Design of Concrete Structures - II: Multiple Choice Questions (MCQ) & Answers

 


Unit 1: Staircases (Limit state method)

Multiple Choice Questions

1.      The effective span of the staircase supported at top and bottom risers by beams spanning in parallel with the riser is

A.     Clear distance between beams

B.     Distance between c/c of beams

C.     Clear distance between beams + d

D.     None of the above

ANS: B

2.     If R and T are rise and tread of a stair spanning horizontally, the steps are supported by a wall on one side and by a stringer beam on the other side, the steps are designed as beams of width

A.     R + T

B.     T – R

C. (R2  +T2)

D.     R - T

ANS: C

3.     If T and R are tread and rise respectively of a stair, then

A.     2R + T = 60

B.     R + 2T = 60

C.     2R + T = 30

D.     R + 2T= 30

ANS: A

4.      The minimum head room over a stair must be

A.     200 cm

B.     205 cm

C.     210 cm

D.     230 cm

ANS:  C

5.      The number of treads in a flight is equal to

A.     risers in the flight

B.     risers plus one

C.     risers minus one

D.     None of the mentioned

ANS: C

6.      For stairs spanning horizontally, the minimum waist provided is

A.     4 cm

B.     6 cm

C.     10 cm

D.     12 cm

ANS: D

7.      For stairs spanning l metres longitudinally between supports at the bottom and top of a flight carrying a load w per unit horizontal area, the maximum bending moment per metre width, is

A.      Wl2/4

B.      Wl2/12

C.     Wl2/10

D.     Wl2/8

ANS: D

8.      The horizontal portion of a step in a staircase is known as

A.     Rise

B.     Flight

C.     Winder

D.     Tread

ANS: D

9.      If longitudinally spanning stairs are casted along with their landings, the maximum bending moment per meter width is taken as

A.     Wl2/8

B.     Wl2/4

C.     Wl2/12

D.     Wl2/10

ANS: A

10.   The effective span of stairs without stringer beams Where supported at the top and bottom risers by beams spanning parallel with the risers, shall be taken as the distance _________ between beams

A.     Centre-to-centre

B.     Clear distance

C.     centre-to-centre +d

D.     Clear distance + d

ANS: A

11.   In the case of stairs with open wells, where spans partly crossing at right angles occur, the load on areas common to any two such spans may be taken as ____ in each direction

A.     2

B.     1/2

C.     1

D.     3/4

ANS: B

12.   In the case of stairs where flights or landings are embedded into walls for a length of not less than 110 mm and are designed to span in the direction of the flight, a _____ mm strip may be deducted from the loaded area and the effective breadth of the section increased by75 mm for purposes of design

A.     150

B.     120

C.     110

D.     100

ANS: A

13.   In the case of stairs where spanning on to the edge of a landing slab, which spans parallel, with the risers, a distance equal to the ___________ or one metre, whichever is smaller.

A.     going of the stairs plus at each end either half the width of the landing

B.     nosing of the stairs plus at each end either half the width of the landing

C.     going of the stairs plus at each end either full the width of the stair.

D.     going of the stairs plus at each end either half the width of the landing

ANS: A

14.   In the case of stairs where the landing slab spans in the same direction as the stairs, they shall be considered as acting together to form a single slab and the span determined as the _______ of the supporting beams or walls

A.     distance inner face-to-face

B.     distance center-to-center

C.     distance outer face-to-face

D.     distance centre - to - centre + d

ANS: B

15.   Self-weight of step per m run will be

A.     R/2 *25

B.     T/2 *25

C.     R/2 *18

D.     T/2 *18

ANS: A


Unit 2: Column Footings

 1.     If the width of the foundation for two equal columns is restricted, the shape of the footing generally adopted, is

