Quick Revision
Civil Engineering
Isochrones:
Isochrones is a line on the map which connects points having an equal time of travel of the surface runoff to the catchment outlet. These are some property of Isochrones:
Isochrones vary with time, It's most commonly used to depict travel times, such as drawing a 30 minute travel time perimeter around a start location. The isochrone below joins up all points within a 45-minute drive from the origin.
Isochrones depict the variation of the pore water pressure along with the depth of the soil sample.
Isochrones are mainly used for transport planning, property search, sales territory planning, etc.
Isobar | Equal Pressure line |
Isohyets | Equal Rainfall line |
Isopleths | Equal Evapotranspiration line |
Isotherm | Equal Temperature line |
Isonif | Equal Snowfall line |
Natural wood defects:
Coarse grain: If the tree grows rapidly, the annual rings are widened. It is known as coarse grain timber and possesses less strength.
Burls: Burls are a deformed growth formed when a tree receives a shock or injury in its young age. Due to its injury, the tree’s growth is completely upset and irregular projections appear on the body of the timber.
Bark pockets: Formed when a small piece of the bark protrudes into the lumber. This area is generally considered unsound.
Bird pecks: Caused by birds, especially woodpeckers, which peck on trees mainly to cause panic to the insects living in or under the bark and in the wood of the tree.
Bangalore method
It is an anaerobic method conventionally carried out in pits.
In the Bangalore method of composting, dry waste material of 25 cm thick is spread in a pit and a thick suspension of cow dung in water is sprinkled over for moistening.
Indore method
It is an aerobic method.
The Indore method of composting in pits involves filling of alternate layers of similar thickness as in the Bangalore method.
However, to ensure aerobic condition the material is turned at specific intervals for which a 60 cm wide strip on the longitudinal side of the pit is kept vacant.
Type of outlets and Definition/Example
Non-Modular Outlets
Discharge depends upon the differences of head between distributary and the water course.
Example – open sluice and drowned/submerged pipe outlet
Semi-Modular Outlets
Discharge is independent of the water course so long as minimum working head is available.
Example- Pipe Outlet, Venturi Flume, Open flume and Orifice semi-module
Modular outlets
Discharge is constant and fixed within the limits irrespective of the fluctuations of the water levels.
Example – Gibb’s Module
Rise and Fall Method:
It is adopted whenever the number of intermediate stations is less and also if the number of shifting of instruments is more
The difference between the levels of consecutive staff points is calculated
The rise and fall method for obtaining the reduced levels of points provides a check on foresight, backlight & intermediate sight.
Generally used for fly leveling, profile leveling or to establish BMs
∑BS - ∑FS = Last R.L – First R.L = ∑Rise - ∑Fall
Collimation Method or Height of instrument method:
This method is generally adopted if there are lot many numbers of intermediate stations and also if the number of shifting of instruments is less
It does not provide a check on Intermediate sights
Height of instrument is calculated at each set up of the instruments
Generally used in contour survey, in small areas
Checks: ∑BS - ∑FS = Last R.L – First R.L
the angle of failure plane relative to the major principle plane in a triaxial test,
Weir:
A weir is a concrete or masonary structure, placed in an open channel over which the flow occurs. It is generally in the form of vertical wall, with a sharp edge at the top, running all the way across the open channel. The notch is of small size while the weir is of a bigger size. The notch is generally made of metallic plate while weir is made of concrete or masonary structure.
Triangular weir:
The expression for the discharge over a triangular weir or notch is
Q =
From this expression flow through the weir depend upon the vertex angle (θ) and coefficient of discharge (Cd) is constant for all the heads, the value of Cd is nearly equal to 0.6.
Rectangular weir:
The expression for the discharge over a rectangular weir or notch is
Q =
Advantage of triangular weir over rectangular weir:
A triangular weir is preferred to a rectangular weir due to following reason.
(1) The expression for discharge for a right angled V- notch or weir is very simple.
(2) For measuring low discharge, a triangular weir gives more accurate results than a rectangular weir.
(3) In case of triangular weir, only one reading, (H) is required for the computation of discharge.
(4) Ventilation of triangular weir is not necessary.
Purlin:
It is a member of truss which are supported on the principle rafter and which transverse loads to the truss. These are some important properties of purlin-
It is a biaxial bending member.
The span of purlin is center to center of truss, purlin is located at the panel point of the truss.
Maximum spacing between purlins is less than 1.4 m.
Angle, Channel, I-sections and Z-sections are used for purlins and girders to support the cladding.
