What is Prestressed Concrete?
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- Опубліковано 22 тра 2024
- Sometimes conventional reinforcement isn't enough. The basics of prestressed concrete.
Prestressing reinforcement doesn't necessarily make concrete stronger. But, it does increase the serviceability of concrete members by reducing the amount of deflection under load. This video explains the two most common types of prestressed concrete: pre-tensioned and post-tensioned. Prestressed concrete is used in all kinds of structures from bridges to buildings to silos and tanks. It’s a great way to minimize cracking and take fuller advantage of the incredible strength of reinforced concrete. Thank you for watching, and let me know what you think!
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You can't end this series until you design a reinforced concrete beam your press can't break. (and you can lift yourself!) :)
Agreed
Lol... good luck? While you're at it, see if he can design a carbon nanotube space elevator that won't collapse under its own weight?
I'd suspect that one of the existing designs could beat his press just by letting the concrete cure for a month or longer.
hit the gym
Or a pasta machine.
I was taught that there are 2 kinds of concrete in the world. Concrete that has cracked, and concrete that's gonna crack.
I hate when people say the same about motorcyclists and crashing
i hate when my motorcycle crashes
Stucco also fits here.
@Rick Sanchez If you're talking about the incan stoneworking, as far as I am aware those are solid stones that were put together quite masterfully. Something roman is probably an exception though.
@Rossirbro I remember my Grandpa telling me about visiting a Mayan pyramid that had concrete at the top, he said the concrete looked absolutely pristine. According to the Mayan guide the pyramid was capped with concrete when it was built. I know it’s Mayan not Inca but it is still pretty cool!
This topic is *solid,* but very *stressful.*
fsmoura just run some rebar through your ears. ..should lighten the load.😅😅 .....oops, I mean 'tension'.😂😂😂
Normally I'm stressed anyway, but for sum reason, I would like to know Mohr
I just love the way you present. Incredible you are.
Steel structures or Trusses or Frames could be interesting topics.
There were some tense moments, but as hard as it may be, in the end you won't crack, you'll just come through stronger.
the comment is cemented into my memory now...
Be careful using the vibrator. If you vibrate it too much the rocks in the mix sink to the bottom.
That'd make an interesting demo...
Two two three Five five six It’s very possible that Grady doesn’t have a lot of experience with that specific piece of technology and Kevin does. Someone who helps builds these structures would be undeniably more of an expert on the equipment they use everyday. There’s no guarantee that Kevin is the expert on this specific thing but there is no need to be an ass about it. It’s just some friendly advice for Grady.
Two two three Five five six
Maybe Grady hasn’t used a vibrator before?
Yeah, being an engineer doesnt mean that you know how to use all machines - engineers can take tips as well.@Two two three Five five six
_"Be careful using the vibrator"_
thats what she said
Okay, okay - I think this one will conclude the series on concrete (for now!). It's time to move on to a new topic :) For now, support the channel by checking out Dashlane - it's free and I hope you find it useful! www.dashland.com/practicalengineering
Flex seal? The best adhesive on this planet!
I love your concrete series - I hope to see more concrete videos in the future! I have no suggestions for new ideas at the moment, but I will let you know if I come up with anything. Thanks for your excellent and informative videos!
Pre fabricated methods of construction?
How do they build bridge bases underwater?
Steel structures!
Hey Grady!
ideas for more:
- how the angle and length of off ramps and curves on highways is determined. (When I was at Thinkercon I found that the off-ramps were short and curved very tightly and I wondered if it was because they do not have snow/winter like we do up here in Ontario)
- More on city/urban infrastructure (ie: how blue is added to green lights because of red/green colour blindness?) horizontal vs vertical stop lights.
- canals?
- why cloverleafs on highways are a terrible design and why they used to think they were fine
- how do they build roads/railroads over permafrost in the north?
- cog railways on mountains?
- airport terminals - we use those a lot and I bet there is lots of design and infrastructure planning in their layout
Have fun!
God I can't even imagine what a nightmare horizontal traffic lights would be. Only reason I can use the road is because I memorised where each light is.
@che3se1495 -- better never visit Quebec then. Or Alberta. Hmm, according to Wikipeda also parts of New Jersey, Pennsylvania, Japan...
