Lime - Tests on Limestone

Tests on Limestones 

The following practical tests are made on limestones to determine their suitability:

• (i) Physical tests 
• (ii) Heat test 
• (iii) Chemical test 
• (iv) Ball test. 

 

(i) Physical Test: 

    Pure limestone is white in colour. Hydraulic limestones are bluish grey, brown or are having dark colours. The hydraulic lime gives out earthy smell. They are having clayey taste. The presence of lumps give indication of quick lime and unburnt lime stones. 

 

(ii) Heat Test: 

    A piece of dry stone weighing W1 is heated in an open fire for few hours. If weight of sample after cooling is W2, the loss of weight is W2 – W1. The loss of weight indicates the amount of carbon dioxide. From this the amount of calcium carbonate in limestone can be worked out. 

 

(iii) Chemical Test: 

    A teaspoon full of lime is placed in a test tube and dilute hydrochloric acid is poured in it. The content is stirred and the test tube is kept in the stand for 24 hours. Vigourous effervescence and less residue indicates pure limestone. If effervescence is less and residue is more it indicates impure limestone. 

    If thick gel is formed and after test tube is held upside down it is possible to identify class of lime as indicated below: 

• Class A lime, if gel do not flow.

• Class B lime, if gel tends to flow down. 

• Class C lime, if there is no gel formation. 

 

(iv) Ball Test: 

    This test is conducted to identify whether the lime belongs to class C or to class B. By adding sufficient water about 40 mm size lime balls are made and they are left undisturbed for six hours. Then the balls are placed in a basin of water. If within minutes slow expansion and slow disintegration starts it indicates class C lime. If there is little or no expansion, but only cracks appear it belongs to class B lime.

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Building with Lime: Past, Present, and Potential, Types and Properties

 

Building with Lime: 

Past, Present, and Potential, Types and Properties

Lime

It is an important binding material used in building construction. Lime has been used as the material of construction from ancient time. When it is mixed with sand it provides lime mortar and when mixed with sand and coarse aggregate, it forms lime concrete. 

Lime is a versatile material that finds applications in various fields, including construction, agriculture, and chemistry. There are two primary types of lime: quicklime (calcium oxide, CaO) and hydrated lime (calcium hydroxide, Ca(OH)2). Let's explore some aspects of lime:

Production:

• Quicklime (CaO): Produced by heating limestone (calcium carbonate, CaCO3) at high temperatures (typically around 900–1000°C) in a process known as calcination.
• Hydrated Lime (Ca(OH)2): Produced by treating quicklime with water.

Uses:

• Construction: Lime has been traditionally used in construction for various purposes, such as mortar and plaster. It reacts with carbon dioxide in the air and slowly turns back into calcium carbonate, resulting in a durable and stable material.

• Soil Stabilization: Lime is used to stabilize soil in construction projects, improving its engineering properties and reducing plasticity.

• Water Treatment: Hydrated lime is often used in water treatment processes to adjust pH levels and precipitate impurities.

• Agriculture: Agricultural lime (usually in the form of crushed limestone) is added to soil to neutralize acidity, providing essential nutrients for plant growth.

• Chemical Industry: Lime is used in various chemical processes, including the production of calcium-based chemicals and as a reactant in industrial processes.

Chemical Properties:

• Quicklime is highly reactive and exothermic when it reacts with water, producing heat.
• Hydrated lime is a dry powder that results from the chemical transformation of quicklime in the presence of water.

Safety Considerations:

• Quicklime is caustic and can cause burns. Proper safety measures, including protective equipment, should be used when handling it.

It's important to note that the application and properties of lime can vary based on the specific type of lime used and the intended use.

 

 

Types of Limes and their Properties 

The limes are classified as fat lime, hydraulic lime and poor lime: 

 

(i) Fat lime: 

It is composed of 95 percentage of calcium oxide. When water is added, it slakes vigorously and its volume increases to 2 to 2.5 times. It is white in colour. 

Its properties are:

• (a) hardens slowly 
• (b) has high degree of plasticity 
• (c) sets slowly in the presence of air 
• (d) white in colour 
• (e) slakes vigorously. 

 

(ii) Hydraulic lime: 

It contains clay and ferrous oxide. Depending upon the percentage of clay present, the hydraulic lime is divided into the following three types: 

• (a) Feebly hydraulic lime (5 to 10% clay content) 
• (b) Moderately hydraulic lime (11 to 20% clay content) 
• (c) Eminently hydraulic lime (21 to 30% clay content) 

The properties of hydraulic limes are: 

• • Sets under water
• • Colour is not perfectly white 
• • Forms a thin paste with water and do not dissolve in water. 
• • Its binding property improves if its fine powder is mixed with sand and kept in the form of heap for a week, before using. 

