Indices of self-purification

Oxygen deficit (D) = Saturation D.O. – Actual D.O.

Deoxygenation curve: In a polluted stream, the DO concentration continues to drop as a result of volatile organic matter’s breakdown. The amount of organic matter still needing to be oxidised at any one time, as well as the reaction’s temperature, affect the rate of de-oxygenation.

Reoxygenation curve: The act of adding oxygen to water in order to balance out the loss of DO caused by deoxygenation is known as reoxygenation.

Curve of oxygen deficit: Deoxygenation and reoxygenation coexist in a flowing, polluted stream that is exposed to the atmosphere. An oxygen deficit will occur if deoxygenation outpaces reoxygenation.

Biological zones in lakes

1. Euphotic zone: The upper layer of lake water where sunlight can enter is referred to as the euphotic zone.
2. Littoral zone: The term “littoral zone” refers to the shallow water near the shore where rooted plants flourish.
3. Benthic zone: A lake’s bottom sediments make up the benthic zone.

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Aeration Methods in Activated Sludge Process There are three methods for aeration in activated sludge process.

1. Diffused air aeration

2. Mechanical aeration

3. Combine aerator

1. Diffused air aeration

Diffusers are used to spread air into the sewage as part of the diffused air aeration process. There are two types of diffusers: Diffusers with plates and tubes.

Plate Diffuser

They are square or rectangle-shaped plates made of high-silica sand or crystalline alumina. This technique involves blowing compressed air through a diffuser with perforated plates. The air escapes through the diffuser plate’s holes and rises in the form of bubbles. As a result, the sewage takes up oxygen from the air.

Tube Diffuser

It comprises of a perforated tube that may be removed for cleaning that is suspended in the waste water near the bottom. The tube is dented with compressed air. Strong air blasts out of the apertures, stirring up the sewage as it does so.

2. Mechanical Aeration

With the aid of some mechanical equipment, the surface of the sewage is vigorously agitated in this way to promote oxygen absorption from the atmosphere. The mechanical aerator comes in two distinct varieties both a horizontal and vertical surface aerator

They are made up of vane-shaped propellers that are powered by electricity and installed on either floating or stationary supports. When they toss the bulk liquid (sewage) through the air, oxygen is transferred to both the surface of the droplets and the surface of the bulk liquid. The currents created by agitation subsequently mix the two surfaces. Ice development during the winter months has a significant impact on this method’s performance.

3. Combine Aerator

This device combines mechanical and diffused air aeration into a single unit. The Dorroco aerator is a popular example of such a combo. Air diffusers and mechanical aerators are both used to aerate sewage. The bottom of the tank has air diffuser plates, and the submerged paddles rotate in the opposite direction from how the compressed air rises from the air diffusers. A motor rotating paddles on a horizontal shaft at 10- to 12-rpm speed.

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Losses can be broadly divided into two categories:

Instantaneous and time-dependent. The immediate losses take place when the tendons are prestressed and when the prestress is transferred to the concrete part. During the prestressed member’s service life, the time-dependent losses take place. Losses resulting from the member’s elastic shortening, friction at the tendon-concrete interface, and anchorage slip occur immediately

The losses due to the shrinkage and creep of the concrete and relaxation of the steel are the time-dependent losses. The causes of the various losses in prestress are shown in the following chart

Elastic shortening:

Members with pretension

The concrete immediately shortens as a result of the prestress when the tendons are severed and the prestressing force is applied to the member. The same degree of tendon shortening also results in prestress being lost.

Members with post-tension

There is no loss if there is only one tendon because the applied prestress is recorded following the elasticity in the member’s shortening If multiple tendons are affected by stretching. A tendon gradually deteriorates when the other tendons are stretched after it. The decrease in prestress (fp) in a tendon caused by the elastic shortening loss is measured. Alteration in the tendon’s strain (p) it is believed that the tendon’s shift in strain is equivalent to the concrete’s strain at the tendon level because of the prestresing force.

