How to set up line and grade in sewer sanitary system construction

n order to place grade and line for developing the sanitary sewer system, four methods are mostly applied. One of these methods or combination thereby may be utilized in the construction. Given below, the detail information on these methods.

Methods of Setting Line and Grade in Construction of Sewer Sanitary System:

1. Stakes or crosses are set up on the surface on an offset from the centerline of sewer sanitary
2. Stakes are set in the bottom of the trench on the sanitary sewer line since the rough grade for the sanitary sewer is finished.
3. Elevations provided for the finished trench grade and sanitary sewer invert whereas sanitary sewer construction proceeds.
4. A laser beam of light set in the manhole or a particular height over sanitary sewer flow line.

1. Stakes or crosses set up on the surface on an offset from the centerline of sewer sanitary: In general, this method is very effective for small diameter sewer sanitary system. Substantially, crosses, stakes, or spikes are arranged at a consistent offset from sewer sanitary centerline.

The excavated soil material should remain at one side of the sewer sanitary trench and the stakes should be arranged at the other side.

If it is required to accomplish an accurate and reasonable job, there should be perfect sheet on which reference points of sanitary sewer stations, offset, and vertical distance from each reference point from projected sanitary sewer invert will have to be recorded.

Finally, the line and grade of sewer sanitary is transmitted to the bottom of the trench with tape and plumb bob unit or tape and level.

2. Stakes are set up in the bottom of the trench on the sanitary sewer line because the rough grade for the sanitary sewer is finished: This method is ideal for large diameter sanitary sewer as well as the sloped trench wall.

For the sloped trench wall, the top width of the trench should have been significantly wide, and the deployment of short offset would not be recommended.

Under this method, surface references are transmitted to the stakes which are arranged at the bottom of trench along sanitary sewer system.

When stakes are set up at the trench bottom, string line should have been drawn among at least three points. The string line should be examined by applying the same process for batter boards.

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Details of Cracking in Concrete

If cracks occur in concrete on regular basis, the appearance of the concrete becomes unpleasant as well as the structure of the concrete becomes feeble.

The cracking can be managed with reinforcement and joints. With foul cracking, the reinforcement is uncovered to air and moisture which may cause rust as well as reduce the strength.

Types of Cracks: Two types of cracks occur in reinforced concrete

Pre-Setting Cracks: It develops prior to solidification of concrete whereas it is still executable.

Hardened Cracking: Here, crack develops as soon as the concrete gets solidified.

Pre-Setting Cracks: Pre-setting cracks mainly develop at the time of placing, compaction and finishing resulting from movement of concrete prior to it gets dried.

The following types of pre-setting cracks mainly exist:

Plastic Settlement cracks
Plastic Shrinkage cracks
Cracks resulting from Movement of The Formwork.

When pre-setting cracks occur, examine them carefully so that they can be easily restrained whereas the concrete is still setting.

If these are identified at the initial stage, fixing is done easily with re-compacting, re-trowelling or re-floating the concrete surface.

Plastic Settlement Cracks: These types of cracks develop once the concrete is arranged, whereas it is still plastic. They become larger as concrete dries and shrinks and like to follow the lines of reinforcement.

Prevention
Re-vibrate the concrete.
Re-trowel the surface.

Search for cracks when the concrete is setting. At this stage, these can be easily settled.

Plastic Shrinkage Cracks: Usually cracking occurs in summer but it may also happen throughout winter. Plastic shrinkage cracks become visible in lines, roughly parallel or in a crazed haphazard way. They are generally 300–600 mm long but may be among 25 mm and 2 m in length.

Prevention: Moisten the subgrade and forms and safeguard concrete from the wind. Retain all materials cool on hot days.

Set, compact and cure in quickest possible time on hot days in order that concrete won’t dry out.

As soon as the concrete is condensed, screeded and floated, use a consistent spray film of EVAPORATIVE RETARDANT (Aliphatic Alcohol) to avoid quick loss of surface moisture, then continue with finishing.

