You can't end this series until you design a reinforced concrete beam your press can't break. (and you can lift yourself!) :)

I was taught that there are 2 kinds of concrete in the world. Concrete that has cracked, and concrete that's gonna crack.

This topic is *solid,* but very *stressful.*

Be careful using the vibrator. If you vibrate it too much the rocks in the mix sink to the bottom.

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!

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.

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 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.

If this is my teacher in engeneering.... MY LIFE WILL NEVER BE BORED

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.

Dude. I LOVE the way you do your sponsorships. I already pay KZfaq 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.

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...

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.

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)

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.

Watched this before final exam for reinforced concrete design 2 this morning. Thanks for simple explanation!

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

Love all these concrete videos! I didnt know it could be this interesting

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

In Italy there was a famous architect who specialised in prestressed concrete, Riccardo Morandi. He designed a bridge in Venezuela over the Maracaibo lake, which is still in use, and later a very similar, but smaller one in Genoa, that unfortunately collapsed 3 years ago due to poor maintenance.

This is the guy, who scored an A in every subject in his engineering college.

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.

Despite the episodes feeling a little recycled and stretched out at times this has been a lovely introductory series.

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.

Thank you for posting more Concrete videos. This is great.

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?

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.

I love this channel, as a electrical engineer I can keep learning new stuff from this channel.

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.

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.

This is the overview of Prestressed concrete and I understood easily what's the difference between RCC and PSC, now I can learn PSC design more easily

I like this man's homework, and the presentation isn't slack, either.

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

Grady's wife: What do you want for Christmas honey? Grady: A construction grade concrete vibrator

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...

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.

I'm a "concrete professional"!

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.

Hello Grady! I am a fan of your videos! As a structural engineer, I want to mention, that models seem to be a little off the dimensions of the beams and overreinforced. So, in addition to bending, destruction occurs from punching along inclined sections.

I used to make precast concrete walls. We used 5/8 7 strand cable that we pulled 240 ft of cable each run and we used around 14 to 30. We had to string it through end panels for tops and bottoms of the walls and blockouts for doors and window or similiar stuff. Then when ready we set up a hydrualic ram and cleared the safety zones for tensioning. 240 ft of cable we stretched around 14 inches. Qc operated the tensioner and had a gauge he watched then when finished we gave him the stretch measurement as a double check cause if he pulled said pressure and then got a 20 inch measurement instead of 12 inch range a strand possibly broke or its strength is compromised another way so we would scrap the cable and redo it. ( made it real fun when we realized after tension engineers didnt call out a plate on the top side of pour needed strand strung though it so we had to detension cable and pull it out and jig the plates and restring and tension it again) supposed to do 1 pour a day boss canceled that pour due to time loss

i wish i'd come up with a good joke, but i'm not good *under tension*

*so this is where it all ends huh?* *THAT STRESSES ME OUT*

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 !!!!

The working years from 1986 to 2009 of having been an Inspector of New Construction of Highways and Bridges for TXDOT... Highly Applaudes you're coverages of the characteristics of the nature concrete has up it's sleeves under tension & compression. 112718

What about concrete additives.....?

Whats with "San Antonio" at the top?

"finally got a construction grade concrete vibrator" casual... Concise and enlightening information none the less. I do always enjoy the professional nature of your short films Grady, very well done.

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.

Concrete university class 2020 :-)

I didn't know my life needed more concrete, but then here we are

Your video series has inspired me to one day build a 3-4 meter monument of myself in concrete, which I hope will stand the test of time and make people in 30 000-40 000 years or so believe i was a great king or mighty fighter or something like that. The plan is to make it so unconvenient to move or destroy that it's just allowed to stay

THank u for this video .I am civil engineering student . 4th year running alhamdulillah . This video helped me a lot.

Hiiiiii from Sydney Australia do I have any fellow Aussie friends

1:32 ultimate strength best strength

More concrete! Addmixtures! Corrosion control. Nano technology. Love this series, it makes explaining things to customer's requests easy peasy. Thank you.

6:37 Предварительно-напряженный железобетон классно взрывается! Хотя если бы с торцов стояли шайбы большей площади, блок бы еще немного продержался .

« Not all cracking is made equal » Me: that’s crackist

*weird flex but ok*

I really like how civil this discussion here is, usually it is a lot more uncivil when talking about such a concrete example. KZfaq comments normally cements its reputation as a trollfest.

It is never useless to learn from this channel! Please do upload videos about loads taking by bridges, especially live loads.

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).

and NOW i know what prestressed concrete is, and why its so awesome.

