Questions & Answers of Concrete Structures

Question No. 6

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?

Question No. 38

A pre-tensioned rectangular concrete beam 150 mm wide and 300 mm depth is prestressed with three straight tendons, each having a cross-sectional area of 50 mm2, to an inital stress of 1200 N/mm2. The tendons are located at 100 mm from the soffit of the beam. If the modular ratio is 6, the loss of prestreeng force (in kN, up to one decimal place) due to the elastic deformation of concrete only is _________

Question No. 115

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

Question No. 130

Group I gives a list of the methods and test apparatus for evaluating some of the properties of Ordinary Portland Cement (OPC) and concrete. Group II gives the list of these properties.

Group I Group II
P. Le Chatelier test 1. Soundness of OPC
Q. Vee-Bee test 2. Consistency and setting time of OPC
R. Blaine air permeability test 3. Consistency or workability of concrete
S. The vicat apparatus 4. Fineness of OPC

The correct match of the items in Group I with the items in Group II is

Question No. 133

Consider the following statements:

P. Walls of one brick thick are measured in square meters.

Q. Walls of one brick thick are measured in cubic meters.

R. NO deduction in the brickwork quantity is made for openings in walls up to 0.1 m2 area.

S. For the measurement of excavation from the borrow pit in a fairly uniform ground, deadmen are left the suitable intervals.

For the above statement, the correct option is

Question No. 140

A simply supported rectangular concrete beam of span 8 m has to be prestressed with a force of 1600 kN. The tendon is of parabolic profile having zero eccentricity at the supports. The beam has to carry an external uniformly distributed load of intensity 30 kN/m. Neglecting the self-weight of the beam, the maximum dip (in meters, up to two decimal places) of the tendon at the mid-span to balance the external load should be _________________

Question No. 17

In shear design of an RC beam, other than the allowable shear strength of concrete (c τ) , there is also an additional check suggested in IS 456-2000 with respect to the maximum permissible shear stress (maxc τ) . The check for  τmax cis required to take care of

Question No. 19

Bull's trench kiln is used in the manufacturing of

Question No. 45

A reinforced concrete (RC) beam with width of 250 mm and effective depth of 400 mm is reinforced with Fe415 steel. As per the provisions of IS 456-2000, the minimum and maximum amount of tensile reinforcement (expressed in mm2) for the section are, respectively

Question No. 46

For M25 concrete with creep coefficient of 1.5, the long-term static modulus of elasticity (expressed in MPa) as per the provisions of IS:456-2000 is ________

Question No. 117

As per IS 456-2000 for the design of reinforced concrete beam, the maximum allowable shear stress τc max depends on the

Question No. 145

A haunched (varying depth) reinforced concrete beam is simply supported at both ends, as shown in the figure. The beam is subjected to a uniformly distributed factored load of intensity 10 kN/m.  The design shear force (expressed in kN) at the section X-X of the beam is ______

Question No. 14

Workability of concrete can be measured using slump, compaction factor and Vebe time. Consider the following statements for workability of concrete:
(i) As the slump increases, the Vebe time increases
(ii) As the slump increases, the compaction factor increases
Which of the following is TRUE ?

Question No. 15

Consider the following statements for air-entrained concrete:
(i) Air-entrainment reduces the water demand for a given level of workability
(ii) Use of air-entrained concrete is required in environments where cyclic freezing and thawing is expected
Which of the following is TRUE ?

Question No. 16

Consider the singly reinforced beam shown in the figure below:

At cross-section XX, which of the following statements is TRUE at the limit state ?

Question No. 18

The development length of a deformed reinforcement bar can be expressed as $\left(\phi\sigma_s/\tau_{bd}\right)$. From the IS:456-2000, the value of k can be calculated as _________.

Question No. 41

The composition of an air-entrained concrete is given below:

Water       :184 kg/m3
Ordinary Portland Cement(OPC)       :368 kg/m3
Sand       :606 kg/m3
Coarse aggregate       :1155 kg/m3

Assume the specific gravity of OPC, sand and coarse aggregate to be 3.14, 2.67 and 2.74, respectively. The air content is ______ litres/m3.

Question No. 43

Consider the singly reinforced beam section given below(left figure). the stress block parameters for the cross- section from IS: 456-2000 are also given below (right figure). The moment of resistance for the given section by the limit state method is ______ kN-m.

Question No. 119

A column of size 450 mm × 600 mm has unsupported length of 3.0 m and is braced against side sway in both directions. According to IS 456: 2000, the minimum eccentricities (in mm) with respect to major and minor principal axes are :

Question No. 141

A simply supported reinforced concrete beam of length 10 m sags while undergoing shrinkage. Assuming a uniform curvature of 0.004 m-1 along the span, the maximum deflection (in m) of the beam at mid-span is _________.

