Went out and took these images of sign posts both on the highway and on a major
boulevard where they have designed break points on the 4x4 wooden
posts. Designed to break where there will be a minimum of potential
harm to drivers/passengers/etc
These are examples of stress raisers from holes in a structural member.
Some have a 3rd hole bored 90* and inbetween those two
Difference to the OP's question is that these are wooden, much higher impact
moments vs frequency of bending moments over a looooong period of time and much
smaller holes (singular, there is an accumulative affect of multiple holes)
Again, it depends on many factors. How much does the OP's tongue bend, not that
it won't bend...it *WILL* bend, just how much. Then the harmonics of
that tongue's application (the OPs setup). There are harmonics to these
sign posts too...mostly wind from Mother Nature and windage from
passing vehicles
The total loss of web material, their distribution (relationship to each other and
to the rest of the web) and how smooth the holes edges are. There are also
other factors
This is along a high way
This is on a boulevard approach to that highway
Welding can create stress raisers too. Depends on the welder's knowledge,
skills and attention to details
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Not sure what your point about the sign post is. They do not fail during normal usage only in extreme cases. I suppose if a car rams into the a-frame, that it will fail too.
TomG2 wrote: Not sure what your point about the sign post is. They do not fail during normal usage only in extreme cases. I suppose if a car rams into the a-frame, that it will fail too.
He is simply trying to illustrate his point made earlier, and in contrast to some other posts, that drilling holes in the web material will weaken the material..
I agree with your earlier post about putting a plate on each side. I think that would bethe best, and probably the safest, solution.
Barney
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Thanks, I knew what his point was. A good looking splice plate will reinforce, protect, and hide the affected area for less than twenty dollars. Problem solved, no sign posts were damaged or photographed during this demonstration.
TomG2 wrote: Thanks, I knew what his point was. A good looking splice plate will reinforce, protect, and hide the affected area for less than twenty dollars. Problem solved, no sign posts were damaged or photographed during this demonstration.
I don't think that I'd go the plate route.
My thinking is that the goal should be to return the Beam as close as possible to is original strength. The beam most likely flexs a little bit when under tow, and my thoughts are that you would probably want the flexing to be the same amount for both the left and right beams.
Adding a plate runs the risk of strengthening one side over the other..
I suppose that one could drill the other beam to match, and then weld plates on both of them.
* This post was
edited 06/24/12 02:19am by Huntindog *
Huntindog
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bartlettj wrote: I wouldn't have them welded, the welding process can cause stress itself. Holes in the middle of an I-beam do not significantly weaken the beam, and round holes do not cause stress to the material. I bet if you look under the trailer you will see lots more holes in the frame that are bigger than that.
Take another look at the pic. It is not an I beam.
Quote: =HuntindogI don't think that I'd go the plate route.
My thinking is that the goal should be to return the Beam as close as possible to is original strength. The beam most likely flexs a little bit when under tow, and my thoughts are that you would probably want the flexing to be the same amount for both the left and right beams.
Adding a plate runs the risk of strengthening one side over the other..
I suppose that one could drill the other beam to match, and then weld plates on both of them.
So, every trailer that has one friction control device mounted, needs a second installed to ensure perfectly balanced A-Frame loading? Not.
Guys, we are down in the weeds here. Clearly there are some of us who are also looking at this from an engineering standpoint, and answering the question exactly as it was asked.
At the end of the day the only way we could get true answers to the "actual" stresses seen is to do a full stress analysis. I doubt that the OP would be so inclined.
So what will likely happen is the OP will go ahead and drill his new holes and probably install a bolt-on strongback (uh-oh, more holes) across the area. The solution involving proper plug welds is the best as it would restore the area to near original condition.
* This post was
edited 06/24/12 05:06am by wmoses *
Folks not in design either forget or never knew that all things are designed
with the worst day out there in mind...when Mr Murphy crosses your path
The OP says his sway control contacts the ground in some instances and going back
to friction bars
That to me, say he drives in some non pavement or even fire road like situations
Then we do NOT know how he loads, what he loads and the biggie...how he drives
Meaning we do NOT know the stresses on his setup, but bet it's higher
than the 'normal' setup.
I've shown how other things manage stress raisers or puts them in there on
purpose. Meaning that any reduction in cross sectional area reduces its strength
Here is another picture of a pickup frame cracked from the cycling of use and
most likely over the limits. Notice that it does have holes in it and it
cracked anyway else where. It must have found a stress raiser on the
top flange where the load is concentrated at the pickup bed contact point
Also notice that person's 'fix'...
* This post was
edited 07/01/12 08:07pm by an administrator/moderator *
Fence posts and rusty frame elements are miles away from a properly installed reinforcing plate. Show us a bunch of a-frames that have been destroyed by the bolt on installation of a friction sway control button. That is much closer to what I, and others, have suggested as a remedy for the OP's problem. Think of is as a plate with 12 holes spaced along the frame instead of the normal 6.
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