 

(iii) Poor lime: 

It contains more than 30% clay. Its colour is muddy. It has poor binding property. The mortar made with such lime is used for inferior works. 

 

IS 712-1973 classifies lime as class A, B, C, D and E. 

 

Class A Lime: 

It is predominently hydraulic lime. It is normally supplied as hydrated lime and is commonly used for structural works. 

 

Class B Lime: 

It contains both hydraulic lime and fat lime. It is supplied as hydrated lime or as quick lime. It is used for making mortar for masonry works. 

 

Class C Lime: 

It is predominently fat lime, supplied both as quick lime and fat lime. It is used for finishing coat in plastering and for white washing. 

 

Class D Lime: 

This lime contains large quantity of magnesium oxide and is similar to fat lime. This is also commonly used for white washing and for finishing coat in plastering. 

 

Class E Lime: 

It is an impure lime stone, known as kankar. It is available in modular and block form. It is supplied as hydrated lime. It is commonly used for masonry mortar

 

 

Structure where  Lime is Used

One of the most iconic and well-known structures that extensively used lime as a binding material is the Roman Pantheon. The Pantheon is an ancient temple located in Rome, Italy, and is renowned for its architectural and engineering marvel.

The Pantheon:

1. Construction Period:

   • The Pantheon was commissioned during the reign of Emperor Hadrian in 118–128 AD. However, the original structure on the site was built by Marcus Agrippa around 27 BC and later rebuilt by Emperor Hadrian.

2. Architectural Features:

   • The Pantheon is known for its remarkable dome, which was the largest unreinforced concrete dome in the world for many centuries.
   • The dome has a central oculus (circular opening) at the top, allowing natural light to enter the interior.

3. Use of Lime in Construction:

   • Lime played a crucial role in the construction of the Pantheon. The Romans used a type of mortar known as pozzolana mortar, which consisted of lime, volcanic ash (pozzolana), and water.
   • Pozzolana mortar is highly durable and has excellent hydraulic properties. The addition of pozzolana allowed the Romans to create concrete that could set underwater and gain strength over time.

4. Concrete Construction:

   • The Pantheon's dome is made of concrete, and the Romans employed a method of constructing concrete using a mixture of lime, pozzolana, and aggregates such as crushed volcanic rock and bricks.
   • The use of this concrete allowed for the creation of large and stable structures, and the Pantheon's dome is a testament to the engineering expertise of the Romans.

5. Durability and Longevity:

   • The Pantheon stands as a testament to the durability of Roman concrete and lime-based mortar. Despite its age, the structure has survived earthquakes and the test of time.

6. Symbolic Importance:

   • The Pantheon has been repurposed over the centuries and is now a Christian church (Basilica di Santa Maria ad Martyres). Its conversion contributed to its preservation.

The Pantheon remains an architectural marvel, and the use of lime-based materials in its construction highlights the ingenuity of ancient Roman engineers. The properties of lime and the technology used in structures like the Pantheon have influenced construction practices throughout history

 

Historical Use of Lime

Lime has a rich history dating back thousands of years, and its use has evolved over time. Here's a brief overview of the history of lime:

1. Ancient Uses:

   • The use of lime can be traced back to ancient civilizations. The Egyptians used a form of lime for various construction purposes, and evidence suggests that lime mortars were used in the construction of the pyramids.
   • The Greeks and Romans also extensively used lime-based materials in their construction projects. The Romans, in particular, developed advanced techniques for producing lime and pozzolana-based concrete, as seen in structures like the Pantheon.

2. Middle Ages:

   • The knowledge of lime production and use continued into the Middle Ages. Medieval builders in Europe used lime mortar for constructing cathedrals, castles, and other structures.
   • Lime kilns, used to produce quicklime by heating limestone, became more widespread during this period.

3. Renaissance and Early Modern Period:

   • The Renaissance saw a revival of interest in classical architecture, and the use of lime continued to be prominent. The development of lime-based plasters and finishes contributed to the aesthetic aspects of buildings during this period.

4. 18th and 19th Centuries:

   • The Industrial Revolution brought about advancements in lime production. Lime kilns became more efficient, and the demand for lime in construction, agriculture, and industry increased.
   • Lime was a key component in mortar for brick construction during the 19th century, contributing to the growth of urban areas.

5. 20th Century:

   • Portland cement, an alternative to lime-based mortars, gained popularity in the construction industry during the 20th century. However, lime continued to be used in heritage restoration and conservation projects due to its compatibility with historic structures.