(Not intending to be flippant -- I thought everywhere had blue mixed in the green these days to allow for red/green colour blindness. Maybe not.)
Cloverleafs are fine for moderate levels of traffic and are a relatively affordable design.
@@che3se1495 colorblind?
@@rfldss89 Yeah, normally not that bad but I just got used to relying on the position to avoid the confusion.
An interesting issue that arises with stressing concrete is that it it is not as good at resisting impact sounds. As an acoustic engineer we test many concrete floor slabs to find their levels of impact insulation. An unstressed slab always is better, compared to a stressed slab, at reducing the levels of impact noise for lower occupants.
I am so glad I stumbled across your comment! I am learning as much as I can about concrete, because I'd like to start building speaker cabinets with it. I'm no engineer, so anything written in English like this is a huge help.
I'm not surprised the pre-stressed stuff transmits sound more readily. It's more compact, and that would include all the cracks, air pockets, etc. I could see how that would provide less resistance for the vibrations to travel.
Do you know anything about volcanic pumice powder being used as an aggregate for "higher strength" mix? Or have any experience with light-weight concretes?
Dude. I LOVE the way you do your sponsorships. I already pay UA-cam for ad-free video, & I'm usually genuinely not interested in all the sponsors I've seen so far, but you are the ONLY one who gives me the option of not having to sit through the ad or try to skip through it, and I *GREATLY* appreciate that. If I'm not interested in the product, then the ad is just an irritant.
You mention the sponsor up front, then do the ad at the end, which allows me the opportunity to decide if I want to watch it, and that is awesome. Thank you!!
Awesome videos too!! 😁👍 I love your scale models; they really drive the point home & make the subject matter easy to visualize.
Pre-stressing is big in tractor trailer trailers. If you look along an empty flatbed trailer you'll see it bows upward. When fully loaded, it's flat. That's one way police can chase down overloaded trucks at a glance. If the trailer is sagging, it's overloaded.
You can actually cheat a bit and run a few beads of welding rod down the entire length of the bottom of the trailer beams. As the beads cool, they'll pull the beams into more of an arc ;-) It gives you a little more "spring" in the bow of the trailer. It won't make any difference at a weigh station obviously. Your weight will be your weight :-) Around here, mostly you only have to worry about weigh stations at state lines.
@ClickThisToSubscribeYes. They use it in manufacturing the trailers to begin with. Mobile home trailers in particular.
The weld beads do create a bit of light pre-stress in the beam, but the basic camber arc is not by its self a form of pre-stress. The beam still deflects about the same inches per ton, you simply changed the starting point.
Camber, not prestressing
I seriously loved this in-depth look at concrete. I have no idea why, I work IT from home. But it still feels like I learned something super useful.
Long ago in my Public Works Admin career, I got to visit a prestress plant to observe a girder being build for a bridge my city had commissioned. The science of the shape, drape and position of the tensioning cables and the arc of the girder form itself was quite interesting.
I love how you go over concepts I JUST talked about in Reinforced Concrete Design, Soil Mechanics, Hydraulics & etc... at UMKC. Keep up the good work!!! Love your content!
If this is my teacher in engeneering.... MY LIFE WILL NEVER BE BORED
Exactly what I was thinking
Thank you for posting more Concrete videos. This is great.
No One Says It Better Than You, My Friend. God Bless You. ..It's good to know there's someone like you in the world. ...the world needs More engineers like you.
first time in my life that engineering lectures dont make me wanna run away. these lectures are so friendly and inviting that they motivateme to staart a career in this field
Love all these concrete videos! I didnt know it could be this interesting
Greetings from Denmark, home of the best sand for concrete. :)
Without prestressed concrete, I would have had far less to do at work for the past year. 14 railroad overpass bridges (reverse T-beams, dang that white, high alcalic cement cures fast!) and 2 parking houses (TT-plates and parking decks, dunno what they are called in english) under the belt. And that's on top of the normally rebarred stairs and landings I have made production drawings for. :)
The heaviest beam I have drawn so far was a 1400mm high and nearly 19m long dual console beam (800mm consoles) weighing 41,86 metric tons. All becsuse the architect wanted to fit in one more parking space between each column in the parking basement under a supermarket with 3 floors of appartments above it...
