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Civil Engineering Interview Questions Part – 19



Question No. 01
What is the biggest dam in America?
Answer: The Grand Coulee Dam Grand -Coulee, Washington
a) Length 5,223 ft b) Height 550 ft

Question No. 02
In the design of elastomeric bearings, why are steel plates inserted inside the bearings?
Answer: For elastomeric bearing to function as a soft spring, the bearing should be allowed for bulging laterally and the compression stiffness can be increased by limiting the amount of lateral bulging. To increase the compression stiffness of elastomeric bearings, metal plates are inserted. After the addition of steel plates, the freedom to bulge is restricted and the deflection is reduced when compared with bearings without any steel plates under the same load. Tensile stresses are induced in these steel plates during their action in limiting the bulging of the elastomer. This in turn would limit the thickness of the steel plates. However, the presence of metal plates does not affect the shear stiffness of the elastomeric bearings.

Question No. 03
What is the indication of shear slump and collapse slump in slump tests?
Answer: There are three types of slump that may occur in slumps test, namely, true slump, shear slump and collapse slump.
(i) True slump refers to general drop of the concrete mass evenly all around without disintegration.
(ii) Shear slump implies that the concrete mix is deficient in cohesion. Consequently, it may undergo segregation and bleeding and thus is undesirable for durability of concrete.

(iii) Collapse slump indicates that concrete mix is too wet and the mix is deemed to be harsh and lean.

Question No. 04
Is the material of formwork (timber or steel) helps to reduce thermal cracks in concreting operation?
Answer: To answer this question, one must fully understand the effect of formwork on the temperature of concreting structure. Without doubt, with better insulation of structure by timber formwork, the overall rise of temperature and hence the peak hydration temperature is also increased. However, for a well-insulated structure, the temperature gradient across concrete element is reduced. Therefore, the use of well-insulated formwork (like timber) increases the maximum temperature and reduces the temperature gradient across the structure at the same time. Hence, whether steel or timber formwork should be used to control thermal cracking is dependent on the restraints and the size of section. If the section under consideration is thick and internal restraint is the likely cause to thermal cracking, then timber formwork should be used. On the other hand, if external restraint is the main concern for thermal cracking, then steel formwork should be used instead.

Question No. 05
What is the importance of critical steel ratio in calculating thermal reinforcement?
Answer: The fulfillment of critical steel ratio means that in construction joints or planes of weakness of concrete structure, steel reinforcement will not yield and concrete fails in tension first. This is important in ensuring formation of more cracks by failure of concrete in tension; otherwise failure in steel reinforcement would produce a few wide cracks which are undesirable.


Question No. 06
What is the purpose of skin reinforcement for deep beams?
Answer: In BS8110, it states that secondary reinforcement should be provided for beams exceeding 750 mm deep at a distance measured 2/3 depth from the tension face. Experimental works revealed that at or close to mid-depth of deep beams, the maximum width of cracks arising from flexure may be about two to three times larger than the width of the same crack at the level of surface where the crack originally forms.
The presence of crack is undesirable from aesthetic point of view. Moreover, it poses potential corrosion problems to reinforcement of deep beams. To safeguard against these crack formation, skin reinforcement is designed on the sides of deep beams to limit the formation of flexural crack widths. Though the principal function of skin reinforcement is to control crack width, it may be employed for providing bending resistance of the section.

Question No. 07
What is the average density of soil?
Answer: For purposes of civil engineering, an average soil will have a density of about 100 to 110pounds per cubic foot. (This can vary a little depending upon how well compacted the soil is.)

Question No. 08
What is the difference between normal bolts and high friction grip bolts?
Answer: High friction grip bolts are commonly used in structural steelwork. They normally consist of high tensile strength bolts and nuts with washers. The bolts are tightened to a shank tension so that the transverse load across the joint is resisted by the friction between the plated rather than the bolt shanks shears strength

Question No. 09
In the design of watermain, the normal practice is to use ductile iron for pipe size less than 600 mm and to use steel for pipe size more than 600 mm. Why?
Answer: For watermain pipe size less than 600 mm, ductile iron is normally used because internal welding for steel pipes below 600 mm is difficult to be carried out. Moreover, it requires only simple jointing details which allow for faster rate of construction. For watermain pipe size above 600 mm, steel pipes are recommended because steel pipes are lighter than ductile iron pipes for the same material strength and therefore the cost of steel pipes is less than that of ductile iron pipes. In addition, in areas of difficult access the lighter mild steel pipes pose an advantage over ductile iron pipes for easy handling.

Question No. 10
In carrying out compression test for concrete, should test cubes or test cylinders be adopted?
Answer: Basically, the results of compression test carried out by using cubes are higher than that by cylinders. In compression test, the failure mode is in the form of tensile splitting induced by uniaxial compression. However, since the concrete samples tend to expand laterally under compression, the friction developed at the concrete-machine interface generates forces which apparently increase the compressive strength of concrete. However, when the ratio of height to width of sample increases, the effect of shear on compressive strength becomes smaller. This explains why the results of compression test by cylinders are lower than that of cubes. Reference is made to Longman Scientific and Technical (1987).


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