A.     Square

B.     Rectangular

C.     Trapezoidal

D.     Triangular

ANS: B

2.     To ensure uniform pressure distribution, the thickness of the foundation is

A.     Kept uniform throughout

B.     Increased gradually towards the edge

C.     Decreased gradually towards the edge

D.     Kept zero at the edge

ANS: C

3.     The self-weight of the footing is

A.     Not considered for calculating the upward pressure on footing

B.     Also considered for calculating the upward pressure on footing

C.     Not considered for calculating the area of the footing

D.     Both (b) and (c)

ANS: A

4.      Design a square footing for a short axially loaded column of size 230 × 300 mm carrying 500 kN load. Use M20 concrete and fe415 steel. SBC of soil is 180 kN/m2

A.     2m × 2m

B.     2.5m x 2.5m

C.     1.67 m x 1.67 m

D.     1 m x 1 m

ANS:  C

5.      The transverse reinforcements provided at right angles to the main reinforcement

A.     distribute the load

B.     resist the temperature stresses

C.     resist the shrinkage stress

D.     all the above

ANS: D

6.      For reinforcement in the short direction, a central band equal to the width of the footing shall be

    







ANS: A

7.      Bottom bars under the columns are extended into the interior of the footing slab to a distance greater than

A.      42 f from the center of the column

B.      42 f from the inner edge of the column

C.     42 f from the outer edge of the column

D.     24 f from the center of the column

ANS: C

8.      The weight of a foundation is assumed as

A.     5% of wall weight

B.     10% of wall weight

C.     12% of wall weight

D.     15% of wall weight

ANS: B

9.      According to I.S.: 456, 1978 the thickness of reinforced concrete footing on piles at its edges, is kept less than

A.     200 mm

B.     300 mm

C.     450 mm

D.     750 mm

ANS: A

10.   A foundation is called shallow if its depth, is

A.     one-fourth of its width

B.     half of its width

C.     three-fourth of its width

D.     equal to its width

ANS: D

11.   According to I.S.: 456, 1978 the thickness of reinforced concrete footing on piles at its edges, is kept less than

A.     5 cm

B.     10 cm

C.     15 cm

D.     25 cm

ANS: C

12.   If p is the net upward pressure on a square footing of side b for a square column of side a, the maximum bending moment is given by

A.     B.M. = pb(c-a)/4

B.     B.M. = pb(b-a)2/4

C.     B.M. = pb(c-a)2/8

D.     B.M. = pb(b+a)/8

ANS: C

13.   The combined footing is required in following situations

A.     If loaded footing of columns overlap

B.     Columns may be near to property line

C.     S. B. C. of soil being less

D.     All a), b) and c)

ANS: D

14.   If is the punching shear resistance per unit area a, is the side of a square footing for a column of side b, carrying a weight W including the weight of the footing, the depth (D) of the footing from punching shear consideration is

A.     D = W (a - b)/4a²bq

B.     D = (a² - b²)/4a²bq

C.     D = (a² - b²)/8a²bq

D.     D = W (a² - b²)/4abq

ANS: B

15.   The unit weights of various materials used for building construction are given in _____

A.     IS:456-2000

B.     IS:875 (Part-I) – 1987

C.     IS:12119-1987

D.     IS: 5816-1999

ANS: B

=============================== ++++ ===============================

Unit 3: Analysis and design of cantilever and counterfort retaining walls

1.     The stability of a retaining wall is checked for which of the following condition

A. Overturning about toe

B. Overturning about heal

C. Both of above

D. None of the above

ANS: A

2. The the maximum load that a structure has to withstand and for which it is to be designed is called as

A. Ultimate load

B. Characteristic load

C. Working load

D. None of the above

ANS: A

3. Which of the following is a type of retaining wall?

I. Simply supported retaining wall

II. Counterfort retaining wall

III. Cantilever retaining wall

A. I and II only

B. II and III only

C. I and III only

D. I, II and III

ANS: B

4.     In Cantilever retaining wall stem, heal slab and toe slab are all acting as cantilever due to pressure from

A.     Backfill only

B.     Soil pressure only

C.     Both a and b

D.     Neither a nor b

ANS:  C

5.      The toe projection of foundation slabs is taken as ____

A.     as one-third of the base

B.     as one sixth of the overall height of the wall

C.     equal to heel slab

D.     below ground surface.

ANS: A

6.      In reinforced & plain concrete footings, the thickness at the edge shall not be less than __________ mm for footing on soil