Glad to hear that in other countries there isn't a war being fought against the personal automobile. Around here, they wouldn't bother to build any parking or they'd put in a dismally inadequate amount.
@@TruthSeekerD you might be surprised but we have no idea what "around here" means for you
Godt det ikke var mig der skulle armere den søjle haha
laughs in Australia
@@TruthSeekerD
Also missing most the point of the post. He used that as an example of an architect gone wild, not a good design philosophy.
Excellent vid as usual!
Thank for sharing your knowledge, experience, & effort!
Your example gadgets really help illustrate the concept you're showing us clearly. Great job!
I’m not recalling if you’ve covered this before, but I recall reading a paper talking about how modern fast-setting high strength concretes are more vulnerable to fractures due to increased thermal expansion while curing than old slower setting concretes.
Your videos make me think of those 1940s-1960s films that explain all kinds of tech stuff. I love those, and i love your videos!
I love the demonstrations of those basic things like how concrete cracks under stress, but doesn't fail.
I have no idea if engineering was more popular in the past than today.
I mean, this channel does have hundreds of thousands of subscribers.
I do often get the feeling that these days, people don't have a feeling for mechanical stuff anymore. But that might very well be because we have all grown up in a world where cars just work and go for 100.000km without special maintenance, where large spans are completely ordinary in big buildings and where tens of millions of transistors fit into your hand.
It's so incredibly ordinary to us, that not that many people stop to ponder 'how did that happen'. I can't blame those people...
Those old films were originally only shown on a limited basis, usually in specific training courses. Second up is that they are too on point for the post-modernist infested system that seems to have a need for adding a bunch of extraneous crap pushing subtle political ends even at the expense of the technical material at hand. UA-cam to the rescue, at least for the moment ...I really don't enjoy having all the eggs in one basket.
Thankyou so much I'm a student of civil engineering n I was searching for this how to perform prestress at collage , that's a great idea given by your video...
I love this channel, as a electrical engineer I can keep learning new stuff from this channel.
Rally enjoyed this series. Also really enjoyed meeting you at Thinkercon. I’d love to see more in water hammer. Is hydraulic fluid susceptible also? Does viscosity change the effect?
Great video as always! I have a question, though (*and an idea for another video!*) Our house is built on a post-tensioned slab, rather than a deep foundation (suburbs of Phoenix). It has warnings imprinted on the concrete never to drill or tap holes, and when asking a construction contractor why, he said "because the entire slab will basically shatter and explode".
Needless to say, as someone with a science and engineering background, I find this... unlikely. Concrete is brittle, but not *that* brittle. But is he right? What *does* happen if you damage pre- or post-tensioned concrete under load?
I'd love to see a video where you build another beam of pre- and post-tensioned concrete, and instead of just amping up the pressure with your press until they fail, instead put them under their design load, and then drill into them to see if they exhibit such a spectacular failure mode as this guy was describing. If they don't, then you could explain why the slab has that warning. I suspect it may simply be because if you damage the reinforcement while you drill into the concrete, *that* could be bad indeed. That I could actually see creating some sort of (minor)explosive failure state as the steel snaps rather than bending like it did in this video.
I love when you talk about member stressing and tensioning and servicing. The vibrating stuff only encouraged the 12 year old in me. Excellent video though, rock hard.
I loved this in-depth look at concrete! I knew a lot of it from my mechanical engineering days, but this covered things in more depth, the the demonstrations are very helpful!
You should now try focusing on shear reinforcement, as the failures you have demonstrated are quite brittle, and in the real world not ideal, as you don’t want a RC member failing so fast. Good videos these are awesome (y)
If you watch the second beam failure at 0.25 speed you can see that the failure mode is actually the back right stressing anchorage. But yeah all the others are shear failure. I doubt he waited very long for the concrete to cure and could have used a larger washer than what was on there.
C Lee yeah that’s a type of failure you have with PT concrete (at the end of the ducts/anchorage). The rest of them throughout the concrete series has been shear failure.
Punching would help .
Great video. Really enjoy your work. Informative and a pleasure to watch. As a plumber I would love to see you cover electrolysis. The importance of dielectric unions and nipples.
