Specifications for elephant-resistant steel poles

[Peter Apps]

Where does the 1 degree requirement for the camera come from? Cameras typically have quite a wide viewing angle, why do you need such a precision?

Simply taking a stronger beam still looks like the easiest option to me.

The 1 degree repeatability in aim comes from tests I did on angle of dip and tilt using a dog the same size as a leopard as a target under controlled test conditions, and from the requirement to have the cameras covering overlapping areas but not dazzling one another with their IR floodlights.

Amen to the stronger beam - but nobody wants to answer that question

 

[Peter Apps]

I was thinking more of a rigid welded pyramid structure with pipe collars at the bottom of the corners for retaining stakes to be driven through. You are right about the structure legs needing to be as strong as a single pole but a welded pyramid joined at the top and with base pipe pieces connecting the bottoms of the three legs is an extremely strong structure (but not necessarily a light weight one for handling purposes).

That would work but would need three times as much steel and three times as much hammering of stakes into the ground.

 

[anorlunda]

nobody wants to answer that question

I think I can get you an answer when I get to my computer tomorrow.

 

[Nidum]

I did a sample case just to see what the magnitude of the problem is .

Simple cantilever / Hollow square steel tube / 1000 mm high / 75 mm across flats / 5 mm wall thickness / Mild steel / 4000 N horizontal load at top

That gives a safety factor of about 1.45 on yield for maximum fibre stress .

 

[Peter Apps]

I did a sample case just to see what the magnitude of the problem is .

Simple cantilever / Hollow square steel tube / 1000 mm high / 75 mm across flats / 5 mm wall thickness / Mild steel / 4000 N horizontal load at top

View attachment 114598

That gives a safety factor of about 1.45 on yield for maximum fibre stress .

Great ! That's what I've been looking for. That is a much heavier pole than I had thought, though not entirely impractical. Hammering it into the ground will be a mission though ! Would you mind looking at what load a 50 x 50 x 3mm square tube could recover from under the same conditions. I already know that I can get 50 x 50 mm into the ground without machinery. Thanks again.

 

[Peter Apps]

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.

 

[Nidum]

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]

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 .

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 .

Thank you again. Deflection while the elephant is busy with its engineering is no problem, as long as the pole recovers to its original position afterwards. If I could make a flexible pole that would stand up again I would give it a try. I suspect that a determined elephant could exert more than 1100 N, but 50 x 50 might be worth trying on the basis that if the first shove does not yield any results it might go away.

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]

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.

 

[anorlunda]

Final question; how much stronger in bending and torsion is square tube compared to angle with the same dimensions ? Is there a simple relationship ?

Not a formula, but just google for sources of angle iron for sale. You should be able to find manufacturer's specs for max bending load.

 

[Nidum]

Final question; how much stronger in bending and torsion is square tube compared to angle with the same dimensions ? Is there a simple relationship ?

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 ?

 

[Nidum]

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

Certainly a problem to be investigated . What sort of ground is there where this camera is to be set up ?

 

[Peter Apps]

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 ?

If angle is a lot weaker than square tube of similar dimensions then the square tube would be the way to go, and there would be no good size of angle. From looking at the videos and the state of the poles after elephants have finished with them I suspect that the elephants first twist the pole using the camera box and bracket as a lever, that flattens the angle at ground level and then it is easy for them to bend it over. If I had my way we would already have replaced all the 40x40 angle with 50x50 square tube (which I know I can drive into the ground if the lower edges are sharpened), which from an earlier answer can handle 1100 N 1m above the ground, but my boss said that it was too expensive. I was hoping to be able to present him with some hard evidence that the square tube is the way to go. It might not prevent all the elephant damage but it would reduce its rate to something I can live with.

 

[bsheikho]

Why don't you disguise the camera inside another animal's costume? How often do animals kick other animals?

 

[Peter Apps]

Certainly a problem to be investigated . What sort of ground is there where this camera is to be set up ?

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 .

 

[Peter Apps]

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.

That's a very handy document, though I will have to look at very carefully to make sure I interpret in correctly. The 500 kg is a guess, but an informed one based on elephants being able to kick harder than they can lift. They will not get their heads down to 1 m to push with their heads. Worse case is a six ton bull putting one front foot on top of the camera box with the other front foot off the ground - that applies more than half his body weight downwards. I have video of a bull casually aiming a camera at the ground by standing on its box with one front foot - both from the camera in the box, and from one of the others in the array. The bracket rotated on the bolt that holds it to the pole, but nothing bent.

I understand that the pole is only one part of the whole picture, but it is very obvious that 40x40 mm angle is too weak, and I was wondering what size of steel would be elephant resistant. Once I know that I can start worrying about the strength of the soil, which I can do nothing about apart from driving the poles deeper. Casting concrete footings is out of the question.

The test scent goes into the dispensers next week, so in any case I cannot now change the setup. But the second phase of the experiment will have the cameras in a more remote area where they will not be visited as often, so the ironwork needs to be more resilient. I will keep you posted.

 

[mfb]

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.

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]

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.

Potentially it is a confounding factor, and I am sure that referees will bring it up when I submit the paper, but the two conditions happen consecutively and the repellent effect I am looking for is a very obvious contrast to the leopards usual behaviour of ignoring the dispensers completely - I am not looking for subtle effects that need sophisticated statistics to tease out the control vs experiment differences. The alternative of doing controls and experiment in the same places at different time is to do them at the same time in different places - but then the exactly equivalent criticism can be levelled. Same places different times also avoids complications with animals getting habituated to the odour.

