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What is the difference between Pre-tension and Post-tension in concrete?

Pre-tension Concrete

Pretension in concrete is the method when the concrete is prestressed with tendons before the placing of the concrete. and It is a suitable method for small structural elements. the pre-tensioning members are produced in the mold.

To pretension concrete the steel is first tensioned in a frame or between anchorages external to the member. The concrete is then cast around it. After the concrete has developed sufficient strength the tension is slowly released from the frame or anchorage to transfer the stress to the concrete to which the tendons have by that time become bonded. The force is transmitted to the concrete over a certain distance from each end of a member known as the transfer length.

Post-tension Concrete

Post tension in concrete is the method when the prestressing process is done after the concrete attains its strength. It is suitable when the structure is heavy and this method is developed due to bearing.

Post-tensioned concrete is made by casting concrete that contains ducts through which tendons can be threaded. An alternative is to cast the concrete around tendons that are greased or encased in a plastic sleeve.

When the concrete has sufficient strength the tendons are tensioned by means of portable jacks. The load is transmitted to the concrete through permanent anchorages embedded in the concrete at the ends of the tendons.

Ducts are usually grouted later or filled with grease to protect the tendons against corrosion. In some applications the post-tensioning tendons are run alongside the concrete member.

Pre-tension Concrete vs Post-tension Concrete

Sr.No	Pretensioning	Post-tensioning
1	Pretension is the technique in which we are imparting tension in strands before placing the concrete.	Post tensioning is done by forming a duct in which strands are pulled (tensioned) after the concrete gains it’s full strength.
2	In this type of concrete, the pre-stressing cables called the strands are tensioned before casting the concrete and then concrete is casted enclosing the tensioned cables.	In this type of concrete, the strands are enclosed within a duct in the form and then concrete is casted. The process of tensioning the strands is carried out after the concrete attains its sufficient strength.
3	Post-tension Concrete	In this method, products are changed according to a structure.
4	Pre-tensioning members are produced in a mould.	Cables are used in place of wires and jacks are used for stretching.
5	It is cheaper because cost of sheathing is not involved in pretensioning	It is costlier because cost of sheathing is required.
6	Pre-tensioning is preferred when the structural element is small and easy to transport	Post-tensioning is preferred when the structural element is heavy.
7	Loss of prestressing isn’t less (about 18 %)	Loss of prestressing isn’t more (about 15 %)
8	Small sections are to be constructed	Size of a member is not restricted, long-span bridges are constructed by post-tensioning
9	It is more reliable and durable	The durability depends upon the two anchorage mechanism

Segregation and Bleeding of concrete – Causes and Mitigation

1. Segregation of Concrete:

Segregation is the separation of constituent materials in concrete. There are three common types of segregation:

Separation of coarse aggregate from the concrete mixture
Separation of cement paste from the concrete during its plastic stage
Separation of water from the concrete mix (Bleeding in concrete)

Segregation of concrete affects strength and durability in structures. When this is detected, elements affected should be demolished.

The segregation includes undesirable properties in the hardened concrete; therefore, it can cause honeycombing and may leads to the development of cavities in the concrete surface.

a – Causes of concrete segregation:

The main causes are:

Use of high water-cement ratio in concrete. This general happens in case of concrete mixed at site by unskilled workers
Excessive vibration of concrete with mechanical needle vibrators makes heavier particles settle at bottom and lighter cement sand paste comes on top.
When concreting is done from height in case of underground foundations and rafts, which causes concrete to segregate.

b – Mitigation:

Segregation can be controlled by maintaining proper proportioning the mix.
By peculiar handling, placing, transporting, compacting and finishing of concrete.
Adding air entraining agents, admixtures and pozzolanic materials in the mix segregation controlled to some extent.
Wherever depth of concreting is more than 1.5 meters, it should be placed through temporary inclined chutes.
The delivery end of chute should be as close as possible to the point of deposit.
Handling, placing and compaction of freshly mixed concrete should be done carefully. A proper vibration also reduces the chances of segregation.

2. Concrete Bleeding:

Bleeding is a form of segregation in which water present in the concrete mix is pushed upwards due to the settlement of cement and aggregate. The specific gravity of water is low, due to this water tends to move upwards.

