buckling. Think of it this way: I can get the needed net area with 2(10x40) = P/Aeff; or I could get it with 2(5x80); but the 5x80 section is much more prone to dishing or out of plane buckling. Look down on the top edge of the pin plate (in plan), and you see the pin plate thickness (t) and its width (2be + Dh), and the pin (Dp) perpendicular to the plane of the plate. Now, if the shackle pin is twisted w.r.t. the plane of the pin plate (its axis makes angles of 100̊ + 80̊ with the plate plane, in plan) or it is canted (not horiz.) w.r.t. the plane of the pin plate (you are not lifting directly above the pin plate); these conditions load the pin plate eccentrically w.r.t. the plane of the plate, and are likely to cause it to buckle. In plan you would see the pin plate take on an “S” shape btwn. the two net tension areas and added torsional loading in the net areas. Or you might see a half sine wave btwn. the two net tension areas, it just rolling over, out of plane and causing high tension on one face of the pin plate. None of which you want. Eq. (3-47) forces you to proportion the net tension area (t vs. be) well, sufficiently stocky, or forces you to use a much lower average tensile stress on the full net area, by virtue of (t)(beff.).

You actually have a number of different things happening at the net tension section in a pin plate. You have the direct normal tensile stress P/[2(t)(be)] and you have a bending moment which causes max. normal tensile stress at the pin hole edge and max. normal compressive stress out at the outer edge of the pin plate; this basically varies linearly from tension at the pin hole, across be, to max. compression at the outer pin plate edge. This bending moment is highly dependant on the relative hole and pin dia’s., and the section modulus is then dependant on t & be. These show up in some fashion in Eq’s. (3-46 & 48). In developing ASME BTH-1 this subject was considered analogous to the stresses in eye-bars or hooks, which were well studied conditions. You might also have torsional stresses, or the face tension stresses due to bending perpendicular to the plane of the plate. These will all combine for a max. tensile stress at a plate corner at the pin hole edge, at about 10 & 2 o-clock. This is a good reason for doing a good job of machining the pin hole in the pin plate and then grinding/machining a 1/16" chamfer all around the hole at its edge/corners.

 

[fancypants]

Just get the word from the horse's mouth. You can easily find Dave on the internet.

 

[JStephen]

Here's the issue as I see it- the equations are defining a limit of beff, NOT a limit of t or be or Fu or FY or DH or be.

The effective width shall be taken as the smaller of the values calculated below: