Just to address some of the repeating comments: 1. I didn't come up with this analogy! I read about it in an engineering book that related it to a stress reduction technique used in the past. You can read more about the theory in Reference 3: Roark's Formulas for Stress and Strain, Chapter 17.2, page 777. I thought it's a crazy idea so I decided to test it. I uploaded the PDF for you here: drive.google.com/file/d/1JE9jCCAGj7MGXMqZQSjOo8KS8XlC5y4D/view?usp=sharing 2. Yes, the method is used for tension members specifically not for beams but my home setup does not facilitate tension testing so I had to improvise. The point is to show that removing material can increase the capacity. 3. Of course this is not a peer-reviewed study so the results should be taken with a grain of salt as there is a lot of variation between the samples, they are way too few, and the testing environment is not strictly controlled. 4. Not many holes are elliptical in practice. In theory this should work with circlar holes (cables, pipes, ventilation, etc) as well, but the capacity gain is probably much less, if any. I used an elliptical hole to make the gains more drastic and hence more interesting for a YT video. I encourage the comments pointing things out, this is great! I like the idea of community notes, I hope it comes to YT as well. Cheers!
Any experiment with wood is going to require a lot more samples to be remotely accurate. You ran your hole-less and single hole samples once? That's not going to cut it, teeheehee. I can see how the relief holes can help in theory, though I imagine the effect will be quite small. Intuitively I expected there to be no significant difference, certainly not detrimental, between the relief holes and the single hole samples since the point of failure is either going to be the top of the board under compression or the bottom under tension. The middle of the board is not under much stresses. This is why you can cut giant holes out of the middle of engineered I-joists without effecting strength significantly.
I’m not an engineer so a video like this is fascinating to me. I would never have thought that removing further material could increase strength. Thanks for make it.
Hello, I am a Timber Engineering faculty member at Virginia Tech. You make some good points, but you there are some probems with your content. First, your model is not the same as your experiment. Beams do not have a uniform tension force. They have a triangular stress distribution where the moment is greatest at the center and typically tension failure is dominant in brittle/semi-brittle materials like wood. I also have issues with your sampling of wood. Saying short samples from the same 2x4 have similar performance is not correct. Strength of wood is dominated by the placement of defects like knots. Locating knots in different places can radically change the strength. I also think you have a flaw in your sampling. Typically, 10-15 pieces are tested for material properties and more for connections / special cases. The flow idea is fine, but I think it is more of a visualization concept. I'm not sure if it is linked to fracture energy, which has the same idea of a more rounded curvature to prevent failure.
Hi Daniel, your points are 100% granted. I am currently completing a PhD in structural dynamics and wave loading at Aarhus Univeristy. I don't have a tensile experimental setup at home, so I had to improvise. The flow analogy is far from perfect, in fact, it's flawed and it works only in very special cases. But don't worry, I know my beam mechanics very well. The concept is from the theory in Reference 4: Roark's Formulas for Stress and Strain, Chapter 17.2, page 777.
@@TheEngineeringHubyou’re a PhD candidate and haven’t figured out sample sizes yet? From the numbers you displayed as conclusive didn’t seem to show any statistical difference with or without the holes. It’s wood. The variations in wood for strength are larger than the margins you declared as significant.
@ClAddict they are not significant by any means, I stated that in the video. More testing is required. Theoretically, this holds water, experimentally, more work is required to prove it.
@@michaellowe5558 I agree he should chill out but to be fair the video does say "confirming the effect" around 6:20 which is statistically unsubstantiated with 1 control and a couple of test samples.
Why did you demonstrate potential flow theory on a beam loaded in tension when your test is a beam with a transverse point load? They're separate loading conditions that require different analysis. Furthermore why didn't you repeat your initial test multiple times? Wood can vary significantly in strength so using only a single point of reference does not make for an accurate test
well if you think about it, the bottom of the cut is breaking in tension, so you're right, its not a very good test to demonstrate the principle in tension, but the bottom 50% is kinda ok. although its still being pushed perpendicularly like you say
The variance is already exceedingly apparent by the numbers 1929, 2010, 2140. I don't know how anyone can think 1820 is definitely significant and not a fluke.
Wood is far from an ideal material for these tests, since it is grained and also nonhomogeneous. For a more sound experiment you would have to repeat the test many times due to the variation in grain patterns. Since the model (beam under tension) differs from the experiment (bending load), preferable would be a more homogeneous brittle material under tensile load, such as concrete made with small aggregate. Also good to know is that ductile materials are not affected by (static) stress concentrations, since they deform locally at the site of concentration and redistribute the stress evenly throughout the zone. A ductile beam with a notch or hole is weaker, but only because of the lack of material. Smoothing out sharp curves and corners won't strengthen them in the same way it does for brittle materials, at least under static loads. I really liked your video and I think it would be really cool if you made another one that shows the effect for ductile vs brittle materials.
Interesting idea, though your slit in the first beam has a lot sharper edges (cat eye shape) than the ovals in the following 3 cases. Also given that you shared stress model for the single opening, it would be nice to see what your modelling software predicts. As for the conclusions, note that your intra-sample variability ( 1929~2140kg) are consistent with standard wood variation and rend the results of your experiment inconclusive. Finally note that the top fibers being crushed before you reach failure mean you are observing variability in wood fibre separation ( delamination ) rather than stress propagation. I am looking forward to seeing a followup, keep up being curious ^_^
I was thinking similarly; that a more accurate or at least predicable/consistent test would be to use vertical slits with varying heights, but a consistent width and top/bottom radii, the lowest height being equal to 2xr.
I agree. I found it interesting that a sample of 3 was used for the condition with many holes but a sample of 1 was used for both the control (unaltered wood) and the first test condition with one hole. Given that wood is not homogeneous, I would have liked to see all of the conditions tested several times. Although, I understand that this was more of a demonstration of the theory, it would be more convincing if the average failure load was used for each condition. As a hobby wood worker, I can tell you that even within the same piece of wood the grain pattern can change dramatically and the presence of a knots is essentially the same as a hole in the wood in terms of the stress lines travelling through the wood. Nonetheless, I found your explanation of water flow as an analogy to stress fascinating. I always like to be able to visualize processes and this will help immensely.
The pointiness of the hole isn't really relevant. In this context at least general dimensions being similar is all that's needed. Consider arches, gothic and Tudor arches both come to a point yet the point of failure is not the apex or keystone.
@@edwardarkwright7116 The failure we are talking about is not that of compression, though (the top of the arch), it is of tension. Think of tension failure like a knife cutting through fibers. She sharper the edge, the more concentrated the shearing force that actually parts the material. I can hang a thousand pounds on sturdy rope tied to a 1" round bar, but only ten or twenty pounds if that same rope is tied to an upward facing dull blade. It can support less and less weight as the blade sharpness increases. Hanging a rope on f fresh surgical scalpel might even sheer through the rope under its own weight.
@@fxm5715 if we read the original comment, the critique was over the shape of the removed material. We both agree it is a matter of tension. We both know that if the crossection of a member contains the same area as another, regardless of shape the bearing load in regards to tension is very similar. In that way your comment I fail to see as relevant
Might not be just him. Something weird seems to be going on with audio on YT lately. I've had to jack up the volume on some channels I've sub to for years only to get blasted on the next video.
I am not sold. Wood is ridiculous for it's inconsistency. To make it at least somewhat scientific you would need to make more than one test with just one hole. Even better: use a solid such as engineered plastic or something.
Yeah, but wood has specific grain pattern/structure. I don't think plastic would be analogues to wood even if it's printed in a way to become similar to wood. It's just my intuition, I wouldn't mind to be proven wrong.
Solid rod is weaker than hollow pipe. If you put a tight fitting steel bearing into a hollow pipe, the pipe will bend near the bearing, the ball bearing not allowing the pipe to deform slightly in a uniform way makes it weaker than the completely hollow pipe. Then, think of a solid rod as a pipe with bearings all the way through it, imagine overlapping bearings in the core. This is a known thing, and much more often mentioned with the pipe example etc. Of course the hollow pipe has to have non-weak wall thickness, etc so there are limits, but it is the general idea of why.
The theory is sound, even if he had used metal or homogenized plastic the result would have been the same. It's not that it actually increases strength per se, just that it decentralizes stress points across a larger part of the material. This principle is used daily in engineering; you have to brace any part so that forces are not focused in any one spot. To that end, sometimes removing material can help as much as adding it.
@@kireduhai9428 right I didn't dispute the theory. All I was saying the experiment isn't worth a damn. But if we want to pick on the theory, shouldn't the maximum bending stress be in the middle, where the cross-section is constant (hopefully) from test to test? What I am saying is while all these additional holes are surely not making it any weaker, all they are actually doing is reducing the weight.
What that also says, is that for construction, 2x4 timber is far stronger than you might imagine when supported correctly and that holes for pipes, cables etc don't necessarily weaken it that much. Good explanation and I found the audio to be just fine. Many thanks.
Practical tensile strength is increased....but not for the entire section. Remember we are comparing against section with center slot and section with center slot and extra holes to smooth the flow. This reduces the risk of failure emanating from the peak load points. I.e. we are making the material behave more uniformly, though theoretical tensile strength in a uniform material won't change.
Horizontal shear is a failure mode most common on short, deep, heavily loaded beams (bending members). Round holes can relieve the strain paths. Holes with reentrant corners are crack propagation points in any material.
Very good job, sir! Forwarding this to our undergraduate engineering professors. Understand the limitations, and it’s great that you used your own time and materials to do something so useful for students.
The flow analogy socks. The top half of the beam is in compression and the bottom half is in tension. The neutral axis has no load. Stress is proportional to the distance from the neutral axis.
I think some are being overly critical in the comments. Yes the experiments would have to be a lot more detailed to have scientific validity, but the overall conclusion is correct. Also, although technically the wood failed first at the press contact point by delamination, we were still able to see the failure on the tension side of the wood block. The stress flow evidently is much different from the examples given, as this is a bending load. However, this was addressed in the video and it still holds that the ellipse concentrates stresses on it's sharp edges, and that the holes may help distribute the flow more evenly My takeaway was that the main point of this video is to show the counterintuitive result that taking away material can make the structure stronger, which is absolutely correct. And i believe it's not reasonable to expect a super detailed experiment on a simple youtube video like this. The use of potential flow as a theoretical justification for why this works is also correct, even if the loading condition isn't the same. And the experiments illustrated your point even if they weren't perfect. I enjoyed this video a lot! I think its also important to say that this does not suggest that adding these holes is optimal or good or desired in a real structure. Real structural solutions often have better ways of reducing stress concentrators. This result, however, does show up a lot in real life -- not by intentionally removing material to make a structure stronger, but by adding material and unintentionally making a structure weaker -- engineers need to be aware of this kind of thing
The guy is just absolutely wrong. It is 'counterintuitive' just because his explanation is wrong! He has variation in results because of different structure of wood in these beams, it's nothing to do with the additional holes! I'm surprised how many people here write positive comments, this is how you do false science.
>the main point of this video is to show the counterintuitive result that taking away material can make the structure stronger, which is absolutely correct. Absolutely not.
Great video mate. It looks like the first piece of wood had a knot that definitely would have aided in the strength through the center of that piece. Wood knots are incredibly strong. So much so that a block splitter won't go through it. Great video mate i really enjoyed it 🤙
Interesting. You had me there though. I originally thought you were going to propose, that a beam with relief voids was going to be structurally stronger than a solid beam. For anyone who is going to point out the cost weight benefits of non-solid beams. Yes, I know, I have the ability to look at cranes, bridges and aircraft wings.
The consideration at 3:50 is wrong and it is often done on wing profiles. There is no reason for a particle to speed up exactly to cover the same horizontal distance, there is of course an increase in speed, but not to that value.
This is what I was going to say. My understanding is that the speedup happens due to the in compressibility of the liquid forcing it to go faster since it has a smaller section to pass through.
When I saw the thumbnail I instantly thought of Gothic cathedrals and how arches distribute load. I agree with a lot of comments the tests need a lot of improvement, but the fact you brought up the idea which under heavy scrutinized research by experts could lead to better wood manipulation in the real world in the future. As a starting point for discussion on further experimental development, this video did just that.
Guitar builder here. I always wondered about this when making transverse struts that would bear the load of the string pressure on the bridge. That part of the guitar top, which acts as an monopolar oscillating plate supported by beams, needs to bear load (about 80 lbs) but also be as lightweight as possible (unsprung mass?). Could this be an improvement? I guess an experiment is about to be born.
We need to consider this material, wood, is a composite structure, and have different properties depending on the direction. A test with metallic will be interesting.
The same idea is very important in the fatigue design of parts. Where comparingly small decrease in peak stress can increase lifetime several times. I had a patent application with this idea in the construction industry for fatigue sensitive parts.
I like engineering I can understand without resorting to mathematical notation that I have never understood. Because of that, I subscribed which is something I have never done before until I see multiple video's
If anyone has ever seen what electricians do in order to run cable then you would know that single holes are drilled through many studs and joists in your house (assuming that it's made of wood). 😅 If relief holes accompanied said holes then you would have a stronger structure. 🤷 I think it's at least a cool concept. Thanks for sharing ✌️
In terms of a video, I think it would have made the point better if you started with the hole in the middle. Otherwise we are sitting through the whole video expecting it to increase the strength relative to the whole beam.
I think the point is... All real-world construction will require holes in structural elements and thoughtfully placed additional holes may improve the strength.
You did a great job on this video and obviously put a lot of work into it. Nice! Don't get caught up in everyone correcting things. They tend to do that on the internet.
The results rely on the crushing snd failure of the wood before the final force measurement. In a solid plank the crushing force causes a long crack through the bulk. In a plank with a hole the crack only propogates to the edge of the hole and the bulk is compressed which makes it stronger in failure. In some cases the void can allow the bulk to act like a lever, spring, or damper. This design would be excellent in something like a bench since the failure mode can take more load after deflection, softening the impact to users. So! Use a bigger plate!!!!
Since there aren't two equal pieces of wood, isn't three samples a very low quantity to state a general conclusion? With more samples, you can use statistical methods to verify if these variations are relevant or not.
Your experiment is absolutely incorrect. 1) You make the big hole differently every time 2) Different beams are different in load capacity because it's wood 3) Only 1 beam tested with no holes and with one big hole.
Although the explanation is a bit shakey, the clip demonstrates that strategically removing material may indeed strengthen beams under certain conditions.
@@evdl3101even his test didn't show that. At best it showed that if you already have a hole, then you can strengthen it with a couple of strategically placed relief holes.
@@kinnikuzeroYou missed the point. Between the two cases of interest, 1) elliptical hole and 2) elliptical hole+side holes, the cross section was the same. You don't have to convince us that a hole makes member weaker than a solid member. That we know. Video author also showed that in the very beginning.
Please test this again with better holes. Your main holes are uneven and crude, and act as shear propagation points. If you do not have the tools to make a smooth oval hole in one go, file down the edges and cuts until the hole is smooth. That should significantly reduce the chance of the wood breaking at the most aggressive cuts of the hole.
Wow !!! That is sooo counterintuitive - and really set me thinking . Video saved - I shall definitely revisit this . What a surprise … thank you for making this . I almost can’t get over that This would imply you could strengthen a joist after a plumber has put a pipe through it by drilling extra holes !! I guess in buildings strength may not be the limiting design case however, where absolute deflection under a given load may well be more critical, and indeed must be lower than a prescribed amount so as to prevent damage to attached brittle materials, and the more nadgered a beam is, the more it will deflect (long before failure). Presumably the coupons with extra holes drilled are deforming more for a given load ? Otherwise why wouldn’t all plumbers do this as a matter of course, and more importantly it be built into building regulations ?
Yeah those samples are from the same beam, but they have knots in them and different grain / growth ring alignment, so not much luck with using wood for modelling this complex load situation here. Also confusing how all of the analysis is about tensile load but the testing is done with a bending load, which makes for a hybrid failure. Props for the effort, though I don't know what exactly I can take away from this.
3:50 please do not perpetuate this idea of fluid having to speed up so it's in line with the rest of the flow. It's plain wrong - that does not happen in real life.
Yes you are correct for a real fluid. The assumption is within potential flow theory which makes some crude assumptions, amongst which that the fluid is inviscid, incompressible, and the flow has no vorticity. This results in that conclusion which of course is limited in real life with real fluids.
Turn the oval 90 degrees and place two of them beside two small round holes stacked in the middle instead. basically an inversion of what you were testing. If the goal is to increase strength by removing material strategically, then goal post is beating the non-altered 2x4. None of your tests did that.
And locating a center hole in a beam at midspan is the BEST place to put the hole to reduce the loss of strength. If you locate the hole near the supports, you will see a very dramatic drop in strength.
There is an anekdot. Aircraft designers struggled with the problem of wing strength for a long time. In the end, some drunkard advised drilling holes in the place where the wing was damaged. It helped. When he was asked how he came up with this solution? Easily! Have you seen the perforations on toilet paper? That's where the paper doesn't tear!
At the end of the day the board with no holes in it was still the sturdiest, I can only see this application being used in a situation where you are utilizing used wood that already has holes in it.
Wheres the test on the drilled beam seen in the thumbnail? I'm not sure the term "flow" on a static material when the reaction to the downward force imposed is omni directional radiative with longer or shorter felt-force vector arrows, but it is a fascinating experiment
Joke from Soviet era: Engineers are developing the first soviet supersonic aircraft. But on all prototypes wings keep tearing of the fuselage. Chief engineer Mykoyan stays late in the office but he can't figgure out any solution. A lady cleaning toilets and rooms comes to do her job. She starts clean the floor. When she gets to mr. Mykoyan, she askes why he is there so late, so he explains her his broblem. And she replies: "tha's simple. just dril even spaced holes along the line of break..". So they try and it works. After success, mr. Mykoyan goes quickly to the cleaning lady to give her thanks. Ad he askes how did she came up with such solution. She replies: "Well boy, theese are years of praxis. Look at our soviet toilet paper, see there theese lines of holes - it never breaks there..."
Isn't one of the advantages of the flying buttress? The others are mass reduction, increased distance of load from the base of the building, reduced liquifaction of subsoils, and a graceful aesthetic. Gaudi's cathedral, La Sagrada Familia, Barcelona, comes to mind.
Hi Dylan, I hope you are doing fine bud! It's an interesting question! I guess it would depend on the connection type (i.e. slip-critical or not) but the fact that these holes are not common around bolts probably means that it doesn't work .. I guess? It should work around pipes, cable holes etc. I found this technique in an older book, but it's probably not a very common practice anymore.
Filling holes with bolts to retain cross sectional area is common. Plate friction helps too. If you were really paranoid ( cautious) you could fix steel bushings into penetrations or fix steel flitching across the penetrations.
I don’t see that the strength increased with the addition of holes compared with the original lumber, rather compared with the piece with the first hole drilled into it. And it should be noted that you need to compare strength to weight ratios, as that is really what you’re comparing. Less weight due to more holes drilled - as opposed to the original solid piece, which being heavier, was also stronger.
I think the point is... All real-world construction will require holes in structural elements and thoughtfully placed additional holes may improve the strength.
It would have been interesting to apply topology optimization in the stress analysis to compare the resulting geometry with the optimal fluid flow theory discussed in the video.
I don't say this as often on the YT channel as in my research work, but topology optimization is definitely beyond the scope of thia study 🤣 It is an interesting idea though, but I suspect the gains are too small to be of any practical use given that manufacturing would be expensive.
Comparing the size of the center hole on the first sample and the additional samples: The first hole is obviously taller making the web on the bottom thinner. Not saying that that invalidates the experiment just that you need to have better controls on your experimental set up. Measurements on width of the bottom web. Radius of the notch all of those things can have a big impact on the results. Also flow is not really similar to stress. The top stress is compressive the bottom stress is tensile. Stress in a beam is zero on the center axis. Flow in a pipe is maximum in the center. So flow analogy is a poor representation for stress. By the way I am a retired professional engineer.
Hi Ron, just to address some of your points: 1. I didn't come up with this analogy! I read about it in an older book that related it to a stress reduction technique used in the past. You can read more about the theory in Reference 3: Roark's Formulas for Stress and Strain, Chapter 17.2, page 777. You can easily find a PDF online for free. I thought it's a crazy idea so I decided to test it. The fluid is a potential flow fluid which has no viscosity, so the flow profile is uniform and there is no flow separation, nor vorticity. It's a special fluid but very often used in my research on offshore wave loading. 2. The method is used for tension members specifically not for beams but my home setup does not facilitate tension testing so I had to improvise. The point is to show that removing material can increase the capacity. 3. Of course this is not a peer-reviewed study so the results should be taken with a grain of salt as there is a lot of variation between the samples, they are way too few, and the testing environment is not strictly controlled. 4. Not many holes are elliptical in practice. In theory this should work with circlar holes as well but the capacity gain is probably much less, if any. I used an elliptical hole to make the gains more drastic and hence more interesting for a YT video. I thank you for your lengthy discussion, and it is very much encouraged. Cheers!
I agree with the other commenters, here. The top of the beam is under compression and the bottom is under tension.... The flow analogy almost needs to be like a source at the top and a sink at the bottom. 🤔
So, are the holes, if we are to take the results on face value, redistributing the stress in the material so that while they take away from the overall capacity to take load, because the beam is already compromised in a very specific area, they move stress away from the point where it will inevitably fail first?
Interesting analogy, I didn't know this approach. Would the beam perform better or worse if the holes were drilled near the bottom instead of the center?
This makes me think about how some people would drill holes into the frame of their BMX bike to make it lighter at the cost of it being easier to crumple under weight. With this, there should be specific areas on the tube that would benefit from losing mass and actually improve structure strength. Neat.
Why cut a rough leaf shape in the beam (creating internal notches) and call it elliptical. There is so much variation in the 'ellipses' cut in each beam that the results are completely useless for comparison purposes. Not to mention the tiny sample size used for a product with such a high degree of natural variance.
Interesting. I would like to have seen multiple tests with a single hole and with no holes just like you did with the last 3 samples to get more normalized baselines.
So a whole board has minimal stresses, a board with a single large hole has stress, and a board with strategically placed holes can minimize the stress of surroundng features.
Thanks for this interesting video and the great analogy. Yet, I am a little bit confused by how the shape of the obstacle should reduce the velocity around it. Given than flow J is equal to velocity v times cross-section area A, the only thing that should matter for the maximum velocity of the liquid (i.e. the maximum stress of the material) is how much wood is left around the hole. Any flaws in my reasoning?
Realize, you can determine that of course there are cases where this works with very basic logic, without even cutting anything. Initial hole creates stress concentration areas, some of that tension pulls at the hole causing the initial failure point. Other holes further out can disconnect some of the tension from fibers pulling at those stress concentration areas, rerouting the stress and making it somewhat less concentrated at that initial failure point, making it fail at a higher total stress. Initial hole = loss, further holes can redistribute loading and can gain back some of the loss by distributing the loading better than only the initial hole did. The difference should be relatively marginal. Can all be worked out without testing or drawing anything.. And of course your 'flow' idea later in the video is basically the same idea. Realize the flowing shape is basically 'disconnect all of the horizontal long fibers in this pattern'. You're essentially turning the smaller bad main hole into a larger hole that is simply discontinuous. You could basically just cut out that larger, better shaped hole instead of multiple small holes.
So the takeaway is, that you shouldn't put a hole at all in beams under tension. But if you have to, make the area around it weaker also. Crazy chaotic video on so many levels. 😅 I have to forget about this now and go back to my workbench.
