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Questions and Answers on Practical Civil Engineering Works

1. Bridge Works

1. Under what situation shall engineers use jacking at one end only and from both ends in prestressing work?
2. What is “preset” during installation of bridge bearings?
3. In incremental launching method of bridge construction, what are the measures adopted to enhance sufficient resistance of the superstructure during the launching process?
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?
5. What are the advantages of assigning the central pier and the abutment as fixed piers?
6. Sometimes the side of concrete bridges is observed to turn black in colour. What is the reason for this phenomenon?
7. In prestressing work, if more than one wire or strand is included in the same duct, why should all wires/strands be stressed at the same time?
8. In the design of elastomeric bearings, why are steel plates inserted inside the bearings?
9. How to determine the size of elastomeric bearings?
10. In a curved prestressed bridge, how should the guided bearings in piers of the curved region be oriented with respect to the fixed bearing in abutment?
11. 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?
12. What are the advantages of piers constructed monolithically with the bridge deck over usage of bearings?
13. Are diaphragms necessary in the design of concrete box girder bridges?
14. What is the advantage of sliding bearings over roller bearings?
15. What are the three major types of reinforcement used in prestressing?
16. Why is the span length ratio of end span/approach span to its neighboring inner spans usually about 0.75?
17. In the design of a simply supported skew bridge, which direction of reinforcement should be provided?
18. What are the functions of grout inside tendon ducts?
19. What is the consideration in selecting the orientation of wing walls in the design of bridge abutments?
20. In joints of precast concrete bridge segments, what are the functions of applying epoxy adhesive?

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

23. Polytetrafluoroethylene (PTFE) is commonly used in sliding bearings. Why?
24. Should raking piles of a bridge abutment be placed under an embankment?
25. How do engineer determine the number of cells for concrete box girder bridges?
26. What is sucker deck principle for variable depth bridge decks?

2. Concrete Structures

1. What are the functions of different components of a typical expansion joint?
2. If on-site slump test fails, should engineers allow the contractor to continue the concreting works?
3. What is the function of shear keys in the design of retaining walls?
4. In designing concrete structures, normally maximum aggregate sizes are adopted with ranges from 10mm to 20mm. Does an increase of maximum aggregate size benefit the structures?
6. What are the major problems in using pumping for concreting works?
7. Is it desirable to use concrete of very high strength i.e. exceeding 60MPa? What are the potential problems associated with such high strength concrete?
8. What are the disadvantages of curing by ponding and polythene sheets?
9. Comparing the rate of “Formwork exceeding 300mm wide, horizontal or at any inclination up to and including 5o to the horizontal” with the rate of “Formwork exceeding 300mm wide, at any inclination more than 85o up to and including 90o to the horizontal”, which one is higher?
10. If concrete compression test fails, should Schmidt hammer test be adopted as an alternative test to prove the concrete strength?

11. What is the indication of shear slump and collapse slump in slump tests?
12. In erection of falsework, for a rectangular panel inside a falsework should it be braced along the two diagonals?
13. In carrying out compression test for concrete, should test cubes or test cylinders be adopted?
14. What is the function of rebate in a typical construction joint?
15. If a contractor proposes to increase concrete cover beyond contractual specification (i.e. 40mm to 70mm), shall engineers accept the proposal?
16. Can grout replace concrete in normal structure?
17. Which type of bar reinforcement is more corrosion resistant, epoxy-coated bars, stainless steel bars or galvanized bars?
18. Can a concrete structure be completely free of expansion joints and contraction joints?
19. Does the presence of rust have adverse impact to the bond performance of bar reinforcement?
20. General Specification for Civil Engineering Works (1992 Edition) Clause 15.09 specifies that tying wires for reinforcement adjacent to and above Class F4 and F5 finishes should be stainless steel wires. Why?
21. For long slender structures like beams, propping is required after removal of formwork. Why?
22. What is the difference in application between open stirrups and closed stirrups in concrete beams?
23. For column reinforcements, why is helical reinforcement sometimes designed instead of normal links?
24. What is the difference between epoxy grout, cement grout and cement mortar?
25. What is the purpose of skin reinforcement for deep beams?

3. Drainage Works

4. Earthworks

5. Piers and Marine Structures

6. Roadworks

7. Pumping Station

8. Reclamation

9. Water Retaining Structures and Waterworks

10. Pipe Jacking and Microtunelling

11. Piles and Foundation

12. General

Vincent T. H. CHU