A.     100 mm

B.     200 mm

C.     150 mm

D.    230 mm

ANS: C

7.      Cantilever retaining walls can be safely used for height, not more than ___.

A.      3 m

B.      4 m

C.     5 m

D.     6 m

ANS: D

8.      The design of a retaining wall assumes that the retained earth is _______

A.     dry

B.     is free from moisture

C.     is not cohesive

D.     consists of granular particles

E.     all the above

ANS: E

9.      The thickness of the base slab of a retaining wall generally provided, is -______

A.     one half of the width of the stem at the bottom

B.     one-third of the width of the stem at the bottom

C.     one-fourth of the width of the steam at the bottom

D.     width of the stem at the bottom

E.      twice the width of the steam at the bottom.

ANS: D

10.   Pick up the incorrect statement from the following:

A.     In the stem of a retaining wall, reinforcement is provided near the earthside

B.     In the toe slab of a retaining wall, reinforcement is provided at the bottom of the slab

C.     In the heel slab of a retaining wall, reinforcement is provided at the top of the slab

D.     None of these.

ANS: D

11.   To have pressure wholly compressive under the base of a retaining wall of width b, the resultant of the weight of the wall and the pressure exerted by the retained earth should have eccentricity not more than ____

A.     b/3

B.     b/4

C.     b/6

D.     b/8

ANS: C

12.   Total pressure on the vertical face of a retaining wall of height h acts parallel to the free surface and from the base at a distance of ____

A.     h/4

B.     h/3

C.     h/2

D.     2h/3

ANS: B

13.   The total pressure on the vertical face of a retaining wall of height h exerted by the retained earth weighing w per unit volume having an angle of surcharge ฮฑ°, is:


ANS: A


14. If H is the overall height of a retaining wall retaining a surcharge, the width of the base slab usually provided, is

A. 0.3 H

B. 0.4 H

C. 0.6 H

D. 0.7 H

ANS: D

15.   The stem of a cantilever retaining wall which retains earth level with top is 6 m. If the angle of repose and weight of the soil per cubic meter are 30° and 2000 kg respectively, the effective width of the stem at the bottom, is

A.     51.5

B.     53.5

C.     52.5

D.     55.5

ANS: B


16. Choose the correct statement from the following:

A. In the stem of a retaining wall, reinforcement is provided near the earthside

B. In the toe slab of a retaining wall, reinforcement is provided at the bottom of the slab

C. In the heel slab of a retaining wall, reinforcement is provided at the top of the slab

D. All of these.

ANS: D

=============================== ++++ ===============================

Unit 4: WATER TANK

1.     In case of water tank permissible stress for concrete in direct tension for grade of concrete M 25 is ___________ N/mm2

A.     1.3

B.     0.9

C.     1.4

D.     1.5

ANS: A

2.     The permissible tensile stress in H.Y.S.D bars on face away from liquid if thickness of member greater than 225 mm is _______N/mm2

A.     150

B.     115

C.     130

D.     190

ANS: D

3.     The permissible tensile stress in M.S. bars on liquid retaining face is ___________ N/mm2.

A.     125

B.     100

C.     115

D.     150

ANS: C

4.     For thickness of slab upto 100 mm in case of water tank the minimum percentage of reinforcement should be ___________

A.     0.1

B.     0.2

C.     0.3

D.     0.4

ANS:  C

5.      In case of water tank for concrete permissible stress in bending tension for grade of M25 concrete is ___________ N/mm2.

A.     1.8

B.     2.5

C.     2.8

D.    2.7

ANS: A

6.      In case of water tanks the permissible tensile stress in shear reinforcement (M.S. bars) for members having thickness less than 225 mm is ___________ N/mm2.

A.      175

B.      125

C.     115

D.     190

ANS: C

7.      The permissible tensile stress in M.S. bars on liquid retaining face is ___________ N/mm2.

A.     115

B.     100

C.     125

D.     150

ANS: A

8.      In water tanks the compressive (permissible) stress in column subjected to direct load is _________ N/mm2 for HYSD bars.

A.     115

B.     125

C.     175

D.     150

ANS: C

9.      The tanks situated underground, the walls of the tanks are to be generally designed for

A.     Earth pressure only

B.     Water pressure only

C.     Both Earth and water pressure

D.     All of these

ANS: D

10.   The floor of the underground water tanks is designed for _________ pressure, for the empty tank condition.

A.     Uplift

B.     Water

C.     Earth

D.     All of these

ANS: D

11.   For design of water tanks the permissible stress in bending tension in HYSD bars is for is ____________ N/mm2 less than 225 mm.

A.     115

B.     140

C.     150

D.     230

ANS: C

12.   In case of water tanks the permissible shear stress for M20 grade concrete is _______ N/mm2

A.     1

B.     1.2

C.     1.25

D.     1.7

ANS: D

13.   The permissible tensile stress in M.S. bars on liquid retaining face is _____ N/mm2.

A.     115

B.     110

C.     125

D.     150

ANS: A

14.  For design of water tanks the permissible stress in bending tension in M.S. bars on face away from liquid is for thickness more than 225 mm. is ____________ N/mm2.

a)                 115

b)                 140

c)                 125

d)                 190

Answer: C

15.  The minimum reinforcement in walls, floors and roofs in each of two directions at right angles, within each surface zone shall not be less than _____ of the surface zone, for HYSD bars.

a)     0.25 %

b)    0.35 %

c)     0.45 %

d)     0.15 %

Answer: B

16.  The minimum reinforcement in walls, floors and roofs in each of two directions at right angles, within each surface zone shall not be less than ____ for mild steel reinforcement bars.

a)     0.65 %

b)    0.64 %

c)     0.46 %

d)     0.35 %

Answer: B

 


Unit 5 Introduction to Pre-stressed concrete

1.     In a load-balanced prestressed concrete beam under self-load the cross-section is subjected to

A. Axial stress

B. Bending stress

C. Axial and bending stress

D. Axial and shear stress

ANS: A


2.     A pre-stressed concrete member

A.     is made of concrete

B.     is made of reinforced concrete

C.     is stressed after casting

D.     possesses internal stresses.

ANS: D

3.     The prestressed concrete beam is suitable for ___________

A.     Large spans

B.     Short spans

C.     Both large and short spans

D.     None of these

ANS: A

4.     In pre stressed concrete section the ______________ section is effective.

a) Above N.A.

b) Below N.A.

c) Partially above and below

d) Entire section

ANS:  D

5.      High strength concrete is used in the prestressed member

a)   to overcome high bearing stresses developed at the ends

b)   to overcome bursting stresses at the ends

c)   to provide high bond stresses

d)   to overcome cracks due to shrinkage

e)   all the above.

