20 Interview Questions for fresher civil Engineers

  1. What is Lacquer paints ?

Lacquer paints are generally applied on structural steel . These are less durable as compared to enamel paints . It consist of resin and nitro-cellulose . It contain alcohol as thinner .

2.Ultimate strength to cement is provided by ?

Di-calcium silicate

3.Under normal conditions using an ordinary cement, the period of removal of the form work, is :

7 days for beam soffits
14 days for bottom slabs of spans 4.6 m and more
21 days for bottom beams over 6 m spans
2 days for vertical sides of columns

4.Why is concrete weak in tension?

Concrete is not a homogeneous material like steel which is strong in both tension as well as compression. It is a composite material and is obtained by mixing cementing materials, water and aggregate (and sometimes admixtures).

5.Difference between singly and doubly reinforced beams?

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. In singly reinforced beam compression, stress resists by the concrete, while in doubly reinforced beam compression steel, counters the compression stress.

6.Why water tanks are still designed by working stress method?

The reason behind the design of water tanks  using the working stress method only are as follows;

  1. Variation of the load is not taken into account in working stress method.
  2. Working stress method is used whenever the design is more conservative.
  3. Commonly water tanks are highly vulnerable because the water level in the tank will drastically vary and there is highly continuous variation in the water pressure inside the tank.
  4. Working stress method fulfils the highest requirement factor and gives one of the traditional methods to account such type of variation.
  5. Serviceability of working stress method is more as compared to Limit state method and hence the lifespan of the structure will automatically extend.

7. Difference between one way & Two way slabs?

The oneway slab is supported by a beam on two opposite side only. The twoway slab is supported by the beam on all four sides. In oneway slab, the load is carried in one direction perpendicular to the supporting beam. In twoway slab, the load is carried in both directions.

8.Weight of Steel bar per metre length?

If we put 1 meter length for each diameter of steel bar in the formula then we will get the unit weight.

  • 6 mm ø bar = 6² x 1/162 = 0.222 kg/m.
  • 8 mm ø bar = 8² x 1/162 = 0.395 kg/m.
  • 10mm ø bar = 10² x 1/162 = 0.617 kg/m.
  • 12mm ø bar = 12² x 1/162 = 0.888 kg/m.
  • 16mm ø bar = 16² x 1/162 = 1.580 kg/m.

9.Weight of 1 cum RCC?

Weight of 1 cubic meter of concrete:- 1 cubic metre of concrete weight around 2.5 metric ton (2500kgs), typically 1m3 of concrete is made up of about 350kg (7bags) cement, 700 kg sand, 1200kg aggregate, about 150 litres of water and 100kg of steel embedded in it as per design structure in case reinforced cement 

10.Why PCC is provided under RCC ?

The main reason of providing PCC is to provide a rigid impervious bed to RCC in the foundation before starting any RCC or masonry work directly on the excavated soil, PCC is done to form a leveled surface and to avoid laying concrete on soil directly so as to avoid mixing with soil and also to prevent soil extracting

11.why main reinforcement is provided on top in case of Cantilever beam?

For cantilever beams the tension zone lies in the upper section and hence the reinforcement bars are provided in top section.. For cantilever beams the tension zone lies in the upper section and hence the reinforcement bars are provided in top section.

12.Difference between effective span & clear span?

In simple words, the centre to centre distance between two supports is called effective span.

The distance between two supports is called clear span.

13.what factors of safety is used in RCC & Steel? & Why?

1.Concrete – for concrete FOS is 1.5 . Concrete is not a homogeneous material, we mix cement,sand,water,aggregates , admixtures to make a concrete; these different materials has different strength and most importantly they won’t be arranged in a same way like honeycomb structure or any symmetrical pattern. So to consider all these effects we use factor of safety. If we consider M20 concrete, for design purpose we take 20/1.5 = 67% of 20 as strength of concrete.

2.Steel: FOS is 1.15 , lesser than that of concrete. Yes, because concrete is made up at site mostly while still is manufactured in factory.

Above mentioned are material FOS. In limit state method we also apply load FOS. That is, we consider 1.5 times of total load on the structure for design purpose.

14.What are functions of main and distribution reinforcement in Slab?