Why would pressure you’re applying be 90 degrees different to the flow lines? Would the flow lines not be representative of the downward force and therefore need to be aligned with the force direction? The video didn’t mention the discrepancy which makes it all not make sense and seem like either a mistake or an important detail glossed over.
As stated in the video, the flow lines are analogous to the stress lines. From beam theory, it is well known that when loaded with a perpendicualr force, the top of the beam is in compression, and the bottom of the beam is in tension. Although not uniform as in a uniaxial case, the flexural stress lines run along the length of the beam as the fluid lines would.
Yes. But the holes have to be in the same location as static load nodes are. However, making extra holes is not a good approach with transient loads. Wind and snow transients usually defy the benefits on building construction applications.
@wildguardian you are right, that was the idea. The holes were easier to produce consistently with the same diameter and location. Cutting out a horizontal ellipse would have been subjected to my imperfect cutting skills
I wonder if a more elastic material would be less subject to this effect than a morr brittle material - able to elastically redistribute load without the extra holes, reducing stress concentration points.
Without multiple test of sample one and two it does not make the samples three, four and five very convincing. Wood being a natural product means there are lots of inconsistencies in it's strength even pieces from the same board because of knots and variations in growth rings that could have been caused by injury to the tree while growing or any number of other factors. Besides the oval holes where inconsistent which would have stressed the board differently for each test.
isnt that the same reason sharp edges are not allowed on high stress components like aircraft landing gear?like a variant of the same theory but instead of rounding the cut external edges , we are rounding the inner holes..a mirror image of the stress distribution
@jeetenzhurlollz8387 yup, I believe the reasoning is the same, just a slightly different way to explain it. In fact, the equations solved to analytically determine the concentration factor are actually very close to the potential flow equations. These topics are definitely related. Cheers!
interesting results, what is clearly visible is that sample 2 failed differently than 3,4,5. 2 might have just been a bad sample or the different failure mode is really because of the extra holes?🤷. even though the setup is not perfect I respect you for trying it out, what i dont like is the short length of the beam, because it clearly impacts the results of 3,4,5,(1?)
Misleading title when all the drilled wood fails over 100 pounds before the default 2x4. Although the strength increase you bring to our attention is intriguing physics.
4:08 "have to enter and exit at the same time" - no, they do not have to. That's a well-known mistake, it also appears in a wrong explanation for the lift force. They do not have to take same time. For example, the separator line that goes through the stagnation point takes infinite time to pass the stagnation points. And the closer you are to the separator the longer the delay. The correct statement is that the incoming flow is equal to the outgoing flow (measured in m³/s and for an incompressible stationary flow).
@alexeykrylov9995 you are correct, that is the case in a real life model. But in a potential flow model where the fluid has no viscosity (hence no shearing forces), no vorticity, and is incompressible, that same time statement also holds.
The conclusion in my opinion is wrong for all the listed parts by the other commentators. 1.) The material under test is non-homogenous 2.) the cutouts are different, thus the stress concentration points are different 3.) Flow can be used as an analogy only for easier understanding, otherwise it has no relevant similarity. The forces in flow diverging around a corner and the stress/strain concentration have no common ground. The only thing relevant in this whole video is that you can reduce the overall weight of the beam by removing material and still retain the majority of the load capacity. This is only due to the cross section. Cross section at the loaded points is the only thing you need to focus on. The rest is just nonsense.
Im assuming that the test might have been better if the oval shape was perfectly cut and not hacked out? U left sharp edges on the internal curve which should have had a perfect radius and not jagged edges. Maybe drill holes at the top and bottom of the oval to start the shape with nice radiused shapes?
I will be honest. I am not an engineer. I just don’t see how flow dynamics, in a piece of wood, perpendicular to where the stress is applied affects the strength of the beam. Even if a beam with multiple holes is stronger than a beam with a single hole. I would think it would work more like a tiered fountain than a wing or a wedge. I sorta get what you’re saying, maybe? Flow dynamics can be similar to the redistribution of stress from an area of lesser material to an area with more material by creating smaller areas of stress as long as the material is laminated like wood?
The stress is not parallel to the load application direction in this case. In fact, the stress direction is longitudinally along the beam's length this is from beam theory. The top of the beam is in compression and the bottom is in tension. It is not the same as a purely tensile test but it is similar. My home testing setup does not facilitate tensile testing so I had to improvise.
If you have variation of 12% within the same sample type - how can you assume that initial 6% difference with - one hole sample type - was somehow more signifiant?
So in summary, if you HAVE to drill a hole through the middle of a wooden member, add relief holes. Otherwise, just don't touch it and you will get the strongest load.
The drill holes looks like the Adamas epaulet sound holes on the top of Ovation guitars. Just an observation but somehow there's a parallel with this video because of "flow".
The point is that if the hole already exists (say because of pipes, cables, ventilation, etc) then you could improve the capacity by drilling holes. Of course no one is saying that you should just drill holes in your beams for no reason.
@@TheEngineeringHub Most of the comments are missing the point. If I wanted to nit pick I would demand you compare structural pine with aircraft spruce.
Why not drill circular holes for uniformity? Also, what about a single circular hole off center? It is a common rule of thumb that holes near or at the edge weaken the beam the most
Just to address some of the repeating comments:
1. I didn't come up with this analogy! I read about it in an engineering book that related it to a stress reduction technique used in the past. You can read more about the theory in Reference 3: Roark's Formulas for Stress and Strain, Chapter 17.2, page 777. I thought it's a crazy idea so I decided to test it. I uploaded the PDF for you here: drive.google.com/file/d/1JE9jCCAGj7MGXMqZQSjOo8KS8XlC5y4D/view?usp=sharing
2. Yes, the method is used for tension members specifically not for beams but my home setup does not facilitate tension testing so I had to improvise. The point is to show that removing material can increase the capacity.
3. Of course this is not a peer-reviewed study so the results should be taken with a grain of salt as there is a lot of variation between the samples, they are way too few, and the testing environment is not strictly controlled.
4. Not many holes are elliptical in practice. In theory this should work with circlar holes (cables, pipes, ventilation, etc) as well, but the capacity gain is probably much less, if any. I used an elliptical hole to make the gains more drastic and hence more interesting for a YT video.
I encourage the comments pointing things out, this is great! I like the idea of community notes, I hope it comes to YT as well. Cheers!
Yes the algorithm favours elliptical holes. That's bizarre.
Thanks for the effort you put into creating your video, and then providing a lovely comment reply summary.
Thankyou for the practical tutorial Guru.🙏
Any experiment with wood is going to require a lot more samples to be remotely accurate. You ran your hole-less and single hole samples once? That's not going to cut it, teeheehee. I can see how the relief holes can help in theory, though I imagine the effect will be quite small. Intuitively I expected there to be no significant difference, certainly not detrimental, between the relief holes and the single hole samples since the point of failure is either going to be the top of the board under compression or the bottom under tension. The middle of the board is not under much stresses. This is why you can cut giant holes out of the middle of engineered I-joists without effecting strength significantly.
I’m not an engineer so a video like this is fascinating to me. I would never have thought that removing further material could increase strength. Thanks for make it.
I would not apply a theory for a isotropic materials for anisotropic materials like wood.
Hello, I am a Timber Engineering faculty member at Virginia Tech. You make some good points, but you there are some probems with your content. First, your model is not the same as your experiment. Beams do not have a uniform tension force. They have a triangular stress distribution where the moment is greatest at the center and typically tension failure is dominant in brittle/semi-brittle materials like wood. I also have issues with your sampling of wood. Saying short samples from the same 2x4 have similar performance is not correct. Strength of wood is dominated by the placement of defects like knots. Locating knots in different places can radically change the strength. I also think you have a flaw in your sampling. Typically, 10-15 pieces are tested for material properties and more for connections / special cases. The flow idea is fine, but I think it is more of a visualization concept. I'm not sure if it is linked to fracture energy, which has the same idea of a more rounded curvature to prevent failure.