Some bleeding is normal but excessive bleeding can be problematic.

Not all bleed water will reach the surface of the concrete but some water may rise and remain trapped under aggregates and reinforcing. This results in the weakening of the bond between the paste and those elements.

a – Bleeding Causes:

The principal causes of bleeding are:

High water-cement ratio to highly wet mix
Badly proportioned and insufficiently mixed concrete

b – Bleeding Effects:

Due to the formation of Laitance, structures may lose its wearing capacity and decreases its life.

Water while moving from bottom to the top, forms continuous channels. Due to these channels, concrete becomes permeable and allow water to move, which forms water voids in the matrix and reduces the bond between aggregate and the cement paste.

Forming of water at the top surface of concrete results in delaying the surface finishing and so concrete becomes permeable and loses its homogeneity.

Excessive bleeding breaks the bond between the reinforcement and concrete.

c – Mitigation:

To avoid concrete bleeding, it is recommended to:

Reduce Water content
Use finer cements
Increase amount of fines in the sand
Use supplementary cementitious materials
Use air entraining admixtures

What is Plum Concrete?

The word plum means large stones which are termed as boulders or coarse aggregates if technically speaking.

The use of plum concrete is preferred if the required thickness of PCC is excessive or large. This is mainly done below the foundations where due to sleep slope of the strata, the quantity of leveling course could be excessive.

The plum concrete is actually an economical variation of mass concrete.

Plumbs above 160 mm and up to any reasonable size may be used in plain concrete work up to a maximum limit of 20 percent by volume of concrete when specifically permitted by the engineer-in-charge. The plums shall be distributed evenly and shall be not closer than 150 mm from the surface.

Uses of plum concrete:

Plum concrete is used at the water channel beds. It is used mostly in mass concrete works like concrete gravity dams or bridge piers in such cases of rocks about 150 mm in size are used as coarse aggregates to mix a plum concrete.

It is used at side slopes of the embankment to provide a protective laver to earthen foundations and bases.

All about Shrinkage Cracks in Concrete – Types and Causes of Shrinkage Cracks

The shrinkage in concrete can be defined as the volume changes observed in concrete due to the loss of moisture at different stages due to different reasons.

Types of Shrinkage in Concrete:

The shrinkages can be classified into the following:

Plastic Shrinkage
Drying Shrinkage
Antogenous Shrinkage
Carbonation Shrinkage

Plastic Shrinkage in Concrete

The water required for concrete strength gain is escaped into the atmosphere due to the process of evaporation, from the surface of the structure, creating cracks on the surface of the structure.

Another reason for shrinkage cracks under plastic shrinkage type is due to the water absorption from the concrete by the aggregate.

Plastic Shrinkage in Concrete

In the case of floors and the pavements, where the surface area is exposed to drying in a large extent compared to the depth when are subjected to the sun and the drying wind, the surface dries very quickly causing plastic shrinkage.

In the case of a mix design where the water cement ratio is high, there is the possibility of excess water pathways causing bleeding. This excess water due to bleeding will accumulate at the surface of the slabs. When these are exposed to dry weather conditions, the surface dries up and collapse creating cracks.

Prevention of Plastic Shrinkage:

The escape of water from the surface can be prevented by covering the surface with the help of polyethylene sheeting. Prevention of water evaporation will prevent plastic shrinkage.
Proper vibration of the concrete can prevent plastic shrinkage.
Plastic shrinkage in concrete structures can be reduced by use of aluminium powder.
The use of expansive cement can also help in the control of plastic shrinkage.

Drying Shrinkage

Drying shrinkage is caused by the loss of surface-absorbed water from the calcium silicate hydrate (C-S-H) gel and also due to the loss of hydrostatic tension in the small pores.

Swelling is the opposite phenomenon of shrinkage.

Drying Shrinkage in concrete

This shrinkage is mainly due to the deformation of the paste, though the aggregate stiffness also influences it. It takes place once the concrete has set is called as the drying shrinkage.

Most of the kinds of drying shrinkage take place in the first few months of the concrete structure life.

