00:00If you've ever been to a construction site, or work in one, you've definitely seen some
00:06steel bars over in the corner, ready to be bent and placed in different structures.
00:12Some people call it iron, construction steel or rebars.
00:16But what are they really, and what are they used for?
00:26Today, we're going to talk about a material that's present in practically every building
00:31you see out there.
00:32But most people don't really know exactly what it is, or what it's used for.
00:37I'm talking about construction steel, that bar you've probably seen at a construction
00:43site near your house, which disappeared after they poured concrete into a structure.
00:48But before continuing with the video, it's important to say that calling these steel
00:53bars used in construction, iron, is wrong.
00:57That's because these bars are a metallic alloy called steel, which contains iron in its composition,
01:03but they are not made of pure iron.
01:06If you want to understand this difference, we have a video explaining all of it, and I'll
01:11put a link to that video at the end of this one.
01:14But let's get to it.
01:15What really is this material?
01:18And why is it so important for the structures we live in?
01:21First of all, it's important to understand that concrete, by itself, is a very good material
01:27for some things, but it's not good at everything.
01:30If you take a block of pure concrete and try to bend it or pull it, with force, it will
01:36break
01:36easily.
01:38That's because concrete is excellent at resisting compression.
01:42In other words, when you squeeze or press something against it, it handles that kind
01:47of load very well.
01:49But when you try to stretch it or twist it, it's weak.
01:53That's exactly where construction steel comes in.
01:57The steel bars used in construction, usually with a reed surface, are specifically designed
02:05to reinforce concrete and give it the ability to withstand tensile and shear forces.
02:14But how can a steel bar inside concrete make a difference?
02:20Well, when you put a steel bar inside concrete, you create what we call reinforced concrete.
02:27This combination is much stronger than concrete alone.
02:31The steel absorbs the tensile forces, while the concrete absorbs the compressive forces.
02:38It's like two materials working together, each doing what it does best.
02:43Imagine a beam made of pure concrete, trying to support the weight of an entire floor of
02:48a building.
02:49Believe me, it would break easily.
02:52Now imagine the same beam, but this time reinforced with steel bars inside it.
02:58That beam will now be able to support much more load, because the steel is there, helping
03:03to withstand the forces that concrete alone couldn't handle.
03:07But what's the story behind this important material?
03:11Steel as we know it today, is the result of centuries of development in engineering.
03:16The idea of combining steel with concrete came up in the 19th century, when engineers
03:21realized that this combination was much more efficient than just using steel alone.
03:26What about the materials?
03:28Since then, rebar, or steel, has evolved a lot.
03:33Nowadays, there are different types of steel for concrete, each with specific characteristics
03:38for different applications.
03:40In Brazil, steel used for this purpose are standardized by AB&T and BR7480, which defines requirements
03:50for the geometry, strength and composition of the bars.
03:53But what exactly are these types of steel that you find out there?
03:56The most common types of steel that you will find at any construction site are CA25 steel,
04:02CA50, and CA60.
04:07The abbreviation A stands for reinforced concrete, and the number right after it shows a characteristic
04:15yield strength.
04:16For example, CA50 is steel with a yield strength of 50 kN per square centimeter, or 500 MPa, while
04:25CA60 can withstand 60 kN per square centimeter, or 600 MPa.
04:32But what is the practical difference between them?
04:34CA50 is more malleable and ductile, which means it can bend and curve better without breaking,
04:41and it's also ribbed.
04:42That's why it's more suitable for the main reinforcement in structures like beams, columns, and slabs.
04:49On the other hand, CA60 is stronger, but less flexible.
04:54It's generally used in secondary reinforcement, or in situations where you need greater strength.
05:00And it can be found both in a smooth form and ripped.
05:04But for using reinforced concrete, the ideal is the ripped type to ensure a stronger bond.
05:10For example, when you buy ready-made welded steel meshes, they are made using CA60 steel.
05:17CA25 steel, on the other hand, has a smooth surface, and it's commonly used in industrial floors
05:24as dower bars, and even as auxiliary reinforcement in precast elements.
05:29Besides that, CA50 is supplied in straight bars, while CA60 can come in coils.
05:38But how are these bars placed inside the concrete?
05:41The process of assembling the steel is quite complex and also very interesting.
05:46After preparing the reinforcement design, which is calculated by an engineer,
05:51you need to assemble a structure.
05:53A structure called reinforcement, which is basically a steel skeleton.
05:58This reinforcement is placed inside a wooden or metal formwork,
06:02and only then is the concrete poured into the formwork and over the reinforcement in the end.