Hi Daniel, your points are 100% granted. I am currently completing a PhD in structural dynamics and wave loading at Aarhus Univeristy. I don't have a tensile experimental setup at home, so I had to improvise. The flow analogy is far from perfect, in fact, it's flawed and it works only in very special cases. But don't worry, I know my beam mechanics very well. The concept is from the theory in Reference 4: Roark's Formulas for Stress and Strain, Chapter 17.2, page 777.
@@TheEngineeringHubyou’re a PhD candidate and haven’t figured out sample sizes yet? From the numbers you displayed as conclusive didn’t seem to show any statistical difference with or without the holes. It’s wood. The variations in wood for strength are larger than the margins you declared as significant.
@ClAddict they are not significant by any means, I stated that in the video. More testing is required. Theoretically, this holds water, experimentally, more work is required to prove it.
@@ClAddict Dude, he's just using some demo's. He's not trying to get a paper published. Take a chill pill.
@@michaellowe5558 I agree he should chill out but to be fair the video does say "confirming the effect" around 6:20 which is statistically unsubstantiated with 1 control and a couple of test samples.
Why did you demonstrate potential flow theory on a beam loaded in tension when your test is a beam with a transverse point load? They're separate loading conditions that require different analysis. Furthermore why didn't you repeat your initial test multiple times? Wood can vary significantly in strength so using only a single point of reference does not make for an accurate test
well if you think about it, the bottom of the cut is breaking in tension, so you're right, its not a very good test to demonstrate the principle in tension, but the bottom 50% is kinda ok. although its still being pushed perpendicularly like you say
its just a demo relax
@@user-lo4me9oe9z it's a demo that doesn't illustrate the concepts being discussed
The variance is already exceedingly apparent by the numbers 1929, 2010, 2140. I don't know how anyone can think 1820 is definitely significant and not a fluke.
@@passerby4507 especially with only one data sample
Wood is far from an ideal material for these tests, since it is grained and also nonhomogeneous. For a more sound experiment you would have to repeat the test many times due to the variation in grain patterns. Since the model (beam under tension) differs from the experiment (bending load), preferable would be a more homogeneous brittle material under tensile load, such as concrete made with small aggregate. Also good to know is that ductile materials are not affected by (static) stress concentrations, since they deform locally at the site of concentration and redistribute the stress evenly throughout the zone. A ductile beam with a notch or hole is weaker, but only because of the lack of material. Smoothing out sharp curves and corners won't strengthen them in the same way it does for brittle materials, at least under static loads. I really liked your video and I think it would be really cool if you made another one that shows the effect for ductile vs brittle materials.
Exactly, cutting the grains doesn't magically distribute load to adjacent ones.
He should have used 3d printed pieces or molded cement/epoxy if CNC metal is cost prohibitive.
Interesting idea, though your slit in the first beam has a lot sharper edges (cat eye shape) than the ovals in the following 3 cases. Also given that you shared stress model for the single opening, it would be nice to see what your modelling software predicts. As for the conclusions, note that your intra-sample variability ( 1929~2140kg) are consistent with standard wood variation and rend the results of your experiment inconclusive. Finally note that the top fibers being crushed before you reach failure mean you are observing variability in wood fibre separation ( delamination ) rather than stress propagation. I am looking forward to seeing a followup, keep up being curious ^_^
I was thinking similarly; that a more accurate or at least predicable/consistent test would be to use vertical slits with varying heights, but a consistent width and top/bottom radii, the lowest height being equal to 2xr.
I agree. I found it interesting that a sample of 3 was used for the condition with many holes but a sample of 1 was used for both the control (unaltered wood) and the first test condition with one hole. Given that wood is not homogeneous, I would have liked to see all of the conditions tested several times. Although, I understand that this was more of a demonstration of the theory, it would be more convincing if the average failure load was used for each condition. As a hobby wood worker, I can tell you that even within the same piece of wood the grain pattern can change dramatically and the presence of a knots is essentially the same as a hole in the wood in terms of the stress lines travelling through the wood. Nonetheless, I found your explanation of water flow as an analogy to stress fascinating. I always like to be able to visualize processes and this will help immensely.
The pointiness of the hole isn't really relevant. In this context at least general dimensions being similar is all that's needed. Consider arches, gothic and Tudor arches both come to a point yet the point of failure is not the apex or keystone.
@@edwardarkwright7116 The failure we are talking about is not that of compression, though (the top of the arch), it is of tension. Think of tension failure like a knife cutting through fibers. She sharper the edge, the more concentrated the shearing force that actually parts the material. I can hang a thousand pounds on sturdy rope tied to a 1" round bar, but only ten or twenty pounds if that same rope is tied to an upward facing dull blade. It can support less and less weight as the blade sharpness increases. Hanging a rope on f fresh surgical scalpel might even sheer through the rope under its own weight.
@@fxm5715 if we read the original comment, the critique was over the shape of the removed material. We both agree it is a matter of tension. We both know that if the crossection of a member contains the same area as another, regardless of shape the bearing load in regards to tension is very similar. In that way your comment I fail to see as relevant
Please normalize your audio. Loud bangs and your quiet voice do not make for a comfortable listening experience
It's a video about wood breaking, not a bedtime story
Really, is that the best gripe you can do on a truly informative piece of work?
@@scotttoner9231 No
The click baity title is also unprofessional and unnecessary
Might not be just him. Something weird seems to be going on with audio on YT lately. I've had to jack up the volume on some channels I've sub to for years only to get blasted on the next video.
@@Humble_Merchanthow in the literal fuck is it a clickbait title? He tested the wood and posed a question, which he answered in the video?
I am not sold. Wood is ridiculous for it's inconsistency. To make it at least somewhat scientific you would need to make more than one test with just one hole. Even better: use a solid such as engineered plastic or something.
Yeah, but wood has specific grain pattern/structure. I don't think plastic would be analogues to wood even if it's printed in a way to become similar to wood.
It's just my intuition, I wouldn't mind to be proven wrong.
@@bezceljudzelzceljsh5799so don't use a printed polymer...
Solid rod is weaker than hollow pipe. If you put a tight fitting steel bearing into a hollow pipe, the pipe will bend near the bearing, the ball bearing not allowing the pipe to deform slightly in a uniform way makes it weaker than the completely hollow pipe. Then, think of a solid rod as a pipe with bearings all the way through it, imagine overlapping bearings in the core.
This is a known thing, and much more often mentioned with the pipe example etc. Of course the hollow pipe has to have non-weak wall thickness, etc so there are limits, but it is the general idea of why.
The theory is sound, even if he had used metal or homogenized plastic the result would have been the same.
It's not that it actually increases strength per se, just that it decentralizes stress points across a larger part of the material. This principle is used daily in engineering; you have to brace any part so that forces are not focused in any one spot. To that end, sometimes removing material can help as much as adding it.
@@kireduhai9428 right I didn't dispute the theory. All I was saying the experiment isn't worth a damn. But if we want to pick on the theory, shouldn't the maximum bending stress be in the middle, where the cross-section is constant (hopefully) from test to test? What I am saying is while all these additional holes are surely not making it any weaker, all they are actually doing is reducing the weight.
6:38
"The flow analogy holds some weight".
I just can't stress enought the pressure this creator channels at the audience.
What that also says, is that for construction, 2x4 timber is far stronger than you might imagine when supported correctly and that holes for pipes, cables etc don't necessarily weaken it that much.
Good explanation and I found the audio to be just fine.
Many thanks.
@@andrewclarkehomeimprovement yup, agreed 👍
Your loading doesn't match you stress analysis. So tell me again how you can increase tensile strength by reducing the section?
The tensile strength isn't increased. The tensile peak loadings within the distressed element are reduced.
Practical tensile strength is increased....but not for the entire section. Remember we are comparing against section with center slot and section with center slot and extra holes to smooth the flow. This reduces the risk of failure emanating from the peak load points. I.e. we are making the material behave more uniformly, though theoretical tensile strength in a uniform material won't change.
