Comparison of reinforced concrete and prestressed concrete

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1. Welcome to our presentation Topic: Comparison of Reinforced Concrete and Prestressed Concrete Presented By: Md . Estiak Hossain Shuvo Daffodil International University E-mail: [email protected] Department of Civil Engineering

2. What is a Reinforced Concrete ? Reinforced concrete (RC) (also called reinforced cement concrete or RCC) is a composite material in which concrete 's relatively low tensile strength and ductility are counteracted by the inclusion of reinforcement having higher tensile strength or ductility. Reinforced concrete , Concrete in which steel is embedded in such a manner that the two materials act together in resisting forces. The reinforcing steel—rods, bars, or mesh absorbs the tensile, shear, and sometimes the compressive stresses in a concrete structure. Reinforced Concrete

3. Prestressed Concrete Prestressed concrete is a structural material that allows for predetermined, engineering stresses to be placed in members to counteract the stresses that occur when they are subject to loading. It combines the high strength compressive properties of concrete with the high tensile strength of steel. Prestressing is the introduction of a compressive force to the concrete to counteract the stresses that will result from an applied load. ... This is done by placing of high tensile steel tendons in a desired profile in which the concrete is to be cast. What is a Prestressed Concrete ?

4. Construction(Reinforced Concrete) Mild Steel bars are placed according to the design. No wires cables and tendons are needed in RCC. Formwork have to be done with a good supervision. Concrete is mixed with essential ratio. Place the mixed aggregates in the reinforcement. concrete should be compacted. Curing for 28 days.

5. Construction( Prestressed Concrete) In slab-on-ground construction, unbonded tendons are typically prefabricated at a plant and delivered to the construction site, ready to install. The tendons are laid out in the forms in accordance with installation drawings that . After the concrete is placed and has reached its required strength, usually between 3000 and 3500 psi (“pounds per square inch”), the tendons are stressed and anchored. The tendons, like rubber bands, want to return to their original length but are prevented from doing so by the anchorages. The fact the tendons are kept in a permanently stressed (elongated) state causes a compressive force to act on the concrete. The compression that results from the post-tensioning counteracts the tensile forces created by subsequent applied loading (cars, people, the weight of the beam itself when the shoring is removed). This significantly increases the load-carrying capacity of the concrete. Since post-tensioned concrete is cast in place at the job site, there is almost no limit to the shapes that can be formed. Limitations of Prestressing The limitations of prestressed concrete are few and really depend only upon the imagination of the designer and the terms of his brief. The only real limitation where prestressing is a possible solution may be the cost of providing moulds for runs of limited quantity of small numbers of non-standard units.

6. ADVANTAGE of REINFORCED CONCRETE Reinforced concrete has a high compressive strength compared to other building materials. Due to the provided reinforcement, reinforced concrete can also withstand a good amount of tensile stress. Fire and weather resistance of reinforced concrete is fair. The reinforced concrete building system is more durable than any other building system. Reinforced concrete, as a fluid material, in the beginning, can be economically molded into a nearly limitless range of shapes. The maintenance cost of reinforced concrete is very low. In structures like footings, dams, piers etc. reinforced concrete is the most economical construction material. It acts like a rigid member with minimum deflection. As reinforced concrete can be molded to any shape required, it is widely used in precast structural components. It yields rigid members with minimum apparent deflection. Compared to the use of prestressed concrete in structure, reinforced concrete requires less skilled labor for the erection of the structure.

7. ADVANTAGE of PRESTRESSED CONCRETE Prestressed concrete sections are thinner and lighter than RCC sections, since high strength concrete and steel are used prestressed concrete. In prestressed concrete, whole concrete area is effective in resisting loads, unlike RCC where concrete below the neutral axis is neglected. Thinner sections in prestressed concrete results in less self weight and hence overall economy. Long span bridges and flyovers are made of prestressed concrete because of lesser self weight and thinner section. So, prestressed concrete is used for heavily loaded structures. Prestressed concrete members show less deflection. Since the concrete does not crack in prestressesd concrete, rusting of steel is minimized. Prestressed concrete is used in the structures where tension develops or the structure is subjected to vibrations, impact and shock like girders, bridges, railway sleepers, electric poles, gravity dams, etc. Precast members like electric poles and railway sleepers are produced in factories using simple pre-stressing methods.

8. DISADVANTAGE of REINFORCED CONCRETE The tensile strength of reinforced concrete is about one-tenth of its compressive strength. The main steps of using reinforced concrete are mixing, casting, and curing. All of this affects the final strength. The cost of the forms used for casting RC is relatively higher. For multi-storied building the RCC column section for is larger than steel section as the compressive strength is lower in the case of RCC. Shrinkage causes crack development and strength loss.

9. DISADVANTAGE of PRESTRESSED CONCRETE Prestressed concrete construction requires very good quality control and supervisions Cost of materials used in prestressed is very high (high tensile steel is about three times costlier than mild steel). Prestressed concrete requires specialized tensioning equipment and devices which are very costly. Prestressed concrete sections are more brittle because of use of high tension steel.

10. In RCC beam the concrete in the compression side of the neutral side of the axis alone is effective. The concrete in the tension side of the neutral axis is ineffective. But in the prestressed concrete beam, the entire section is effective. Reinforced concrete beams are generally heavy. They always need shear reinforcements besides the longitudinal reinforcement for flexure. Prestressed concrete beams are lighter. By providing the curved tendons and the pre-compression, a considerable part of the shear is resisted. In reinforced concrete beams, high strength concrete is not needed. But in prestressed concrete beams, high strength concrete and high strength steel are necessary. High strength concrete is needed to resist high stresses at the anchorages. High strength steel is needed to transfer large prestressing force. Reinforced concrete beams being massive and heavy are more suitable in situations where the weight is more desired than strength. Prestressed concrete beams are very suitable for heavy loads and longer spans. They are slender and artistic treatments can be easily provided. Cracks do not occur under working loads. Even if a minute crack occurs when overloaded, such crack gets closed when the overload is removed. The deflections of the prestressed concrete beams are small. In reinforced concrete beams, there is no way testing the steel and the concrete. In prestressed concrete beams, testing of steel and concrete can be made while prestressing . The Summary of comparisons between the RCC and prestressed concrete

11. Reference: 1. 2. 3. 4. 5. Design of Prestressed Concrete Sturctures . Written by T.Y. LIN NED H. BURNS Prestressed Concrete Lecture By Uzzwal Kumar Deb Nath

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