This assumption is called strain compatibility between concrete and steel. The strain in concrete at the level of the tendon is calculated from the stress in concrete (fc) at the same level due to the prestressing force. A linear elastic relationship is used to calculate the strain from the stress.

For ease of calculation, the stress in concrete at the level of CGS can be used to determine the loss in all tendons. When tendons are stretched one after the other in a post-tensioned member, this simplification cannot be applied. The calculation is shown separately for the following member categories.

• Axial Members That Are Pre-Tensioned
• Members with Pre-tensioned Bending
• Axial Members with Post-tension
• A member that bends under tension

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The evaluation of the following is included in the analysis of members under flexure, much like the analysis of members under axial load.

1. Permitted prestress determined by permitted stresses during transfer.
2. Tensions caused by service loads. These are contrasted with the permitted pressures under service circumstances.
3. Superhuman fortitude. On the basis of factored loads, this is compared to the demand.
4. The overall behaviour of load versus deformation. This section presents the analyses at transfer and under service loads. “Analysis of Member under Flexure,” presents the analysis for the ultimate strength individually.

Assumptions

These factors are taken into account while analysing members that are flexed.

• The Bernoulli hypothesis states that plane segments remain plane until they fail.
• For bonded tendons, there is a perfect bond between concrete and prestressing steel.

The analysis involves three principles of mechanics.

•  Equilibrium of internal forces with the external loads. The compression in concrete (C) is equal to the tension in the tendon (T). The couple of C and T are equal to the moment due to external load.
• The compatibility of bonded tendons with concrete and steel strains. The first presumption that a plane section will remain plane after bending is also included in the formulation. The compatibility for unbonded tendons is in terms of deformation.
• Constitutive connections between the stresses and strains experienced by the materials Changes in Internal Forces Compression in the concrete (C) and tension in the steel (T) values in reinforced concrete members subjected to flexure rise with increasing external stress. The shift of the lever arm (z) is not significant.

Variation of Internal Forces:

When prestress is transferred in members of prestressed concrete that are subject to flexure, C is situated close to T. Only their own weight is balanced by the couple C and T. When the load is in service, C moves higher and the lever arm (z) enlarges. There isn’t much diversity in C or T. This discrepancy is schematically explained for a simply supported beam under uniform load in the following figure.

Analyses conducted under service loads and during transfer are comparable. They are therefore given collectively. When subjected to service loads, a prestressed part typically doesn’t crack. Steel and concrete are handled like elastic materials. The superposition principle is used. It is ignored that bending increases the tension in the prestressing steel.

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The various stages of the pre-tensioning operation are summarised as follows.

1. Anchoring of tendons against the end abutments
2. Placing of jacks
3. Applying tension to the tendons
4. Casting of concrete
5. Cutting of the tendons.

During the cutting of the tendons, the prestress is transferred to the concrete with elastic shortening and camber of the member.

Advantages of Pre-tensioning:

The relative advantages of pre-tensioning as compared to post-tensioning are as follows.

• Pre-tensioning is suitable for precast members produced in bulk.
• Prestressed concrete structure Dr.Amlan K and prof.Devdas Menon
• In pre-tensioning large anchorage device is not present.

Negative effects of pre-tensioning:

The following are the relative drawbacks.

• The pre-tensioning process needs a prestressing bed.
• Before the concrete reaches a sufficient strength, it must wait in the prestressing bed.
• Over the transmission length, concrete and steel should be well-bonded.

Devices:

The essential devices for pre-tensioning are as follows.

• Prestressing bed
• End abutments
• Shuttering / mould
• Jack
•  Anchoring device

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Coagulants are selected based on the PH of the water. Because it is inexpensive and simple to store as solid crystals for extended periods of time, alum, or aluminium sulphate, is commonly employed in all treatment plants.

The amount of coagulants that should be added to the water varies on the type of coagulant, the turbidity, colour, PH, temperature, and mixing and flocculation times of the water. A Jar test, as seen in Fig, is used to establish the ideal coagulant dose needed for a water treatment facility.