Very intersting to use fluid dynamics to evaluate load stress. Very cool comparison
Horizontal shear is a failure mode most common on short, deep, heavily loaded beams (bending members). Round holes can relieve the strain paths. Holes with reentrant corners are crack propagation points in any material.
Very good job, sir! Forwarding this to our undergraduate engineering professors. Understand the limitations, and it’s great that you used your own time and materials to do something so useful for students.
Really like the fluid flow analogy.
The flow analogy socks. The top half of the beam is in compression and the bottom half is in tension. The neutral axis has no load. Stress is proportional to the distance from the neutral axis.
I think some are being overly critical in the comments. Yes the experiments would have to be a lot more detailed to have scientific validity, but the overall conclusion is correct. Also, although technically the wood failed first at the press contact point by delamination, we were still able to see the failure on the tension side of the wood block.
The stress flow evidently is much different from the examples given, as this is a bending load. However, this was addressed in the video and it still holds that the ellipse concentrates stresses on it's sharp edges, and that the holes may help distribute the flow more evenly
My takeaway was that the main point of this video is to show the counterintuitive result that taking away material can make the structure stronger, which is absolutely correct. And i believe it's not reasonable to expect a super detailed experiment on a simple youtube video like this. The use of potential flow as a theoretical justification for why this works is also correct, even if the loading condition isn't the same. And the experiments illustrated your point even if they weren't perfect. I enjoyed this video a lot!
I think its also important to say that this does not suggest that adding these holes is optimal or good or desired in a real structure. Real structural solutions often have better ways of reducing stress concentrators. This result, however, does show up a lot in real life -- not by intentionally removing material to make a structure stronger, but by adding material and unintentionally making a structure weaker -- engineers need to be aware of this kind of thing
The guy is just absolutely wrong. It is 'counterintuitive' just because his explanation is wrong! He has variation in results because of different structure of wood in these beams, it's nothing to do with the additional holes! I'm surprised how many people here write positive comments, this is how you do false science.
>the main point of this video is to show the counterintuitive result that taking away material can make the structure stronger, which is absolutely correct.
Absolutely not.
Great video mate. It looks like the first piece of wood had a knot that definitely would have aided in the strength through the center of that piece. Wood knots are incredibly strong. So much so that a block splitter won't go through it. Great video mate i really enjoyed it 🤙
Interesting. You had me there though. I originally thought you were going to propose, that a beam with relief voids was going to be structurally stronger than a solid beam.
For anyone who is going to point out the cost weight benefits of non-solid beams. Yes, I know, I have the ability to look at cranes, bridges and aircraft wings.
This information would be useful for determining the impact of drilling holes for routing pipes, wiring or other needs to drill into beams.
5:49 that 6% change is not even half of the random variabilitybin strenght of that kind of wood, and basically mean nothin at all
Top quality 👌 really cool analogy and I love the new style with bench testing. Keep it up!
🙏🙏🙏 more to come
The consideration at 3:50 is wrong and it is often done on wing profiles. There is no reason for a particle to speed up exactly to cover the same horizontal distance, there is of course an increase in speed, but not to that value.
This is what I was going to say. My understanding is that the speedup happens due to the in compressibility of the liquid forcing it to go faster since it has a smaller section to pass through.
6:37 the flow analogy definitely holds some weight!! Good one!!!!!!
When I saw the thumbnail I instantly thought of Gothic cathedrals and how arches distribute load.
I agree with a lot of comments the tests need a lot of improvement, but the fact you brought up the idea which under heavy scrutinized research by experts could lead to better wood manipulation in the real world in the future.
As a starting point for discussion on further experimental development, this video did just that.
Guitar builder here. I always wondered about this when making transverse struts that would bear the load of the string pressure on the bridge. That part of the guitar top, which acts as an monopolar oscillating plate supported by beams, needs to bear load (about 80 lbs) but also be as lightweight as possible (unsprung mass?). Could this be an improvement? I guess an experiment is about to be born.
I'm a physicist by nature, but this engineering is fascinating. Subscribed 🙂
@Doomquill Thank you, sir 🙏
Wow that’s amazing insight, very counter intuitive but brilliantly shown, well done.
That is pretty cool, thanks for sharing. Charles
We need to consider this material, wood, is a composite structure, and have different properties depending on the direction. A test with metallic will be interesting.
The same idea is very important in the fatigue design of parts. Where comparingly small decrease in peak stress can increase lifetime several times. I had a patent application with this idea in the construction industry for fatigue sensitive parts.
Similar patent using hybrid materials to arrest crack growth that's now standard materials design for aerospace and high temperature composites.
I like engineering I can understand without resorting to mathematical notation that I have never understood.
Because of that, I subscribed which is something I have never done before until I see multiple video's
If anyone has ever seen what electricians do in order to run cable then you would know that single holes are drilled through many studs and joists in your house (assuming that it's made of wood). 😅 If relief holes accompanied said holes then you would have a stronger structure. 🤷 I think it's at least a cool concept. Thanks for sharing ✌️
In terms of a video, I think it would have made the point better if you started with the hole in the middle. Otherwise we are sitting through the whole video expecting it to increase the strength relative to the whole beam.
no, cause the answer should be obvious from the beginning - whole beam should be the winner in most cases, if no defects in the beam
I think the point is... All real-world construction will require holes in structural elements and thoughtfully placed additional holes may improve the strength.
You did a great job on this video and obviously put a lot of work into it. Nice! Don't get caught up in everyone correcting things. They tend to do that on the internet.
@@DoctorRustbelt 🙏🙏🙏🙏
The artistic potential is crazy with this
5:51 - 5:59 Than you. "Natural variability in the wood" was my first thought.
Thanks for making this video.
The results rely on the crushing snd failure of the wood before the final force measurement. In a solid plank the crushing force causes a long crack through the bulk. In a plank with a hole the crack only propogates to the edge of the hole and the bulk is compressed which makes it stronger in failure. In some cases the void can allow the bulk to act like a lever, spring, or damper. This design would be excellent in something like a bench since the failure mode can take more load after deflection, softening the impact to users.
So! Use a bigger plate!!!!
Since there aren't two equal pieces of wood, isn't three samples a very low quantity to state a general conclusion? With more samples, you can use statistical methods to verify if these variations are relevant or not.
Your experiment is absolutely incorrect. 1) You make the big hole differently every time 2) Different beams are different in load capacity because it's wood 3) Only 1 beam tested with no holes and with one big hole.
Although the explanation is a bit shakey, the clip demonstrates that strategically removing material may indeed strengthen beams under certain conditions.
@@evdl3101nope, cutting a hole in a member reduces its cross sectional area making it weaker.
Exactly. Do this 100 times, with identical holes. Basing results on a single beam of wood is kind of ridiculous.
@@evdl3101even his test didn't show that. At best it showed that if you already have a hole, then you can strengthen it with a couple of strategically placed relief holes.
@@kinnikuzeroYou missed the point. Between the two cases of interest, 1) elliptical hole and 2) elliptical hole+side holes, the cross section was the same.
You don't have to convince us that a hole makes member weaker than a solid member. That we know. Video author also showed that in the very beginning.
okay, thanks for the info! I'm running right now to drill as many holes as I can on my apartment building support beams!
Pretty much one of the first optimizations we did in structures class, a cantilevered wing spar with distributed load.
Excellent use of the word "comprise"!
I don't need to finish watching this video to know this is wrong. Your hack job on cutting the holes is a good representation of your experiment.
🤦♂
Please test this again with better holes. Your main holes are uneven and crude, and act as shear propagation points. If you do not have the tools to make a smooth oval hole in one go, file down the edges and cuts until the hole is smooth. That should significantly reduce the chance of the wood breaking at the most aggressive cuts of the hole.
Nicely done!
Wow !!! That is sooo counterintuitive - and really set me thinking .
