Why Concrete Needs Reinforcement
In the last video we talked about concrete 101, and why concrete is a great building material But I did not mention its greatest weakness. Hey I’m grady and this is practical engineering. In today’s episode, we are continuing with a series on concrete with a discussion of reinforcement / reinforcement. ~ Music This video is sponsored by Skillshare – we’ll talk more about that later. To understand the greatest weakness of concrete, we first need to know a little bit about “material mechanics” It is the luxurious way of saying “how materials behave under stress / pressure”. Stress, in this case, does not refer to anxiety or existential dread but rather But instead The inner forces of matter. There are three basic types of stress: Pressure (push together) Tensile (pull backward) And shear (slip along a line or surface).
And not all substances can resist every type of stress alike. It turned out that the concrete was very strong in pressing but very weak in tensile strength. However, you don’t have to take my word for that. Here is the illustration These two concrete cylinders were poured from the same eye And we will see how much pregnancy you can bear before failure First, the pressure test.
(Shake a hand pump). Under pressure, the cylinder broke when tolerated with 1,000 pounds (that’s 450 kilos). For concrete, this is very low because I included a lot of water in this mixture. The reason is that my tensile strength testing tools are not sophisticated enough Some “eye” screws were thrown into this sample, and now I hung them from the rafters at a store This bucket was filled with gravel, but that was not sufficient weight for sample failure. So, I added another weight to push it to the limit The weight of this bucket was only about 80 pounds or 36 kilos, which is less than 10% of the compressive strength.
All this to say, you should not make a rope of concrete. In fact, without some way to fix this weakness of tensile stress You should not make any kind of structural element from concrete, because it is rarely exposed a structural element Just to press! In fact, almost all structures are exposed to a mixture of stresses. This is no more obvious than the traditional beam / beam Especially this traditional beam / beam is made at home from pure concrete here in my garage. Applying force to this beam / keel causes internal stress to emerge, here’s how it looks The upper part of the beam / beam is subjected to pressure stress. The lower portion of the beam is tested for tensile stress Perhaps you can guess where the failure will happen on this concrete package as you were Continue to increase your pregnancy. It happens almost immediately, but you can see that the crack forms at the bottom The beam, where the tensile pressure is higher, and spreads upward until the beam fails. You see what I’m talking about here: my concrete, on its own, doesn’t make good structure Material.
There are so many sources of tension that he couldn’t resist on his own. Therefore, in most cases, we add reinforcement to improve its strength. Reinforcement inside concrete creates a compound of materials, with concrete providing strength Against the compressive pressure during reinforcement, it provides strength against tensile stress. The most common type of reinforcement used in concrete is deformed steel, more common Known as rebar.
I made a new beam with two threaded steel cast bars at the bottom of the concrete. These chains should function like deformed hills in a regular rebar to create some grip Between concrete and steel. Under the press, the first thing you notice is that this beam is much stronger than the previous. We are already above strength that failed in the unsupported sample. But the second thing you notice is that failure occurs a little slower. You can easily see the crack formation and post it before the package fails. This is actually a very important part of reinforcing concrete with steel.
It changes the type of failure from the fragility of the situation, as there is no warning of anything It is wrong, to the ductile position, where you see cracks formed before a complete loss Of strength. This gives you an opportunity to learn about the potential of the disaster and we hope to address it before Happen or occur. Armature works well for most reinforcement situations. It is relatively cheap, well tested, and understood. But it does have some disadvantages, one of the main one is that it is passive reinforcement. The steel goes on with pressure, so the armature cannot start working to help resist tension even She had a chance to stretch it out. Often this means that the concrete has a crack before the rebar can take any of the Tensile pressure of the organ.
Cracking concrete is not necessarily bad – after all, we just ask for concrete To resist compressive forces, which can do just fine with cracks. But there are some cases where you want to avoid cracks or excessive slope It can come from passive armature. For these situations, you might consider going to an active promotion, also known as Prestressed concrete. Prestress means applying pressure to the reinforcement before applying concrete in service. One way to do this is to put tension on the rebar and concrete strings Cast. Once the concrete treatments, the tension will remain inside, transferring pressure Emphasis on concrete through friction with reinforcement. Most beams of concrete bridges are prestressed in this way. Check all that reinforcement on the bottom of this beam. Another method of reinforcement is called reinforcement after stretching. In this way, the stress in the reinforcement is developed after the concrete is cured. For this next sample, the plastic sleeve was thrown into the concrete. Steel bars can slide smoothly in these sleeves. Once the beam is healed, the nuts tighten the rods to strain them.
Under the press, this beam was not more powerful than the traditionally reinforced beam, however It took more pressure before cracks formed. Also, this one was not as dramatic because instead of the actual steel failure Rods, strings on nuts were so failed first. I hope these demonstrations will help clarify the reason necessary strengthening in most applications From concrete – to add tensile strength and to change the failure mode from brittle to Ductile. Just like the last video, I scratch a very complex and detailed surface Theme. Many engineers spend their entire career studying and designing reinforced concrete structures. However, I have some fun playing with concrete and I hope you find it interesting.
I would love to continue this series on concrete, so if you have questions about this, you can post Them in the comments below. Maybe I can respond to it in the next video. Thanks for watching, and let me know what you think! Thanks for Skillshare for taking care of this video. Just about every step of video production for this channel is something I’ve learned Through tutorials and online videos. We all know how diverse the quality of this content can be.
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