  • Primary reinforcement (Main Steel) refers to the steel which is employed to guarantee the resistance needed by the structure as a whole to support the design loads.
  • Secondary reinforcement(Distribution Steel), also known as distribution or thermal reinforcement, is employed for durability and aesthetic reasons, by providing enough localised resistance to limit cracking and resist stresses caused by effects such as temperature changes and shrinkage.

15.What is the difference between development length and anchorage length?

Development Length is the length of the bar that is surrounded by the concrete beyond any section in an RCC beam, which would be capable enough to resist the applied pulling force. Now this Length is a must requirement in an RCC member because if that length is not available then the reinforcement steel wouldn’t be able to resist the pull and it will come out which will lead to failure.

Specifically in bottom zone, where there is a tensile force acting on the bottom reinforcement , it becomes an important check in the design of an RCC beam. As per code, IS 456:2000, required Development Length Ld should be less than or equal to 1.3M1/V +Lo .

Where, M1 = Moment of resistance of steel bars at the considered section

Lo = Sum of embedded Length beyond the center of support and equivalent bed length of mechanical Anchorage.

V= Vertical Shear force at the section.

Here comes our term Anchorage Length.

If you simply go by the meaning of the word, it is definitely related to some stopping type mechanism and it is the simplest interpretation of the word.

Anchorage Length is the equivalent length of the reinforcement bar which is considered to be available when a straight bar is bent through some angle. Ofcourse, it’s now of no doubt that it is provided only at the support.

If I go by mathematical explanation then suppose, if at any section you need a development length required as Ld =60cm (say) , and based on the above equation, the length of bar available from the centre of the support to the section is 48 cm(say). Now yo need 12cm of reinforcement more to satisfy the Ld requirement. At this time, now if you just bent the bar 90° upward, then because of bending an additional amount of 8xDiameter of bar got provided. Now you need only an extra length of

12–8xDiameter of Reinforcement, to meet the Ld requirement.

Further it is to be noted that Lo has max value of 12xDiameter of bar. So bending and extesnion of bar beyond the center of support to satisfy the Ld requirement has to be in limitations to that.

16.Briefly explain the functions of shear reinforcement.why minimum shear reinforcement is provided for beams?

How can we resist the shear failure?

Imagine this scenario that a cloth is being torn. How do we make cloth normal again? By stitching! We do the same to concrete when it is tearing. Since shear can start at any point and propagate placing stirrup at one point is not a solution. We need to place reinforcement at all locations so that (more near supports) so that we can arrest shear failure. HYSD bars have ribs which tightly bonds with concrete as a stitch so that the crack won’t propagate. This rebar is called stirrup.

Equations to design shear:

Vus=0.87fyAsvdsvVus=0.87fyAsvdsv

This is the equation used to calculate spacing svsv for a vertical stirrup.

Minimum shear equation:

Asvsv=0.40.87fyAsvsv=0.40.87fy

Here fyfy is yield strength of reinforcement bar and not of longitudinal bar.

Minimum shear is provided to ensure sudden shear collapse which is brittle in nature.

17.How much quantity of steel required for 1m3 concrete ?

Thumb Rule for Steel in Kg/m3

1) thumb rule for steel in rcc slab is 80 kg/cubic meter of wet volume of concrete

2) thumb rule for steel in beam is 120 kg/cubic meter of wet volume of concrete

3) thumb rule for steel in column is 160 kg/cubic meter of wet volume of concrete

4) thumb rule for steel in footing is 40 kg/cubic meter of wet volume of concrete

5) thumb rule for steel in rcc structure is 100- 120 kg/cubic meter of all calculated wet volume of concrete.

6) thumb rule for steel in rcc structure is 3.5 Kg to 4 kg/ sq ft of built up area.

18.The minimum thickness of load bearing RCC wall is:

minimum thickness of load bearing RCC wall should be 100 mm to prevent failure.

19.What should be the slump value of slab, column, and beams?

Columns and beams are congested and hence need more flow 120mm+/-20mm slump should be enough.

Slabs could have less flow and hence 100mm+/-20mm slump should be enough.

20.What does a setback line mean?

In land use, a setback is the minimum distance which a building or other structure must be set back from a street or road, a river or other stream, a shore or flood plain, or any other place which is deemed to need protection. In some cases, building ahead of a setback line may be permitted through special approval.

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