Autogenous Shrinkage

The water is necessary for the hydration of hydrated cement. This process of water withdrawal from the capillary pores to carry out the hydration of hydrated cement is called as self-desiccation.

The shrinkage dealt with such conservative system can be named as autogenous shrinkage or autogenous volume change.

Autogenous Shrinkage in concrete

This can be largely avoided by keeping the surface of the concrete continuously wet; conventional curing by sealing the surface to prevent evaporation is not enough and water curing is essential. With wet curing, water is drawn into the capillaries and the shrinkage does not occur. Note that autogenous shrinkage is separate from and additional to conventional drying shrinkage, which will start when water curing ceases.

Carbonation Shrinkage:

Carbonation Shrinkage is a decrease in either length or volume of a material(concrete) resulting when carbon dioxide present in the atmosphere reacts in the presence of water with the hydrated cement. Calcium hydroxide gets converted to calcium carbonate and also some other cement compounds are decomposed. Such a complete decomposition of calcium compound in hydrated cement is chemically possible even at the low pressure if carbon dioxide in normal atmosphere. Carbonation penetrates beyond the exposed surface of concrete only very slowly.

Carbonation Shrinkage in concrete

The rate is penetration of carbon dioxide depends also on the moisture content of the concrete and the relative humidity of the ambient medium. Carbonation is accompanied by an increase in weight of the concrete and by shrinkage. Carbonation Shrinkage is probably caused by dissolution of crystals of calcium hydroxide and deposition of calcium carbonate in its place.

Factors affecting Shrinkage:

The main factors affecting shrinkage are listed below:

Material Selection
Water cement ratio: Shrinkage is mostly influenced by the water-cement ratio of concrete. It increases with the increases in the water-cement ratio
Environment conditions : It is one of the major factors that affect the total volume of shrinkage. Shrinkage is mostly occurred due to the drying condition of the atmosphere. It increases with the decrease in the humidity.
Chemical composition of Cement :The chemical composition of cement used for concrete & mortar also has some effect on shrinkage. Rapid hardening cement has greater shrinkage than Ordinary Portland Cement.
Aggregates : Aggregates with moisture movement and low elastic modulus cause large shrinkage. The rate of shrinkage generally decreases with the increase of the size of aggregates. It is found that concrete made from sandstone shrinks twice than that of concrete of limestone.
Type of cement used
Admixture in concrete : The shrinkage increases with the addition of accelerating admixtures due to the presence of calcium chloride (Cacl2) in it and it can be reduced by lime replacement.
Size and shape of concrete specimen
Temperature

Highway Design – Introduction to Horizontal and Vertical Alignment

The layout of a highway is comprised of two components: A horizontal component which is viewed from above and the vertical component which is viewed from the side.

The horizontal alignment dictates the left or right turning required to remain on the roadway, while the vertical alignment exerts forces on the vehicle as the grade along the roadway changes.

Horizontal Alignment:

In the horizontal perspective, a roadway is primarily comprised of tangent, or straight, sections which are smoothly connected by curves.

The horizontal curves that are used to provide drivers with the transition from one tangent to the next tangent are typically simple curves which are an arc of circle.

These curves have a single radius value which represents the sharpness or flatness of the curve.

Highway Geometric Design – Horizontal Curve Equations

A tangent roadway section has an infinite radius, since it is a straight line and a horizontal curve has a single, finite radius. Therefore, a spiral transition is used in some instances to help make the shift from a tangent to a curve a little smoother.

Geometric relationships and equations can be used to find important information for reach curve. This information includes the radius, the length of the curve, the change in direction of the two tangents, and other factors depending on our needs.

Several points of interest along the curve include the location where the tangents intersect, which is known as the Point of Intersection. The location where the vehicle leaves the tangent section and begins to drive along the curve, is known as the point of curvature.

Types Of Horizontal Curves:

Horizontal curves are of different types as follows:

1.Simple circular curve

2.Compound curve

3.Reverse curve

4.Transition curve

1. Simple Circular Curve

Simple circular curve is normal horizontal curve which connect two straight lines with constant radius.

2. Compound Curve

Compound curve is a combination of two or more simple circular curves with different radii. In this case both or all the curves lie on the same side of the common tangent.

