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Concrete Structures (GATE)

GATE preparation quiz covering IS 456-2000, limit state design, prestressed concrete, beams, columns, shear, torsion, and concrete material properties

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Questions

Question 1 Multiple Choice (Single Answer)

A concrete beam of rectangular cross section of size 120 mm (width) and 200 mm (depth) is pre-stressed 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

  1. 2.5 N/mm2 (compression), 10 N/mm2 (compression)
  2. 10 N/mm2 (tension), 3.75 N/mm2
  3. 3.75 N/mm2 (tension), 3.75 N/mm2 (compression)
  4. 2.75 N/mm2 (compression), 3.75 N/mm2 (compression)
Question 2 Multiple Choice (Single Answer)

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

  1. II and III
  2. I, II and III
  3. I and II
  4. I and III
Question 3 Multiple Choice (Single Answer)

Consider the following statements:

  1. The compressive strength of concrete decreases with increase in water-cement ratio of the concrete mix.
  2. Water is added to the concrete mix for hydration of cement and workability.
  3. Creep and shrinkage of concrete are independent of the water-cement ratio in the concrete mix.
    The true statement(s) is/are
  1. 1 and 2
  2. 1, 2 and 3
  3. 2 and 3
  4. only 2
Question 4 Multiple Choice (Single Answer)

The percentage loss of pre-stress 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

  1. 0.0175
  2. 0.175
  3. 1.75
  4. 17.5
Question 5 Multiple Choice (Single Answer)

A reinforced concrete beam of rectangular cross section of breadth 230 mm and effective depth 400 mm is subjected to maximum factored shear force of 120kN. The grades of concrete, main steel and stirrup steel are M20, Fe415 and Feb250 respectively. For the area of main steel provided, the design shear strength $ \tau_c $ is per IS: 456-2000 is 0.48 N/mm2. The beam is designed for collapse limit state.

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

  1. 40
  2. 115.323
  3. 250
  4. 400
Question 6 Multiple Choice (Single Answer)

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

  1. 11
  2. 9
  3. 7
  4. 5
Question 7 Multiple Choice (Single Answer)

A reinforced concrete beam of rectangular cross section of breadth 230 mm and effective depth 400 mm is subjected to maximum factored shear force of 120 kN. The grades of concrete, main steel and stirrup steel are M20, Fe415 and Feb250 respectively. For the area of main steel provided, the design shear strength $ \tau_c $ is per IS: 456-2000 is 0.48 N/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

  1. 50.42
  2. 130.56
  3. 151.67
  4. 200.23
Question 8 Multiple Choice (Single Answer)

For avoiding the limit state of collapse, the safety of R.C. structures is checked for appropriate combinations of dead load (DL), imposed load or live load (IL), wind load (WL) and earthquake load (EL). Which of the following load combinations is NOT considered?

  1. 0.9 DL + 1.5 WL
  2. 1.5 DL + 1.5 WL
  3. 1.5 WL + 1.5 EL
  4. 1.5 DL + 1.5 WL + 0.5 EL
Question 9 Multiple Choice (Single Answer)

In the limit state design method of concrete structures, the recommended partial material safety factor$(\gamma_m)$for steel according to IS:456-2000 is

  1. 1.5
  2. 1.15
  3. 1.00
  4. 0.87
Question 10 Multiple Choice (Single Answer)

Maximum strains in an extreme fibre in concrete and in the tension reinforcement (Fe - 415 grade and Es = 200 kN/mm2) in a balanced section at limit state of flexure are respectively

  1. 0.0035 and 0.0038
  2. 0.002 and 0.0018
  3. 0.0035 and 0.0041
  4. 0.002 and 0.0031
Question 11 Multiple Choice (Single Answer)

The effective length of a column in a reinforced concrete building frame, as per IS: 456-2000, is independent of the

  1. frame type i.e. braced (no sway) or unbraced (with sway)
  2. span of the beam
  3. height of the column
  4. loads acting on the frame
Question 12 Multiple Choice (Single Answer)

The working stress method of design specifies the value of modular ratio, m = 280/ $(3\sigma_{cbc})$, where $\sigma_{cbc}$is the allowable stress in bending compression in concrete. To what extent does the above value of m make any allowance for the creep of concrete?

  1. No compensation
  2. Full compensation
  3. Partial compression
  4. The two are unrelated
Question 13 Multiple Choice (Single Answer)

As per IS : 456-2000, consider the following statements
I. The modular ratio considered in the working stress method depends on the type of steel used
II. There is an upper limit on the nominal shear stress in beams (even withshear reinforcement) due to the possibility of crushing of concrete in diagonal compression.
III. A rectangular slab whose length is equal to its width may not be a two-way slab for some support conditions.

The TRUE statements are

  1. only I and II
  2. only II and III
  3. only I and III
  4. I, II and III
Question 14 Multiple Choice (Single Answer)

Assuming concrete below the neutral axis to be cracked, the shear stress across the depth of a singlyreinforce rectangular beam section

  1. increases parabolically to the neutral axis and then drops suddently to zero value.
  2. increases parabolically to the neutral axis and then remains constant over the remaining depth
  3. increases linearly to the neutral axis and then remains constant up to the tension steel
  4. increases parabolically to the neutral axis and then remains constant up to the tension steel.
Question 15 Multiple Choice (Single Answer)

Consider the following statements :
I. The width-thickness ratio limitations on the plate elements under compression in steel members are imposed by IS: 800-1984 in order to avoid fabrication difficulties.
II. In a doubly reinforced concrete beam, the strain in compressive reinforcement is higher than the strain in the adjoining concrete.
III. If a cantilever I-section supports slab construction all along its length with sufficient friction between them, the permissible bending stress in compression will be the same as that in tension.

The TRUE statements are

  1. only I and II
  2. only II and III
  3. only I and III
  4. I, II and III
Question 16 Multiple Choice (Single Answer)

IS : 1343 – 1980 limits the minimum characteristics strength of prestressed concrete for post tensioned works and pretension work as

  1. 25 MPa, 30 MPa respectively
  2. 25 MPa, 35 MPa respectively
  3. 30 MPa, 35 MPa respectively
  4. 30 MPa, 40 MPa respectively
Question 17 Multiple Choice (Single Answer)

The partial factor of safety for concrete as per IS : 456-2000 is

  1. 1.50
  2. 1.15
  3. 0.87
  4. 0.446
Question 18 Multiple Choice (Single Answer)

In the design of beams for the limit state of collapse in flexure as per IS : 456-2000, let the maximum strain in concrete be limited to 0.0025 (in place of 0.0035). For this situation, consider a rectangular beam section with breadth as 250 mm, effective depth as 350 mm, area of tension steel as 1500 mm2, and characteristic strengths of concrete and steel as 30 Mpa and 250 MPa respectively.

At the limiting state of collapse in flexure, the force acting on the compression zone of the section is

  1. 326 kN
  2. 382.668 kN
  3. 424 kN
  4. 542 kN
Question 19 Multiple Choice (Single Answer)

In the design of beams for the limit state of colapse in flexure as per IS : 456-2000, let the maximum strain in concrete be limited to 0.0025 (in place of 0.0035). For this situation, consider a rectangular beam section with breadth as 250 mm, effective depth as 350 mm, area of tension steel as 1500 mm2, and characteristics strengths of concrete and steel as 30Mpa and 250 MPa respectively.

The depth of neutral axis for the balanced failure is

  1. 140 mm
  2. 156 mm
  3. 168 mm
  4. 185 mm
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