- #36
Peter Apps
- 26
- 3
Thank you - I look forward to seeing what you get.anorlunda said:I think I can get you an answer when I get to my computer tomorrow.
Thank you - I look forward to seeing what you get.anorlunda said:I think I can get you an answer when I get to my computer tomorrow.
Nidum said:Problem with more slender poles will be deflection .
For the 50 mm square tube you mention a load of 1100 N will give same SF but top deflection now > 8 mm .
Nidum said:Problem with more slender poles will be deflection .
For the 50 mm square tube you mention a load of 1100 N will give same SF but top deflection now > 8 mm .
Peter Apps said:Final question; how much stronger in bending and torsion is square tube compared to angle with the same dimensions ? Is there a simple relationship ?
Peter Apps said:Final question; how much stronger in bending and torsion is square tube compared to angle with the same dimensions ? Is there a simple relationship ?
anorlunda said:Unless the tube is anchored in concrete (or buried 3-4 meters deep), a strong push will move the dirt and make the post lean no matter how strong the tube
Nidum said:Answer to specific question is that angle would be a lot weaker . More generally though it's better to compare strengths of beams of different sections but same weight . There are no simple formula relationships as such but it would be quite easy to prepare some strength comparison charts with a spread sheet .
In many of these types of problem it is usually easier to just select and compare a few sizes and shapes of beam until you find something suitable .
A problem with angles is that they do not have the same strength in all directions and they can twist as well as bend even with simple direct loads .
What would be a good size of angle to suit your purposes if it could be shown to be strong enough ?
The ground is for the most part a sandy clay mix. It gets very soft when it is wet - and this year we have had getting on for three times the annual average rain - which makes it easier for animals to push things over, but also easier to drive the poles in deeper. There is nothing I can do about the soil, but I can do something about the strength of the poles, and even in wet sand the 40x40 mm angles were being bent over at ground level, so were weaker than the soil. There are a total of 19 cameras at five sites, and they have been out there for just over two months recording with no scent in the dispensers. Next week I add scent to the dispensers and the cameras record the animals' responses. I wish there was a detailed description I could link to, it is part of this project; https://www.bpctrust.org/bioboundary-project.asp .Nidum said:Certainly a problem to be investigated . What sort of ground is there where this camera is to be set up ?
anorlunda said:I'm pretty busy today. I was going to look up the answer here
http://www.midaliasteel.com/files/3813/6394/3187/DCT_CF_Small.pdf
but perhaps you can look it up yourself. You want the maximum bending load for a cantilever 1m long. The tables include different sizes of square structural steel tubes. My guess is 100 mm or 4 inches.
But 1m is pretty short. It won't make much difference in cost or weight to go for gross overkill with a 6 inch or 8 inch square tube. Then you don't need the answer for the minimum size that does the job. After all, your 500 kg number is, I assume, just a guess. An elephant might be able to do many times as much.
I still haven't heard an answer to preventing the post from being moved regardless of strength. Unless the tube is anchored in concrete (or buried 3-4 meters deep), a strong push will move the dirt and make the post lean no matter how strong the tube. Focus on tube strength is only a partial answer.
Edit: good luck. Perhaps you can post again in the future to let us know how it worked.
Not directly on topic, but I wonder if it could be a problem if your "no scent" and "with scent" samples are not collected at different times of the year.Peter Apps said:There are a total of 19 cameras at five sites, and they have been out there for just over two months recording with no scent in the dispensers. Next week I add scent to the dispensers and the cameras record the animals' responses.
mfb said:Not directly on topic, but I wonder if it could be a problem if your "no scent" and "with scent" samples are not collected at different times of the year.
pervect said:Rampaging elephants have been known to uproot trees and "mow down" telephone poles. (See for instance http://www.historylink.org/File/5270). So I suspect that an attempt to make a mounting proof against an elephant will probably be expensive. It's not quite clear to me how the telephone poles failed - did the poles break, or were their foundations inadequate? (I suspect the later, especially given that the trees were listed as being uprooted).
In either case, I would think that It would be better to find a mounting system that doesn't irritate the elephants than to try to engineer one that can resist them. Which also allows us to pass the buck back to the zoologists :-). I wouldn't be surprised if there's an opportunity for a paper on the solution, once the problem is solved.
More research on the historical incident in question might give more insight into just what an elephants destructive capabilities are.
For the engineering aspects, I found https://www.clear.rice.edu/mech403/HelpFiles/ImpactLoadFactors.pdf which looked interesting. If I'm reading the article right, you might need a beam (pole) that could support 100 or even 1000 elephants statically to withstand the dynamic impact force. I'd guess an elephant might weight between 5-10 tons, at the higher figure we'd need a beam that could support 10,000 tons. And foundations to match.
Using the approach from this paper, to get a better answer, one would need to estimate the velocity of impact of the elephant. I'm not going to hazard a guess, but just outline the general approach from the paper I mentioend. Conservatively assuming the efficiency factor is 100 percent, one would assume the pole had to store that much energy. (Perhaps one could argue that a lower efficiency is needed, I don't have a good grasp on it though.). This would give the peak deflection, a static analysis of the beam (which is the engineering model for the pole) would have to be done to assure that the beam (pole) didn't fail under these conditions.
Are the repellents you are testing attracting the elephants and triggering the destructive behaviour. Do you have posts with cameras as controls, that are not attacked as often by elephants?Peter Apps said:Since I am testing the repellent effects of chemicals from scent marks I cannot add any extra repellents to the setup.
Baluncore said:Are the repellents you are testing attracting the elephants and triggering the destructive behaviour. Do you have posts with cameras as controls, that are not attacked as often by elephants?
If you regularly provided a reward for elephants on the posts, could you train elephants to not destroy the reward bearing posts. Do not provide more reward if the post is damaged. Take the camera, but leave the damaged posts so elephants will learn that damaging posts is not rewarding.
anorlunda said:@Peter Apps ,
I think that your problem is fun. We are very willing to help. But putting my engineer's hat on, I must say the following.
Your requirements are so fuzzy and ill defined, and your numerical estimates so crude, that the very idea of calculating the minimum size post is preposterous. It wastes your time and our time to even try. Given the uncertainties, you should get something 10x times stronger than you think. (maybe 50x)
If you insist on the minimum size, then spend your time sharpening your requirements and validating your estimates. Calculating the answer before the problem is well defined is not productive.
What I suggested more than once, is that you stop calculating and compensate for uncertainty by adding huge safety factors and oversize it.Peter Apps said:Contrary to you claim about calculating before the problem is well defined, other posters have been able to produce sensible and useful answers working from my crude estimates for loading. How on Earth do you suggest that I go about "validating my estimates" - equip poles with strain gauges and wait for wild elephants to push against them ? Do you seriously think that anyone would fund that ?