3. Reverse Curve

Reverse curve is generated when two simple circular curves bending in opposite directions are meet at a signle point and that points is called as point of reverse curvature. The center of both the curves lie on the opposite sides of the common tangent such that the radii of both the curves may be same or different.

Types of horizontal curves

4. Transition Curve

A curve of variying radius is termed as transition curve. It is generally provided on the sides of circular curve or between the tangent and circular curve and between two curves of compound curve or reverse curve etc. Its radius varies from infinity to the radius of provided for the circular curve.

Transition curve helps gradual introduction of centrifugal force by gradual super elevation which provides comfort for the passengers in the vehicle without sudden jerking.

Spiral Curve

Spiral is a type of transition curve which is recommended by Indian Road Congress as ideal transition curve because of its smooth introduction of centrifugal acceleration. It is also called as clothoid.

TS = Tangent to spiral
SC = Spiral to curve
CS = Curve to spiral
ST = Spiral to tangent
LT = Long tangent
ST = Short tangent
R = Radius of simple curve
T_s = Spiral tangent distance
T_c = Circular curve tangent
L = Length of spiral from TS to any point along the spiral
L_s = Length of spiral
PI = Point of intersection
I = Angle of intersection
I_c = Angle of intersection of the simple curve
p = Length of throw or the distance from tangent that the circular curve has been offset
X = Offset distance (right angle distance) from tangent to any point on the spiral
X_c = Offset distance (right angle distance) from tangent to SC
Y = Distance along tangent to any point on the spiral
Y_c = Distance along tangent from TS to point at right angle to SC
E_s = External distance of the simple curve
θ = Spiral angle from tangent to any point on the spiral
θ_s = Spiral angle from tangent to SC
i = Deflection angle from TS to any point on the spiral, it is proportional to the square of its distance
i_s = Deflection angle from TS to SC
D = Degree of spiral curve at any point
D_c = Degree of simple curve

Bernoulli’s lemniscate

In this curve, the radius decreases as the length increases and this causes the radial acceleration to keep on falling. The fall is, however, not uniform beyond a 30 o deflection angle. We never use this type of curve on railways.

Vertical Alignment:

In the vertical perspective, a roadway is also comprised of tangents which are smoothly connected by curves. For vertical alignment, the tangents represent grades which can either be flat, uphill or downhill.

The typical vertical curve is a symmetric, parabolic curve whose shape is defined by the parabolic equation.

The information required to fully define a vertical curve is the elevation of the beginning of the curve, the grades of the two tangents that are connected ad the length of the curve.

The naming convention of vertical alignment is similar to horizontal alignment. Several points of interest along the curve include that the location where the tangents intersect, which is known as the Point of Vertical Intersection.

The location where the vehicle leaves the tangent grade and begin to drive along the curve, is known as the point of vertical curvature.

The point where the curve ends and the vehicle returns back to the tangent grade is known as the Point of Vertical Tangency.

Highway Geometric Design – Vertical Curve Equations

Types Of Vertical Curves:

In general parabolic curve is preferred as vertical curve in the vertical alignment of roadway for the ease of movement of vehicles. But based on the convexity of curve vertical curves are divided into two types

1.Valley curve

2.Summit curve

1. Valley Curve (sag curve)

Valley curve connects falling gradient with rising gradient so, in this case convexity of curve is generally downwards. A second name for valley curve is sag curve.

They are formed when two gradients meet as any of the following four ways:

When a negative gradient meets another mild negative gradient
When a negative gradient meets a level zero gradient
When a negative gradient meets with a positive gradient
When a positive gradient meets another steeper positive gradient

2. Summit Curve (crest curve)

Summit curve connects rising gradient with falling gradient hence, the curve has its convexity upwards. A second name for summit curve is crest curve.

They are formed when two gradients meet as in any of the following four ways:

When a positive gradient meets another positive gradient.
When positive gradient meets a flat gradient.
When an ascending gradient meets a descending gradient.
When a descending gradient meets another descending gradient.

What is a Highway Impact Attenuator?