6. Contemporary Uses:

   • Today, lime is still utilized in various industries. In construction, lime is employed for mortar, plaster, and soil stabilization. It remains an essential material in the restoration of historic buildings.
   • Agricultural lime, which is crushed limestone or dolomite, is used to neutralize soil acidity and improve crop yields.

Throughout history, lime has played a crucial role in the development of architectural and construction practices. Its enduring popularity is attributed to its versatility, durability, and compatibility with a wide range of materials. The historical use of lime in iconic structures highlights its significance in the built environment.

 

Chemical Constituents of Lime

Lime is a general term that refers to a range of calcium-containing inorganic materials. The two primary types of lime are quicklime (calcium oxide, CaO) and hydrated lime (calcium hydroxide, Ca(OH)2). Let's delve into the constituents of each:

1. Quicklime (Calcium Oxide, CaO):

   • Chemical Formula: CaO
   • Production: Quicklime is produced by heating limestone (calcium carbonate, CaCO3) in a lime kiln at high temperatures (typically around 900–1000°C) in a process known as calcination.
   • Properties:
     • Quicklime is a white, crystalline solid at room temperature.
     • It is highly reactive with water, producing heat in an exothermic reaction.
     • When quicklime reacts with water, it forms hydrated lime (calcium hydroxide).

2. Hydrated Lime (Calcium Hydroxide, Ca(OH)2):

   • Chemical Formula: Ca(OH)2
   • Production: Hydrated lime is produced by adding water to quicklime. This process is known as slaking or hydration.
   • Properties:
     • Hydrated lime is a dry, fine powder.
     • It is less reactive than quicklime but still exhibits some reactivity with water.
     • The chemical reaction between quicklime and water results in the formation of calcium hydroxide.

3. Pozzolana (Optional Constituent in Lime-Based Materials):

   • Definition: Pozzolana refers to siliceous or siliceous and aluminous materials that, in themselves, possess little or no cementitious value but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds possessing cementitious properties.
   • Examples: Volcanic ash, fly ash, and certain natural clays are examples of pozzolanic materials.
   • Use: Pozzolanic materials are often added to lime-based materials, like mortars and concretes, to enhance their properties, such as setting time and strength.
     

The chemical reactions involved in the production of lime and its subsequent use in construction involve the transformation of calcium carbonate into calcium oxide and, eventually, into calcium hydroxide. These reactions are fundamental to the functionality and versatility of lime-based materials in various applications, from traditional mortar and plaster to more advanced construction techniques.

 

Clay and Lime Reactivity

The presence of clay in Lime Affect:

The presence of clay in lime can significantly influence the properties and performance of lime-based materials. While lime is often used in construction for its binding and stabilizing properties, the addition of clay can affect various aspects, such as workability, strength, and durability. Here are some effects of the presence of clay in lime:

1. Workability:

   • Positive Aspect: Small amounts of clay can enhance the workability of lime mortars. Clay acts as a plasticizer, making the mix more malleable and easier to work with.
   • Negative Aspect: Excessive clay content can lead to poor workability, making the lime mix difficult to handle and apply.

2. Setting Time:

   • Positive Aspect: Clay can contribute to the setting and hardening of lime-based materials by promoting pozzolanic reactions. Pozzolanic reactions involve the combination of lime with silica and alumina in the clay, forming compounds with cementitious properties.
   • Negative Aspect: Excessive clay content may lead to delayed setting times, affecting the construction schedule. It's crucial to find the right balance to achieve a reasonable setting time.

3. Strength:

   • Positive Aspect: The addition of clay can enhance the strength of lime-based materials. Pozzolanic reactions contribute to the development of additional cementitious compounds, improving the overall strength and durability.
   • Negative Aspect: Very high clay content may lead to a reduction in strength and durability, as excessive amounts of clay can disrupt the formation of a well-structured matrix.

4. Durability:

   • Positive Aspect: Properly proportioned clay content can improve the durability of lime-based materials, making them more resistant to weathering and environmental factors.
   • Negative Aspect: Excessive clay content can lead to poor durability, as it may result in shrinkage, cracking, and reduced resistance to freeze-thaw cycles.

5. Compatibility:

   • Positive Aspect: Clay can improve the compatibility of lime with certain aggregates, providing a more cohesive mix.
   • Negative Aspect: Incompatibility issues may arise if the clay content is too high, leading to segregation or poor adhesion with other materials.

In summary, the presence of clay in lime can have both positive and negative effects on properties depending on the proportion and the specific application. It requires careful consideration and proper mixing to achieve the desired balance between workability, strength, and durability. Engineers and builders often conduct tests and evaluations to determine the optimal clay content for a given lime-based material in order to achieve the desired performance.