As a former home inspector, I would love to see this too. I saw di-electric unions on water heaters often and also saw what happens when you don't have them.
@@truckertech9272 I'm having a home inspected tomorrow... what's a di-electric union?!?
@@843292 This YT video covers it really well.
ua-cam.com/video/6eqKsYw-2cI/v-deo.html
Watched this before final exam for reinforced concrete design 2 this morning. Thanks for simple explanation!
I was waiting for this video. Glad to watch!
I really love the way you handle the sponsor pitch. You mention it in the beginning which you probably have to and then leave it for the end of the video where I can just turn it off. No looking for the actual start of your video.
Just soldier through it, UA-cam analytics tells him where viewers tend to stop watching, and that probably affects sponsorship revenue.
Dark Phoenix You get a free video. You know, the video you're watching. It actually took time and money to make, and all he asks is that you listen to the sponsorship.
@@gabrielfraser2109 exactly. The sponsors probably wouldn't keep paying if they know their advertisement is not being watched. If I enjoy a creator, I always watch them.
Idea: advancements in the plastics side of composites.
I tell people all the time about how a carbon fiber bike is really just "plastic with stuff in it." People tend to focus on the fabrics because they are visually interesting.
I spent several years as a buyer for a chain of bike shops and could clearly see, if steel bikes had remained the standard they would cost far more than plastic bikes do now. They are far more labor intensive and have several engineering limitations when it comes to tubing dimensions and bike sizing.
To the uninitiated: steel road bikes were sold in ++1cm sizes from 48cm to at least 61cm with many models/brands selling higher and lower sizing.
The plastic bike lead to the innovation of "compact geometry" and shifted the sizing of bikes from, mostly frame specific sizing, to a more flexible individual fit by changing the bars, stem, and seat post.
A steel bike of the past would come in at least 13 sizes for each model. Modern bikes are offered in less than half the number of sizes per model. This greatly lowered the investment needed per model for wholesale distribution networks and retailers alike. That change lead to the diversification of the bicycle market into all kinds of specialties.
The molding technology has come a long long way, especially the interior forming technologies currently available. There are also lots of interesting advancements in doping additives like hollow and/or lightweight fillers.
The one tech that I think is a bit more interesting is the addition of basalt dope for carbon fiber wheel braking surfaces. The fact that a clincher tire mount flange can be incorporated into a rim design with a plastic braking surface is remarkable. The heat of a 180lb person/bike stopping quickly from 60mph+ coming down a mountain with a thin piece of plastic stopping them is voodoo.
Those are the usual geeky talking points. The aspect that I've never heard about in any depth is how the actual epoxy plastics have changed and evolved on the chemical side. At most people will talk about the mechanical design aspects like, "real structural carbon fiber fabrics are almost always a uniweave with around a 45 degree lay up. Or they will mention the diameter and refinement of the individual carbon threads, combined with higher vacuum power, and resin percentage control are the factors that determine weight versus strength in the composite.
People like to focus on the fiber because dumb monkeys buy shiny things. They don't like to remind people, ultimately carbon fiber composites are just plastic with stuff in it. What's the real story on the plastics side of current composites engineering?
-Jake
I get the feeling you are talking a much higher end bike than what I ride.
@@petroelb
Which of my six are we talking about?
Felt AR4 (main/rebuilding on the stand now)
LeMond Tourmalet (main back up/steel is real - fun to stomp others riding carbon bikes with)
Cannondale SuperSix HM (cracked)
Cannondale R900 (in pieces under my bed)
Cannondale Jekyll (storage)
Bianchi 928 (parted in storage)
...the benefits of making next to nothing for a paycheck while working in bike shops...
Compact geometry is completely independent of the basic frame material.
The main limit on steel is the low dent resistance of very thin wall large diameter tubes needed to take advantage of steel's properties in this application.
I am quite familiar with aerospace composite engineering (experimental airplane structural components more specifically) and... no, a composite is not just plastic with stuff in it. In fact the polymer matrix (which is not a thermoplastic in over 99% of carbon fiber products) is only there to bond the fibers into a fixed position, very little primary strength and stiffness is contributed by the matrix. The fibers are of very high elastic modulus and the polymer is of modest to low elastic modulus, the matrix may be to 10% of ultimate stress/strain when the fibers fail, and the matrix won't have the ultimate strength to take up the slack after the fibers have broken; think of a rubber coated steel wire.
