Question
No. 46
Should
joints of concrete kerbs be in line with the joints in concrete carriageway?
Answer: In normal practice, joints are
provided in road kerbs to cater for concrete expansion and contraction.
However, the location of joints in kerbs is not arbitrary and they should match
with joints in concrete carriageway. Otherwise, it is very likely that cracks
may form in concrete kerbs at location of pavement joints (Ministry of
Transport (1955)).
Question
No. 47
In case
mud waves occur during reclamation, what are the possible solutions to rectify
the situation?
Answer:
- Option 1 – Complete Removal of All Disturbed Mud: To remove all disturbed mud once mud waves occur is the fastest way to treat the problem. After that, filling material is used for replacing the disturbed mud. However, this option is a rather expensive option because it involves dredging of all disturbed mud and replacement of large amount of fill.
- Option 2 – Accelerated consolidation of Disturbed Mud: This option involves placement of surcharging loads on top of mud waves, together with installation of band drains to accelerate the consolidation of disturbed mud. This method suffers from the drawback that sufficient long time is required for the consolidation process of mud.
- Option 3 – Partial Removal of Disturbed Mud: This option is a combination of the first two options in which the top weak layer of mud is removed while the lower mud is treated with surcharging with band drain installation.
Note: Mud
waves refer to excessive displacement of mud due to successive slip failure
during reclamation.
Question
No. 48
For
compaction of free-draining sands or gravels, what is the optimum moisture content
to achieve maximum density?
Answer: The compaction curve of sandy
materials is totally different from that of clayey materials. For sands or
gravels, there are two situations of maximum density, namely the completely dry
condition and the complete water saturation. For moisture content of sands and
gravels between these two states, the dry density obtained is lower than that
obtained in the above-mentioned states. The presence of capillary forces
account for the difficulty of compaction sand at water contents between
virtually dry and saturated state. They are formed in partially filled water
void between soil particles and perform as elastic ties cementing soil
particles together. Reference is made to Lars Forssblad (1981).
The
compaction curve for clay is suitable for the majority of soil types except
sands and gravels because a small amount of clay in soils is sufficient to make
the soils impermeable.
Question
No. 49
What
is the world’s largest concrete dam?
Answer: The Grand Coulee Dam is said to be the largest concrete dam. Currently
the world's largest concrete dam is the Itaipu Dam, an accomplishment of two
neighboring countries, Brazil and Paraguay in South America.
Though it is not finished yet, the Three
Gorges (or Sandapong) Dam on the Yangtze River in China will take over as the largest
upon its completion, which is slated for 2009.
Question
No. 50
What are
the main reasons for conducting pull-out tests for soil nails?
Answer: There are mainly four reasons for
this test:
- To check and verify the bond strength between soil and grout adopted during the design of soil nails. This is the main objective of conducting soil nail pull-out test.
- To determine the bond strength between soil and grout for future design purpose. However, if this target is to be achieved, the test nails should be loaded to determine the ultimate soil/grout bond with a upper limit of 80% of ultimate tensile strength of steel bars.
- To check if there is any slippage or creep occurrence.
- To check the elastic and plastic deformations of test nails. This is observed during the repeated loading and unloading cycles of soil nails.
Note:
Pull-out tests are carried out by applying specified forces in an attempt to
pull out the constructed soil nails.
Question
No. 51
In
Hiley’s formula for driven piles i.e. R = E/(s + 0.5c), why is a coefficient of
0.5 applied for the term elastic deformation of piles and soil?
Answer: Hiley’s formula is based on the
principle of energy conservation in which the energy brought about by hammers
during the action of hitting are transferred to piles in ground. When the
hammer force and displacement is plotted, the energy absorbed by piles is the
area under the curve. Since the curve of elastic component is linear with a
positive slope, the area i.e. energy should be the area of triangle (0.5 × R ×
c) where ‘R’ is reaction force and ‘c’ is elastic compression due to helmet,
piles and soil system. For settlement, it is of horizontal line in
force-displacement diagram and hence the energy transferred to pile-soil system
is (R × s).
Question
No. 52
In
designing sewer pipes, why are vitrified clay pipes commonly used for pipe size
less than 600 mm while precast concrete pipes with PVC lining is used for pipe
size exceeding 600 mm?
Answer: The market price of vitrified clay pipes is
generally less than that of precast concrete pipes with PVC lining. Therefore,
for small size of pipes (pipe diameter less than 600 mm) it is more economical
to use vitrified clay pipes. However, vitrified clay pipes do suffer from the
problem of brittleness and its effect is even severe for larger size of pipes.