 

Contact of Lime and Hardened Concrete:

When lime comes into contact with hardened concrete, it can lead to a phenomenon known as delayed ettringite formation (DEF). Ettringite is a crystalline compound that forms as part of the cement hydration process. However, when lime is introduced to hardened concrete under certain conditions, it can react with existing constituents and cause DEF. Here's an explanation of the process and its potential negative effects on hardened concrete:

Delayed Ettringite Formation (DEF):

1. Reaction Mechanism:

   • In the presence of moisture and elevated temperatures, lime can react with tricalcium aluminate (C3A) in the cementitious matrix.
   • This reaction forms ettringite crystals, which expand as they grow.

2. Negative Effects on Hardened Concrete:

   • Expansion and Cracking: The formation of ettringite crystals can lead to the expansion of concrete. This expansion, if significant, may cause internal stresses and cracking within the concrete. Cracking is a critical concern as it can compromise the structural integrity and durability of the concrete.

   • Reduced Strength and Durability: The expansion associated with delayed ettringite formation can result in a decrease in the compressive strength of the concrete. Additionally, the cracking induced by the expansion may allow harmful substances such as water, chlorides, and other aggressive agents to penetrate the concrete, reducing its long-term durability.

   • Aesthetic Issues: Cracking and expansion due to DEF can also lead to aesthetic concerns, impacting the appearance of the concrete surface.

   • Structural Concerns: In severe cases, the internal stresses and cracking caused by delayed ettringite formation may compromise the overall structural performance of the concrete.

3. Conditions Favoring DEF:

   • DEF is more likely to occur under specific conditions, including high temperatures during the curing period, elevated moisture levels, and the presence of reactive aggregates.
   • The use of high-lime-content materials or the introduction of lime after concrete has hardened can contribute to the risk of DEF.

4. Prevention and Mitigation:

   • To minimize the risk of DEF, it's essential to control the mix design, curing conditions, and the quality of materials used in concrete construction.
   • The careful selection of cement types, aggregates, and admixtures can help mitigate the potential negative effects of lime on hardened concrete.

In summary, the interaction of lime with hardened concrete leading to delayed ettringite formation poses challenges in terms of expansion, cracking, and potential reductions in strength and durability. As such, it is crucial to follow good concrete practices, consider material compatibility, and carefully control mix proportions to minimize the risk of DEF and its associated negative effects.

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Index Properties and Key Parameter of Soil - Civil Engineering

Index Properties and Parameters of Soil 

DEFINITIONS OF BASIC KEY TERMS OF SOIL

Index Properties of Soil  

Water Content

Water content (w) is the ratio of the weight of water to the weight of solids.often expressed as a percentage

Index Properties of Soil 

Void Ratio

Void ratio (e) is the ratio of the volume of void spaces to the volume of solids.The void ratio is usually expressed as a decimal quantity.
 

Index Properties of Soil

 Porosity

Porosity (n) is the ratio of the volume of voids to the total volume of soil. 
 

Index Properties of Soil

 Degree of Saturation

Degree of saturation (S) is the ratio of the volume of water to the volume of voids. 
 

Index Properties of Soil

 Bulk Unit weight

Bulk unit weight (γ) is the weight density, that is, the weight of a soil per unit volume. 
 

Index Properties of Soil

 Saturated Unit Weight

Saturated unit weight (γsat) is the weight of a saturated soil per unit volume. 
 

Index Properties of Soil

 Dry Unit Weight

Dry unit weight (γd) is the weight of a dry soil per unit volume. 
 

Index Properties of Soil 

 Effective Unit Weight

 Effective unit weight (γ′) is the weight of a saturated soil submerged in water per unit volume. 

Index Properties of Soil

 Relative Density

Relative density (Dr) is an index that quantifes the degree of packing between the loosest and densest state of coarse-grained soils. 
 

Index Properties of Soil

 Density Index

Density index (Id) is a similar measure (not identical) to relative density. 
 

Index Properties of Soil

 Unit Weight

Unit weight ratio or density ratio (Rd) is the ratio of the unit weight of the soil to that of water. 
 

Index Properties of Soil

 Swell Factor

Swell factor (SF) is the ratio of the volume of excavated material to the volume of in situ material (sometimes called borrow pit material or bank material). 
 

Index Properties of Soil

 Liquid Limit

Liquid limit (LL) is the water content at which a soil changes from a plastic state to a liquid state. 
 

Index Properties of Soil 

 Plastic Limit

Plastic limit (PL) is the water content at which a soil changes from a semisolid to a plastic state. 
 

Index Properties of Soil

 Shrinkage Limit

Shrinkage limit (SL) is the water content at which a soil changes from a solid to a semisolid state without further change in volume. 
 

