# Civil Engineering Interview Questions Part – 10

By JP

Question No. 01
In the design of pipe jacking, what particular areas on pipe joints should engineers take care of?
Answer: Since in pipe jacking, the jacked pipes could hardly be jacked in the designed level and alignment and some deviation from the original one is commonly acceptable provided that the deviation are within the tolerance of the Contract. However, in order to avoid damage made to the pipe joints due to overstressing, it is necessary to estimate the stress concentrations resulting from these angular deflections.
Note: Pipe jacking is a trenchless method in which pipes are jacked underground from jacking pits and receiving pits.

Question No. 02
In the design of service reservoirs, how are reservoir floors designed to prevent leakage of water due to seasonal and shrinkage movements?
Answer: There are in general two main approaches in designing floors of service reservoirs:
(i) In the first method, movement joints are designed in each panel of reservoir floors so that they can expand and contract freely. Each panel is completely isolated from one another and a sliding layer is placed beneath them to aid in sliding.
(ii) The second method, on the contrary, does not make provision to free movement. Due to seasonal and shrinkage movements, cracks are designed to occur in the reservoir floors such that very tiny cracks are spread over the floor and these cracks are too small to initiate corrosion or leakage. However, in this case, the amount of reinforcement used is much larger than the first approach.

Question No. 03
In erection of false-work, for a rectangular panel inside a false-work should it be braced along the two diagonals?
Answer: When a rectangular panel is subject to an eccentric load or a lateral load, it tends to deform into a parallelogram with one diagonal shortening and the other elongating. Theoretically, it is sufficient to brace along one of the diagonals (the one in tension). If one diagonal is only allowed to brace inside the rectangular panel, it should be not braced in the diagonal in compression because under severe lateral loading the diagonal may buckle leading to failure of structure. However, in actual situation lateral loads may come from both sides of the panel and hence it should be braced in both diagonals.

Question No. 04
What are the applications of modulus of elasticity?

Answer: 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.

Question No. 05
What are the functions of different components of paint?
Answer: For normal paint application, there are mainly three main components of paint, namely primer, undercoat and finishing coat.
Primer: This is the first layer of a typical painting system and it is used to inhabit corrosion and provide a good bond for subsequent coats.
Undercoat: This component acts as a barrier to corrosion agents and even out irregularities of bonding surface. It also serves to hide the underlying background and prevent the details and color of the area of application to affect the designed color and finishing details of paint.
Finishing coat: This is the final layer of a typical painting system and it protects the underlying layers from the effect of adverse weather conditions (e.g. sunlight) and to provide the designed properties of paint like color, impermeability, wearing resistance, etc.

Question No. 05
Why is the span length ratio of end span/approach span to its neighboring inner spans usually about 0.75?
Answer: From aesthetic point of view, an odd number of spans with a decrease in length in the direction of abutment are desirable. Moreover, spans of equal length are found to be boring. However, the arrangement of irregular span lengths is not recommended because it gives a feeling of uneasiness. From structural point of view, for a multi-span bridge with equal span length, the sagging moment at the mid-span of the end span/approach span is largest. In order to reduce this moment, the span length of end span/approach span is designed to be 0.75 of inner spans. However, this ratio should not be less than 0.40 because of the effect of uplifting at the end span/approach span support.
Note: End span refers to the last span in a continuous bridge while approach span refers to the first span of a bridge.

Question No. 06

What is the tallest man made structure in the world?
Answer: The tallest artificial structure is Burj Khalifa, a skyscraper in Dubai that reached 829.8 m (2,722 ft) in height on January 17, 2009. By April 7, 2008 it had been built higher than the KVLY-TV mast in North Dakota, USA.

Question No. 07
After the construction of watermain, prior to hydrostatic pressure test, swabbing is carried out. What is the purpose of swabbing?
Answer: Pipelines should be tested before commissioning to check the strength of watermain and the absence of leak. Before carrying out hydrostatic pressure test, swabbing is conducted to clear out rubbish and dirt left inside the pipeline during construction. Swabbing is required for pipes less than 600mm diameter because for larger size of pipes, they can be inspected internally to ensure cleanliness.
After carrying out of hydrostatic pressure test, test for water sterilization is then conducted which involves collecting water sample from the pipeline. The purpose is to check the water quality like colour, turbidity, odour, pH value, conductivity etc. and is compared with the quality of water drawn from water supply point.

Question No. 08
What are the functions of grout inside tendon ducts?
Answer: Grout in pre-stressing works serves the following purposes:
(i) Protect the tendon against corrosion.
(ii) Improve the ultimate capacity of tendon.
(iii) Provide a bond between the structural member and the tendon.
(iv) In case of failure, the anchorage is not subject to all strain energy.

Question No. 09
Is the procurement of third party insurance necessary to be incorporated in contract for construction works?
Answer: The purpose of third party insurance is to protect contractors from bankruptcy in case there are severe accidents happened to the third party due to the construction work. Therefore, in government contracts, contractors are requested contractually to procure third party insurance from the commencement of contract until the end of Maintenance Period. If contractors have the financial capability to handle the claims due to accidents to third party, the client is not bound to include this requirement in the contract.

Question No. 10
What is absolute pressure?
Answer: Absolute pressure is simply the addition of the observed gage pressure plus the value of the local atmospheric pressure.

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