Video saved - I shall definitely revisit this . What a surprise … thank you for making this .
I almost can’t get over that
This would imply you could strengthen a joist after a plumber has put a pipe through it by drilling extra holes !!
I guess in buildings strength may not be the limiting design case however, where absolute deflection under a given load may well be more critical, and indeed must be lower than a prescribed amount so as to prevent damage to attached brittle materials, and the more nadgered a beam is, the more it will deflect (long before failure).
Presumably the coupons with extra holes drilled are deforming more for a given load ? Otherwise why wouldn’t all plumbers do this as a matter of course, and more importantly it be built into building regulations ?
Yeah those samples are from the same beam, but they have knots in them and different grain / growth ring alignment, so not much luck with using wood for modelling this complex load situation here. Also confusing how all of the analysis is about tensile load but the testing is done with a bending load, which makes for a hybrid failure.
Props for the effort, though I don't know what exactly I can take away from this.
3:50 please do not perpetuate this idea of fluid having to speed up so it's in line with the rest of the flow. It's plain wrong - that does not happen in real life.
Yes you are correct for a real fluid. The assumption is within potential flow theory which makes some crude assumptions, amongst which that the fluid is inviscid, incompressible, and the flow has no vorticity. This results in that conclusion which of course is limited in real life with real fluids.
@@TheEngineeringHub No, even within potential flow theory it is wrong.
Turn the oval 90 degrees and place two of them beside two small round holes stacked in the middle instead. basically an inversion of what you were testing.
If the goal is to increase strength by removing material strategically, then goal post is beating the non-altered 2x4. None of your tests did that.
You’ve imagined a conclusion that was never intended.
And locating a center hole in a beam at midspan is the BEST place to put the hole to reduce the loss of strength. If you locate the hole near the supports, you will see a very dramatic drop in strength.
There is an anekdot. Aircraft designers struggled with the problem of wing strength for a long time. In the end, some drunkard advised drilling holes in the place where the wing was damaged. It helped. When he was asked how he came up with this solution? Easily! Have you seen the perforations on toilet paper? That's where the paper doesn't tear!
At the end of the day the board with no holes in it was still the sturdiest, I can only see this application being used in a situation where you are utilizing used wood that already has holes in it.
Wheres the test on the drilled beam seen in the thumbnail?
I'm not sure the term "flow" on a static material when the reaction to the downward force imposed is omni directional radiative with longer or shorter felt-force vector arrows, but it is a fascinating experiment
Joke from Soviet era: Engineers are developing the first soviet supersonic aircraft. But on all prototypes wings keep tearing of the fuselage. Chief engineer Mykoyan stays late in the office but he can't figgure out any solution. A lady cleaning toilets and rooms comes to do her job. She starts clean the floor. When she gets to mr. Mykoyan, she askes why he is there so late, so he explains her his broblem. And she replies: "tha's simple. just dril even spaced holes along the line of break..". So they try and it works. After success, mr. Mykoyan goes quickly to the cleaning lady to give her thanks. Ad he askes how did she came up with such solution. She replies: "Well boy, theese are years of praxis. Look at our soviet toilet paper, see there theese lines of holes - it never breaks there..."
😂
At end supports vertical shear stress higher .
In center 90% of stress is in outer fibers .
Isn't one of the advantages of the flying buttress? The others are mass reduction, increased distance of load from the base of the building, reduced liquifaction of subsoils, and a graceful aesthetic. Gaudi's cathedral, La Sagrada Familia, Barcelona, comes to mind.
It's not counter-intuitive. You spread the stress over a larger area, so you reduce it at the weakest point. It actually makes sense
Interesting counterintuitive results! I wonder if this would work the same if the initial hole was filled by a bolt to attach another member.
Hi Dylan, I hope you are doing fine bud! It's an interesting question! I guess it would depend on the connection type (i.e. slip-critical or not) but the fact that these holes are not common around bolts probably means that it doesn't work .. I guess? It should work around pipes, cable holes etc. I found this technique in an older book, but it's probably not a very common practice anymore.
Filling holes with bolts to retain cross sectional area is common. Plate friction helps too.
If you were really paranoid ( cautious) you could fix steel bushings into penetrations or fix steel flitching across the penetrations.
I don’t see that the strength increased with the addition of holes compared with the original lumber, rather compared with the piece with the first hole drilled into it. And it should be noted that you need to compare strength to weight ratios, as that is really what you’re comparing. Less weight due to more holes drilled - as opposed to the original solid piece, which being heavier, was also stronger.
I think the point is... All real-world construction will require holes in structural elements and thoughtfully placed additional holes may improve the strength.
It would have been interesting to apply topology optimization in the stress analysis to compare the resulting geometry with the optimal fluid flow theory discussed in the video.
I don't say this as often on the YT channel as in my research work, but topology optimization is definitely beyond the scope of thia study 🤣 It is an interesting idea though, but I suspect the gains are too small to be of any practical use given that manufacturing would be expensive.
Comparing the size of the center hole on the first sample and the additional samples: The first hole is obviously taller making the web on the bottom thinner. Not saying that that invalidates the experiment just that you need to have better controls on your experimental set up. Measurements on width of the bottom web. Radius of the notch all of those things can have a big impact on the results. Also flow is not really similar to stress. The top stress is compressive the bottom stress is tensile. Stress in a beam is zero on the center axis. Flow in a pipe is maximum in the center. So flow analogy is a poor representation for stress. By the way I am a retired professional engineer.
Hi Ron, just to address some of your points:
1. I didn't come up with this analogy! I read about it in an older book that related it to a stress reduction technique used in the past. You can read more about the theory in Reference 3: Roark's Formulas for Stress and Strain, Chapter 17.2, page 777. You can easily find a PDF online for free. I thought it's a crazy idea so I decided to test it. The fluid is a potential flow fluid which has no viscosity, so the flow profile is uniform and there is no flow separation, nor vorticity. It's a special fluid but very often used in my research on offshore wave loading.
2. The method is used for tension members specifically not for beams but my home setup does not facilitate tension testing so I had to improvise. The point is to show that removing material can increase the capacity.
3. Of course this is not a peer-reviewed study so the results should be taken with a grain of salt as there is a lot of variation between the samples, they are way too few, and the testing environment is not strictly controlled.
4. Not many holes are elliptical in practice. In theory this should work with circlar holes as well but the capacity gain is probably much less, if any. I used an elliptical hole to make the gains more drastic and hence more interesting for a YT video.
I thank you for your lengthy discussion, and it is very much encouraged. Cheers!
I agree with the other commenters, here. The top of the beam is under compression and the bottom is under tension.... The flow analogy almost needs to be like a source at the top and a sink at the bottom. 🤔
So, are the holes, if we are to take the results on face value, redistributing the stress in the material so that while they take away from the overall capacity to take load, because the beam is already compromised in a very specific area, they move stress away from the point where it will inevitably fail first?
Interesting analogy, I didn't know this approach. Would the beam perform better or worse if the holes were drilled near the bottom instead of the center?
"european sized 2 by 4"
brain cells have left the room...
Codes limit holes to be maximum 1/3 of the total depth. Its also tricky without lots of tests to prove as wood is anisotrophic.
That’s really interesting, I guess the holes let the wood flex more which increases the fracture threshold
This is an excellent video.
How about the wood distribution strenght? All the wood surely have different fiber patern... does it have effect?
This makes me think about how some people would drill holes into the frame of their BMX bike to make it lighter at the cost of it being easier to crumple under weight. With this, there should be specific areas on the tube that would benefit from losing mass and actually improve structure strength. Neat.
So the releaf holes make it so compression and tension forces spread evenly on the remaining material?
I think that's a good way of thinking about it! Great point!
Interesting, but why make an elliptical hole when 99.9% of the time the shape cut through a beam is gonna be circular?
Why cut a rough leaf shape in the beam (creating internal notches) and call it elliptical.
There is so much variation in the 'ellipses' cut in each beam that the results are completely useless for comparison purposes.