To begin the experiment, a sample of water is first taken in each jar, and then varied doses of coagulant are added. Each jar’s addition of coagulant is reported along with its quantity. The paddles are then all revolved for around 10 minutes at a speed of 30 to 40 RPM with the assistance of an electric motor. Following that, the speed is slowed down and the paddles are rotated for 20 to 30 minutes. The paddles are stopped from rotating, and the floc that has formed in each Jar is documented and allowed to settle. The ideal dose of coagulants is the one that produces the best floc.

It is possible to feed or enable the entry of the coagulants either in powder form (dry feeding) or in solution form (wet feeding). The following techniques are used to combine the coagulant and water to create the floc.

1. Centrifugal pump
2.  Compressed air
3. Hydraulic jump
4.  Mixing channel
5.  Mixing basins with buffle walls
6. Mixing basins with mechanical means

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• A cross section of the river that is accurately representative. Artificial cuts, etc. should not contaminate the cross section.
• If the location of the bridge is near an existing natural crossing, the hydraulic cross section should cross an adjacent, undisturbed natural channel. It would be beneficial to use the cross section inside 100 m U/S or D/S.
• Spill channels need to be discovered, designated, and accommodated for adequately.
• Use the appropriate coefficient of stiffness. Since the nature of the stream changes depending on the material’s qualities and the growth of vegetation, etc., the same stiffness coefficient shouldn’t be used for the bed and the banks.
• The accuracy of the calculated velocity should be evaluated in connection to the stream’s bed material, as pebbles in the stream and low flow velocity typically do not coexist.
• It is important to be aware of the possibilities of high tides and floods occurring simultaneously in tidal streams. Discharge using the conventional methods, i.e., using Manning’s formula, should be carefully calculated and compared to Inglis discharge under such circumstances.
• It is best to use discretion when deciding whether to use the computed or observed H.F.L. as the design level. Obstacles like rice fields, bunds, blocked spill channels, etc. may have an impact on the observed H.F.L. Use the higher of the two figures as the design H.F.L.
• The details of the various stages are described below.

1. HFL (observed) Highest recorded flood levels. (50 years of data)
2. Manning’s discharge is equal to Inglis discharge at the HFL(Inglis) Flood level.
3. Manning’s discharge is equal to the Modified Inglis discharge at the HFL(Modified Inglis) Flood level.
4. Ordinary flood level (O.F.L.). When a bridge clears a flood without submerging it, the flood level is at this point, and traffic will not be disrupted beyond what is reasonable.

• The maximum interruptions allowed on various road standards are as follows:- National Highways – There are no delays.

AFFLUX:

A waterway is crossed by bridges, which might have a single span or numerous spans. Piers must be built in the riverbed for a bridge with many spans. The natural flow is obstructed by these piers. When there is a significant obstacle, the water level upstream is slightly higher than it is downstream.

It is known as afflux when the level rises. Designers assess the afflux and take it into account when creating the substructure in order to keep the superstructure dry during floods.

Afflux is defined as heading up of water when they hit any obstruction. In bridges the water hit at u/s side.

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The dynamic properties of the structure such as natural period, damping and mode shape
play a crucial role in determining the response of the building. Besides other characteristics of the building system also affect the seismic response such as ductility, building foundation, the response of non-structural elements etc.

Mode Shapes and Fundamental Period:

• The elastic properties and mass of building cause to develop a vibratory motion when they are subjected to dynamic action.
• This vibration is similar to vibration of a violin string, which consists of a fundamental tone and the additional contribution of various harmonics.
• The vibration of a building likewise consists of a fundamental mode of vibration and the additional contribution of various modes, which vibrates at higher frequencies.
• Fundamental period of vibration can be determined by the code-based empirical for the fundamental modes of the building may be determined by any one of several methods developed for the dynamic analysis of structures.
• On the basis of time period, building may be classified as rigid (T<T 1.0 sec).
• Buildings with higher natural frequencies, and a short natural period, tend to suffer higher accelerations but smaller displacement.
• In the case of buildings with lower natural frequencies, and a long natural period, this is reversed: the buildings will experience lower accelerations but larger displacements.

