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General features and junction of tank wall and base slab 2times pg499,503 5.
#Prestressed concrete notes cracked
Pg192 6.types of flexural failure pg190 Unit-3 1.factors influencing deflection pg 151 2.291-10.1 3times veey imp 3.magnel method 8m pg 290 4.short and long term deflection of cracked member pg163,171 Unit-4 1.types of composite construction very imp 3 times pg 410 2.418-14.4 3.413-14.1 2times 4. methods of prestressing 3 times very imp. External forces (Dead load, Live load etc.).Now after loading there are two kinds of forces on the beam, Now the steel tendon wants to gain its original length and tensile stresses are transformed into a compressive stress in the concrete. So, how does it work? In the real life, high tensile strength steel wires are inserted into the beam section and they are stretched and anchored, then released. We have learned why and when we should use prestressed concrete. Like this, in prestressed concrete, initial compression is given to be balanced by future loading that will create tension. In other words, the bands and the staves were prestressed before they were subjected to any service loads. When the bands were tightened, they were under tensile prestress, which in turn created compressive prestress between the staves and enabled them to resist hoop tension produced by internal liquid pressure. The basic principle of prestressing was applied to construction, perhaps centuries ago, when ropes or metal bands were wound around the wooden staves to form a barrel (see Figure 1). Tung-Yen Lin, a civil engineering professor at the University of California, explained it in the introductory chapter of his book “ Design of Prestressed Concrete Structures". Imagine a barrel made of wooden staves and metal bands. In fact, the practice of prestressing things is very older in our day to day life. The concept of prestressed concrete is not so difficult. detailed example can be found in the PCA Notes on ACI 318-05 Building Code. Here comes this new concept- Pre-stressed concrete. The idea of prestressed concrete has been developed around the latter decades. In the way of traditional RC structure, for these larger beam spans, we should provide larger depth which is often too much that, for a bridge over a river, there will be no enough space under the bridge for ships to pass it. But what about some megastructures with larger beam span? Think about a flyover or famous Gateway Bridge in Australia, Incheon Bridge in South Korea or Ringhals nuclear reactor in Sweden where external loading is very high. This is why we add some steel bars at the bottom section so that it can resist most of the tension and save concrete from cracking. So, it tries to be elongated and guess what? It cracks. And so we see after external loading, in the bottom part of concrete, a tension zone occurred. We know, concrete is good at compression but very weak in tension. Okay, before get started let’s go back to some basics first. Now, the question is, why we need this complexity? This initial compression is introduced by high strength steel wire or alloys (called ‘tendon’) located in the concrete section.
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Pre-stressed concrete is a form of concrete where initial compression is given in the concrete before applying the external load so that stress from external loads are counteracted in the desired way during the service period.