Not to mention the tiny sample size used for a product with such a high degree of natural variance.
To show how v-shape cutout resists tear force with and without additional flex cutouts.
It will make the effect more pronounced. A circular hole is more "aerodynamic" than the elliptical one so will concentrate stresses less.
Interesting. I would like to have seen multiple tests with a single hole and with no holes just like you did with the last 3 samples to get more normalized baselines.
So a whole board has minimal stresses, a board with a single large hole has stress, and a board with strategically placed holes can minimize the stress of surroundng features.
Dude, do more testing please
Thanks for this interesting video and the great analogy. Yet, I am a little bit confused by how the shape of the obstacle should reduce the velocity around it. Given than flow J is equal to velocity v times cross-section area A, the only thing that should matter for the maximum velocity of the liquid (i.e. the maximum stress of the material) is how much wood is left around the hole. Any flaws in my reasoning?
Realize, you can determine that of course there are cases where this works with very basic logic, without even cutting anything. Initial hole creates stress concentration areas, some of that tension pulls at the hole causing the initial failure point. Other holes further out can disconnect some of the tension from fibers pulling at those stress concentration areas, rerouting the stress and making it somewhat less concentrated at that initial failure point, making it fail at a higher total stress.
Initial hole = loss, further holes can redistribute loading and can gain back some of the loss by distributing the loading better than only the initial hole did. The difference should be relatively marginal. Can all be worked out without testing or drawing anything..
And of course your 'flow' idea later in the video is basically the same idea. Realize the flowing shape is basically 'disconnect all of the horizontal long fibers in this pattern'. You're essentially turning the smaller bad main hole into a larger hole that is simply discontinuous. You could basically just cut out that larger, better shaped hole instead of multiple small holes.
So the takeaway is, that you shouldn't put a hole at all in beams under tension. But if you have to, make the area around it weaker also.
Crazy chaotic video on so many levels. 😅
I have to forget about this now and go back to my workbench.
Why would pressure you’re applying be 90 degrees different to the flow lines? Would the flow lines not be representative of the downward force and therefore need to be aligned with the force direction? The video didn’t mention the discrepancy which makes it all not make sense and seem like either a mistake or an important detail glossed over.
As stated in the video, the flow lines are analogous to the stress lines. From beam theory, it is well known that when loaded with a perpendicualr force, the top of the beam is in compression, and the bottom of the beam is in tension. Although not uniform as in a uniaxial case, the flexural stress lines run along the length of the beam as the fluid lines would.
Yes. But the holes have to be in the same location as static load nodes are. However, making extra holes is not a good approach with transient loads. Wind and snow transients usually defy the benefits on building construction applications.
Well since all the holes grouped together are a horizontal elipse why didn't you trid eliptical horizontal holes?
@wildguardian you are right, that was the idea. The holes were easier to produce consistently with the same diameter and location. Cutting out a horizontal ellipse would have been subjected to my imperfect cutting skills
I wonder if a more elastic material would be less subject to this effect than a morr brittle material - able to elastically redistribute load without the extra holes, reducing stress concentration points.
Without multiple test of sample one and two it does not make the samples three, four and five very convincing. Wood being a natural product means there are lots of inconsistencies in it's strength even pieces from the same board because of knots and variations in growth rings that could have been caused by injury to the tree while growing or any number of other factors. Besides the oval holes where inconsistent which would have stressed the board differently for each test.
isnt that the same reason sharp edges are not allowed on high stress components like aircraft landing gear?like a variant of the same theory but instead of rounding the cut external edges , we are rounding the inner holes..a mirror image of the stress distribution
@jeetenzhurlollz8387 yup, I believe the reasoning is the same, just a slightly different way to explain it. In fact, the equations solved to analytically determine the concentration factor are actually very close to the potential flow equations. These topics are definitely related. Cheers!
the additional holes made it stronger vs the one hole, but they were all weaker than the beam WITHOUT holes.
interesting results, what is clearly visible is that sample 2 failed differently than 3,4,5. 2 might have just been a bad sample or the different failure mode is really because of the extra holes?🤷. even though the setup is not perfect I respect you for trying it out, what i dont like is the short length of the beam, because it clearly impacts the results of 3,4,5,(1?)
One can be stronger if the pieces were already different before you drilled the first hole.
Misleading title when all the drilled wood fails over 100 pounds before the default 2x4.
Although the strength increase you bring to our attention is intriguing physics.
The flow analogy holds some weight, indeed.
BRB drilling holes in my basement joists.
4:08 "have to enter and exit at the same time" - no, they do not have to. That's a well-known mistake, it also appears in a wrong explanation for the lift force. They do not have to take same time. For example, the separator line that goes through the stagnation point takes infinite time to pass the stagnation points. And the closer you are to the separator the longer the delay. The correct statement is that the incoming flow is equal to the outgoing flow (measured in m³/s and for an incompressible stationary flow).
@alexeykrylov9995 you are correct, that is the case in a real life model. But in a potential flow model where the fluid has no viscosity (hence no shearing forces), no vorticity, and is incompressible, that same time statement also holds.
The conclusion in my opinion is wrong for all the listed parts by the other commentators. 1.) The material under test is non-homogenous 2.) the cutouts are different, thus the stress concentration points are different 3.) Flow can be used as an analogy only for easier understanding, otherwise it has no relevant similarity. The forces in flow diverging around a corner and the stress/strain concentration have no common ground. The only thing relevant in this whole video is that you can reduce the overall weight of the beam by removing material and still retain the majority of the load capacity. This is only due to the cross section. Cross section at the loaded points is the only thing you need to focus on. The rest is just nonsense.
Im assuming that the test might have been better if the oval shape was perfectly cut and not hacked out? U left sharp edges on the internal curve which should have had a perfect radius and not jagged edges. Maybe drill holes at the top and bottom of the oval to start the shape with nice radiused shapes?
I will be honest. I am not an engineer. I just don’t see how flow dynamics, in a piece of wood, perpendicular to where the stress is applied affects the strength of the beam. Even if a beam with multiple holes is stronger than a beam with a single hole. I would think it would work more like a tiered fountain than a wing or a wedge. I sorta get what you’re saying, maybe? Flow dynamics can be similar to the redistribution of stress from an area of lesser material to an area with more material by creating smaller areas of stress as long as the material is laminated like wood?
The stress is not parallel to the load application direction in this case. In fact, the stress direction is longitudinally along the beam's length this is from beam theory. The top of the beam is in compression and the bottom is in tension. It is not the same as a purely tensile test but it is similar. My home testing setup does not facilitate tensile testing so I had to improvise.
If you have variation of 12% within the same sample type - how can you assume that initial 6% difference with - one hole sample type - was somehow more signifiant?
I didn't
That is an interesting website you have there bud. A like and subscibe coming your way.
So in summary, if you HAVE to drill a hole through the middle of a wooden member, add relief holes. Otherwise, just don't touch it and you will get the strongest load.
Yup
Stop drilling cracks in aircraft alluminium skins can be thought of similarly? Thank you Most satisfying.
The drill holes looks like the Adamas epaulet sound holes on the top of Ovation guitars. Just an observation but somehow there's a parallel with this video because of "flow".
2303kg
The point is that if the hole already exists (say because of pipes, cables, ventilation, etc) then you could improve the capacity by drilling holes. Of course no one is saying that you should just drill holes in your beams for no reason.
@TheEngineeringHub yes,hopefully the plumber or other craft person watches this. Anyway, good explanation. I'll stay subscribed
@@art1muz13 ty🙏🙏 appreciate it
@@TheEngineeringHub i think you have to elaborate this in the intro of this vid, mate
@@TheEngineeringHub Most of the comments are missing the point. If I wanted to nit pick I would demand you compare structural pine with aircraft spruce.
Why not drill circular holes for uniformity?
Also, what about a single circular hole off center? It is a common rule of thumb that holes near or at the edge weaken the beam the most
A more rigorous analytical approach where this kind of thing shows up is generative design