Building Frequency and Ground Period:

• Inertial forces generated in the building depend upon the frequencies of the ground on which the building is standing and the building’s natural frequency
• When these are near or equal to one another, the building’s response reaches a peak level.
• Past studies show that the predominant period at a firm ground site 0.2-0.4 sec rigid structures (0-0.3) will have more unfavourable seismic response than flexible structures ,while period on soft ground can reach 2.0 sec or more.
• Seismic response of flexible structures (t>1.0) on soft foundation sites will be less favourable than that of rigid structure.
• Building fundamental periods of approximately 0.1N (where, N is the number of storey)

Damping:

• The degree of structural amplification of the ground motion at the base of the building is limited by structural damping.
• Damping is the ability of the structural system to dissipate the energy of the earthquake ground shaking.
• Since the building response in inversely proportional to damping in a building possesses, the sooner it will stop vibrating–which of course is highly desirable from the standpoint of earthquake performance.
• In a structure, damping is due to internal friction and the absorption of energy by the building’s structural and non-structural elements.
• There is no numerical method available for determining the damping. It is only obtained by experiments.

Ductility:

• Ductility is defined as the capacity of the building materials, systems, or structures to energy by deforming in the inelastic range.
• The safety of building from collapse is on the basis of energy, which must be imparted to the structure in order to make it fail. In such instance, consideration must be given to structure’s capacity to absorb energy rather than to its resistance.
• Therefore ductility of a structure in fact is one of the most important factors affecting its earthquake performance.
• The primary task of an engineer designing a building to be earthquake resistant is to ensure that the building will possess enough ductility.
• The ductility of a structure depends on the type of material used and also the structural assembly.

Seismic Weight:

• Seismic forces are proportional to the building weight and increases along the height of building.
• Weight reduction can be obtained by using lighter materials or by reducing the filling and other heavy equipment’s not essential for building construction.

Quality of Construction and Materials:

• Grade of concrete not achieved in site – reasons.
• Poor execution of the concrete joint/ discontinuity-quality of concrete
• Reinforcement detailing not taken care of appropriately.
• Accumulation of sawdust, dust and loose materials at the surface of joint.
• Result: A defective concrete joint, which contributed significantly to causing of failure of many building in past earthquakes.

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Groundwater hydrology may be defined as the science of occurrence distribution and movement of water below the surface of the earth.

Scopes of groundwater hydrology:

• Groundwater is defined as the water that fills all of the spaces in the geological strata. This saturation zone, which differs from unsaturated or aeration zones in which voids are filled with water and air, is significant for engineering works, geological investigations, and water supply development, and the true occurrence of water in these will be highlighted here.
• Unsaturated zones arise around the saturated zone and extend up to the ground surface, including soil moisture within the root zone of water, which is an important concern in agricultural Botany and soil science.
• Groundwater is significant in petroleum engineering; three fluid systems including gas, oil, and water, as well as two-fluid systems involving soil and water, occur frequently in petroleum production. As a result, groundwater hydrology emphasises the amount of petroleum existing in the earth depends on the type of load system.
• Groundwater is the world’s largest supply of freshwater, excluding freshwater glaciers. The amount of groundwater within 800 metres of the ground surface is 30 times that of streams, hence it is given special attention.

Vertical distribution of groundwater:

The vertical distribution of surface water is divided into the following two zones

1. Aeration Zones

The zone of aeration is located above the zone of saturation and reaches up to the ground surface. This zone contains voids that are partially filled with water and partially filled with air. The water that occurs in this zone is known as vadose water.

The zone of aeration is further divided into three main parts

1.1 Soil water zone:

The water zone in the soil extends from the ground surface to the primary root zone. When the soil in the zone is irrigated or when it rains, the soil gets saturated. Under the pull of gravity, excess water drains through the soil and enters the intermediate zone as gravitational water. After gravitational water drains out, the remaining water is known as capillary water. The water in the soil water zone is gradually depleted by operation and transpiration from vegetal growth on the ground surface, and if it is not replenished, the water content may be reduced to the point where only a thin film of moisture on the surface of the soil particle remains absorbed as hygroscopic water.