In mixed traffic, different vehicles move at different speeds.
For practical conditions, IRC recommends that superelevation should be provided to fully counteract the centrifugal force due to 75 % of design speed by neglecting lateral friction.
Plinth area: Plinth area is calculated by taking the external dimensions of the building at the floor level excluding plinth offset if any. All floors, area of walls at the floor level shall be included in the plinth area.
Floor area: Floor area is the total area of floor in between walls and consists of floor of all rooms, verandahs, passages, corridors, staircase, kitchen etc.
Circulation area: Area used for movement of person in the building.
Horizontal circulation area (passages, corridors, balconies etc.) = 10% - 15% of plinth area
Vertical circulation area (staircase, lifts etc.) = 4% - 5% of plinth area
Carpet area: Carpet area is a useful area or liveable area or lettable area.
Carpet area = (total floor area – circulation area – bath, wcs)
1. Radiometric Resolution:-
The radiometric resolution of an imaging system describes its ability to discriminate very slight differences in energy.
The finer the radiometric resolution of a sensor, the more sensitive it is to detect small differences in reflected or emitted energy.
It refers to the sensitivity of sensor to incoming radiance.
2 Spatial Resolution:-
Measurement of the minimum distance between two objects that will allow them to differentiate from one another in an image.
Spatial resolution of the sensor refers to the size of the smallest possible feature that can be detected.
Spatial resolution is a measure of smallest object that can be resolved by the sensor, or the size of area on the ground represented by each pixel. Pixel size is used to determine resolution quality.
3. Spectral Resolution:-
Spectral resolution describes the ability of a sensor to define fine wavelength intervals. The finer the spectral resolution, the narrower the wavelength range for a particular channel or band.
Spectral resolution refers to the specific wavelength intervals in electromagnetic spectrum that a sensor can record.
Narrow bands have higher spectral resolution.
4. Temporal Resolution:-
Each satellite has its own unique revisit schedule for obtaining image of a particular area.
The frequency at which the sensor revisits an area is known as temporal resolution.
For example, if a satellite images the same area every 10 days, then its temporal resolution would be 10 days.
Temporal resolution is an important factor to consider in change detection studies i.e. crop growth etc.
Hence, temporal resolution is the amount of time taken by sensor to return to a previously recorded location.
Examples – Landsat, GOES and NOAA
Silt regulation works are required to preformed to control the erosion along the banks.
Two popular silt regulation works are as silt excluders and ejectors.
Silt excluders silt control device consisting of a number of rectangular tunnels - provided parallel to the axis of head regulator and terminating near the under sluiced weir - to allow the clearer water to flow through the head regulator. Silt excluders are constructed on the bed of the river, upstream of the head regulator.
Silt ejectors also called silt extractors, and it extracts the silt from the canal water after the silted water has travelled a certain distance in the off-take canal. Silt ejectors are constructed on the bed of the canal and a little distance downstream from the head regulator.
These works are, therefore, constructed on the bed of the canal, and little distance downstream from the head regulator.
Tacheometry
The most common method of measuring horizontal distances is chaining and that for measuring vertical distances is differential levelling. Both of these methods give results to required accuracy. When the ground is rough and more observations at a faster rate are acceptable, then tacheometry is the choice.
Reduced level (RL) of station A = RL of bench mark + BS reading – FS reading
The carpet area of residential building may be 50 % to 65 % of the plinth area of building with a target of 65 %.
Concept:
Carpet area of building is the useful area or liveable area or lettable area. This is the total floor area minus the circulation area, verandahs, corridors, passages, staircase, lifts, entrance hall, etc. and minus other non-usable areas as sanitary accommodations (bath and W.Cs.), air conditioning room etc.
For office building carpet area is the useable area and for residential building carpet area is the liveable area and should exclude the kitchen, pantry, stores, and similar other room which are not used for living purposes.
The carpet area of a building for any storey shall be the floor area excluding the following:
(a) Sanitary accommodation, (b) verandahs, (c) corridors and passages, (d) kitchen and pantries, (e) stores in domestic buildings, (f) entrance hall and porches, (g) stair cases and mumties, (h) shafts for lifts, (i) barsaties, (j) garages, (k) canteens, (l) air conditioning ducts and air conditioning plant room.
The carpet area of an office building may be 60 % to 75 % of plinth area of the building with a target of 75 %.
The planners should aim to achieve a target to 75 % of the plinth area. The carpet area of residential building may be 50 % to 65 % of the plinth area of building with a target of 65 %.