Question No. 144

According to the concept of Limit State Design as per IS 456:2000, the probability of failure of a structure is _________.

Question No. 145

In a pre-stressed concrete beam section shown in the figure, the net loss is 10% and the final pre-stressing force applied at X is 750 kN. The initial fiber stresses (in N/mm2) at the top and bottom of the beam were:

Question No. 16

Match the information given in Group – I with those in Group - II.

Group – I Group – II
P Factor to decrease ultimate strength to design strength                      1 Upper bound on ultimate load
Q Factor to increase working load to ultimate load for design 2 Lower bound on ultimate load
R Statical method of ultimate load analysis 3 Material partial safety factor
S Kinematical mechanism method of ultimate load analysis 4 Load factor
   

Question No. 19

While designing, for a steel column of Fe250 grade, a base plate resting on a concrete pedestal of M20 grade, the bearing strength of concrete (in N/mm2) in limit state method of design as per IS:456-2000 is ________________

Question No. 117

The first moment of area about the axis of bending for a beam cross-section is

Question No. 120

The flexural tensile strength of M25 grade of concrete, in N/mm2, as per IS:456-2000 is __________

Question No. 121

The modulus of elasticity, E=5000fck where fck is the characteristic compressive strength of concrete, specified in IS:456-2000 is based on

Question No. 4

Maximum possible value of Compacting Factor for fresh (green) concrete is:

Question No. 6

The creep strains are

Question No. 35

A rectangular concrete beam 250 mm wide and 600 mm deep is pre-stressed by means of 16 high tensile wires, each of 7 mm diameter, located at 200 mm from the bottom face of the beam at a given section. If the effective pre-stress in the wires is 700 MPa, what is the maximum sagging bending moment (in kNm) (correct to 1-decimal place) due to live load that this section of the beam can withstand without causing tensile stress at the bottom face of the beam ? Neglect the effect of dead load of beam. ________________

Question No. 7

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

Question No. 8

Which one of the following is categorised as a long-term loss of prestress in a prestressed concrete member?

Question No. 33

A concrete beam prestressed with a parabolic tendon is shown in the sketch. The eccentricity of the tendon is measured from the centroid of the cross-section. The applied prestressing force at service is 1620 kN. The uniformly distributed load of 45 kN/m includes the self-weight.

The stress (in N/mm2) in the bottom fibre at mid-span is

Question No. 52

The cross-section at mid-span of a beam at the edge of a slab is shown in the sketch. A portion of the slab is considered as the effective flange width for the beam. The grades of concrete and reinforcing steel are M25 and Fe415, respectively. The total area of reinforcing bars (As) is 4000 mm2. At the ultimate limit state, xu denotes the depth of the neutral axis from the top fibre. Treat the section as under-reinforced and flanged (xu > 100 mm).

The value of xu (in mm) computed as per the Limit State Method of IS 456:2000 is

Question No. 53

The cross-section at mid-span of a beam at the edge of a slab is shown in the sketch. A portion of the slab is considered as the effective flange width for the beam. The grades of concrete and reinforcing steel are M25 and Fe415, respectively. The total area of reinforcing bars (As) is 4000 mm2. At the ultimate limit state, xu denotes the depth of the neutral axis from the top fibre. Treat the section as under-reinforced and flanged (xu > 100 mm).

The ultimate moment capacity (in kNm) of the section, as per the Limit State Method of IS 456:2000 is

Question No. 5

A 16 mm thick plate measuring 650 mm x 420 mm is used as a base plate for an ISHB 300 column subjected to a factored axial compressive load of 2000 kN. As per IS 456-2000,The minimum grade of concrete that should be used below the base plate for safely carrying the load is

Question No. 6

Consider a reinforcing bar embedded in concrete. In a marine environment this bar under goes uniform corrosion, which leads to the deposition of corrosion products on its surface and increase in the apparent volume of the bar. This subjects the surrounding concrete to expansive pressure. As a result, corrosion induced cracks appear at the surface of  concrete. Which of the following statements is TRUE?

Question No. 8

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

Question No. 33

consider a bar of diameter "D"embedded in a large concrete block as shown in the adjoining figure, with a pull out of force P being applied. Let σb and σst be the bond strength (between the bar and concrete) and the tensile strength of the bar, respectively. If the block is held in position and it is assumed that the material of the block dies not fail, which of the following options represents the maximum value of P?

Question No. 34

Consider two RCC beams, P and Q, each having the section 400 mm × 750mm (effective depth,d=750mm) made with concrete having a τcmax=2.1 N/mm2 . For the reinforcement provided and the grade of concrete used, it may be assumed that the τc =0.75 N/mm2 .The design shear in beam P is 400 kN and in beam Q is 750 kN.Considering the provisions of IS 456-2000, which of the following statements is TRUE?

