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What is the difference between under reinforced & over reinforced section?

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What is the difference between under reinforced & over reinforced section?

The yield strain of concrete is reached before the ultimate strength of steel. Over reinforced beam section undergoes a compressive failure. The percentage of tensile reinforcement is more than the amount of reinforcement provided for a balanced section.

What is over reinforced?

An over-reinforced beam is one in which the tension capacity of the tension steel is greater than the combined compression capacity of the concrete and the compression steel (over-reinforced at tensile face).

What are the results of over reinforced and under reinforced concrete?

The over-reinforced section is considered critical when compared with the under-reinforced condition. If over-reinforced, the section can fail suddenly without warning as a result of crushing the concrete. However, in under-reinforced conditions, the section provides more warning prior to the failure.

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Why is over reinforced section not considered for design purpose?

Why over-reinforced sections shall be avoided while designing the sections using limit state method? A section having percentage of tension steel greater than the critical percentage is known as over-reinforced section. Hence, this type of failure is usually avoided in ultimate strength design.

Why it is not preferred to design over reinforced section?

OVER REINFORCED SECTION: Steel in the section is more than that of required for a balanced section, i.e Xu > Xumax. Failure is in concrete , causes a brittle/sudden failure without any prior warning. As per Limit state method of design of over reinforced sections should be avoided.

What is the difference between singly reinforced section and doubly reinforced section?

A Singly reinforced beam holds a steel bar in the tension zone, but in doubly reinforced beams, steel bars are given in both zones, tension, and compression. While in the doubly reinforced beam, compression steel resists compressive stresses and constitutes the addition moment of resistance.

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What is the difference between under-reinforced & over reinforced section?

by Author

What is the difference between under-reinforced & over reinforced section?

The yield strain of concrete is reached before the ultimate strength of steel. Over reinforced beam section undergoes a compressive failure. The percentage of tensile reinforcement is more than the amount of reinforcement provided for a balanced section.

What is an under-reinforced beam?

An under-reinforced beam is one in which the tension capacity of the tensile reinforcement is smaller than the combined compression capacity of the concrete and the compression steel (under-reinforced at tensile face).

What is Xumax?

Xumax is the maximum depth of neutral axis at failure condition at which concrete reaches to a maximum strain of 0.0035, At this condition steel will be in plastic zone with continuous yielding or deformation. Xumax Equation: Xumax / 0.0035 = d-xumax / (0.87fy/Es + 0.002)

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What is a doubly reinforced beam?

Such reinforced concrete beams having steel reinforcement both on tensile and compressive faces are known as doubly reinforced beams. Doubly reinforced beams, therefore, have moment of resistance more than the singly reinforced beams of the same depth for particular grades of steel and concrete.

In which condition a doubly reinforced beam is used?

Doubly reinforced sections are used in the following conditions: When the dimensions (b x d) of the beam are restricted due to any constraints like availability of head room, architectural or space considerations and the moment of resistance of singly reinforced section is less than the external moment.

When and where doubly reinforced beam is required?

Necessity of Doubly reinforced sections due to the following conditions : When the dimensions (b×d) of the beam are restricted due to any constraints like availability of head room, architectural or space considerations and the moment of resistance of singly reinforced section is less than the external moment.

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