By only theory it's was difficult for me to understand the concept of pretension and post tension in concrete but this live practical cleared my concept. Thanks

I've been using KZfaq for more than 12 years. Your channel just broke my record of liking videos of a single channel in short period of time. Or maybe physics is what fascinates me the most..

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".

good video....clear, brief, and to the point.....it might have been augmented at the end by a demonstration of how a prestressed concrete bridge section is actually made at the factory

I'd like to see a video on how and *why* concrete is aerated (via autoclave or other means) in certain applications, and explaining *when* aerated concrete is preferable to more densely consolidated concrete.

I like the post-stressed version most! nice idea.

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!

Building on Permafrost would be an interesting topic. Here in Alaska its a huge issue, and some really cool solutions have been developed (pipelines, building foundations, etc)

I've worked I the steel game for around 5 years and never fully understood the difference between conventional and p.t decks. This gives clarify and should be taught befor when ever someone is new to the game

Wonderful!! It makes sense that prestressed isn't significantly stronger than simply reinforced, but I hadn't articulated that. Thanks for the insight!

Something I’ve wondered about but never took time to investigate: what is prestressed concrete? Thanks for a clear, elegant tutorial! Suggestion: a video of the manufacture of large prestressed structures and how the the massive forces in production and usage are managed....or not!

Neat, I'm a dummy that didn't do well in school but I learned something here. Thank you for that.

The Morandi Bridge (the Genoa Highway bridge that collapsed on 14 aug 2018) was one of the first structures built in prestressed concrete (mid 1960's). But the blame, apart from the criminal absence of mantainance, is air contaminants and pollutants that went right through the cement and corroded the steel inside (and the concrete itself)

Seriously I have never understood the prestressed concrete theory but now I have seen the practical

This video is very interesting. It's really important for students to study with visual presentations so that we can imagine and know what we are actually dealing with. It's so annoying that our instructors jumped to a topic and disregard the definition of prestressed. They already discussed the basic concepts of prestressed without giving definition. I just know after I watched this amazing video that the purpose of pre-stressing is to reduce deflection. Didn't mention in our class 😑

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.

Fun fact - in my province, post-tension concrete spans require periodic inspections by an engineer to retain occupancy. It's an expense that condo corporations are only beginning to feel as the buildings where this is common are requiring service. They are SUPER useful to create building designs with fewer columns, but they add significant costs to the owners over time.

Enjoyed the video. I was hoping you would also talk about the post tensioning with cables and rebar. In a lot of beams you have rebar continuous across the bottom and cables running through it as well in a Cosin arch with the high points above the theoretical supports and the low point of the cable at the center of the beam.

Engineering is fuckin' wild, I appreciate the work they do, but goddamn you people are essentially physical magicians to me

Great explanation and demonstration as usual. The vibrator...Dont get carried away with it. Too much vibration in the mixture and you wind up with air bubbles due to cavitation.

It should be noted for those that care that a prestressed and poststressed member is almost always reinforced with non stressed steel as well.

You guys always had the toys I wanted back when I was younger

Thank you for your videos from Guatemala. I have a question, and I hope I can see a video about this subject. So, what about the transversal reinforcements inside concrete beams? What exactly are they doing? It represents a improvement in resistance? Cool videos. You are the real mvp!

Nice shot of the Ft. Duquesne Bridge at 1:35 for any Pittsburghers...

I really like wood as a construction material. I'd like to see you attempt to make a steel, concrete, wood, and composite structures (mini bridges? or hollow cube ) and testing them. You could even go as far as making a box that fits them and light the test subjects on fire, and see which one survives the best. Nice surprises could come out of this.

thanks, Grady your videos are so cool and interesting for me

Your example gadgets really help illustrate the concept you're showing us clearly. Great job!

Great series you have! Would love to see a a few videos on bridges and tunnels. Keep up the great work!

explanation is understandable and your efforts to explain the theory is outstanding to me. good job pak.

As a follow up of Genoa Bridge collapse i find this video incredible interesting... THX! Subscribed and like.

Excellent vid as usual! Thank for sharing your knowledge, experience, & effort!

There is an underground parking garage near me and when you park on the ground level you can feel the structure moving. Definitely an unsettling feeling but interesting to experience

It's interesting that in my appreticeship to a architectural draftsman I learned what reinforced concrete is but not that there is something like tensioned concrete

Omg, your channel is so good. Better than a lot of my university professors

Very good job explaining the basics, and thank you so very much for knowing it doesn't make it flexurally stronger than mild reinforcing!

A fascinating, clear explanation a layperson can understand. Thanks for the explanation.

I love concrete. Not an engineer or even wanna-be engineer, yet I find this stuff (everything on his channel) fascinating.

Very noticeable difference in the modes of failure between the two members.