Question No. 9

As per India standard code of practice for prestressed concrete (IS:1343-1980) the minimum grades of concrete to be used for post-tensioned and pre-tensioned structural elements are respectively

Question No. 52

A doubly reinforced rectangular concrete beam has a width of 300 mm and an effective depth of 500mm. the beam is reinforced with 2200 mm2 of steel in tension and 628 mm2 of steel in compression. The effective cover for compression steel is 50mm. Assume that both tension and compression steel yield. The grades of concrete and steel used are M20 and Fe250 respectively. The stress lock parameters (rounded off to first two decimal places) for concrete shall be as per IS 456:200.

The depth of neutral axis is

Question No. 53

A doubly reinforced rectangular concrete beam has a width of 300 mm and an effective depth of 500mm. the beam is reinforced with 2200 mm2 of steel in tension and 628 mm2 of steel in compression. The effective cover for compression steel is 50mm. Assume that both tension and compression steel yield. The grades of concrete and steel used are M20 and Fe250 respectively. The stress lock parameters (rounded off to first two decimal places) for concrete shall be as per IS 456:200.

The moment of resistance of the section is

Question No. 5

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

Question No. 7

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

Question No. 33

A rectangular concrete beam of width 120 mm and depth 200 mm is prestressed by pretensioning to a force of 150 kN at an eccentricity of 20 mm. The cross sectional area of the prestressing steel is 187.5 mm2. Take modulus of elasticity of steel and concrete as 2.1×105 MPa and 3.0×104 MPa respectively. The percentage loss of stress in the prestressing steel due to elastic deformation of concrete is

Question No. 34

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

Question No. 4

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

Question No. 5

In the design of a reinforced concrete beam the requirement for bond is not getting satisfied. The economical option to satisfy the requirement for bond is by

Question No. 37

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

Question No. 38

A reinforced concrete column contains longitudinal steel equal to 1 percent of net cross-sectional area of the column. Assume modular ration as 10. the loads carried (using the elastic theory) by the longitudinal steel and the net area of concrete, are Ps and Pc respectively. The ration Ps/Pc expressed as percent is

Question No. 39

A pre-tensioned concrete member of section 200mm × 250mm contains tendons of area 500 mm2 at the centre of gravity of the section. The prestress in tendons is 1000N/mm2. Assuming modular ratio as 10, the stress (N/mm2) in concrete is

Question No. 74

A reinforced concrete beam of rectangular cross section of breadth 230 mm and effective depth 400 mm is subjected to a maximum factored shear force of 120 kN. The grade of concrete, mains steel and stirrup steel are M20, F415 and Feb 250 respectively. For the area of main steel provided, the design shear strength τc as per IS : 456-2000 is 0.48N/mm2. The beam is designed for collapse limit state

The spacing (mm) of 2-legged 8 mm stirrups to be provided is

Question No. 75

A reinforced concrete beam of rectangular cross section of breadth 230 mm and effective depth 400 mm is subjected to a maximum factored shear force of 120 kN. The grade of concrete, mains steel and stirrup steel are M20, F415 and Feb 250 respectively. For the area of main steel provided, the design shear strength τc as per IS : 456-2000 is 0.48N/mm2. The beam is designed for collapse limit state

In addition, the beam is subjected to a torque whose factored value is 10.90 kNm. The stirrups have to be provided to carry a shear (kN) equal to

Question No. 37

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

Question No. 38

The percentage loss of prestress due to anchorage slip of 3 mm in a concrete beam of length 30 m which is post-tensioned by a tendon with an initial stress of 1200 N/mm2 and modulus of elasticity equal to 2.1 x 105 N/mm2 is

Question No. 39

A concrete beam of rectangular cross-section of size 120 mm (width) and 200 mm (depth) is prestressed by a straight tendon to an effective force of 150 kN at an eccentricity of 20 mm (below the centroidal axis in the depth direction). The stresses at the top and bottom fibres of the section are

Question No. 40

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

Question No. 78

A singly reinforced rectangular concrete beam has a width of 150 mm and an effective depth of 330 mm. The characteristics compressive strength of concrete is 20 MPa and the characteristics tensile strength of steel is 415 MPa. Adopt the stress block for concrete as given in IS 456-2000 and take limiting value of depth of neutral axis as 0.48 times the effective depth of the beam.

The limiting value of the moment of resistance of the beam in kN.m is

Question No. 79

A singly reinforced rectangular concrete beam has a width of 150 mm and an effective depth of 330 mm. The characteristics compressive strength of concrete is 20 MPa and the characteristics tensile strength of steel is 415 MPa. Adopt the stress block for concrete as given in IS 456-2000 and take limiting value of depth of neutral axis as 0.48 times the effective depth of the beam.

The limiting area of tension steel in mm2 is