Moreover, it is rather time consuming to deliver clay pipes products because
the majority of them are manufactured in Europe. Hence, for larger size of
sewer pipes (diameter more than 600 mm) it is customary to use precast concrete
pipes with PVC lining.
Question
No. 53
What
is rigging?
Answer: In sailing, the ropes used to move the sails around so the boat will
move in the right direction when the wind blows.
Question
No. 54
What are
the considerations in selecting marine plants and land plants for installation
of band drains?
Answer: For installation of band drains by
marine plants, it must have sufficient water depth to accommodate the marine
plants in the first place. However, due to the effect of tides and waves, the
establishment of the position for installation of band drains and the
subsequent installation works may be affected. In addition, the establishment
cost of marine plants is higher than that of land plants.
For
installation of band drains by land plants, difficulty may be encountered during
the installation of band drains through the reclaimed layer e.g. C&D
material. Land plants may take longer construction time due to the
above-mentioned difficulty. Sometimes when the supply of public fill is
increased suddenly, it may be preferable to place these fill immediately into
position and in this situation the installation of band drains (originally installed
by marine plants) is delayed so that the construction of band drains is changed
to using land plants.
Question
No. 55
What
is the distance between railway tracks?
Answer:
In U.S, its 4 feet and 8.5 inches
In India, its 5 feet 6 inches
Question
No. 56
Why are
most marine piles circular in cross section?
Answer: For marine piles, there are several
options available for selection, namely H-piles, circular pipes and box piles. However,
only circular piles and box piles are suitable for marine application because
of the following two reasons suggested by G. M. Cornfield (1968):
- Circular piles and box piles possess high column buckling strength. For marine structures like jetties, piles are well above seabed level and therefore the column buckling effect is significant when compared with other structures. Therefore, it is essential to use pile sections which have relatively high buckling strength in piers.
- Circular piles and box piles display high energy absorbing capability. For marine structures like dolphins and fenders, which require substantial amount of berthing energy to be absorbed, these piles sections are inevitably good choices. In marine structures, it appears that circular sections prevail over the box sections. The main reason is that the range of section available for selection of circular piles is more than that of box piles.
Question
No. 57
What
is the purpose of the gap in the road on this bridge?
Answer: Purpose of the gap in the road is to allow the road to expand and
contract with temperature changes without causing damage or deformation to the
road.
Question
No. 58
What is
the mechanism of cavitation in pipes and drains?
Answer: Cavitation refers to the formation of air
bubbles in fluid in low-pressure condition which is lower than the saturation
pressure. It is a potentially damaging condition in which the fluid in pipes or
sewers is at high velocities. By Bernoulli’s Equation, at high flow velocities,
the pressure head of fluid is reduced accordingly. As the fluid pressure is
less than saturation pressure, dissolved gases are released from the fluid and
these air bubbles will suddenly collapse when the flow enters into a region of
higher pressure. This produces a high dynamic pressure which causes damage to
the pipelines due to its high frequency.
Question
No. 59
What is
the importance of geo-textiles and sand in reclamation works?
Answer: For geo-textiles used in reclamation,
they serve mainly the following two purposes:
- They separate reclamation fill from marine mud;
- They may act as reinforcement to enhance the stability of reclamation. However, the reinforcement function is still under heated debate because its performance as reinforcement depends on several factors like the directional strength of woven geo-textiles and damage effect by installation of vertical band drains.
For sand:
- It spreads the load of future public dump on top of it;
- It acts as drainage path for dissipation of excess pore water pressure for band drain installation.
Question
No. 60
Why
is the statue of liberty made of copper?
Answer: Copper is a very durable material when exposed to weather and is soft
enough that it can be easily molded to curved shapes such as those in the
Statue of Liberty. It is also traditionally used in buildings for complex
roofs, so there would have been trades people available trained to use it.
Other metals that can be molded are lead but
it does not have the attractive verdigris color, and gold much is more expensive
Question
No. 61
Why is
shallow bedrock condition unfavourable for open berth piers?
Answer: The most severe load on piers
generally is the horizontal load due to berthing of large vessels. Since the
widths of open berth piers are relatively small so that they provides a short
lever arm to counteract the moment induced by berthing loads. Moreover, the
dead load of open berth piers are normally quite light and therefore the
resisting moment provided by the dead load of pier structures may not be
sufficient to counteract the moment generated by berthing loads.
To aid in
providing adequate resistance to the overturning moment by the berthing load,
the soil resistance above bedrock contributes to stabilizing moment. For
commonly adopted marine piling type, i.e. driven steel tubular piles with
reinforced concrete infill, driven piles can at most be founded on top of rock-head
surface. In case the rock-head level is shallow, then the little soil cover may
result in insufficient lateral resistance to the berthing load.