Index Properties of Soil

 Plasticity Index

Plasticity index (PI) is the range of water content for which a soil will behave as a plastic material (deformation without cracking). 
 

Index Properties of Soil

 Liquidity Index

Liquidity index (LI) is a measure of soil strength using the Atterberg limits (liquid and plastic limits based on test data). 
 

Index Properties of Soil

 Shrinkage Index

Shrinkage index (SI) is the range of water content for which a soil will behave as a semisolid (deformation with cracking).

 

 

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Common Building Stones - Qualities and Uses

The Qualities and Uses of common Building Stones 

Common Building Stones 

The following are the some of commonly used stones: 

• (i) Basalt and trap 
• (ii) Granite 
• (iii) Sand stone 
• (iv) Slate
•  (v) Laterite 
• (vi) Marble
•  (vii) Gneiss 
•  (viii) Quartzite. 

 

Their qualities and uses of Building Stone

(i) Basalt and Trap: 

    The structure is medium to fine grained and compact. Their colour varies from dark gray to black. Fractures and joints are common. Their weight varies from 18 kN/m3 to 29 kN/m3. The compressive strength varies from 200 to 350 N/mm2. These are igneous rocks. They are used as road metals, aggregates for concrete. They are also used for rubble masonry works for bridge piers, river walls and dams. They are used as pavement.

qualities and uses of Building Stone

 

 (ii) Granite: 

    Granites are also igneous rocks. The colour varies from light gray to pink. The structure is crystalline, fine to coarse grained. They take polish well. They are hard durable. Specific gravity is from 2.6 to 2.7 and compressive strength is 100 to 250 N/mm2. They are used primarily for bridge piers, river walls, and for dams. They are used as kerbs and pedestals. The use of granite for monumental and institutional buildings is common. Polished granites are used as table tops, cladding for columns and wall. They are used as coarse aggregates in concrete.

qualities and uses of Building Stone

 

 (iii) Sand stone: 

    These are sedimentary rocks, and hence stratified. They consist of quartz and feldspar. They are found in various colours like white, grey, red, buff, brown, yellow and even dark gray. The specific gravity varies from 1.85 to 2.7 and compressive strength varies from 20 to 170 N/mm2. Its porosity varies from 5 to 25 per cent. Weathering of rocks renders it unsuitable as building stone. It is desirable to use sand stones with silica cement for heavy structures, if necessary. They are used for masonry work, for dams, bridge piers and river walls.

qualities and uses of Building Stone

 

 (iv) Slate: 

    These are metamorphic rocks. They are composed of quartz, mica and clay minerals. The structure is fine grained. They split along the planes of original bedding easily. The colour varies from dark gray, greenish gray, purple gray to black. The specific gravity is 2.6 to 2.7. Compressive strength varies from 100 to 200 N/mm2. They are used as roofing tiles, slabs, pavements etc.

qualities and uses of Building Stone

 

 (v) Laterite: 

    It is a metamorphic rock. It is having porous and sponges structure. It contains high percentage of iron oxide. Its colour may be brownish, red, yellow, brown and grey. Its specific gravity is 1.85 and compressive strength varies from 1.9 to 2.3 N/mm2. It can be easily quarried in blocks. With seasoning it gains strength. When used as building stone, its outer surface should be plastered.

qualities and uses of Building Stone

 

 (vi) Marble: 

    This is a metamorphic rock. It can take good polish. It is available in different pleasing colours like white and pink. Its specific gravity is 2.65 and compressive strength is 70–75 N/ mm2. It is used for facing and ornamental works. It is used for columns, flooring, steps etc.

qualities and uses of Building Stone

 

(vii) Gneiss: 

    It is a metamorphic rock. It is having fine to coarse grains. Alternative dark and white bands are common. Light grey, pink, purple, greenish gray and dark grey coloured varieties are available. These stones are not preferred because of deleterious constituents present in it. They may be used in minor constructions. However hard varieties may be used for buildings. The specific gravity varies from 2.5 to 3.0 and crushing strength varies from 50 to 200 N/mm2.

qualities and uses of Building Stone

 

 (viii) Quartzite :

     Quartzites are metamorphic rocks. The structure is fine to coarse grained and often granular and branded. They are available in different colours like white, gray, yellowish. Quartz is the chief constituent with feldspar and mica in small quantities. The specific gravity varies from 2.55 to 2.65. Crushing strength varies from 50 to 300 N/mm2. They are used as building blocks and slabs. They are also used as aggregates for concrete

qualities and uses of Building Stone

 

 

 

source - Basic Civil Engineering written by -SS bhavikatti

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Stability of Slopes in Earth Dam

