Commonly used joints in sewer pipes

The following types of sewer joints are generally found :-

1. Bell and Spigot Joints.
2. Collar Joints.
3. Flexible Joint.
4. Expansion Joint.
5. Flanged Joint.

Bell and Spigot joints: This joint is also termed as socket and spigot joint. This type of joint is mostly found in cast iron pipes containing different sizes and concrete pipes under 60 cm in diameter.

The pipes which should be attached with this joint are built up in such a manner that one end is expanded and the other end is normal. The expanded end is defined as socket or bell and the normal end is spigot. The spigot end is placed into the bell end and the void of the joint is stuffed with molten lead or bitumen or cement mortar.

Collar joints: In this type of joint, the ends of sewer are plain.

Prior to attach, the pipes are carried face to face at the equivalent level and a collar of marginally larger diameter is arranged over the joint. Then the annular gap among the pipes and the collar is stuffed with cement mortar (1:1). The collar joints are utilized for sewers of big diameter.

Flexible joint: This joint is utilized at such areas where settlement is subject to happen as soon as the pipe is arranged. With this type of joint, one pipe contains spigot end and other pipe contains socket end. The spigot is set up into the socket and the annular space developed among the socket and spigot is stuffed with bitumen.

Expansion joint: This joint is adopted at places where pipes expands or contracts due to variation in atmospheric temperature. Here the socket end is cast flanged and the spigot end is plain. A flanged ring and a rubber gasket are arranged in place on the spigot end. Then the spigot end is entered into the socket end nut and bolts are secured.

Flanged joint: This joint is frequently utilized for temporary work. The pipe applied in this type of joint contains flanges on both ends. At the time of joining the pipes, a rubber gasket is entered among the flanges and nut bolts are secured.

To get more information, go through the following link

Commonly used joints in sewer pipes

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Arka Roy


Impact of impurities in water on concrete properties

If the water applied for concrete preparation contain impurities, the properties of concrete is influenced in the following manner:

a) The strength & longevity of concrete is decreased because of the existence of the impurities in the mixing water. It is found that water with extreme amount of dissolved salts weakens the compressive strength by 10 to 30% as compared to potable water.
b) The setting time of cement is modified. Existence of Zinc chlorides delays the setting of concrete to significantly so that no strength test can be done at 2 and 3 days.Contrary, the existence of calcium chloride speeds up the setting and hardening.
c) Existence of extreme chlorides leads to dampness, surface efflorescence & raise the corrosion of reinforcing steel.
d) Existence of algae in water decreases the bond among aggregate & comet paste & as a result the strength of concrete is reduced significantly.

e) Existence of sugar up to 0.15% by weight of cement delays the setting of cement and the early strength is decreased. When the quantity of sugar is raised to 0.2% by weight of cement ,setting is expedited.
f) The existence of vegetable oils provides detrimental effect on the concrete strength, specifically at later ages.

Name of Impurities – Allowable limit
1.Organic matter – 200 mg/lit
2.Inorganic matter – 3000 mg/lit
3.Sulfates ( as SO2 ) – 400 mg/lit
4.Chlorides (as Cl)
a) For plain concrete – 2000 mg/lit
b) For R. C. C. – 500 mg/lit
5.Suspended matter – 2000 mg/lit

Impact of impurities in water on concrete properties

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Arka Roy

Bar Bending Schedule For Floor Slabs

Bar bending schedule is an important structural working document that rightly gives the disposition, bending shape, total length, and quantity of all the reinforcements that have been provided in a structural drawing.

It is often provided in a separate sheet (usually A4 paper) from the structural drawing.

The bar marks from structural detailing drawing are directly transferred to the bar bending schedule. We normally quantify reinforcements based on their total mass in tonnes or kilograms. For smaller projects, you can quantify based on the length needed.

Unit mass of rebars

The unit mass of the reinforcements is obtained from the density of steel. The density of steel provided for this purpose is 7850 kg/m3.

Suppose, there is a bar with 12mm dia;

The area is calculated by (πd2)/4 = (π × 122)/4 = 113.097mm2 = 0.0001131m2

Based on a unit length of the bar, it is established that the volume of a metre length of the bar is 0.0001131m3.

Density = Mass/Volume = 7850 kg/m3 = Mass/0.0001131

So, the unit mass of 12mm bar = 7850 × 0.0001131 = 0.888 kg/m

So, for any diameter of bar;

Basic weight = 0.00785 kg/mm2 per metre

Weight per metre = 0.006165 ϕ2 kg

Weight per mm2 at spacing s(mm) = 6.165ϕ2/s kg

ϕ denotes diameter of bar in millimetres
Bending Shapes
There exist some basic standard shapes with specific shape codes in the code of practice.
The length of reinforcement bars can be determined with the following relation;

Length of bar = Effective Length + Width of Support – Concrete cover (s) – Tolerances
The standard values of tolerances (deductions) are provided in the table below;

To get more details, go through the following link

Bar Bending Schedule For Floor Slabs

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Arka Roy

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.