06:08As the concrete begins its curing process and hardness, it completely surrounds the reinforcement,
06:14creating a much stronger bond between the two materials.
06:18The ripped surface of the steel is essential for this, because it strengthens the bond between the steel and the
06:25concrete,
06:26preventing the steel from slipping inside the concrete when the structure is subjected to stress.
06:32Construction steel is present in practically all structural parts of reinforced concrete buildings.
06:38In the foundations, it helps resist the forces between the structure and the ground.
06:43In the columns, they help support the weight of the entire structure above and prevent buckling.
06:50In the beams, they resist the bending forces caused by the weight of the floors.
06:55In the slabs, they distribute the weight evenly and also resist bending forces.
07:02Even in smaller structures like retaining walls and stairs, you find this type of steel.
07:09But there's something important you need to know about construction steel that a lot of people don't know.
07:15Many people ask me if reinforcing steel can be welded or not.
07:20Well, the answer is yes and no.
07:23And that will depend mainly on the chemical composition of the steel, especially the carbon content.
07:30To know for sure if you can weld it or not, look for the abbreviation S after the number on
07:37the bar.
07:38For example, regular CA50 steel cannot be welded.
07:43But CA50S with that S at the end means it can be welded.
07:48Now you might be wondering, what is the size of the steel used in a construction project?
07:55Well, steel comes in different bar sizes, measured by diameter.
07:58The most common bar sizes range from 5 mm up to 40 mm in diameter.
08:05Smaller diameter bars are used in small structures or in secondary reinforcement,
08:13while larger diameter bars are used in large structures that need to support a lot of weight.
08:17Each bar size has a specific area, which helps engineers calculate how much material will be needed for a structure.
08:26By default, the maximum length of a CA50 steel bar is 12 meters.
08:33But there are cases where you can request longer lengths directly from the steel mills.
08:39But then you have to assess if it's worth it, because the price of these bars that don't follow the
08:4512 meter standard goes up a lot since they're a different batch.
08:49In my life as an industrial project engineer, I've only seen a bar longer than 12 meters used once in
08:56my entire life.
08:58But that's because the company that needed this bar was the very one supplying the steel for the project.
09:05But what's the importance of choosing the right type of steel for a project?
09:10Well, choosing the right type is essential for the safety and durability of a structure.
09:15If you use steel with less strength than required, the structure can fail.
09:20The same thing happens if you use a smaller steel area than what is needed according to calculations.
09:26The structure can also fail.
09:29Now, if you use steel with much higher strength and a much larger amount than necessary, you will be spending
09:36money unnecessarily.
09:38That's why engineers do very precise calculations, to determine what type and what amount of steel is needed for each
09:46part of the structure.
09:48This drawing in my hand is a reinforcement drawing, which shows exactly where each bar is needed, their sizes, bands
09:56and diameters.
09:57This is so that the structure reaches the required strength.
10:01Before this drawing was produced, calculations were made that take into account several factors and loads that the structure will
10:09support, as well as following the applicable standards.
10:13But there's something else you should know about steel that might be even more important.
10:17The quality of steel is extremely important.
10:22That's why there are rigorous quality control tests, that check if the steel meets the requirements set by technical standards.
10:30These tests check the strength of the material, the chemical composition and the geometry of the rips and several other
10:37aspects.
10:39Reputable construction companies always check the origin of the steel and require quality certificates from suppliers.
10:47This ensures that the structure will be safe and durable.
10:52So, the next time you walk by a construction site and see those exposed steel bars, you know exactly what
10:58they are and what they are for.
11:01The steel inside the concrete is the invisible hero of structures, working silently within the concrete to keep everything standing
11:10and safe.
11:11Your opinion is important to us, so if you enjoyed the video, subscribe to the channel if you haven't already,
11:17give the video a like and turn on the notification bell.
11:20And if you want to help us produce this and lots of other content here on the platform, consider becoming
11:26a member and chip in for coffee and cheese bread and be remembered in our videos.
11:32Are you looking to grow professionally or develop a new technical skill? Scan the QR code over here or the
11:39link in the description and discover a page with all the courses we recommend.
11:43So, did you already have an idea about how the steel in the concrete, the…
11:47So, have you ever stopped to think about the rebar under your feet or around you that's inside the concrete
11:54where you live or work?
11:55Leave it here in the comments because I want to know.
11:57Here on the site there are two interesting video options that you need to watch to expand your knowledge and
12:02explore your curiosity.
12:04And if you want to support us, give the video a like, subscribe to the channel, turn on the notification
12:08bell and consider becoming a member of the channel.
12:11That's it engineering enthusiasts, sending you all a big hug and I'll see you in the next video.
