In this post, we will discuss Commonly asked civil engineer Interview questions answers. These questions answers may be helpful for the interview preparation.

This post is posted by Mr. A.K.Singh, Having 15 years of experience, now he is working in L&T Construction.

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Question1.   Sometimes the side of concrete bridges is observed to turn black in color. What is the reason for this phenomenon?

Answer:  In some cases, it may be due to the accumulation of dust and dirt. However, for the majority of such phenomenon, it is due to fungus or algae growth on concrete bridges. After rainfall, the bridge surface absorbs water and retains it for a certain period of time. Hence, this provides a good habitat for fungus or algae to grow. Moreover, atmospheric pollution and proximity of plants provide nutrients for their growth. Application of painting and coating to bridges help to solve this problem.

Question2. What are the advantages of assigning the central pier and the abutment as fixed piers?

• For abutment pier to be assigned as fixed pier while the bridge is quite long, the longitudinal loads due to the earthquake are quite large. As the earthquake loads are resisted by fixed piers, the size of fixed piers will be large and massive. In this connection, for better aesthetic appearance, the selection of abutment as fixed piers could accommodate the large size and massiveness of piers. Normally abutments are relatively short in height and for the same horizontal force, the bending moment induced is smaller.
• For the central pier to be selected as the fixed pier, the bridge deck is allowed to move to start from the central pier to the end of the bridge. However, if the fixed pier is located at the abutment, the amount of movement to be incorporated in each bearing due to temperature variation, shrinkage, etc. is more than that when the fixed pier is located at the central pier. Therefore, the size of movement joints can be reduced significantly.

Question3. In the construction of a two-span bridge (span length = L) by using span-by-span construction, why is a length of about 1.25L bridge segment is constructed in the first phase of construction?

Answer: Span-by-span construction means that a bridge is constructed from one bridge span to another until its completion.

Basically, there are mainly three reasons for this arrangement:

• The permanent structure is a statically indeterminate structure. During construction by using span-by-span construction, if the first phase of construction consists of the first span length L only, then the sagging moment in the mid-span of the partially completed bridge is larger than that of the completed two-span permanent structure. To avoid such occurrence, 0.25L of bridge segment is extended further from the second pier which provides a counteracting moment, thereby reducing the mid-span moment of the partially completed
• The position of 1.25 L countering from the first pier is the approximate location of the point of contra flexure (assume that the two-span bridge is uniformly loaded) in which the bridge moment is about zero in the event of the future loaded bridge. Therefore, the design of the construction joint in this particular location has the least adverse effect on the structural performance of the
• In case of a prestressed bridge, prestressing work has to be carried out after the construction of the first segment of the bridge. If the prestressing work is conducted at the first pier which is heavily reinforced with reinforcement, it is undesirable when compared with the prestressing location at 1.25L from the first pier where there is relatively more space to accommodate prestressing.

Question4. Define Monolithic construction ?

Answer: Monolithic construction means that piers are connected to bridge decks without any joints and bearings.

Question5. Are diaphragms necessary in the design of concrete box girder bridges?

Answer:  Diaphragms are adopted in concrete box girder bridges to transfer loads from bridge decks to bearings. Since the depth of diaphragms normally exceeds the width by two times, they are usually designed as deep beams. However, diaphragms may not be necessary in case bridge bearings are placed directly under the webs because loads in bridge decks can be directly transferred to the bearings. This arrangement suffers from the drawback that changing of bearings during future maintenance operation is more difficult. In fact, diaphragms also contribute to the provision of torsional restraint to the bridge deck.

Question6. What is the advantage of sliding bearings over roller bearings?

Answer: In roller bearing for a given movement the roller bearing exhibit a change in pressure center from its original position by one-half of its movement based on David J. Lee. However, with the sliding bearing, a sliding plate is attached to the upper superstructure and the moving part of bearing element is built in the substructure. It follows that there is no change in pressure center after the movement.

Question7. Why is the span length ratio of end span/approach span to its neighboring inner spans usually about 0.75?

Answer: From the aesthetic point of view, an odd number of spans with a decrease in length in the direction of the abutment is 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 the 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.

Question8. In joints of precast concrete bridge segments, what are the functions of applying epoxy adhesive?

Epoxy adhesive is applied in these joints for the following purposes according to International Road Federation (1977):

• It seals up the joints completely between precast concrete segments to protect the prestressing tendons.
• By filling voids and irregularities along the segment joints, it helps to reduce stress concentrations otherwise it will be developed. and
• It helps in transferring of shear between the joints in case a large single shear key is used.

Question9. Under what situation should engineers use pot bearings instead of elastomeric bearings?

Answer: In the event of high vertical loads combined with the large angle of rotations, rubber bearings are undesirable when compared with pot bearings. For instance, elastomeric bearings require large bearing surfaces so that compression can be maintained between the contact surfaces between the bearings and piers. Moreover, it also leads to uneven distribution of stress on the piers and some of these highly induced stresses may damage the piers. Consequently, pot bearings are better alternatives than elastomeric bearings.

Question10. If on-site slump test fails, should engineers allow the contractor to continue the concreting works?

Answer: In fact, there are two thoughts regarding this issue.

one thought is rather straightforward: the contractor fails to comply with contractual requirements and therefore as per G. C. C. Clause 54 (2)(c) the engineer could order the suspension of the Works. Under the conditions of G. C. C. Clause 54(2)(a) – (d), the contractor is not entitled to any claims of cost which is the main concern for most engineers. This is the contractual power given to the Engineer in case of any failure in tests required by the contract, even though some engineers argue that slump tests are not as important as other tests like compression test.

The second thought is to let the contractor continue their concreting works and later on request the contractor to prove that the finished works comply with other contractual requirements e.g. compression test. This is based upon the belief that workability is mainly required to achieve design concrete compression strength. In case the compression test also fails, the contractor should demolish and reconstruct the works accordingly. In fact, this is a rather passive way of treating construction works and is not recommended because of the following reasons:

• Workability of freshly placed concrete is related not only to strength but also to the durability of concrete. Even if the future compression test passes, failing in slump test indicates that it may have an adverse impact to the durability of completed concrete structures.
• In case the compression test fails, the contractor has to deploy extra time and resources to remove the work and reconstruct them once again and this slows down the progress of works significantly.

This post is posted by Mr. A.K.Singh, Having 15 years of experience, now he is working in L&T Construction.

You can also share your knowledge here

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