Highway impact attenuators are devices which are generally used to reduce the impact resulting from a motor vehicle collision, where those impacts might damage other vehicles, motorists, or structures nearby.

In some cases, they are also designed to redirect a colliding vehicle away from roadway machinery, workers, or some other fixed structure. Impact attenuators be classified into three distinct categories, which are based on the engineering method which is used to reduce the kinetic energy of a colliding automobile.

Impact Attenuator Categories:

Momentum transfer, in which the impacting vehicle’s momentum is transferred to containers having sand or water in them, thereby successively lowering the speed of a colliding vehicle.

Material deformation, this category uses crushable materials which absorb energy by creating a crumple zone.

Friction: these work by causing a steel cable to be pushed through an angled slot, thereby transforming kinetic energy into harmless heat.

Impact Attenuator Types:

There are several types, and most of these can be frequently seen along roadsides at locations where it is necessary to protect those kinds of objects and individuals.

Crash cushions:

These attenuators are constructed of several segments, all of which crumple into each other when struck by a colliding automobile, and these are often used because of their reusable nature.

After being struck by a colliding vehicle, they can return to their original form and can be used again. Fitch barriers are sand-filled plastic containers, most often colored yellow with a black lid.

They are generally set up in a triangular arrangement between a highway and an exit line, also known as the gore point, and always along the most likely collision line.
The containers which are most forward usually have the least amount of sand in them, with each successive barrel having a higher level of sand.

This allows an impacting vehicle to decelerate more or less smoothly, rather than striking a solid obstruction in a violent manner.

Crash cushions are often implemented along the shoulders of a roadway where it is necessary to protect against collisions with the hazard directly behind them. They can be ground-mounted or surface-mounted and situated on top of a concrete pad.

Water-filled impact attenuators:

They are filled with water which absorbs the force of a colliding auto. Since these are not anchored to the ground, they can easily be redeployed to locations where they are needed.

The water in the containers helps absorb all the kinetic energy so that there is less damage to objects behind the containers, and to the occupants of the colliding vehicle. In cold climates, when water-filled options are used, it will be necessary to include an additive such as magnesium chloride to prevent them from freezing.

Gating impact attenuators:

They permit vehicles that collide with them from the side, to pass right through, and are often used because they’re so economical. However, they do require more clearing space around them in order to be effective, because, without sufficient space, it might be possible for an impacting automobile to pass through and collide with another hazard.

Non-gating impact attenuators:

They do stop the motion of head-on impacts, but also deflect vehicles which strike the sides of the barrier. These types are more expensive because they are anchored, but they require less space than gating versions.

Fitch barriers:

They are most often used at temporary construction worksites, for example at the end of a concrete barrier. They are also used at bridge piers, wide medians, and for two-sided protection.

Where are These Cushions Placed?

Highway impact attenuators are often placed forward of objects along the freeway such as overpass supports, crash barrier introduction, and gore points.

They are frequently used at the side of road construction projects, where there is a greater likelihood of collision with construction equipment and or individuals. Truck-mounted versions is another type which are deployed on vehicles that happen to be susceptible to being hit from behind, for example, maintenance vehicles, road construction vehicles, and snowplows.

How Tower Cranes Build Themselves

When it comes to building skyscrapers, there is no piece of construction equipment more essential than the tower crane. These heavy lifting machines dominate city skylines, hoisting materials and machinery to some of the highest construction sites on Earth.

They have become a part everyday life in almost every major city as contractors race to build high-rise after high-rise, and more than 100 000 can be found in operation around the world at any given time.

Despite how common tower cranes are, they often seem to appear in the sky out of nowhere leaving many of us wondering how they got there in the first place.

The vast majority are erected using mobile cranes that are larger in size, but obviously this cannot always be done when you are building a record-breaking structure and taller cranes simply don’t exist.

Some construction sites in dense urban areas may not have enough space for a large mobile crane either, and many projects also require tower cranes to be erected in stages so that they rise in unison with the constructer portion of the building.

In these scenarios, the cranes must raise themselves to the final working height all on their own using a method known as climbing, and that is what we will be looking at in this post.

In general terms, climbing a tower crane simply refers to the process of adding or removing sections of the mast in order to increase or decrease the overall height.

