Question & Answer for Civil Engineers

1. What are the causes of building collapse?  
Ans. The Passage of time is one reason. Buildings also collapse due to weak foundations. Earthquakes, hurricanes and other natural disasters can also damage the structure of the buildings and cause it to collapse. Bombings or demolition of buildings is also other reasons.

2. What are the applications of modulus of elasticity?
Ans. As the term implies, "Modulus of Elasticity” relates to the elasticity or "flexibility" of a material. The value of modulus of elasticity is very much significant relating to deflection of certain materials used in the construction industry. Take for example the general E value of mild carbon steel is about 200 GPA compared to about 70 GPA for aluminum. This simply translate that aluminum is 3 times flexible than steel.

3. How do you measure concrete?
Ans. Cubic feet, Cubic yards, Cubic Meter

4. Which is stronger solid steel rod or hollow steel pipe?
Ans. On a per pound basis, steel pipe is stronger in bending and is less likely to buckle in axial compression.

5. What is aggregate?

Ans. Aggregate is the component of a composite material used to resist compressive stress.

6. How do you calculate the power of a centrifugal pump?

Ans. The input power, that is, the power required to operate the pump should be stated in Hp (horsepower) on the pump's nameplate. It can also be calculated by the 3-phase power equation:

P(in Hp) = VI(1.7 c) = Rated Voltage x Rated Current x 1.73/ %Efficiency

If this is a consumer grade pump that operates on 120 Vac, then the equation becomes P = VI, simply multiply the operating voltage, 120 x current (which is the number followed by the letter "A".The output power, which really is not technically power, but rated in Gpm (gallons per minute), or capacity should also be on the nameplate. If you have the make, model, and (not necessarily needed) the serial number (also on the nameplate) you could call the manufacturer's customer service dept. As an application engineer, I have contacted countless manufacturers’, and service dept's for assistance. It is now big deal to them, they will be happy to answer your questions.

7. What is rigging?
Ans. In sailing, the ropes used to move the sails around so the boat will move in the right direction when the wind blows.

8. What is absolute pressure?
Ans. Absolute pressure is simply the addition of the observed gage pressure plus the value of the local atmospheric pressure.

9. How do we calculate absolute pressure?
Ans. Absolute is equal to gauge pressure plus atmospheric.

10. What is Gravity flow?
Ans. Gravity flow is fluid flowing due to the forces of gravity alone and not to an applied pressure head. In the Bernoulli equation, the pressure term is omitted, and the height and velocity terms are the only ones included.

11. What do you mean by honeycomb in concrete?
Ans. Some people call it an air pocket in the concrete or a void. It is the exposed course aggregates on surface of concrete without covered by mortar or surrounding the aggregate particles.

12. What is the purpose of the gap in the road on this bridge?
Ans. Purpose of the gap in the road is to allow the road to expand and contract with temperature changes without causing damage or deformation to the road.

13. What is a projection line?
Ans. Projection line is the way, in which the earth is shown on a flat piece of Paper.

14. What are moment of inertia and its importance in civil engineering?
Ans. The moment of inertia measures the opposition any kind of body will have against a certain momentum (along that same axis) trying to rotate that body.

15. What is the absolute pressure scale?
Ans. Absolute pressure is calculated from a vacuum (0 PSI) and atmospheric pressure is 14.7 PSIa or 14.7 PSI above a vacuum 1 PSI on a tire pressure gauge is called 1 PSIg = 15.7 PSIa 10 PSIg=24.7 PSIa 100 PSIg=114.7 PSIa etc.

16. What is diversion tunnel in a dam?
Ans. When a dam is to be built, a diversion tunnel is usually bored through solid rock next to the dam site to by pass the dam construction site. The dam is built while the river flows through the diversion tunnel.

17. How do you maintain water pressure?
Ans. If you have water pressure and wish to maintain it, do not cause flow in the line, which will reduce pressure due to friction. To keep pressure up, reduce friction by increasing the line size or eliminating some other restriction.

18. What are some structures that may be subjected to fatigue?
Ans. Bridges, hydraulic presses, burners trains

19. Why does the pressure increase under soil?
Ans. Soil pressure increases with depth due to the overburden or self-weight of the soil and due to loads imposed upon the soil.
For example, the pressure variation below the depth of soil is linear and the relation is given by pressure = unit wt * depth. As depth increases, there will be a linear increase in the soil pressure.

