Civil Engineering Interview Questions Part – 8
Should dolphins be designed in a rigid manner, i.e. resting on several raking piles?
Answer: In designing dolphins, they are normally supported on a system of three to four raking piles. This in essence is a rigid structure and exhibits little flexibility e.g. movement against impact and berthing loads by vessels. In fact, this kind of design may not be desirable in terms of maintenance because the dolphins are readily susceptible to damage by high berthing vessels. To rectify this situation, some energy absorption devices like rubber/plastic fenders have to be installed to reduce the impact load deriving from its own deflection. On the other hand, by designing dolphins as flexible structures capable for allowing slight deflection, it helps to reduce the large forces generated during berthing of vessels. In this connection, one way of designing dolphins as flexible structures is by provision of a single pile only. Note: For a rigid structure, it takes up external loads without undergoing excessive deformations.
Question No. 64Who built the sears tower? Answer: While he did not build the structure (he died in l959), there is some evidence the idea was suggested under a different name (Illinois Building) by Frank Lloyd Wright, one of the few true skyscrapers in which he had a role. The original design for the Illinois Building would have topped off at 5,280 Feet! The Swears tower is a quarter of this at most, but there are similarities.
Question No. 02
What is the strongest bridge for a school contest?
Answer: If you are making a spaghetti bridge, bunch it all together in a triangular prism or a big brick and just fill the gaps with Paste.
Question No. 03
Why are intermediate jacks designed in some pipe jacking projects?
Answer: When the process of pipe jacking stops, building up of resistance is very fast in some soil. For instance, increase in jacking force of 20%-40% is required for a stoppage of pipe jacking for just several hours. Hence, it is recommended that pipe jacking should be carried out in a continuous operation. For a long pipeline, the frictional forces established between the jacking pipes and soil is high. Sometimes, such resisting forces may be so high that they can hardly be overcome by the jacks in jacking pits. Moreover, even if the jacks can overcome the high frictional forces induced during
Jacking, high loads are experienced in jacking pipes during driving. Jacking pipe materials e.g. concrete may not have sufficient strength to resist these stresses and hence pipe strength is another factor that governs the need for consideration of using intermediate jacks.
Question No. 04
What is the best type of wood glue?
Question No. 05
What is the purpose of adding cooling pipes or even using cold water for concrete in concreting operation?
Answer: All these measures aim at reducing the placing temperature and reducing thermal cracks induced during concreting of massive pours. Since the final concreting temperature should be the ambient temperature, reducing the initial placing temperature will also lower the peak hydration temperature. Therefore, the temperature difference between the hydration peak and the ambient temperature is reduced accordingly and subsequently the thermal effect to concrete structure can be reduced by controlling the placing temperature.
Question No. 06
What are the advantages of using top-down approach in basement construction?
Answer: The advantages of top-down approach are listed below:
(i) The structures above ground can be carried out simultaneously with the structures below ground. This greatly reduces the time for construction.
(ii) By using this approach, settlement can be reduced.
(iii) Since the permanent columns and slabs can be utilized to support loadings during construction, it saves the cost of formwork. Note: Top-down approach means construction of basement is carried out from ground level downwards.
Question No. 07
In selection of water stop, shall engineers use plain dumb-bell type or center-bulb type?
Answer: The plain dumb-bell type is used for joint location where small movements are anticipated. Therefore, construction joints are desirable locations of this type of water stop. On the other hand, center-bulb type water-stop is suitable for expansion joints or locations where lateral and shear movements occur due to settlement or deflection. Reference is made to W. L. Monks (1972).
Question No. 08
Why are two gate valves required in normal practice to form a washout valve?
Answer: In fact, the situation is analogous to that of fire hydrants in which two gates valves are installed with a single fire hydrant. Washout valves are used for normal maintenance work of watermain like allowing flowing out of water during cleaning of watermain. At the junction where a tee-branch out to a washout point, a gate valve is installed to separate the two pipelines. However, this gate valve is open during normal operation while another gate valve further downstream is installed (closed during normal operation). If the downstream gate valve is not installed in position, then the pipe section of branched-out watermain will be left dry during normal operation and there is a high probability that damage to watermain and frequent leakage would occur. With the downstream gate valve installed, the segment of branched-out watermain contains water in normal operation. In case there is any leakage, it can be readily detected by using the two gate valves.
Question No. 09
What is an ice dam sock?
Answer: If you have never used an ice dam melting sock on your roof before, you will find that they provide an inexpensive method for removing roof ice dams and improving your home’s heating efficiency. Roof ice dams are an annoying source of roof damage, leaks, and heat loss in the winter. The main causes are drip melt from improperly capped warm air vent pipes and poor roof insulation. Laying an ice melt sock onto the roof so it crosses the ice dam and overhangs the gutter, will melt through the snow and ice and create a channel for water to flow down into the gutters or off the roof. If done properly those ice sickles that form as the snow melts from the edges of the gutters will never appear, they too are a cause of much damage and are dangerous to life and limb.
Question No. 10
In concrete compression test, normally 150 mm × 150 mm × 150 mm concrete cube samples is used for testing. Why isn’t 100 mm × 100 mm × 100 mm concrete cube samples used in the test instead of 150mmx150mmx150mm concrete cube samples?
Answer: Basic force supplied by a concrete compression machine is a definite value. For normal concrete strength application, say below 50MPa, the stress produced by a 150 mm × 150 mm × 150 mm cube is sufficient for the machine to crush the concrete sample. However, if the designed concrete strength is 100MPa, under the same force (about 2,000 kN) supplied by the machine, the stress under a 150mmx150mmx150mm cube is not sufficient to crush the concrete cube. Therefore, 150 mm × 150 mm × 150 mm concrete cubes are used instead to increase the applied stress to crush the concrete cubes. For normal concrete strength, the cube size of 150 mm × 150 mm × 150 mm is already sufficient for the crushing strength of the machine.