Question
No. 62
Where
is the world’s longest elevator and how long is it?
Answer: Gold mines in South Africa go a few kilometers below the surface. The world’s
deepest mine now is the Mponeng, is a gold mine in South Africa's North West
Province. It extends over 4 kilometres below the surface, and is considered to
be one of the most substantial gold mines in the world. The lift itself
descends 3037 m to a point 1200 m below sea level.
Question
No. 63
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. 64
Who
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. 65
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. 66
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’s material 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. 67
What
is the best type of wood glue?
Answer: Noob
Question
No. 68
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. 69
What are
the advantages of using top-down approach in basement construction?
Answer: The advantages of top-down approach
are listed below:
- The structures above ground can be carried out simultaneously with the structures below ground. This greatly reduces the time for construction.
- By using this approach, settlement can be reduced.
- Since the permanent columns and slabs can be utilized to support loadings during construction, it saves the cost of form-work.
Note:
Top-down approach means construction of basement is carried out from ground
level downwards.
Question
No. 70
In
selection of waterstop, 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 waterstop. 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. 71
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. 72
What
is an ice dam sock?
Answer: If you have never used a 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 a 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. 73
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 150 mm × 150 mm × 150 mm concrete cube samples?
Answer:
Basically, the 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.
Question
No. 74
In pipe
jacking/microtunneling, it is commonly accepted that cover depths of jacking
pipes cannot be too shallow (i.e. less than 2D where D is the diameter of jacking
pipes). Why?
Answer: For pipe jacking/microtunneling, the
causes of large settlement are loss of face stability, failure to stabilize
ground around shafts, presence of annular space around pipes and shield, drag
along pipe joints, etc. The settlement mechanism of shallow depths of pipe jacking/microtunneling
is the formation of a settlement trough on top of the jacking pipes. The width
of the trough depends on soil properties; the larger is the cover depth of
jacking pipes, the larger is the width of settlement trough. For the same soil
volume loss due to pipe jacking/microtunneling, the width of settlement trough
for shallow cover depth is smaller and therefore it results in a larger
vertical maximum settlement.
Question
No. 75
What
is the force exerted by the Tacoma narrows bridge?
Answer: The force exerted to the Tacoma narrows bridge was initially the wind
resistance. The wind resistance caused the whole bridge to act as a system with
forced vibration with damping.
Question
No. 76
What is
the mechanism of protection by hot dip galvanizing?
Answer: Hot dip galvanizing protects
steel/iron from corrosion by:
- It forms a metallic zinc and zinc-iron alloy coating on top of steel surface. This zinc coating reacts with moisture in atmosphere to from zinc salts which act as an insulating layer for steel/iron.
- Zinc is higher than steel/iron in the galvanic series and when these dissimilar metals with different electrical potential are in contact, the zinc anode corrodes and offers sacrificial protection to steel/iron and hence steel/iron is protected from corrosion.
Question
No. 77
Comparing
the rate of “Formwork exceeding 300 mm wide, horizontal or at any inclination
up to and including 5° to the horizontal” with the rate of “Formwork exceeding
300 mm wide, at any inclination more than 85° up to and including 90° to the horizontal”, which one is higher?
Answer:
The item “Formwork exceeding 300 mm
wide, at any inclination more than 85° up to and including 90°
to the horizontal” refers to formwork formed vertically and when compared with
formwork erected in horizontal plane, the amount of false-work required is
smaller.
The item “Formwork exceeding 300 mm wide,
horizontal or at any inclination up to and including 5° to the horizontal” refers to formwork to be
erected in horizontal position and in general it requires much false-work to
support this type of formwork. Therefore, the rate for this item is higher than
the one mentioned in the above paragraph.
Question
No. 78
In pre-stressing
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?
Answer:
If wires/strands are stressed individually inside the same duct, then those
stressed strand/wires will bear against those unstressed ones and trap them.
Therefore, the friction of the trapped wires is high and is undesirable.
Question
No. 79
What
is a kip?
Answer: 1 kip = 1000 lbs
Question
No. 80
What is
the difference between fasteners, bolts and screws?
Answer: Fastener is a general term to
describe something which is used as a restraint for holding things together or
attaching to other things.
The main
physical distinction between screws and bolts is that screws are entirely full
of threads while bolts contain shanks without threads. However, a better
interpretation of the differences between the two is that bolts are always
fitted with nuts. On the contrary, screws are normally used with tapped holes.
Question
No. 81
How
do you measure concrete?