The concept is fairly straightforward in principle, but it is quite difficult to execute safely in the field with catastrophic consequences if anything should go wrong. It is one of the most dangerous operations that can be performed with a tower crane, and it is only carried out when absolutely necessary to complete a project.

Before climbing can begin, a tower crane must first be erected to an initial height using a suitable mobile crane.

The process begins by constructing a stable foundation, which usually consists of a large concrete slab reinforced with steel rebar, and this takes place about a month before the crane goes vertical so that concrete has enough time to cure.

Once the concrete has reached its full strength, the first steel truss section of the mast is lifted into place, and it is secured with anchor bolts that are embedded in the foundation. Additional sections are then stacked on top of one another to complete the tower portion of the crane, and they are fastened together with high-strength steel bolts.

The mast is topped off with a slewing unit, which is basically a turntable that allows the top of the crane to rotate, and this serves as base for the operator’s cab and lifting components.

The exact arrangement of the top assembly varies depending on the type of tower crane, but the one shown here has a hammerhead configuration with a cathead and a fixed jib that cannot be moved up or down.

The cathead is the first component to be installed on top of the slewing unit, followed by the counter jib and working jib, and these are connected with steel tie rods that help to transfer loads to the mast.

Once the top assembly is complete, a counterweight is then added to the counter jib, which normally consists of several concrete slabs.

The counterweight helps to balance the load when the crane is performing a lift, effectively reducing the bending moment, or torque, that must be carried by the mast.

Since the working jib is fixed on this particular crane, a trolley system must be used to adjust the radius of the hook so that the load can be positioned closer or further from the mast. This is not the case luffing jib tower cranes, however, as they can adjust the radius simply by raising or lowering the working jib.

In either case, the ability to change the position of the load makes it possible to perfectly balance the crane on top of the mast, and this is essential for the climbing process to be carried out safely.

When a tower crane is ready to be climbed, a steel climbing frame is first assembled around the base of the tower, and it is lifted up to the underside of the slewing unit. The frame has a square cross-section with a lattice structure around three sides, but the front is left open so that new mast sections can pass through.

The top is securely fastened to the underside of the slewing unit with high-strength steel bolts, and a hydraulic jack at the bottom is positioned over a push point on the existing mast.

A new mast section is then hoisted up to the frame, where it is either placed on a steel tray or suspended from a guide rail that extends out above the opening. At this point, the top of the crane must be perfectly balanced over the jack before it can be lifted, which is accomplished by placing a weight on the hook to offset the counterweights.

An additional mast section is typically used for this, and it is positioned at a precise radius from the mast so that there is no net moment applied onto the climbing frame.

The crane top essentially behaves like a large balance scale during the climb, and it could topple off the mast if its center of gravity is not in line with the jack. In addition, the climbing frame is not designed to carry significant torsion, and it is extremely important that the crane is not slewed during the climbing process.

The new mast sections are therefore arranged in a straight line on the ground to eliminate any need to rotate the crane, and the operator will usually leave the cabin during the climb so that the crane cannot be slewed accidentally.

Once the crane is confirmed to be in balance and all safety checks have cleared, the hydraulic cylinder is then pressurized to take the weight of the crane top, and the slewing unit is unbolted from the top of the mast.

The cylinder is used to lift the climbing frame along with the top of the crane until there is enough clearance to insert a new mast section, which usually requires several strokes depending on the cylinder’s length.

The mast section can then be maneuvered inside the frame, where it is bolted to the underside of the slewing unit, and the hydraulic cylinder is depressurized so that the bottom of the new section engages with the top of the existing mast.

After the joints are securely fastened, the cylinder is retracted and repositioned on the next push point, and the whole cycle can repeat until the crane reaches the desired height.

One the process is complete, the climbing frame will either be lowered down the mast or removed entirely until it is needed to raise the crane higher or to bring it back down at the end of construction.

11 Common Types of Cranes

1. Floating Crane :

A floating crane is a ship with a crane specialized in lifting heavy loads. They are useful for loading and unloading heavy items to and from ships. They are also used for transferring equipment from one vessel or platform to another, moving around equipment on the sea deck, and recovering or placing equipment on the seabed.

