SUBJECT : CIVIL ENGINEERING 2

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INDIAN SCHOOL OF BUSINESS

MANAGEMENT & ADMINISTRATION

AN ISO 9001 : 2008 CERTIFIED INTERNATIONAL B-SCHOOL

SUBJECT : CIVIL ENGINEERING

1. Under what situation shall engineers use jacking at one end only and from both ends in

Pre-stressing work?

Answer: During pre-stressing operation at one end, frictional losses will occur and the pre-stressing force decreases along the length of tendon until reaching the other end. These frictional losses include the friction induced due to a change of curvature of tendon duct and also the wobble effect due to deviation of duct alignment from the centre-line. Therefore, the pre-stress force in the mid-span or at the other end will be greatly reduced

2. What is “preset” during installation of bridge bearings?

Answer: “Preset” is a method to reduce the size of upper plates of sliding bearings in order to save cost.

The normal length of an upper bearing plate should be composed of the following components = length of bearing + 2xirreversible movement + 2xreversible movement.

3. In incremental launching method of bridge construction, what are the measures adopted to enhance sufficient resistance of the superstructure during the launching process?

Answer: (i) During the launching process the leading edge of the superstructure is subject to a large hogging moment. In this connection, steel launching nose typically about 0.6-0.65 times span length is provided at the leading edge

4. In bridge widening projects, the method of stitching is normally employed for connecting existing deck to the new deck. What are the problems associated with this method in terms of shrinkage of concrete?

Answer: In the method of stitching, it is a normal practice to construct the widening part of the bridge at first and let it stay undisturbed for several months. After that, concreting will then be carried out for the stitch between the existing deck and the new deck. In this way, the dead load of the widened part of bridge is supported by itself and loads arising from the newly constructed deck will not be transferred to the existing deck which is not designed to take up these extra loads.

5. Sometimes the side of concrete bridges is observed to turn black in colour. 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

6. How to determine the size of elastomeric bearings?

Answer: For elastomeric bearing, the vertical load is resisted by its compression while shear resistance of the bearing controls the horizontal movements.

The design of elastomeric bearings is based on striking a balance between the provision of sufficient stiffness to resist high compressive force and the flexibility to allow for translation and rotation movement.

7. 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 centre from its original position by one-half of its movement based on David J. Lee. However, with sliding bearing a

8. What are the functions of grout inside tendon ducts?

Answer: Grout in prestressing works serves the following purposes:

(i) Protect the tendon against

9. What are the shortcomings of grillage analysis which is commonly used in structural analysis of bridges?

Answer: In designing the number of cells for concrete box girder bridges, in case the depth of a box girder bridge exceeds 1/6 or 1/5 of the bridge width, then it is recommended to be designed as a single cell box girder bridge. However, if the bridge depth is smaller than 1/6 of the bridge width, then a twin-cell or multiple cell is a better. However, one should note that even for wider bridges with small depths, the number of cells should be minimized because there is not much improvement in transverse load distribution when the

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-

11. Can grout replace concrete in normal structure?

Answer: The mixture of cement and water alone cannot replace concrete (Longman Scientific and Technical (1987)) because:

(i) Shrinkage of grout is several

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