# Questions & Answers of Concrete Design- Basic Working Stress

According to IS 456 - 2000, which one of the following statement about the depth of netural axis $\style{font-family:'Times New Roman'}{{\mathrm\chi}_{\mathrm u,\mathrm{bal}}}$ for a balanced reinforced concrete section is correct?

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Let the characteristic strength be defined as that value, below which not more than 50% of the results are expected to fall. Assuming a standerd deviation of 4 MPa, the target mean strength (in MPa) to be considered in the mix design of a M25 concret would be

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As per IS 456:2000, in the Limit State Design of a flexural member, the strain in reinforcing bars under tension at ultimate state should not be less than

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The cross-section of a thermo-mechanically treated (TMT) reinforcing bar has

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The modulus of rupture of concrete in terms of its characteristic cube compressive strength (fck) in MPa according to IS 456:2000 is

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For limit state of collapse, the partial safety factors recommended by IS 456:2000 for estimating the design strength of concrete and reinforcing steel are respectively

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Column I gives a list of test methods for evaluating properties of concrete and Column II gives the list of properties

 Column I Column II P. Resonant frequency test 1. Tensile strength Q. Rebound hammer test 2. Dynamic modulus of elasticity R. Split cylinder test 3. Workability S. Compacting factor test 4. Compressive strength

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A reinforced concrete structure has to be constructed along a sea coast. The minimum grade of concrete to be used as per IS: 456-2000 is

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Un-factored maximum bending moments at a section of a reinforced concrete beam resulting from a frame analysis are 50, 80, 120 and 180 kNm under dead, live, wind and earthquake loads respectively. The design moment (kNm) as per IS: 456-2000 for the limit state of collapse (flexure) is

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Consider the following statements:

 I. The compressive strength of concrete decreases with increase in water-cement ratio of the concrete mix. II. Water is added to the concrete mix for hydration of cement and workability. III. Creep and shrinkage of concrete are independent of the water-cement ratio in the concrete mix.

The TRUE statements are

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Consider the following statements:

 I. Modulus of elasticity of concrete increases with increase in compressive strength of concrete. II. Brittleness of concrete increases with decrease in compressive strength of concrete. III. Shear strength of concrete increases with increase in compressive strength of concrete.

The TRUE statements are