What are the strongest shapes in building?
Answer: The pillars
Question No. 02
In a curved pre-stressed bridge, how should the guided bearings in piers of the curved region be oriented with respect to the fixed bearing in abutment?
Answer: To determine the orientation of guided bearings, one should understand the movement of curved region of a pre-stressed bridge. Movement of pre-stress and creep are tangential to the curvature of the bridge (or along longitudinal axis) while the movement due to temperature and shrinkage effects are in a direction towards the fixed pier. If the direction of guided bearings is aligned towards the fixed bearing in the abutment, the difference in direction of pre-tress and creep movement and the guided direction towards fixed bearing would generate a locked-in force in the bridge system. The magnitude of the lock-in force is dependent on the stiffness of deck and supports. If the force is small, it can be designed as additional force acting on the support and deck. However, if the force is large, temporary freedom of movement at the guided bearings has to be provided during construction.
Question No. 03
If concrete compression test fails, should Schmidt hammer test be adopted as an alternative test to prove the concrete strength?
Answer: The Schmidt hammer test is based on the elastic rebound of hammer which presses on concrete surface and it measures the surface hardness of concrete. Since the test is very sensitive to the presence of aggregates and voids at the concrete surface, it is necessary to take more than 10 readings over the area of test. However, it should be noted that Schmidt hammer test measures surface hardness only but not the strength of concrete. Therefore, it may not be considered a good substitute for concrete compression test.
Question No. 04
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 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.
Question No. 05
How do you maintain water pressure?
Answer: If you have water pressure and wish to maintain it, do not cause flow in the line, which will reduce pressure due to friction. To keep pressure up, reduce friction by increasing the line size or eliminating some other restriction.
Question No. 06
What is the difference in arranging pumps in series and in parallel?
Answer: For identical pumps with similar functions, if the pumps arranged in series, the total head is increased without a change to maximum discharge. On the other hand, for pumps arranged in parallel to one another, the discharge is increased without any changes to maximum head.
Question No. 07
What is the function of rebate in a typical construction joint?
Answer: Construction joints are created on sites to facilitate the construction process. However, if improperly constructed, the completed construction joints will leave an uneven scar on the concrete surface and affect significantly its appearance. To avoid this, a rebate is formed during the first pour of one side of construction joint. After the other pour is concreted, it will hide the uneven joint inside the rebate.
Question No. 08
Shall a layer of wearing course or additional thickness be designed on the surface of piers?
Answer: In the design of piers, consideration should be given to the effect of wearing action caused by passengers, other traffics and even sometimes vehicles. In maritime environment, the durability and integrity of concrete is detrimental to the servicing life of piers because it acts an essential barrier to chloride attack. However, in view of these gradual wear and tear generated by the loading traffic, some forms of surface protection should be provided on top of pier surface like wearing course or additional increase in concrete cover.
Question No. 09
The spacing of manholes in straight sections for different pipe sizes is stated in Storm-water Drainage Manual. How are these figures arrived at?
(i) For pipe size < 300 mm, rodding is usually adopted in which workers place about 1 m long rods through the pipes to the location of blockage and manually operate the rod to clear the blockage.
(ii) For pipe size < 700 mm, water-jetting is normally employed in which water is supplied from nearby fire hydrants and pressurized water jet is used for clearing blockage.
(iii) Winching method is adopted for all sizes of pipes. For instance, for pipe size exceeding 1050 mm, it is stated in Storm-water Drainage Manual that maximum intervals between manholes along straight lengths should be 120 m. This is because for sizes over 1050 m, the main method of pipe maintenance is by winching whose maximum length of operation is 120 m. Similarly, the maximum intervals of manholes for other straight pipes are derived from their corresponding maintenance methods.
Question No. 10
What is unit weight of normal concrete?
Answer: 145 PCF