Prime coat:
The prime coat is an application of low viscous cutback bitumen to an absorbent surface like granular bases on which binder layer is placed. It provides bonding between two layers. Unlike the tack coat, prime coat penetrates into the layer below, plugs the voids, and forms a watertight surface.
Seal Coat:
Seal Coat Seal coat is a thin surface treatment used to water-proof the surface and to provide skid resistance.
Tack coat:
Tack coat is a very light application of asphalt, usually asphalt emulsion diluted with water. It provides proper bonding between two layers of binder course and must be thin, uniformly cover the entire surface, and set very fast.
The bituminous prime coat is the first application of low viscosity liquid bituminous material over an existing porous or absorbent pavement surface like the WBM base course.
On Indian railways standard length of BG rail = 13 m
So, total no. of rail required in 1.024 km or 1024 m
= 1024/13 = 78.78 = 80 (in round figure)
Sleeper density = M + 7
M = length of rail
So, sleeper density = 13 + 7 = 20
No. of sleepers = 20 × 80 = 1600
Creep
Age at loading | Creep coefficient |
7 days | 2.2 |
28 days | 1.6 |
1 year | 1.1 |
Testing and counting of pathogens (disease-causing micro-organisms) in raw water can be done with great difficulty as tests involved are very costly.
Hence, in order to minimize the cost, instead of testing the raw water for pathogens it is tested for coliforms, which themselves are harmless micro-organisms but their presence or absence indicates the presence or absence of pathogens in raw water.
The Coliforms like E-Colli and B-Colli are the most common types which are used for this purpose.
Testing of Coliforms can be done by using methods such as Membrane filter technique, Most Probable Number (MPN) and B-Colli Index etc.
Ultrasonic pulse velocity test of concrete:
It is a non-destructive test. The ultrasonic pulse velocity method as described for green concrete can also be used to determine the strength of hardened concrete. The flaws, quality of concrete, reinforcement, moisture content, temperature of concrete materials etc. affect the pulse velocity and suitable adjustments should be made in evaluating the concrete strength. Ultrasonic pulse velocity test is not used to measure the strength of wet concrete.
Quality of concrete and pulse velocity:
General condition Pulse velocity(m/sec)
Excellent Above 5000
Good 4000-5000
Questionable 3000-4000
Poor 2000-3000
Very poor Below 2000
Efflorescence: This is caused because of alkalies present in bricks. When bricks come in contact with moisture, water is absorbed and the alkalies crystallize. After drying, grey or white powder patches appear on the brick surface.
The degree of efflorescence is given as:
(a) NIL – When there is no perceptible deposit of efflorescence.
(b) SLIGHT- Not more than 10% area of the brick covered with a thin deposit of salt.
(c) MODERATE- Covering up to 50% area of the brick.
(d) HEAVY- Covering 50% or more but unaccompanied by powdering or flacking of the brick surface.
(e) SERIOUS- When there is a heavy deposit of salts accompanied by powdering and/or flacking of the exposed surfaces.
Bitumen:
Bitumen is a petroleum product obtained by the distillation of petroleum crude oil. Bitumen is hydrocarbon material of either natural of pyrogenous origin, found in gaseous, liquid semisolid or solid form. Bituminous material is widely used in road construction and maintenance.
Bitumen emulsion:
It is a condition in which bitumen is suspended in an aqueous medium. It is used for Patch-up work.The biggest advantage of bitumen emulsion is that it can be used in rainy season also.
Cutback bitumen:
Cutback bitumen is a type of bitumen which is obtained when viscosity of bitumen is reduced by volatile diluent. It is generally used in colder regions.
Coal tar:
Tar is also a bituminous material obtained by the destructive distillation of coal or wood.It has the same appearance as bitumen but both have different characteristics.
Compaction of concrete by vibration:
This is the most common and widely used method of compacting concrete for any structural element. The vibrations imparted to the fresh concrete reduce the internal friction between the particles of concrete by setting the particles in motion and thus produced a dense and compacted mass. On vibration, the concrete mix gets fluidized and the internal friction between the aggregate particles reduces, resulting in entrapped air to rise to the surface. On losing entrapped air the concrete get denser.
The various types of vibrators in use are needle, from work, table or platform, and surface vibrators.
Needle vibrator:
These are also known as immersion, internal, or poker vibrator. Needle vibrator can be used for any type of concrete work.This consists of a steel tube, called poker, having an eccentric vibrating element inside it, a flexible shaft and power unit.
Formwork vibrator:
These are also known as external or shutter vibrators. These are generally used under the following circumstances.