Stability of Slopes in Civil Engineering point

slopes of earth are of two types

1. Natural slopes
2. Man made slopes

The slopes whether natural or artificial may be

1. Infinite slopes
2. Finite slopes

Slope stability -

It is very important in design and construction of earth dam. the result of slope failure can often be catastrophic, involving the loss of property and many lives

Causes of Failure of Slopes

1.Gravitational Forces
2. Seepage Forces - forces due to seepage water.
3.Erosion of the surface of slopes due to flowing water
4.The sudden lowering of water adjacent to a slope
5. Forces due to earthquakes

Erosion n the surface of a slope may be the cause of the removal of a certain weight of soil, and may thus lead to an increased stability as far as mass movement is concerned. On the other hand, erosion in the form of undercutting at the toe may increase the height of the slope, or decrease the length of the incipient failure surface, thus decreasing the stability.

When there is a lowering of the ground water or of a free-water surface adjacent to the slope,for example in a sudden draw-down of the water surface in a reservoir there is a decrease in the buoyancy of the soil which is in effect an increase in the weight. This increase in weight causes increase in the shearing stresses that may or may not be in part counteracted by the increase in shearing strength,depending upon whether or not the soil is able to undergo compression which the load increase tends to cause . If a large mass o f soil is saturated and is of low permeability, practically no volume changes will be able to occur except at a slow rate, and in spite of the increase of load the strength increase may be inappreciable.

The shear strength of soil is assumed to follow Coulomb's law

s = c + σ. tan ϕ

where,
c' - effective unit cohesion 

σ' = effective normal stress on the surface of rupture = (σ - u) 

σ - total normal stress on the surface of rupture
u - pore water pressure on the surface of rupture 

ϕ' = effective angle of internal friction.

FACTOR OF Safety

stability analysis, two types of factors of safety are normally used. 

They are

1. Factor of safety with respect to shearing strength.
2. Factor of safety with respect to cohesion. This is termed the factor of safety with respect to height.

 

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The Economist Nicholas Stern gave the most Impressive analysis in the year 2006 on 

The Economist Nicholas Stern gave the most Impressive analysis in the year 2006 on -

Climate Change

 

 

In 2006 climate economist Nicholas Stern published the Stern Review on the Economics of Climate Change, a report that offered the first systematic examination of the costs of addressing climate change and impacts on the global economy.The report marked a fundamental shift away from climate change being viewed primarily as an issue of science, to also being one of economics.

Read more

 

 

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Canal Falls - Irrigation Engineering

CANAL FALLS 

Whenever the available natural ground slope is steeper than the designed bed slope of the channel, the difference is adjusted by constructing vertical ‘falls’ or ‘drops’. 

Types of falls 

1. Ogee falls:

Water is gradually led down by providing convex and concave curves. 

2. Rapid falls: 

Long slopes of 1 : 15 to 1 : 20 with boulder facings are known as rapids. They are quite satisfactory but very expensive and hence became obsolete. 

3. Trapezoidal Notch Falls: 

It consists of a number of trapezoidal notches across the channel wit h a smooth entrance and a flat circular lip projecting downstream from each notch. There will be neither drawdown nor heading up of water, as the channel approaches the fall. Now these are obsolete since simpler, economical and better modern falls are developed. 

 

 Well type/cylinder/syphon well falls: 

This type consists of two wells, one for inlet and another for outlet connected by a pipe. The down stream well is necessary in the case of falls greater than 1.8 m and for discharge greater than 0.29 cumecs. This type of falls are very effective for larger drops with smaller discharges. 

 

 Simple vertical drop (Sarda type fall): 

1. It is a raised crest fall with a vertical impact 

2. It is simple and economical 

3. In it canal drops into a water cushion. 

 

 Straight Glacis Falls: 

1. In this type, a straight glacis, sloping generally at 2 : 1, is provided after a raised crest. 

2. It is suitable up to 60 cumecs discharge and 1.5 m drop. 

 

Montague Type Fall: 

In this type the straight glacis is replaced by a parabolic glacis to improve energy dissipation. 

 

Inglis fall or Baffle fall: 

For as straight glacis type fall a baffle platform and a baffle wall are added. 

 

• Vertical drops – suitable up to 15 cumecs and upto 1.5 m fall. 
• Straight glacis – suitable for discharge up to 60 cumecs and 1.5 m fall. 
• Baffle fall – suitable for all discharge and more 1.5 m fall. 
• Well type – suitable for high drops and low discharge 

A fall to be used as a meter must be provided with a broad crest.

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Docks and Harbour - Civil Engineering study

 Docks and Harbour

•      Harbour is a sheltered area of the sea in which vessels can be launched, built or taken for repair or could seek refuge in time of storm and provide facilities for loading and unloading of cargo and passengers.

