Civil engineering interview question and answers
Answer :
- Batching: The process of measurement of the different materials for the making of concrete is known as batching. batching is usually done in two ways: volume batching and weight batching. In case of volume batching the measurement is done in the form of volume whereas in the case of weight batching it is done by the weight.
- Mixing: In order to create good concrete the mixing of the materials should be first done in dry condition and after it wet condition. The two general methods of mixing are: hand mixing and machine mixing.
- Transportation and placing of concrete: Once the concrete mixture is created it must be transported to its final location. The concrete is placed on form works and should always be dropped on its final location as closely as possible.
- Compaction of concrete: When concrete is placed it can have air bubbles entrapped in it which can lead to the reduction of the strength by 30%. In order to reduce the air bubbles the process of compaction is performed. Compaction is generally performed in two ways: by hand or by the use of vibrators.
Answer :
Curing is the process of maintaining the moisture and temperature conditions for freshly deployed concrete. This is done for small duration of time to allow the hardening of concrete. The methods that are involved in saving the shrinkage of the concrete includes:
- Spraying of water: on walls, and columns can be cured by sprinkling water.
- Wet covering of surface: can be cured by using the surface with wet gunny bags or straw
- Ponding: the horizontal surfaces including the slab and floors can be cured by stagnating the water.
- Steam curing: of pre-fabricated concrete units steam can be cured by passing it over the units that are under closed chambers. It allows faster curing process and results in faster recovery.
- Application of curing compounds: compounds having calcium chloride can be applied on curing surface. This keeps the surface wet for a very long time.
Answer :
During the installation of bridge bearings the size of the upper plates is reduced to save the material costs. This process is known as preset. Generally the upper bearing plate comprises of the following components:
- Length of bearing
- 2 x irreversible movement.
- 2 x reversible movement.
The bearing initially is placed right in the middle point of the upper bearing plate. No directional effects of irreversible movement is considered. But since the irreversible movement usually takes place in one direction only the displaced direction is placed away from the midpoint. In such cases the length of the upper plate is equal to the length of the length of the bearing + irreversible movement + 2 x reversible movement.
Answer :
In order to make a elastomeric bearing act/ function as a soft spring it should be made to allow it to bulge laterally and also the stiffness compression can be increased by simply increasing the limiting amount of the lateral bulging. In many cases in order to increase the compression stiffness of the bearing the usage of metal plates is made. Once steel plates are included in the bearings the freedom of the bulge is restricted dramatically, also the deflection of the bearing is reduced as compared to a bearing without the presence of steel plates. The tensile stresses of the bearings are induced into the steel plates. But the presence of the metal plates does not affect the shear stiffness of the bearings.
Answer :
The major types of reinforcements used in prestressing are:
- Spalling Reinforcement: The spalling stresses leads to stress behind the loaded area of the anchor blocks. This results in the breaking off of the surface concrete. The most likely causes of such types of stresses are Poisson`s effects strain interoperability or by the stress trajectory shapes.
- Equilibrium reinforcements: This type of reinforcements are required where several anchorages exist where the prestressing loads are applied in a sequential manner.
- Bursting Reinforcements: These kinds of stresses occur in cases where the stress trajectories are concave towards the line of action of load. In order to reduce such stresses reinforcements in the form of bursting is required.
Answer :
Some of the most common arrangements of wing walls in cases of bridge arguments are as follows:
- Wing walls parallel to abutments: This method is considered to take least amount of time to build and is simple as well. But on the downside this method is not the most economical. The advantage of this type of design being that they cause the least amount of disturbance to the slope embankment.
- Wing walls at an angle to abutments: This design method is considered to be the most economical in terms of material cost.
- Wing walls perpendicular to abutments: The characteristic of this design is it provides an alignment continuous with the bridge decks lending a support to the parapets.
Answer :
When the depth of a box girder bridge exceed 1/6th or 1/5th of the bridge width then the design recommended is that of a single cell box girder bridge. But in case the depth of the bridge is lower than 1/6th of the bridge width then a twin-cell or in some cases multiple cell is the preferred choice. One should also note that even in the cases of wider bridges where there depths are comparatively low the number of cells should be minimized. This is so as there is noticeably not much improvement in the transverse load distribution when the number of cells of the box girder is higher than three or more.
Answer :
Pot bearings are preferred over elastomeric bearings in situations where there are chances of high vertical loads in combinations of very large angle of rotations. Elastomeric bearings always require a large bearing surface so that a compression is maintained between the contact surfaces in between the piers and the bearings. This is not possible to maintained in high load and rotation environment. Also the usage of elastomeric bearings leads to the uneven distribution of stress on the piers. This results in some highly induced stresses to be targeted at the piers henceforth damaging them. Due to the above reasons pot bearings are preferred over elastomeric bearings in such cases.