20. What is the distance between railway tracks?
Ans. 4 feet, 8 1/2 inches.

Basic rules for design of beam

Basic rules for design of beam:-

1. Effective span:- In the case of simply supported beam the effective length,

L = i. Distance between the centre of support

ii.  Clear span + eff. Depth

     eff. Span = least of i. & ii.

2. Effective depth:- The normal distance from the top edge of beam to the centre of tensile reinforcement is called effective depth. It is denoted by ‘d’.

d= D- effect. Cover

where D= overall depth

3. Bearing :- Bearings of beams on brick walls may be taken as follow:

• Up to 3.5 m span, bearing = 200mm
• Up to 5.5 m span, bearing =300mm
• Up to 7.0 m span, bearing =400mm

4. Deflection control:- The vertical deflection limits assumed to be satisfied if  (a) For span up to 10m

               Span / eff. Depth = 20

              (For simply supported beam)

              Span / eff. Depth = 7

              (For cantilever beam)

(b) For span above 10m, the value in (a) should be multiplied by 10/span (m), except for cantilever for which the deflection calculations should be made.

(c) Depending upon the area and type of steel the value of (a&b) modified as per modification factor.

5. Reinforcement :-

(a) Minimum reinforcement:- The minimum area of tensile reinforcement shall not be less than that given by the following:

                       Ast = 0.85 bd / fy

(b)Maximum reinforcement:- The maximum area of tensile reinforcement shall not be more than 0.4bD

(c)Spacing of reinforcement bars:-

i. The horizontal distance between to parallel main bars shall not be less than the greatest of the following:

• Diameter of the bar if the bars are of same diameter.
• Diameter of the larger bar if the diameter are unequal.
• 5mm more than the nominal maximum size of coarse  aggregate.

ii. When the bars are in vertical lines and the minimum vertical distance between the bars shall be greater of the following:

• 15mm.
• 2/3^rd of nominal maximum size of aggregate.
•  Maximum diameter of the bar

6. Nominal cover to reinforcement :- The Nominal cover is provided in R.C.C. design:

• To protect the reinforcement against corrosion.
• To provide cover against fire.
• To develop the sufficient bond strength along the  surface area of the steel bar.

As per IS 456-2000, the value of nominal cover to meet durability requirements as follow:-

Exposure conditions	Nominal cover(mm) Not less than
Mild Moderate Severe Very severe Extreme	20 30 45 50 75

 

Procedure for Design of Singly Reinforced Beam by Working Stress Method

Given :

(i) Span of the beam (l)

(ii) Loads on the beam

(iii)Materials-Grade of Concrete and type of steel.

1. Calculate design constants for the given materials (k, j and R)

                        k = m σcbc /  m σcbc + σst

where k is coefficient of depth of Neutral Axis

                       j = 1- k/3

where j is coefficient of lever arm.

                       R= 1/2 σcbc kj

where R is the resisting moment factor.

2. Assume dimension of beam:

  d = Span/10  to  Span/8

Effective cover = 40mm to 50mm

b = D/2  to  2/3D

3. Calculate the effective span (l) of the beam.

4. Calculate the self weight (dead load) of the beam.

Self weight = D x b x 25000 N/m

5. Calculate the total Load & maximum bending   moment for the beam.

Total load (w) = live load + dead load

Maximum bending moment, M = wl2 / 8 at the centre of beam for simply supported beam.

                                              M = wl2 / 2 at the support of beam for cantilever beam.

6. Find the minimum effective depth

                           M = M            

                               = Rbd2

                       dreqd. = √ M / R.b

7. Compare dreqd. With assumed depth value.

(i) If it is less than the assumed d, then assumption is correct.

(ii) If dreqd. is more than assumed d, then revise the depth value and repeat steps 4, 5 & 6.

8. Calculate the area of steel required (Ast).

                        Ast = M / σst jd

Selecting the suitable diameter of bar calculate the number of bars required

               Area of one bar = π/4 x φ2 = Aφ

             No. of bars required = Ast /Aφ

9. Calculate minimum area of steel (AS) required by the relation:

AS =  0.85 bd / fy

   Calculate maximum area of steel by the area relation:

   Maximum area of steel = 0.04bD

 Check that the actual ASt provided is more than minimum and less than maximum required.

10. Check for shear and design shear reinforcement.

11. Check for development length.

12. Check for depth of beam from deflection.