•     Port is a harbour where terminal facilities like stores, landing of passengers and cargo are added.

TYPES OF HARBOURS

• 1. Natural harbour It is an inlet protected from storms and waves by natural configuration of land.Mumbai, Kandla and Karwar are examples of natural harbours.

• 2. Semi-natural harbour The harbour in which natural configuration of land prefects the harbour on sides only and needs man-made protection at the entrance. Vishakhapatnam is a semi-natural harbour.

• 3. Artificial harbour It is harbours protected by man-made structures like breakwaters or bydredging. Chennai is a man-made harbour.

 

Classification Based on Utility

• 1. Harbour of refuge: Used to anchor ships in storms.

• 2. Fisheries harbours.

• 3. Commercial harbours.

• 4. Military harbours: Seabird at Karwar is a military harbour.

Classification Based on Location

• 1. Canal harbour.

• 2. Lake harbour.

• 3. River harbour.

• 4. Sea harbour.

 

Natural Phenomenon Influencing Location of Harbour on Seashore

1. Littoral Drift 

    The process of carrying the drifting sand and depositing it on seashore is known as littoral drift. If a harbour is constructed in the path of the littoral drift, there will be accumulation of sand on one side and erosion on the other side of the harbour. Groynes are used to protect the shore by trapping littoral drift.

2. Tides 

    The artificial rise and lower of mean sea level periodically is known as tide. It is observed that the general water level rises and falls, approximately in a period of twelve hours and twenty-five minutes. It is also observed that much higher water levels and much lower water levels occur on new and full moons. These tides are called spring tides. Water levels which occur about seven days from new and full moons are moderate and are called neap tides. The total height of spring tides is about 1.5 to 2.0 times that of neap tides.

3. Waves and winds 

    Wind generates waves on water bodies. In maritime works, speed of wind is expressed in knots. One nautical mile is the length of one minute of arc of a meridian on earth surface. Since radius of earth of equator is about 6378 km, 1 nautical mile = 6378 >× pi/180 >×1/60  km,
    i.e., 1 nautical mile is 1.852 km. Hence, one knot is 1.852 km/hour.
In 1805, Admiral Beafort of British Navy classified wind into 12 categories starting from calm (Beafort No. 0) to Hurricane (Beafort No. 12) depending upon velocity is km/hour. A wind is said to be calm if velocity is about 1.6 km and is said to be hurricane if it is above 120 km/hour.Height and length of wave: Thomas Stevenson gave a formula for estimating wave height in meters as h = .34(F)^1/2 , where F is the fetch in km. However, waves cannot attain full height in shallow water. No wave can have a height greater than the depth of water.
    Berlin’s formula for finding the wavelength is L = 1/2pi × g t^2= 1.56 t^2

 

FEATURES OF A HARBOUR

 

1. Harbour entrance 

    Depth and width required at the entrance are more than those required in the channel since it is more exposed to waves. Entrance should be wide enough for navigational requirement. However, it should not be too wide to increase the wave height within the harbour.

 

2. Approach channel 

    The dredged fairway through which ships proceed from the open sea to the harbour basin is known as approach channel. The depth should be sufficient for navigation of design vessels at all the time.

3. Turning basin 

    It is the area required for mano-euvring the ship when it enters or leaves the berth, so that it moves head on.

4. Sheltered basin 

    It is the area protected by shore and breakwaters.

5. Breakwaters 

    The protective barrier constructed to enclose harbours and to keep the waters undisturbed by the rough sea are called breakwaters. Types of breakwaters used are

• 1. Heap or mound breakwater
• 2. Mound with superstructure
• 3. Upright wall breakwater.

    Breakwaters should be designed to resist hydro-static forces, action of wind and waves, solvent action of seawater and sea insects. The breakwater height is 1.2 to 1.25 times the height of the waves expected, above the mean sea level.

6. Wharves and quays 

    The platforms provided along the shore or breakwater for ships to come close enough for loading or unloading are called wharves. Wharves along and parallel to the shore are generally called quays. Wharves and quays have back-fill of earth or other materials and have wide platform at top.

7. Jetties 

    A jetty is a narrow strip structure projecting from the shore into water with berths on one or both sides.

8. Lock and locked basin 

     Locked basin is an enclosed basin wherein a number of vessels can be berthed and has an entrance controlled by lock gate.

9. Fender 

    The cushion provided on the face of a jetty for absorbing shocks by ships is known as fender. They may be rubber strips, timber grills, concrete or rubber fenders.

10. Slip 

    The space of water between two adjacent piers where ships are berthed is known as slip. For safe navigation and provide enough space for barges to load and unload, the slip should be three to four times the beam of largest ship to be accommodated.