The polymers used are most often epoxy or cross linked polyester, but some use polyimides for high temp applications and dynamic bearing surfaces without the use of metal inserts, vinyl-esters for a water barrier in submerged items like boat hulls(prevents osmotic-pressure blistering), phenolics also pop up a fair amount as they tend to be dimensionally stable easy to bond post cure and economical in certain production situations also somewhat fire retardant.
Epoxies adhere to most fibers better than polyesters but epoxies are more expensive and have lower modulus of elasticity and the only time adhesion tends to be a primary concern is with aramid fibers[kevlar tm], which are in turn only used where you need loads of toughness and impact resistance and so the lower modulus is not a detriment as aramid composites tend to be relatively flexible in any case, and due to low adhesion designs should limit compression loading. (as the matrix, especially bonding with the fiber, does play a fair roll in compression loading)
Specific variations on resin products within a chemical family tend to come down to processing performance as much as final product strengths: cure temps, cure time, viscosity, sensitivity to mixing ratios, defect rates with a given process, shelf life, etc.. The needs of resin for frozen pre-impregnated fabric to be cured in an autoclave is quite different from the needs of a field repair using any of a wide variety of fibers over some mystery base polymer.
@@mytech6779
Cool read.
The steel bike compact geometry limitations comment is really referring to the practice of lugged frames where the lug shells were designed for use on multiple frame sizes. Filet brazing is possible but was always more labor intensive and required more skilled labor in general. The cost effective/low end/entry level bike market is what I'm primarily referring to as the limitation.
You know far more than I do about polymers and composites, but that's exactly the kind of stuff I'd like to hear about in details I might better understand. I have as much experience as can be expected from someone that painted with PPG DBC and Omni for years professionally, and played around with a few amateur composite projects. I've also picked more than a few engineer's brains at Interbike in Vegas, but I'm no expert, just exceedingly curious.
-Jake
MyTech you sound like you know your material's science. What could i put over large 220watt solar panels in place of the front-glass that was cracked into thousands of tiny pieces falling out. It needs to be transparent, & preferably lightweight and rain&sun.heat/cold proof. Preferably paint/pour/spread/stick/iron-on as opposed to cut (like glass) and size on. Is there a resin/epoxy/laminar/sheet etc whatever that fits the bill? I'm not sure if i can just leave the solar-crystals exposed without a covering and dust them off once in awhile. I assume the glass was there to keep them dry but what do i know.
I seriously love this channel. I've learned so much about concrete here.
Fabulous videos, Grady. I’m a big fan of your work.
Grady's wife: What do you want for Christmas honey?
Grady: A construction grade concrete vibrator
lt's the other way around. He asks her and that's her answer.
I'm a "concrete professional"!
Good luck to you sir!!
@@PallavTHEsinha Thanks! I just make the cad drawings at a precast concrete company, but I think that counts, right?
Excellent explanation and demo!
Very good job explaining the basics, and thank you so very much for knowing it doesn't make it flexurally stronger than mild reinforcing!
How about doing something with Roundabouts. Show how do drive them and how they are safer than traditional intersections. Also show how they drive them in Europe and how they would function better in the US if they where driven correctly.
Greetings from Australia where we imported roundabouts from the UK but forgot to teach people how to use them.And we usually make them too small.
Dan: the challenge here is roundabouts are not common enough in the u.s. for people to really be comfortable with them. In Europe, they are commonplace and everybody is mostly on the same page about procedure.
This is the guy, who scored an A in every subject in his engineering college.
and it shows!
Great explanation and test. Love your videos.
Excellent video. Great work. Thank you for teaching.
What about concrete additives.....?
Whats with "San Antonio" at the top?
It's the best place to live obviously
He lives there.
@@babylonfive I figured as much. Thanks!
It is never useless to learn from this channel! Please do upload videos about loads taking by bridges, especially live loads.
An amazing video on such an important thing that virtually surrounds us. Great job done!! Loved the video! Highly informative
i wish i'd come up with a good joke, but i'm not good *under tension*
that was such a stressed joke
This is sorta stretched out a bit
Just bubble out with a concrete vibrator
Your comedy isnt *cracked* out to be all that much, but im still *pulling* for you.
fsmoura all of these jokes are gay
I didn't know my life needed more concrete, but then here we are
Great video as always!