2. Harbour Cranes:

They are normally used in harbour container lifting operations. Due to their compact design, Harbour Cranes are the world‘s most flexible and powerful cargo handling equipment in ports and container terminals. Today, they can be electrified by means of powerful motorized cable reels, largely keeping their flexibility and agility within the quay infrastructure.

3. Crawler Cranes:

They can move around on site and the crane is stable on its track without outriggers. The main advantage of crawler cranes is that they can move around on site and perform each lift with little set-up, since the crane is stable on its tracks with no outriggers. An additional advantage is that crawler cranes are capable of traveling with a load.

4. Rough terrain Cranes:

They are mounted with four rubber tires and specifically designed to operate on OFF-ROAD and ROUGH surfaces.

All terrain cranes are considered as the luxury version of a mobile hydraulic cranes, used in common construction sites.

5. Truck mounted Crane:

It is a self propelled loading-unloading machine mounted on a truck body.

6. Level Luffing Crane:

A level luffing crane is a crane mechanism where the hook remains at the same level whilst luffing.

7. Railroad Crane:

A railroad crane is a type of crane used on a railroad for, accident recovery work, permanent way maintenance or freight handling in goods yards.

8. Tower Cranes:

Tower cranes are commonly used in construction of tall buildings.

9. Side Boom Cranes:

They are commonly used to lift industrial pipes lines. Side booms are built to meet the unique demands of pipeline customers.

10. Aerial Cranes:

An aerial crane or flying crane is a helicopter used to lift loads.

11. Gantry Crane:

A gantry crane is a crane built at the top of a gantry, which is capable of lifting some of the heaviest loads in the world.

Railway Switch and Crossings – How train change the track?

Railroad track Crossing is the most important steering system in the railroad track. It consists of two parallel steel rails set a fixed distance the standard gauge is 4 feet 8.5 inches.

In the track change process, the inner rim of the wheel called a flange is comparatively greater in diameter than the outer part which prevents the wheel from sliding off the track.

Switchs:

Switch rails or point blades are the movable rails that guide the wheels towards either the straight or the diverging. Track stock rails are the running rails immediately alongside the switch rails against which the switch rails lay when in the closed position points operating rods.

Point blades

Stock Rail

Points operating machine also known as a point switch machine or switch motor is a device for operating railway turnouts especially at a distance.

POE Rods

Points Operating Equipment

Crossing:

Crossing is a pair of switches that connect two parallel rail tracks allowing a train on one track to cross over to the other check rails also known as guard rail laid parallel to a running track to guide the wheels. All these rails are non-movable.

Rail track Crossing

Crossing nose as a device on introduced at the point where gauge faces cross each other to permit the flanges of the railway vehicle to pass from one track to another.

Crossing Nose

The Main Railway Track Components

The distance between the two tracks on any railway route is known as railway gauge. The wooden or concrete supports for the rail tracks are known as a sleeper as British English or cross tie as American English.

Railway Gauge

Sleepers:

A sleeper is a rectangular support for the rail tracks. It is laid perpendicular to the rail sleepers and transfer loads to the track ballast and subgrade.

Sleepers hold the rails upright and keep them spaced to the correct gauge.

Sleeper

Railway Fastening System

Ballast:

Ballast is the name for the stones beneath the track. It forms the track bed upon which railroad sleepers are laid and is used to bear the load from the railroad ties to facilitate drainage of water and also to keep down vegetation that might interfere with the track structure.

Railway Ballast

The ballast also holds the track in place as trains roll over it and absorb the noise. It typically consists of a crushed stone rail fastening system. It is referred to as a group of railway fasteners that are used to fasten steel rail to railway sleeper.

Fish Plate:

Fish plate is used to join two different rail tracks without welding leaving some gaps at the joining of the track so that when they get heated it doesn’t bend. There are foor bolts that hold up the tracks together.

Fish Plate

Rail Track GAP

There is another type of fish plate called juggled fish plate. This is a specially designed fish plate with convexity in the center to accommodate weld collar at newly welded joints to protect defective welded joints and to carry out emergency repair of weld failures.

Joggled Fishplate