11. Docks 

    Docks are enclosed areas for berthing ships, to keep them afloat at a uniform level. There are two types of docks:

• 1. Wet docks: Docks used for berthing of vessels to facilitate loading and unloading of passengers and cargo.
  

• 2. Dry docks: The docks used for repairs of vessels are known as dry docks.
  

12. Aprons 

    The open space left immediately in front of the berth is known as apron. It is used for loading, unloading and for installing railway track, road or conveyors. The width of apron usually varies from 10 m to 25 m, depending upon the traffic.

13. A dock requires transit sheds, warehouses, cold storage and guardhouse, etc.

Maintenance Dredging

    Dredging is defined as excavation under water. To maintain navigation depth dredging is required.

Types of dredges:

• 1. Dipper dredger
• 2. Grapple dredgers
• 3. Bucket elevator or ladder dredgers
• 4. Suction dredgers

Navigational Aids

    For safe, efficient and comfortable travel of ships into harbour navigation aids are required. They are in the form of illuminated signals or lights. They may be classified as the following.

• 1. General lights They guide the ships along the coast and through rivers serving as approaches to more than one harbour. They may be light houses, or light ships.
  

• 2. Local lights They guide the ships to harbours through approach channels to the berths. They are light houses, fixed structures, channel markers, floating buoys, lights on shore, wharves, breakwaters, etc.
  

 

 

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STIFFENERS - PLATE GIRDER

What is Stiffener

In  steel  building  construction when  the web  of  a  plate  girder  acting  alone  (that is  without stiffeners)  proves  inadequate,  stiffeners  may  be  provided  for  specific purpose as follows. 

To improve the buckling strength of a slender web due to shear intermediate  transverse  and  longitudinal web stiffeners;  to  prevent  local  buckling of  the web  due  to  concentrated  loading load-carrying stiffener.

• To  prevent  local crushing of the web due to concentrated loading bearing stiffener; 
• To provide torsional restraint to beams and girders at supports torsional stiffener;
• To provide local reinforcement to a web under shear and bearing diagonal stiffener.
• To transmit tensile forces applied to a web through a flange—tension stiffener are provided. 

 

Arrangement of Stiffeners

 Basically there are only two types of stiffeners, 

    Intermediate stiffeners and Bearing stiffeners. 

    The intermediate web stiffeners are used to prevent the web from buckling due to shear and,

    The bearing stiffeners to prevent crushing of web under concentrated loads.

    Any of these stiffeners may be required to perform more than one function and thus its design should comply with the requirements of all the functions for which designed. 

    For example, a bearing stiffener will be designed to check the crushing of web under concentrated load and will be checked in addition to local buckling (crippling) of the web due to the concentrated load as load bearing stiffener.

    Further, if provided at support it may also be called upon to provide end anchorage for tension field action to develop (in case tension field method of design is adopted). Such an end bearing stiffener is termed end post.

    The web of plate girder is assumed to be supported over the edges of the stiffeners. Angle sections are used if the connections are riveted/bolted,and flat sections are used if the connections are welded.

 

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Matrix Method of Structure Analysis - Stiffness and Flexibility one liner

Matrix Method of Analysis

Stiffness Method of Analysis

• Int the stiffness method of analysis it is not essential to select the redundant or to know whether the structure is determinate or indeterminate.
• Base unknowns to be determined in the analysis are the displacement components of various joints.
• For calculation of displacement and establishment of equation of equilibrium we develop stiffness matrix.
• It is necessary to identify the redundants in force method of analysis.
• In stiffness method displacements/ roatation (degree of freedom) are unknown. In the Kani's method of anlysis, actual end moment in any member is calculated by superposition of fixed end moment, moment due to rotation of near end and far end and moment due to displancement and sway of plane fram.
• In stiffness method of analysis joint displacements are unknown which are equal to the kinematic inderminacy of the structure.
• Stiffness matrix are always symmetrical about its main diagonal due to Maxwell's reciprocal theorem.
• Stiffness matrix method is modification of slope deflection method which uses equilibrium equation to determine the kinematic (displacement) response of structure and then force response.

Flexibility Method of Analysis

• In the flexibility method redundant forces are unknowns.
• Flexibility matrix is inverse of stiffness matrix and vice-versa.
• Flexibility matrix is square matrix and its element are symmetrical about diagonal due to Maxwell's reciprocal theorem.therefor flexibility  matrix and it's transpose are equal.
• To develop flexibility matrix, structure has to be stable and in equilibrium.
• Elements of main diagonal of stiffness matrix and flexibility are always positive because at a point,displacement will always occur in the direction of force applied at that point.
• Flexibility method is used conveniently to analyze inteterminate structures by force method

 

 

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