I love this channel! It has taught me so much. Please keep going like this. Music and voice match really well and information density is awesome
*so this is where it all ends huh?*
*THAT STRESSES ME OUT*
*TOO MUCH PRESSURE, I'M ABOUT TO CRACK*
*solid* joke 👌id laugh but im too *dense*
I see what u did there
Thanks for throwing stones in the mix......
RACIST FROG REEEEEEEEEEEEEEEEEEEE!
Concrete university class 2020 :-)
Great series you have! Would love to see a a few videos on bridges and tunnels. Keep up the great work!
I don't do anything with engineering and your profession (engineering) but it sure is a joy to watch this and learn. Thank you for well executed video and your great attention to detail !!!!
Hiiiiii from Sydney Australia do I have any fellow Aussie friends
Sure. Up in Brisbane. These videos are great
Fun fact: in Australia, the pre-stressed concrete rebar is _compressed_ instead of _distended,_ because it's in the Southern Hemisphere, and thus spinning the other way.
Perth engineering dropout reporting!
I am not Australian, but I do know that the Sydney opera house is held together by steel cables, effectively compressing the concrete into itself.
Brisbane here
1:32 ultimate strength best strength
Awesome video! Thanks for the help showing the difference visually. Definitely helped me understand the difference for my mid-term Monday!
Yeeees! Thanks for continuing the concrete series!!
« Not all cracking is made equal »
Me: that’s crackist
*weird flex but ok*
Great video! thanks for doing it!
Grady! I Love these videos so much, you are such an inspiration to me! Thank you so much for making videos.
Excellent series of videos, thank you very much from Brazil! Keep the great work!
Another fantastic video!
Great stuff as usual Grady!
I have only arrived at concrete today, but I can already tell there are two types of concrete channel on youtube.
One that talks about concrete, and one that actually pours their own concrete.
Good job.
This is an excellent explanation. Thank you.
I've loved this concrete series. Thanks!
Wow... superb explanation...
Always Great Videos!!
Binge watching this series and all your previous. thoroughly enjoying.
Can you consider doing a vid on concrete foundations and how they strengthen a building. I know the rough principles but you do cover some awesome detail in remarkable brevity.
Very good. Thanks for the clarity. 👍
Great demonstration! thank you sir!
Anyway.
This was enjoyable easy to understand and informative. Just like the methods you show us your videos get the job done elegantly and effectively.
I hope we'll see your work for many years to come.
You are the only reason I have started taking intereset in my subject
As always, so informative. A real Teacher.
Thanks for posting these video's.
Awesome final episode in the concrete series!
Love this channel! Tons of good information
Thank you for this very informative tutorial
I really like your videos, thank for your work!
Thanks for the video, Grady!
Great video, very well articulate. Thanks!
Wonderful!!
It makes sense that prestressed isn't significantly stronger than simply reinforced, but I hadn't articulated that. Thanks for the insight!
Excellent. It is great to have an understanding, presented in simple terms, of how things around us work.
thanks, Grady your videos are so cool and interesting for me
I like the post-stressed version most! nice idea.
Excellent video!
Great vid, I heard a mate say sometimes pre-tensioned steel reo can sometimes whip out of wet concrete and you don't want to be anywhere near it if does.
Love your channel. Things like this have always interested me. Your demos and explanations are always entertaining and easy to understand. Keep up the good work. :-)
Dope video man!!
Clear speaking voice and great explanations. Quality videos!
I love your vids dude!! As a mechanical engineer I love learning about the stuff you civils do!! Crazy awesome stuff!!!
As a technical translator. I had never fully understood what they meant with the pre-stressing and the post-stressing thing! Thank you! The explanation goes straight into my translation office's termbase (our database for terminology).
Nicely done! Keep it up!
This is pretty cool, awesome video as always.
My day always gets better when you upload a new video, especially about concrete. I love the demonstrations you take the time to build. They help a lot in understanding the concepts! ... I'm not going to comment on the "construction grade cocncrete vibrator".
Great video man