 

[pervect]

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.

 

[Peter Apps]

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.

I am sure that you are right that there will be paper or two on successful solutions.

I think that it is important to stress that these elephants are not "rampaging"; they do not come charging in and butt the poles with their heads, they approach quite deliberately, sniff around, then kick or pull on the cameras and poles. Any impact from kicking is nowhere near the impact load of a charging elephant. I would upload videos from the cameras but they are 15 MByte each and my internet is not up to it.

Also I do not expect to have mountings that resist all elephants all the time. If I could reduce current rates of damage by 90% while still using steelwork that can be installed in the field without heavy machinery I would be happy. Asking how strong different sizes of steel are was one step towards that goal. I designed the camera boxes by rule of thumb applied to what I can buy locally (lip channel) and they have protected the cameras against elephants, baboons, hippos, hyaenas, and wild dogs (just from memory) - the only camera that has been damaged while in a case was one where an elephant uprooted the pole and dropped the pole and camera in the road, where it was run over by a ten-ton truck (sadly the elephant put the camera face down so there is no video but the tyre tracks tell the story). As you can imagine the box was considerably squashed and the camera case was cracked, but the camera still works. Making the boxes to resist ten-ton trucks would be the design overkill equivalent of designing a pole to resist a full scale elephant attack from a bull n musth.

There is a limit to how concealed the cameras can be - they use IR floodlights at night and although I cannot see the glow I suspect that elephants and other animals can (there is literature on animal responses to camera light and sound, but it does not necessarily apply to the cameras I am using). Also, when the cameras are installed and serviced it is inevitable that they get human scent on them, which may upset elephants. For my particular application I cannot use scented repellents like chillis, or masking scents.

Snapshot Serengeti https://www.snapshotserengeti.org/#/home put cameras on 75x75 mm poles for a long-term fixed point survey. I will contact them to find out how they got them into the ground.

 

[Baluncore]

Since I am testing the repellent effects of chemicals from scent marks I cannot add any extra repellents to the setup.

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.

 

[Peter Apps]

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.

There are no repellents there as yet - I am running with no scent as a control. In any case the scent will not be at the cameras; it will be in dispensers 5 m from two of the cameras at each array and 15 m from the other two. In an earlier study elephants took no special notice of the repellent.

As I said in an earlier reply; training a whole population of elephants is utterly impractical. In any case, the training protocol you propose would not work with any animal that I can think of.

 

[anorlunda]

@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.

 

[Peter Apps]

@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.

Well, thank you for your inputs. I disagree that the problem is "fun" - elephants damaging equipment and pushing cameras out of alignment are a serious drain on resources and productivity is an under-resourced project with a very serious aim; to find new ways of managing large predator behaviour so that we can limit their impacts on livestock agriculture and thereby reduce the human-wildlife conflict that is the single major cause of declines in large predator populations all over the world.

If the dimensions of a steel square tube 1m long that can recover after having a 500 kg mass hung on the end in cantilever loading is fuzzy I am not sure what would consider to be exact. I do not have the luxury of working in a field where problems are well defined in an engineering sense - but I do the best I can with the resources available. Fortunately some other posters have been helpful enough to work with my crude numbers, and have come up with pole sizes that were somewhat larger than I expected; 75mm square instead of 50 mm square, but certainly not 10 times or 50 times larger as you suggest. Forgive me for being blunt but what is preposterous here is your suggestion that I use 500 mm square for a 10 times margin or 2.5 m square for 50 times - I am camera trapping in the African bush, not building advertising hoardings alongside a highway. Doubtless with your engineer's hat on you can suggest that I go for solid instead of tube, but I do not have heavy machinery to move it around.

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 ?

 

[anorlunda]

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 ?

What I suggested more than once, is that you stop calculating and compensate for uncertainty by adding huge safety factors and oversize it.

And I was not all negative, I provided you with a link to tables where non-engineers could simply look up an answer.

 

[jack action]

I'm surprised that it wasn't suggested earlier, but I would use 4 angles driven in the ground in a square arrangement, with other angles bolted to them to form 'X' braces. The bigger the square, the more it will resist torsion and bending.

On the upside, the camera can be put inside the square, thus it doesn't give a lever to the elephant to twist the angles.

If you also cover the assembly with bolted pieces of plywood or sheet metal, it will prevent the elephant from using the 'X' braces as handle to twist or pull the angles. Heck, if you use thick enough plywood, the 'X' braces might not even be necessary.

 

[Baluncore]

A better shape might be a cone made from a sheet of memory plastic, shaped like a “witches hat”. Apex angle might be about 60°. Bury and pin the skirt down in soil with sticks or rocks on skirt to keep it fixed and hidden. Camera is in a steel box which is bolted to the internal surface of cone. Lens looks through a small hole near the top of the cone. There need to be a number of small air holes, including some near the top above the camera box to allow thermal air circulation for cooling during the day in hot sun.

An elephant would have trouble gripping the closed cone. If the cone was crushed, then the plastic would slowly stand back up once the elephant had gone and the cone warmed up in the sun.

Problems: The smell of remaining plasticiser, pick the right material and vent it in the sun. Cost of roto-molding.
Advantages: Light weight, stacks well, memory-plastic can be driven over by a truck, then reused.
Available in any colour, or cover with cheap glue and throw local soil at the surface once installed.

Multiple use, can be made of white plastic, or painted white and used to mark an airstrip. Sales cover the cost of manufacture and research.