Answer: Cubic feet, Cubic yards, Cubic Meter
Question
No. 82
What are
the advantages of piers constructed monolithically with the bridge deck over
usage of bearings?
Answer:
Basically, piers constructed monolithically with the bridge deck are
advantageous in the following ways:
- Movement of the bridge deck is achieved by the bending deformation of long and slender piers. In this way, it saves the construction cost of bearings by using monolithic construction between bridge deck and piers. Moreover, it is not necessary to spend extra effort to design for drainage details and access for bearing replacement. On the other hand, in maintenance aspect substantial cost and time savings could be obtained by using monolithic construction instead of using bearings as bridge articulation.
- Monolithic construction possesses the shortest effective Euler buckling length for piers because they are fixed supports at the interface between bridge deck and piers.
Note:
Monolithic construction means that piers are connected to bridge decks without
any joints and bearings.
Question
No. 83
What
is braced excavation all about?
Answer: Excavations are braced to prevent the cavein of surrounding unstable
soil.
Question
No. 84
In the
design of pipe jacking, what particular areas on pipe joints should engineers take
care of?
Answer: Since in pipe jacking, the jacked
pipes could hardly be jacked in the designed level and alignment and some
deviation from the original one is commonly acceptable provided that the
deviation are within the tolerance of the Contract. However, in order to avoid
damage made to the pipe joints due to over-stressing, it is necessary to
estimate the stress concentrations resulting from these angular deflections.
Note: Pipe
jacking is a trenchless method in which pipes are jacked underground from
jacking pits and receiving pits.
Question
No. 85
In the
design of service reservoirs, how are reservoir floors designed to prevent leakage
of water due to seasonal and shrinkage movements?
Answer: There are in general two main
approaches in designing floors of service reservoirs:
- In the first method, movement joints are designed in each panel of reservoir floors so that they can expand and contract freely. Each panel is completely isolated from one another and a sliding layer is placed beneath them to aid in sliding.
- The second method, on the contrary, does not make provision to free movement. Due to seasonal and shrinkage movements, cracks are designed to occur in the reservoir floors such that very tiny cracks are spread over the floor and these cracks are too small to initiate corrosion or leakage. However, in this case, the amount of reinforcement used is much larger than the first approach.
Question
No. 86
In
erection of false-work, for a rectangular panel inside a false-work should it
be braced along the two diagonals?
Answer:
When a rectangular panel is subject
to an eccentric load or a lateral load, it tends to deform into a parallelogram
with one diagonal shortening and the other elongating. Theoretically, it is
sufficient to brace along one of the diagonals (the one in tension). If one
diagonal is only allowed to brace inside the rectangular panel, it should be
not braced in the diagonal in compression because under severe lateral loading
the diagonal may buckle leading to failure of structure.
However, in actual situation lateral loads
may come from both sides of the panel and hence it should be braced in both
diagonals.
Question
No. 87
What
are the applications of modulus of elasticity?
Answer: As the term implies, "Modulus of Elasticity relates to the
elasticity or "flexibility" of a material. The value of modulus of elasticity
is very much significant relating to deflection of certain materials used in
the construction industry. Take for example the general E value of mild carbon
steel is about 200 GPA compared to about 70 GPA for aluminium. This simply
translate that aluminium is 3 times flexible than steel.
Question
No. 88
What are
the functions of different components of paint?
Answer: For normal paint application, there
are mainly three main components of paint, namely primer, undercoat and
finishing coat.
- Primer: This is the first layer of a typical painting system and it is used to inhabit corrosion and provide a good bond for subsequent coats.
- Undercoat: This component acts as a barrier to corrosion agents and even out irregularities of bonding surface. It also serves to hide the underlying background and prevent the details and colour of the area of application to affect the designed colour and finishing details of paint.
- Finishing coat: This is the final layer of a typical painting system and it protects the underlying layers from the effect of adverse weather conditions (e.g. sunlight) and to provide the designed properties of paint like colour, impermeability, wearing resistance, etc.
Question
No. 89
Why is
the span length ratio of end span/approach span to its neighboring inner spans
usually about 0.75?
Answer:
From aesthetic point of view, an
odd number of spans with a decrease in length in the direction of
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 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.
Note: End span refers to the last span in a
continuous bridge while approach span refers to the first span of a bridge.
Question
No. 90
What
is the tallest man made structure in the world?
Answer: The tallest artificial structure is Burj Khalifa, a
skyscraper in Dubai that reached 829.8 m (2,722 ft) in height on January 17,
2009. By April 7, 2008 it had been built higher than the KVLY-TV mast in North
Dakota, USA.
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