Answer :
During the pumping operation the pump exerted pressure must overcome any friction between the pumping pipes and the concrete, also the weight of the concrete and the pressure head when the concrete is placed above the pumps. Since only water is pump able, all the pressure generated is by the water that is present in the concrete. The major problem due to pumping are segregation effects and bleeding. In order to rectify and reduce these effects, generally the proportion of the cement is increased in order to increase the cohesion , which leads to the reduction of segregation and bleeding. Also if a proper selection of the aggregate grading can vastly improve the concrete pump ability.
Answer :
The primary purpose of curing is to reduce the heat loss of concrete that is freshly placed to the atmosphere and in order to reduce the temperature gradient across the cross-section of the concrete. Ponding is not preferred for curing as this method of thermal curing is greatly affected by cold winds.
In addition to that in ponding large amounts of water is used and has to be disposed off from the construction sites. Polythene sheets are used on the basis that it creates an airtight environment around the concrete surface henceforth reducing the chances of evaporation over fresh concrete surfaces. But the usage of polythene can be a drawback as it can be easily blown away by winds and also the water lost by self-desiccation cannot be replenished.
Answer :
Slump tests are performed to empirically measure the work ability of fresh concrete. It is used to measure the consistency of the concrete. In general there are three different types of slumps that occur in slump tests. They are as follows:
- True Slump: This type of slump is characterized by the general drop of the concrete mass evenly without visible signs of deterioration or disintegration.
- Shear Slump: It indicates that the concrete mix is deficient in cohesion. This type of slump leads to segregation and bleeding. Henceforth in the long run effecting the durability of the concrete.
- Collapse Slump: This type of slump is indicates that the mix of concrete is simply too wet. The mix is considered to be harsh and lean.
Answer :
Once the process of concreting is performed the striking of the formworks should be done as soon as possible as delay in this process can lead to the discoloration of the concrete structures. In case of long structures particularly long span structures once the structures have attained enough strength to support themselves it is essential to provide them with propping as creep deflection can take place which can greatly reduce the integrity of the structure.
Due to the above mentioned reasons propping should be done after the removal of formwork. Also the props should not be made to stand long as it can lead to overstress for the structures.
Answer :
The formation of air bubbles in a fluid due to low pressure conditions lower than the saturation pressure is known as cavitations. This is considered to be a high potential damage condition where the strength and durability of the pipes can be greatly reduced. Cavitation works on the principle of Bernoulli's Equation.
When fluids are at high velocities the pressure head of fluids reduce accordingly. But since the fluid pressure is lower than the saturation pressure the dissolved gases get released from the flowing fluid. These air bubbles suddenly collapse on entering a region of high pressure. This leads to the damage of the pipelines as a high level of dynamic pressure is created.
Answer :
Beddings are primarily made up of granular or concrete materials. They are primarily used for the following purposes:
- They are used to provide a more uniform support for the under pipes so that the bending moment longitudinally can be reduced greatly.
- In order to enable the pipes to get more load-supporting strength.
- They are also used to act as a platform to achieve a more correct alignment and level pre and post construction.
- In case of pipes which contain spigot and socket joints, it enables pipes to get supported along pipe lengths in place of sockets. Otherwise it can lead to uneven stress being induced on the pipes eventually damaging it.
Answer :
Pull out tests are performed for primarily the following reasons:
- In order to detect and the verification of the bond strength among the soil and the grout adopted during the design of soil nails. This is considered to be as the primary objective of performing pull out tests for soil nails.
- For the detection of any slippage or occurrence of creeps.
- To detect the elastic and deformations (plastic) of any of the test nails employed. Observations are made during the loading and unloading cycles of the soil nails repetitively.
- To achieve the perfect balance the test nails should always be loaded so that the ultimate soil/grout mixture with an upper limit of 80%.
Answer :
The advantages and disadvantages of using plastic fenders are as follows:
Plastic fenders are low in strength with a relatively high resistance to abrasion. Plastic fenders are resistant to chemical and biological attacks. Plastic fenders have moderate energy absorption capacity. The berthing reactions are also comparatively moderate and depends on the point of contact. Also since they are made from recycled material they are environmental friendly.
The advantages and disadvantages of using timber fenders are:
timber fenders are low in strength and are very susceptible to marine borer attacks and rotting. The energy absorption capacity is very low. Also generally the contact pressure between the vessels and the fender are high.
Answer :
The concrete safety fencings are made to contain vehicles in their carriageway being travelled so as to reduce the chances of rebounding into the roads leading to more hazards. In the case of normal fencings upon vehicle crashes the fencings give away so as to absorb as much energy as possible henceforth reducing the impact on the vehicles.