Compaction of concrete is required to be done in a very thin or very densely congested reinforced section.
In addition to internal vibrations, compaction is required to be done specially in the cover area where at time needle or poker vibrator is unable to do satisfactory compaction.
Compaction of very stiff concrete is required to be done because such concrete cannot be compacted by internal vibrators.
Formwork vibrators are used for concreting column, thin walls and precast units.
Surface vibrator:
These are also known is screed board vibrators. Surface vibrators are used for floor and roof slabs and pavement surfaces. These are effective only up to a thickness of 150 mm of concrete but can be used up to 250 mm. Surface vibrator cause movement of fine particle to the top and hence add the finishing operation.
As per sinking found method, Further work of money is given as:
F=A((1+i)N−1i)
Where ‘F’ is future work i.e. Amount available to owner after 25 tears.
‘A’ is annual amount which is being sets aside as sinking fund by owner every year.
i → rate of interest
N → Period considered.
Pig Iron:
Pig iron is the product obtained after smelting of calcined ore in a blast furnace.
Iron oxide must be reduced in order to obtain iron and this can be done only in a blast furnace.
Pig iron has a very high carbon content, typically 3.5 - 4.5%.
Wrought iron:
Wrought iron is the purest form of iron.
It is an iron alloy with a very low carbon (less than 0.08%) content in contrast to cast iron (2.1% to 4%).
Stainless steel:
Stainless steel is an alloy of iron and chromium.
Stainless steel has about 10.5% of chromium and less than 1.2% carbon.
Stainless Steel is very resistant to corrosion which is due to the presence of chromium.
We can improve strength by increasing the percentage of Chromium.
Stainless Steel is manufactured through Electric Arc Processes, Continuous Casting etc.
Steel:
It is an alloy of iron and carbon.
Iron is the base metal in steel.
Carbon is added to improve the strength of steel.
It has various applications like in infrastructure, electrical appliances, metals, etc.
Explanation:
Blast furnace:
A vertical shaft furnace that produces liquid metals by the reaction of a flow of air introduced under pressure into the bottom of the furnace with a mixture of metallic ore, coke (blast furnace fuel), and flux fed into the top.
In a blast furnace, coke (C) reacts with oxygen to form carbon monoxide, which then reacts with iron oxide to form carbon dioxide and pig iron.
Pig iron is obtained by the chemical reduction of iron ore.
This process of reduction of the iron ore to pig iron is known as smelting.
Hence, the iron produced in the blast furnace is pig iron.
Produced pig iron is used for subsequent processing into steel, and they are also employed in processing lead, copper, and other metals.
Factor affecting workability:
1. Large size aggregates increase the workability due to lesser surface area, as finer aggregates composition means larger surface area exposure for reaction i.e. hydration of cement, and thus reduced workability.
2. The higher value of the water-cement ratio would increase the workability of the concrete but may reduce the compressive strength of the mix. Hence, an increase in water content must be accompanied by an increase in cement content.
3. Angular and rough aggregates reduce the workability of the concrete as rough texture allows good bonding among the aggregate which comes at the cost of workability to some extent.
Annual depreciation = (purchase price - salvage value) / useful life
A rectangular plate will not experience any shear lag effect when connected to a gusset plate.
Shear lag is the non-uniform straining of member due to tension and it occurs when action and reaction do not pass through the centre of gravity of cross section.
The shear lag effect can be reduced if there is symmetry in connection i.e. eccentricity due unsymmetrical connection is minimum as much as possible.
When double angle member placed symmetrically to gusset plate i.e. placed back to back on opposite side of gusset plate, no shear lag effect is developed.
An I Section with bottom flange Connected to gusset plate, An angle member with one leg connected to gusset plate and two angle members placed back to back on same side of gusset plate , these are unsymmetrical sections, where action and reaction do not passes through the CG as shown in figure, so shear lag effect may occur.
The 98th percentile speed is adopted for geometric design of highway.
Geometrical design speed = 98th percentile speed
Safe speed limit = 85th percentile speed
Minimum speed limit = 15th percentile speed
Mass Haul Curve:
This is a curve representing the cumulative volume of earthwork at any point on the curve, the manner in which earth to be removed.
It is necessary to plan the movement of excavated soil of worksite from cuts to fill so that haul distance is minimum to reduce the cost of earthwork.
The mass haul diagram helps to determine the economy in a better way.
The mass haul diagram is a curve plotted on a distance base with the ordinate at any point on the curve representing the algebraic sum of the volume of earthwork up that point.