It is recommended to set concrete at the cooler times of the day.

Repair Cracks is closed with alteration in the plastic concrete.

For more information, go through the following link onlinecivilforum.com



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Published By
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www.constructioncost.co
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Method of constructing post tension RCC slab

In this construction video tutorial, you will learn how post tension RCC slabs are built up as well as how post tensioning is performed and benefits of post tensioning process.

POST TENSION SLAB: It refers to the slab that is tensioned as soon as the slab is developed. Reinforcement is arranged to avoid the compression.

In Post tension slab, cables or steel tendons are utilized to substitute the reinforcement. Post-tensioning offers a solution to get rid of the natural weakness of concrete in tension as well as optimize its strength in compression.

In concrete structures, this is obtained by arranging high-tensile steel tendons/cables in the element prior to start the casting. If the concrete attains the required strength, the tendons are pulled with special hydraulic jacks and retained in tension with specially designed anchorages which are attached at each end of the tendon.

It creates compression at the edge of the structural member that increases the strength of the concrete for resisting tension stresses.

If tendons are correctly curved to a specific profile, they will exert, other than compression at the perimeter, a useful ascendant set of forces (load balancing forces) that will neutralize applied loads, alleviating the structure from a portion of gravity effects.

In this type of concrete slab, cables are affixed in place of reinforcement. In Steel reinforcement the gapping among bars is 4inch to 6inch while in Post tension slab the gapping is in excess of 2m.

Go through the following video tutorial, to get more details on post tension slab.

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Rajib Dey

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Benefits of raft foundation

Raft foundation stands for a type of foundation developed for the reinforced concrete slab having consistent thickness (150 mm to 300 mm) that expands over the large area particularly whole footprint of the building.

It provides support to the columns or walls and transmits the load from structure to large area of ground. Once it is built up, it seems mat of concrete extends over large area, as a result it is also known as mat foundation.

The slab bears the load of entire building and delivers it to ground, so it is assessed to float on ground similar way the raft floats on ground.

Raft Foundation is effective under the following situations :-

When the soil at site contains a low bearing strength, thus load required for being allocated over big area.

When it is ineffective to arrange individual or any other type of foundation. As for instance, when the strip foundation would encompass 50% or more area of building footprint, in such conditions raft foundation is very useful.

When there are chances for unnecessary settlement or differential settlement, when other type of foundation is arranged. In this way, settlement chances are minimized by setting up raft foundation.

When the soil situated below is unstable and might comprise of pockets of easily compressible soil, which may lead to individual footing failure. By arranging raft foundation, this risk is reduced.

If it is required to build up basement, raft foundation is necessary. It’s unreasonable and creates various issues if other types of foundation are arranged except for raft foundation at the time of providing basement. Raft foundation is very suitable for transmitting load and also functions as a floor for basement.

Why raft foundation is necessary if the bearing strength of soil is low?

Generally, it is found that if the soil contains low bearing strength, the raft foundation is arranged at site.

Benefits of raft foundation.

Raft foundation transmits the total load of the building to the soil below.

The deign of raft foundation is simple.
The total load on building (dead + live + other loads + self weight of building and foundation) is estimated.

This total load of building is divided with total area of foundation (i.e. footprint of building). It provides us stress on per sq.m of soil.

For raft foundation the load transfer area of footing is much more as compared to the other types of foundation, therefore, the stress on soil is much lesser, thus it can be avoided by soil having low bearing capacity. The risk of shear failure can also be resisted.

To get more information on raft foundation, go through the following link unsolvedengineering.co.in



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Published By
Rajib Dey
www.constructioncost.co
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How to calculate the height of an object on the basis of given angle & distance

By watching this construction video tutorial, you will be able to work out the height of any object on the basis of angle and distance provided. It is very useful for surveyors.