But in the case of concrete barriers their purpose is not to absorb energy of vehicles crashing into the barrier but to retain them. They have a curved design so as to allow the vehicles that hit them to slightly go up on the barrier but not overturn. They also prevent the vehicle from again getting back on the road by rebounds. This helps in vastly reducing the chances of other vehicle hazards.
Answer :
Some of the reasons why granular sub-base is not preferred in concrete carriageways:
- Sub bases are permeable and hence water can seep through them easily. The soil particles get pumped out through the joints on the application of traffic loads. This results in the creation of voids underneath the pavement structure. This leads to the weakening of the concrete surface and it can crack easily upon intense traffic loads.
- Instead if lean concrete is used for carriageways it greatly increases the strength of the roads and the load carrying capacity of the roads is increased.
- Sub-bases implementation requires a lot of workmanship which can lead to an un-uniform distribution of the sub-base. This can lead to the cracking of the carriageway when there is severe traffic loading.
Answer :
The purpose of separation membrane between the concrete pavement slab and the sub-base are as follows:
- The separation membrane reduces the frictional forces between the concrete slabs and the sub-base. The membrane aids the movement of the concrete slab in reference to the sub-base when changes in the level of the moisture and temperature occurs.
- It aids in the segregation of sub-base materials from freshly placed concrete.
- The separation membrane also helps in the reduction of cement and water loss in the form of immature concrete. Immature concrete greatly affects the strength of the concrete. It also affects the durability of it.
A good example of a separation membranes is polythene sheeting which is commonly used.
Answer :
The components of a typical waterproofing system on the roof of a pumping station are as follows:
- Right above the structural finish level of the roof ( concrete ) a uniform thickness screed is applied so as to facilitate the application of the waterproofing membrane. The surface provide for the membrane should always possess good cohesion properties and must be thin so as to prevent any un-uniformity. This thin layer also acts as a layer of thermal insulation.
- Right above this layer the waterproofing membrane is deployed to secure the water tightness of the roof.
- In order to enhance the thermal insulation of the roof an insulation board is sometime placed right above the waterproof membrane. The insulation board helps in the maintenance of a stable temperature in both weathers.
Answer :
There are several solution to the rectification of the problem of mud waves:
- Complete removal of all the disturbed mud: This method can be considered to be one of the fastest methods. As soon as the disturbed mud is removed some filling material is used to replace the disturbed mud. But economically this method can be expensive as compared to others.
- Accelerated consolidation of disturbed mud: In this method surcharging loads are placed on top of the mud waves. Along with this band drains are installed to accelerate the consolidation process. This method is quite slow compared to the other methods.
- Partial removal of the disturbed mud: This method is the hybrid of the above two methods where the top layer is removed whereas the lower level is treated with the surcharging process.
Answer :
The primary purposes of geotextiles and sand in reclamation works are as follows:
- Geotextiles: They are used to separate the marine mud from the reclamation fill. Also geotextiles are used as reinforcements in reclamation processes to increase its stability. It is still debated as to whether the usage of geotextiles is better or are the old processes followed are better as the performance has not been comparable to the conventional methods.
- Sand: In reclamation process sand is used to spread the load of any future public dumps placed on top of it. Sand also acts as a drainage for the excess pore water pressure of band drain installations.
Answer :
Joints which are formed from the cope level to the toe level of seawalls through a complete vertical plane are known as slip joints. Such joints are designed so as to handle the differential settlements between the seawalls adjacent panels. In the slip joints the aggregates inside the half-rounds channels enables some vertical movements.
These vertical movements are induced by differential settlements. This enables in the interlocking of the adjacent panels of the seawalls to link the panels in one unit against the earth pressure ( lateral ) which is exerted on the seawalls.
Answer :
The washout valves are primarily used for normal maintenance works such as that of water main. This can be like to allow water to flow out during the cleaning of the water main. The junctions at which a pipe branches out to a washout point usually a gate valve is installed so that the two pipelines are separated. The gate valve installed above usually remains open during normal operation. Another gate valve is installed further downstream and this remains closed during normal operation of the washout valve.
In case this valve is not installed then the pipe section of the branched out pipe would remain dry during normal operation and high chances of damage and leakage can take place. When the downstream valve is installed the branched out water main contains water under normal operation. With two gate valves installed a leakage can be detected immediately.
Answer :
In general there are two main approaches of designing the reservoir floors to prevent leakage of water due to seasonal and shrinkage movements:
- In this approach the movement joints of the reservoir floor panels are such that the free expansion and contraction of the panels takes place. Every panel is isolated from the other panels and two panels have a sliding layer between them to help in sliding.
- The second method does not provide any room for free movement. With seasonal and shrinkage movements, some cracks are designed to voluntarily occur on the floors of the service reservoirs. These tiny cracks are spread throughout the floor and are simply too minute to cause any leakage or corrosion of the floors. But the difference also in this method is that the amount of reinforcement used is much more than the first approach.