A haul refers to the transportation of your project’s excavated materials. The haul includes the movement of material from the position where you excavated it to the disposal area or a specified location. A haul is also sometimes referred to as an authorized haul.
Haul = Σ Volume of earthwork × Distance moved.
The IS 1200 code gives mode of measurement of various construction work like RCC, PCC, Brick work etc. However, it does not specify the any allowable wastage in construction materials. These wastages are generally mutually agreed between contractor and client.
As thumb rule following wastage are generally considered in various construction material:
:
Material Standard Wastage in %
Cement 1
Reinforcing Steel 3
Coarse Aggregate 2.5
Fine Aggregate 2.5
Stone Masonry 25
Structural Steel 5 to 10
Tiles 7 to 10
Volume of Stone Masonry = 100 cum
Considering 25 % Wastage, Volume of stone masonry required is 1.25 × 100 = 125 cum.
Guide banks are meant for guiding and confining the flow in a reasonable waterway at the site of the structure i.e., channelize the flow of the river
Guide Banks or Bell’s Bunds:
Rivers in flood plains submerge very large areas during flood periods.
Naturally, when some structure is to be constructed across such a river (for example, bridge, weir, etc.), it is very expensive to construct the work spanning the whole width of the river.
To economies, some training work may be constructed to confine the flow of water within a reasonable waterway.
Leachate
As rainwater infiltrates through landfill waste, it becomes contaminated with dissolved and suspended matter originating from the decomposing waste.
Leachate that escapes from a landfill can contaminate groundwater, surface waters, and soil, potentially polluting the environment and harming human health.
The composition of the resulting leachate varies according to the nature of the landfill material, which may include biodegradable, non-biodegradable, organic/inorganic, and toxic/non-toxic waste.
Lacey’s Silt Theory of Canals
Lacey stated that a channel may not be in regime condition even if it is flowing with non-scouring and non-silting velocity. Therefore, he distinguished three regime conditions as follows :
True regime
Initial Regime
Final Regime
1. True regime
A channel is said to be in regime condition if it is transporting water and sediment in equilibrium such that there is neither silting nor scouring of the channel. But according to Lacey, the channel should satisfy the following conditions to be in regime condition.
Canal discharge should be constant.
The channel should flow through incoherent alluvium soil, which can be scoured as easily as it can be deposited and this sediment should be of the same grade as is transported.
Silt grade should be constant.
Silt charge, which is the minimum transported load should be constant.
If the above conditions are satisfied, then the channel is said to be in true regime condition. But this is not possible in actual practice. Hence lacey defined two other conditions which are initial and final regime conditions.
2. Initial Regime
A channel is said to be in initial regime condition when only the bed slope of channel gets affected by silting and scouring and other parameters are independent even in non-silting and non-scouring velocity condition. It may be due to the absence of incoherent alluvium. According to Lacey’s, regime theory is not applicable to initial regime condition.
3. Final Regime
If the channel parameters such as sides, bed slope, depth etc. are changing according to the flow rate and silt grade then it is said to be in final regime condition. The channel shape may vary according to silt grade as shown in the figure below :
Note:
Lacey’s specified that the regime theory is valid for final regime condition only and he also specified that semi-ellipse is the ideal shape of regime channels.
As per IS 800: 2007 limit of slenderness ratio for tension member where reversal of stress is due to loads other than wind or seismic shall not exceed 180.
Refer table 3 of IS800: 2007, we get following values of maximum slenderness ratios for tension members:
Maximum Slenderness Ratios for tension members
:
Maximum Slenderness Ratios for tension members | |
A tension member in which reversal of stress due to loads other than wind or seismic loads. | 180 |
A member normally acting as a tie in roof truss or a bracing system but subjected to reversal of stresses resulting from the action of wind or earthquake forces. | 350 |
Tension Members (other than Pre-tensioned members) | 400 |
Annual irrigation intensity:
By adding intensities of irrigation for all the crop seasons we obtain the annual intensity of irrigation.
Annual intensity of irrigation can be more than 100%.
The annual irrigation intensity is usually found to be in the range of 40 to 60%. But needs to be raised in the range of 100 to 180% by cultivating larger parts of CCA with more than one crop in a year.
Intensity of irrigation is the percentage of Culturable Commanded c (CCA) to be irrigated annually for a particular crop season.
CCA is portion of gross commanded area that is cultivable.
CCA = Gross Command Area – Uncultivable area (pasture lands, ponds, townships, waste land)