In brief, the height of an object is determined by calculating the distance from the object and the angle of elevation of the top of the object.

The tangent of the angle refers to the object height that is divided by the distance from the object. In this way, the height is obtained.

The calculation is made on the basis of the following formula :-

SinØ = P/H = Perpendicular/Hypotenuse

CosØ = B/H = Base/Hypotenuse

TanØ = P/B = Perpendicular/Base

Suppose, in a triangle, the angle is taken as 45 degree. The opposite of the angle should be always taken as perpendicular and opposite site of the perpendicular should be taken as hypotenuse. The horizontal line is taken as base and it’s measurement is 10 meter.

Now, all the values should be put on the above formulas to check which one is matched to determine the height. Watch the following video tutorial to learn the remaining calculation process.

To get more information, go through the following video tutorial.

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How to use kani’s method for making analysis of continuous beam

In this construction video tutorial, the renowned civil engineer, Mr. Parag Pal, has briefly explained how kanis method is used to continuous beam that contains fixed ends, to evaluate the beam and obtain the final moments.

The continuous beam comprises of the point load and the UDL load.

This method was developed by Dr. Gasper Kani of Germany in 1947.

The method provides a iterative scheme for employing slope deflection method. It is mostly recognized for frame analysis.

It comprises allotting the unidentified fixed end moments of structural members to adjoining joints, with the purpose of meeting the conditions of continuity of slopes and displacements.

Benefits:

1. Kani’s method circulates the total joint moment at any phase of iteration.

2. The more crucial feature of Kani’s method is that it is self reformative. If any fault occurs at any phase of iteration, amendment is made in consequent steps.

Framed structures are seldom symmetric and dependent on side sway, therefore Kani’s method is considered as greatest and much easier as compared to other methods like moment distribution method and slope displacement method.

To get more information on kani’s method, go through the following video tutorial.

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www.constructioncost.co
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Different types of beam section in RCC structures

In this construction video tutorial, you will gather information on different types of beam section in RCC structures. Usually, there are three types of beam sections which range from balanced beam section , under reinforced beam section and over reinforced beam section.

It is known that a beam comprises of two components i.e. reinforcement and concrete.

Balanced Beam Section: If the ratio of steel to concrete in a section prevails in such a manner that the strain in steel and strain in concrete attain their maximum values all at once, the section is identified as a balanced or critical section and the percentage of steel in this section is defined as critical steel percentage.

Under-Reinforced Beam Section: Under-reinforced section: A section that contains steel percentage below the critical percentage is called as under-reinforced section. As steel lacks to adjust compression in concrete, the tensile strain in steel attains yield value whereas the highest compressive strain in concrete is under its ultimate crushing value.

The section undertakes large rotational deformations from the preliminary phase of yielding of steel to the final stage of crushing of concrete, providing adequate warning of impending failure.

Given below, an extensive lists of different types of basic geometry formulas :-

Yielding of steel in under-reinforced beam section does not signify that the structure has failed, because if steel yields, extreme deflection and cracking in beam will happen prior to failure which provides sufficient time to occupants to escape ahead of the section fails.

The failure in under-reinforced beam section occurs as the concrete attains its ultimate failure strain of 0.0035 prior to steel attains its failure strain which is greater than 0.20 to 0.25.

Over-Reinforced Beam Sections: Reinforced concrete beam sections, in which the failure strain in concrete is attained sooner than the yield strain of steel is obtained, are known as over-reinforced beam sections.

If over-reinforced beam is designed and loaded to complete strength then the steel in tension zone will not yield much prior to the concrete attains its ultimate strain of 0.0035. It happens because of little yielding of steel, the deflection and cracking of beam does not happen and provide enough warning prior to failure.

Failures in over-reinforced sections happen suddenly. This type of design is not approved in practice of beam design.

To get more in-depth information, go through the following video tutorial.

Video Source: Tutorials Tips

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Rajib Dey
www.constructioncost.co
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