1.2 Intermediate zone:

Zone in the middle This zone normally contains non-moving vadose water, also known as pellicular water, which extends from the bottom edge of the soil water to the upper limit of capillaries. In the form of hygroscopic and capillary water, which is kept in place by molecular and surface tension forces. This zone may temporarily retain some extra water, which will flow downwards as gravitational water.

1.3 Capillary zone:

The capillary zone extends from the water table up to the limit of the capillary rise of water. The thickness of this zone is depending on the texture of soil formation.

2. Zone of saturation:

Under hydrostatic pressure, all the voids in the saturation zone are filled with water. At the top, the zone of saturation is confined by either a limiting surface of saturation known as the water table or impermeable strata. If a well penetrates a zone of saturation with the water table, the pressure is equal to atmospheric pressure. The well’s upper surface is formed by the static water level, which is at the same elevation as the water table.

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An earthquake is the disturbance of the earth induced by the passage of seismic wave radiation from a source of elastic energy. The focus or hypocentre is the location where the rupture begins or an earthquake is generated. Epicentre is the place on the earth’s surface directly above the focus of an earthquake. The focal depth of an earthquake is the depth of the focus below the earth’s surface.

Type of seismic waves:

Systematic waves: It is the largest train of energy released during an earthquake and travels as seismic energy in all directions through the earth layers refracting and reflecting in each interface.

They are further classified into body waves and surface waves:

Body waves: These are the type of waves that travel through the earth in all directions and to all depths.

Body waves are further classified into P waves and S waves.

P waves:

• These are longitudinal waves.
• They are the fastest.
• Compressional waves.
• Resembles to sound waves.
• Capable of travelling through solid-liquid and gases.
• First to reach the systematic station.
• The ground is alternatively compressed and deleted in direction of propagation.

S waves:

• These are transfer waves.
• They are slower compared to P waves.
• These are Shear waves.
• Resembles that of light waves.
• Travels only through solid surfaces.
• The ground is displaced perpendicular to the direction of propagation.
• Maximum destruction in association with l-waves.

Surface waves: These are the types of rays that travel through the surface of the ground.

Surface waves are further classified into L waves and Rayleigh waves.

L waves:

• Surface motion is similar to that of S waves.
• Does not include a vertical component.
• They are dispersive in nature.

Rayleigh waves:

• Particles oscillate in an elliptical path.
• Include these include vertical components.
• They are not dispersive in nature.

Measurement of an earthquake:

1. Magnitude:

Magnitude is a quantitative measure of the actual size of earthquake earthquakes that are often classified into different groups based on their size. The magnitude of an earthquake is a single number and does not vary from place to place. Each magnitude is based on the direction of what is the measurement of seismic waves.

2. Intensity

Intensity is a quantitative measure of actual shaking at a location during an earthquake and is assigned in Roman capital numerals. There are many intensity scales commonly used or modified Mercalli intensity scale and MSK scale. Both skills are quite similar and range from 1 to 12 the intensity scales are based on three features of shaking perception by the people and animal’s performance of building and changes to the natural surroundings. The intensity of the earthquake becomes weak outside the epicentre.

Types of earthquakes:

Tectonic earthquake:

The most common type of earthquake is tectonic earthquakes these are produced when the rock breaks suddenly in response to various geological forces. Tectonic earthquakes are significantly important to the study of the earth’s interior and of tremendous social significance because they pose a greater hazard. 95% of the world’s seismic energy is released by tectonic earthquakes.

Volcanic earthquake:

The second well-known type of earthquake accompanies volcanic eruption. A volcanic earthquake is still defined as one that occurs in conjunction with volcanic activity but it is believed that while eruption the earthquake both result from tectonic forces in the rocks they need not walk together. The actual mechanism of field production in a volcanic earthquake is similar to that of a tectonic earthquake.

Interplate earthquakes:

Earthquakes occur along the edge of the interacting plates.

Intraplate earthquake:

Earthquakes occur within the plate boundaries.

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