ANS: E

6.      The concept used for the analysis of a prestressed concrete section is

A.      Stress concept

B.      Strength concept

C.     Load balancing concept

D.     All above

ANS: D

7.      High strength of concrete is required for prestressed concrete work because _____

A.     Large prestressing force is applied

B.     High bond stress is required

C.     Bursting stress is more

D.     All of above

ANS: D

8.      In prestressed concrete section _______section is effective.

A.     Above N.A.

B.     Partially above and below

C.     Below N.A.

D.     Entire

ANS: D

9.      In design of rectangular P.S.C. beam the eccentricity of tendons is given by________

A.     (2 Md + Ml)/2p

B.     (Md + 2Ml)/2p

C.     2 Md + 2MI/p

D.     None of these

ANS: A

10.   In design of rectangular P.S.C. beam the eccentricity of tendons is given by________

A.     2 Md + Ml/2p

B.     Md + 2Ml/2p

C.     2 Md + 2MI/p

D.     None of these

ANS: D

11.   How is the deflection in RC beam controlled as per IS 456?

A.    By using large aspect ratio

B.    By using small modular ratio

C.    By controlling span to depth ratio

D.    By moderating water cement ratio Water

ANS: C

12. If the loading on a prestressed rectangular beam, is uniformly distributed, the tendon to be provided should be

A. straight below the centroidal axis

B. parabolic with convexity downward

C. parabolic with convexity upward

D. straight above the centroidal axis

ANS: B

13. In a prestressed member it is advisable to use

A. low strength concrete only

B. high strength concrete only

C. low strength concrete but high tensile steel

D. high strength concrete and high tensile steel

E. high strength concrete but low tensile steel

ANS: D

14. A pre-stressed concrete member is preferred because

A. its dimensions are not decided from the diagonal tensile stress

B. large size of long beams carrying large shear force need not be adopted

C. removal of cracks in the members due to shrinkage

D. all the above.

ANS: D

15. The cable profile in prestressed concrete beam to resist UDL throughout the span shall be preferably

A. Along NA

B. Parallel to NA

C. Triangular

D. Parabolic

ANS: D

16. Minimum grade of concrete used for prestressed work should have a cube strength of ___________ N/mm2 for post tensioned.

a) 25

b) 30

c) 35

d) 40

Answer: B

17. For pre-tensioned prestressed concrete, the grade of concrete shall be not less than M ___.

a) 30

b) 35

c) 40

d) 45

Answer: C


Unit 6: Analysis of Symmetrical and unsymmetrical sections

1.     The profile of cable in prestressed concrete beam is usually similar to ___________

A.     Shear force diagram

B.     Bending moment diagram

C.     None of a and b

D.     T. M. diagram

ANS: B

2.    The cable profile in prestressed concrete beam to resist u.d.1 throughout the span shall be preferably.

A.     Along NA

B.     Parallel to NA

C.     Triangular

D.     Parabolic

ANS: D

3.     In C.C.L. standard system____________ number of wires is tensioned at a time.

A.     2

B.     4

C.     6

D.     12

ANS: C

4.     Safe stress in concrete at service is ________ fck.

a) 0.3

b) 0.4

c) 0.6

d) 0.5

ANS:  B

5.      Safe stress in concrete at transfer is ________ fck.

a) 0.3

b) 0.4

c) 0.6

d) 0.5

ANS: D

6.      The permissible tensile stress in concrete is _______ √fck

A.      0.125

B.      0.129

C.     0.126

D.     0.127

ANS: B

7.      If a rectangular prestressed beam of an effective span of 5 meters and carrying a total load 3840 kg/m, is designed by the load balancing method, the central dip of the parabolic tendon should be

A.     5 cm

B.     10 cm

C.     15 cm

D.     20 cm

ANS: B

8.      P is the prestressed force applied to the tendon of a rectangular prestressed beam whose area of cross-section is A and sectional modulus is Z. The maximum stress f in the beam, subjected to a maximum bending moment M, is


   





ANS: C

9.      If A is the sectional area of a prestressed rectangular beam provided with a tendon prestressed by a force P through its centroidal longitudinal axis, the compressive stress in concrete, is

A.     P/A

B.     2P/A

C.     A/P

D.     P/2A

ANS: A

10.   If Md and Mt are the maximum bending moments due to dead load and live load respectively and F is the total effective pressure, for a balanced design of a prestressed concrete beam of steel, is