Answer :
Sorption is a concomitant phenomenon of adsorption and absorption.
Adsorption describes the phenomenon in which molecules that are present in a fluid (liquid or gas), concentrated spontaneously on a solid surface by a finite time.
Answer :
Young's modulus (E) describes tensile elasticity, or the tendency of an object to deform along an axis when opposing forces are applied along that axis; it is defined as the ratio of tensile stress to tensile strain. It is often referred to simply as the elastic modulus.
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 aluminum. This simply translate that aluminum is 3 times flexible than steel.
Answer :
Think about pulling a bar in tension. Load divided by cross-sectional area is force, or stress. But what cross section are you considering? Before starting pull, the bar had a known cross-section of (lets say) 0.5" wide x metal thickness. It's easy to measure these, since it is your starting material. At any load, the engineering stress is the load divided by this initial cross- area. While you are pulling, the length increases, but the width and thickness shrink.
At any load, the true stress is the load divided by the cross-area at that instant. Unless thickness and width are being monitored continuously during the test, you cannot calculate true stress. It is, however, a much better representation of how the material behaves as it is being deformed, which explains its use in forming simulations. In circle grid analysis, engineering strain is the % expansion of the circle compared to the initial diameter of the circle. The relationships between engineering values and true values are:
σ = s (1+e) ε = ln (1+e)
Where "s" and "e" are the engineering stress and strain, respectively, and " " and " " are the true stress and strain, respectively.
Answer :
The routine maintenance is the minor and consistent rePAirs that are engaged in the school premises. Examples could include PAinting, replacement of fixtures, louver blades, furniture rePAirs, and PAtching cracks in the school buildings.
The major maintenance could also be a total rehabilitation of the school, either school buildings or any other project within the school community. It could be total restructuring of the lighting system in the school or sanitary system.
Answer :
After calculating the anticiPAted traffic for the bridge, cement/reinforced- with- rebar stanchions are sPAced over the freeway to accommodate the bridge. An 'off-ramp' from the freeway to the bridge is constructed, as is an 'on-ramp' to the subsequent road. Cement/rebar slabs are built and lifted with cranes to form the platform, and voila! Drive carefully.
Although the bridge deck/roadway is almost always a concrete slab, the structure that holds up the bridge deck can be reinforced concrete, structural steel, or a combination of steel and concrete.
Answer :
Aggregate is the component of a composite material used to resist compressive stress.
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Soil reinforcement is the act of improving soil strength to enable it support or carry more load.
Two common examples are:
- Mixing a soil amendment such as lime into weak clayey soil and re-comPActing to improve soil-bearing caPAcity (often done under the road base in highway construction)
- Installing plastic or composite webbing layers (called geo-grid material) alternating with comPActed soil to produce a stronger sloped soil structure (often done on steep roadway embankments to improve strength and stability)
Answer :
Excavations are braced to prevent the cave-in of surrounding unstable soil.
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.
Answer :
Alloying is not always done to produce a 'superior' material, but to produce materials having a desired requirement in the industry or elsewhere. A classic case is of lead solder (containing lead & tin), in which the melting point of the constituent elements are lowered, not necessarily a desirable property.
Alloying can be carried out using hot press method (a sheet of material is sandwiched with alloying material), rolling the heated base metal in a drum full of alloying metal powder, using hot spraying, galvanizing (dipping the base in a molten solution of alloying material) etc. Sometimes the alloying material is added in small proportions to the molten base metal (e.g., in production of different types of steel).
Answer :
The tallest man made structure is the KVLY-TV mast which is 2063 feet tall. The worlds tallest man made structure is Burj Dubai which is 800 meter tall.
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On a per pound basis, steel pipe is stronger in bending and is less likely to buckle in axial compression.
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Cubic feet, Cubic yards, Cubic Meter.
Answer :
Absorption generally refers to two phenomena, which are largely unrelated. In one case, it refers to when atoms, molecules, or ions enter some bulk phase - gas, liquid or solid material. For instance, a sponge absorbs water when it is dry.
Absorption also refers to the process by which the energy of a photon is taken up by another entity, for example, by an atom whose valence electrons make transition between two electronic energy levels. The photon is destroyed in the process. The absorbed energy may be re-emitted as radiant energy or transformed into heat energy. The absorption of light during wave proPAgation is often called attenuation. The tools of spectroscopy in chemistry are based on the absorption of photons by atoms and molecules.
Adsorption is similar, but refers to a surface rather than a volume: adsorption is a process that occurs when a gas or liquid solute accumulates on the surface of a solid or, more rarely, a liquid (adsorbent), forming a molecular or atomic film (the adsorb-ate). It is different from absorption, in which a substance diffuses into a liquid or solid to form a solution.
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