Advantages of doubly reinforced beam


  • Design of Doubly Reinforced Concrete Rectangular Beams with Example
  • Reinforced cement concrete advantage – Use
  • What is Doubly & Singly reinforced Beam-why we provide it
  • Doubly Reinforced Beams
  • Under-reinforced v/s Over-reinforced
  • Design of Doubly Reinforced Concrete Rectangular Beams with Example

    There are different types of concrete that do not include reinforcements. Gravity structures such as retaining walls, mas concrete dams, etc are constructed without reinforcements. They are constructed in a way that does not develop the tensile stresses in the section.

    If no tension in the concrete, no reinforcement is required for such structures. This does not mean that it applies to all the structural elements. For example, concrete columns subjected to pure compression when the tension stresses induced by the bending moments are less than the axial compression. Though the section is in full compression, we have provided the reinforcements at least to avoid buckling. The nature of the structure decided with it is to be reinforced concrete or unreinforced concrete.

    The most widely used construction material is the reinforced concrete when compared to other materials such as steel and timber. The combination of reinforcement with concrete provides the required strength. Adjustment to the element sizers is made based on the applied loads such as axial force, bending moments, shear forces, torsional moments, etc. Both the cast in situ concrete and precast concrete can be reinforced. Why do we Need Reinforcements?

    Consider a beam. The cantilever beam indicates above shows the strain variation within the section. Compression stress can be born by concrete and tension stress will be transferred to reinforcement as concrete cannot carry such large stress without cracking.

    Generally, there are two categories for reinforced concrete depending on the reinforcement requirement. They are Singly reinforced Doubly reinforced The nature of the load and amount of load will decide whether it is required to provide compression reinforcement or not. The articles Desing of singly reinforced beam and Design of doubly reinforced section could be referred for a method of designing a section.

    Attention shall be made to the durability requirements and durability of concrete when reinforced concrete is designed. Concrete could deteriorate due to various issues such as carbonation, chlorination, etc. Therefore, necessary cover to the reinforcement, grade of concrete, and relevant water-cement ration, suitable construction material, ect. Concrete Grade Selected based on the exposure class and as per the durability requirements.

    The standards BS provide a comprehensive guide to select the concrete. Reinforcements Reinforcement shall be tested in accordance with the relevant standards before use.

    The sequence of tenting and sampling shall be as per the specification or relevant code. Factors affecting strength of concrete The article factors affecting strength of concrete could be referred to for more information. Serviceability Limit State All the structures are checked for the serviceability limit state.

    It is the state that the structure checked for factored loads. Sizing of foundations, deflections, crack control, etc are checked for the serviceability limit state. Ultimate Limit State All the structures are designed for the ultimate limit stage. Load factors are based on the type of loads and as per the relevant standards. Reinforcement in reinforced concrete The usual reinforcement is provided in the reinforced concrete structure.

    Apart from that other types of reinforcements such as fiber reinforcement are also used in the construction as reinforcements to bear the tensile stresses in the concrete. Waterproofing All the reinforced concrete structures constructed underground or below the water table are subject to damping and subsequent it could lead to corrosion when such reinforced concrete exposed to oxygen.

    Depending on the importance of the structure, structures are waterproofed. This can be considered a durability requirement. The article advantage and disadvantage of reinforced concrete could be referred for more enforcement on its usage. You may also like

    Reinforced cement concrete advantage – Use

    Post comments: 0 Comments Learn: Types of R. A beam made up of plain cement concrete will have low load carrying capacity and will fail by cracking in the tension zone. It is therefore reinforced by placing steel bars in the tensile zone.

    These bars will take up the tensile stresses and thus increase the load carrying capacity or strength of the beam. The steel placed in the tensile zone, is called as longitudinal steel or main steel. Thus, the beam forms a part of the floor system. When the beam bends, a part of the slab also bends along with the beam. So, the intermediate beams in a floor system act as T beams and the end beams as L beams. The beams in which a portion of the slab acts together with the beam for resisting compressive stresses are called as flanged beams.

    Figure 2. In this method, the ultimate compressive strength of concrete and the yield stress of steel are divided by the appropriate factors of safety to get the allowable or permissible stresses in the materials under working loads. Fundamental assumptions of elastic theory of bending The fundamental assumptions of elastic theory of bending are explained below: A section which is plane before bending remains plane after bending.

    This assumption implies that the strain above and below the neutral axis are proportional to the distance from the neutral axis i. The concrete and steel reinforcement are perfectly bonded. It means that the tensile strain in steel reinforcement is equal to the tensile strain in concrete surrounding the steel. All tensile stresses are taken up by steel and none by concrete. This assumptions implies that the contribution of concrete to take tension is completely neglected and the concrete is assumed to be cracked in the tension zone.

    The stress-strain relationship of steel and concrete under working loads is a straight line. It implies that stress distribution is also linear like strain distribution, with a zero at the neutral axis to maximum value at the extreme fibres. The modulli of elasticity of steel Es and concrete Ec are constant. There are no initial stresses in steel and concrete.

    What is Doubly & Singly reinforced Beam-why we provide it

    It is important to notice that it is the yielding stain that is considered as failure strain in steel and not the ultimate fracture strain. The steel still has to undergo strain hardening, softening and then fracture. Over Reinforced Section The steel provided in the beam is such that concrete reach the limiting values of strain prior to steel.

    This results in breaking of concrete and since now there is no concrete present to take the compression the beam fails suddenly. The additional margin that we get in under reinforced section helps in prevention of a sudden failure and provide the necessary warning to the inhabitants of the building.

    We do this with the help of interactive android applications and accompanying web articles and videos. Our apps have helped more than thousand students across the world to understand and learn the concepts of structural engineering.

    Check out our apps on the google play store. The beams in which a portion of the slab acts together with the beam for resisting compressive stresses are called as flanged beams.

    Doubly Reinforced Beams

    Figure 2. In this method, the ultimate compressive strength of concrete and the yield stress of steel are divided by the appropriate factors of safety to get the allowable or permissible stresses in the materials under working loads. Fundamental assumptions of elastic theory of bending The fundamental assumptions of elastic theory of bending are explained below: A section which is plane before bending remains plane after bending.

    This assumption implies that the strain above and below the neutral axis are proportional to the distance from the neutral axis i.

    Under-reinforced v/s Over-reinforced

    The concrete and steel reinforcement are perfectly bonded. It means that the tensile strain in steel reinforcement is equal to the tensile strain in concrete surrounding the steel. All tensile stresses are taken up by steel and none by concrete. This assumptions implies that the contribution of concrete to take tension is completely neglected and the concrete is assumed to be cracked in the tension zone.

    The stress-strain relationship of steel and concrete under working loads is a straight line.


    thoughts on “Advantages of doubly reinforced beam

    • 04.08.2021 at 14:33
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      It is grateful for the help in this question how I can thank you?

      Reply
    • 12.08.2021 at 00:33
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      Very much a prompt reply :)

      Reply

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