A. e = (Md/F+Mt/2F)

B. = (Md/2F+Ml/F)

C. = (Md/2F+Ml/3F)

D. = (Ml/3F+Ml/2F)

ANS: B

11.  If the tendon is placed at an eccentricity e below the centroidal axis of the longitudinal axis of a rectangular beam (sectional modulus Z and stressed load P in the tendon) the stress at the extreme top edge

A.    is increased by PZ/e

B.    is increased by Pe/Z

C.    is decreased by PZ/e

D.    is decreased by Pe/Z

E.     Remains unchanged

ANS: C

12.   If the loading on a prestressed rectangular beam is uniformly distributed, the tendon to be provided should be

A.     straight below centroidal axis

B.     parabolic with convexity downward

C.     parabolic with convexity upward

D.     straight above centroidal axis

ANS: B

13.  In a prestressed member it is advisable to use

A.    low strength concrete only

B.    high strength concrete only

C.    low strength concrete but high tensile steel

D.    high strength concrete and high tensile steel

E.     high strength concrete but low tensile steel

ANS: D

14.  A pre-stressed concrete member is preferred because

A.    its dimensions are not decided from the diagonal tensile stress

B.    large size of long beams carrying large shear force need not be adopted

C.    removal of cracks in the members due to shrinkage

D.    all the above.

ANS: D

15.  For pre-tensioned prestressed concrete, the grade of concrete shall be not less than M ___.

a)     30

b)     35

c)     40

d)     45

Answer: C



Unit 7: Losses in prestress

(Note Q 6 & 7 carries 5 Marks each)

1.     If C is creep coefficient, f is original prestress in concrete, m is the modular ratio, E is Young's modulus of steel and e is shrinkage strain, the combined effect of creep and shrinkage is:

A.     (1 - C)mf - eE

B.     (C - 1)mf + eE

C.     (C - 1)mf - eE

D.     (1 - C)mf + eE

ANS: B

2.     In case of pre-tensioned RC beam.

A.     Shrinkage of concrete is of order 3 x 104

B.     Relaxation of steel can be ignored

C.     Only one wire can be stretched at a time

D.     Even mild steel can be used for prestressing.

ANS: D

3.     Relaxation losses for prestressing steel at 1000 Hrs and at 27°C for internal stress 0.7fp is ___

A.    0 N/mm2

B.    35 N/mm2

C.    70 N/mm2

D.    90 N/mm2

ANS: C

4.     Relaxation losses for prestressing steel at 1000 Hrs and at 27°C for internal stress 0.6fp is ___

A.    0 N/mm2

B.    35 N/mm2

C.    70 N/mm2

D.    90 N/mm2

ANS: B

5.     For straight or moderately curved structures, with curved or straight cables, the value of prestressing force P, at a distance x meters from the tensioning end and acting in the direction of the tangent to the curve of the cable shall be calculated as below:

A.    Px = Po e-(ยต ฮฑ + kx)

B.    Px = Po e-(ยตฮฑ - kx)

C.    Px = Po (1 - ยตฮฑ - kx)

D.     Px = Po e ( ยตฮฑ + kx)

ANS: A

6.     A Post-tensioned concrete beam 250 mm wide & 360 mm deep has a span of 12 m. the beam is prestressed by steel wires of area 350 mm2 provided with a parabolic profile ACEDB with eccentricity at midspan of 60 mm with an initial prestress of 1250 N/mm2. The percentage loss of prestress in the wires due to friction only, at midspan will be_______. If ยต = 0.30 and k = 0.0015 per meter.

A.    3.4%

B.    1.5%

C.    4.4%

D.    5.6%

ANS: B

7.     A Prestressed concrete beam is provided with a tendon with parabolic profile with ฦŸ = 0.06o, the tendon is being tensioned from end A. Calculate the percentage loss of prestress due to friction, from end A to the end B. Take ยต = 0.30 and k = 0.0015 per meter. Stress in tendon at A = 1050 N/mm2.

A.    3.4%

B.    1.5%

C.    5.4%

D.    5.6%

ANS: C



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