Video Source: F&U-FORYOU

Method of constructing post tension RCC slab

Published By
Arka Roy

How soil cement is used in earthfill dams & embankments

Now-a-days soil cement as a facing material for earthfill dams is considered very cost-effective where proper riprap is unavailable near the site.

A fairly rigid foundation is suitable in order that deformation after disposition of soil-cement is not vital; however, no uncommon design features should be integrated into the embankment.

Normal embankment construction methods are followed, with perhaps proper precaution to make sure a minimum of embankment consolidation and foundation settlement once the construction is completed.

The soil-cement is normally arranged and compacted in stair-step horizontal layers. It provides greater construction efficiency and operational potency. With standard embankment slopes of 2:1 and 4:1, a horizontal layer with 8 feet width will set least protective thicknesses of about 2 and 3l/2 feet correspondingly, measured normal to the slope.

It starts at the lowest layer of soil-cement, each subsequent layer is stepped back a distance equivalent to the product of the compacted layer thickness in feet times the embankment slope.

As for instance, if the compacted thickness is 6 inches and the slope is 2:1, the step back is = 0.5(2) = 1 foot. The normal compacted layer thickness is 6 inches. Soil-cement layers of this dimension is positioned efficiently and compressed with standard highway equipment.

A plating system that develops a single soil-cement layer parallel to the slope is often applied in less critical areas for slope protection. If the soil-cement facing does not start at natural ground level, the lower part of the embankment should remain on a flatter slope than the part safeguarded by the soil-cement; or a beam is arranged at the lowest elevation of the facing. It is necessary that the soil-cement expand underneath the minimum water level and over the maximum water level.

The top of the facing should contain a freeboard allowance of minimum 1.2 times the projected maximum wave height, or 5 feet, whichever is higher. The edges of the finished soil-cement layers should not be cropped since the rounded starstep effect allows retard wave runup. Soil-cement is produced with different types of soils.

The main standard for finding out the soil type is gradation. Coarse sandy or gravelly soils having about 10 to 25 percent material passing the No.200 sieve are perfect (American Society for Testing and Materials Standard Sieve Series). These soils are sufficiently stabilized with from 3 to 5 sacks of cement per cubic yard of compacted soil cement.

Standard compaction and placement control for soil-cement is recommended. If the amount of material smaller than the No.200 sieve surpasses 35 percent, some effort to determine a coarse material is appropriate from a processing cost standpoint. Soils with 50 percent or more material passing the No.200 sieve are not suggested for being applied in their natural state.

To get more details, go through the following link

How soil cement is used in earthfill dams & embankments

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Arka Roy

Segregation of concrete – Causes and Remedies

Segregation means the partition of course materials (cement, sand, aggregates) from other mass. When the water quantity in the concrete mix is increased, the greater sized aggregates are detached thus results in segregation.

Therefore, concrete should be free from segregation as concrete not only gets weak but lack of consistency also brings unwanted properties in the hardened state. The segregation can be avoided with the choice of proper grading and careful handling.

Reasons for segregation :

Carrying concrete mixes for long distance.

Imperfectly proportioned mix where adequate matrix does not exist to unite the aggregates.

Dropping concrete from height places (underground foundation & rafts).

Vibrating concrete for long time.

Segregation is available in two types – Initially (in too dry mixes), the coarse aggregate is segregated or settling down from the rest of the matrix, secondly ( in too wet mixes ), the paste or matrix is detached away from coarse aggregate. In case of segregation, remixing for a short time may transform concrete again homogeneous.

The following precautions should be taken to get rid of concrete segregation :-

The concrete mix should be perfectly designed with best possible quantity of water i.e. not too wet nor too dry.

The proportion of the mix should be correct.

Ensure the concrete is mixed perfectly at the proper speed in a transit mixture for minimum two minutes.

Concrete should not become excessively wet or dry.

Refrain from arranging concrete from long height.

There should be proper transportation of concrete through shortest route.

Air entraining admixture and pozzolanic materials should be used in mix.

Select coarse and fine aggregate with approach specific gravity.

The vibrator should be used for exact time period (not too long or short).

Don’t permit concrete to flow.

The formwork should be firm.

The formwork should not be vibrated.

Video Source: Civil Engineers

Segregation of concrete – Causes and Remedies

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Arka Roy

Bridge pile cap construction details

This construction video is based on pile cap construction process for building up a bridge. The video is specifically designed for bridge engineer.

The video throws light on the following topics :-

a. Pile Head Breaking
b. Granular laying
c. CC work
d. Rebar Fabrication

The construction method of bridge is segregated into two parts :-

Substructure (pile foundation, pile cap, pier, pier cap)

Superstructure (bearing, girder, slab)

Definition of pile cap: It belongs to a structural member that is positioned and generally attached on the top of a pile or a group of pier to transfer the loads into the pile or group of piles to relate them into a bent.

Functions of pile cap
To disperse a single load evenly over the pile group as well as over a larger area of bearing potential.

To laterally strengthen separate piles and enhance complete durability of the group.
To arrange the required combined resistance to stress organized by the super structure and ground movement.
To transfer the loads of the building to the foundations and the ground soil layers despite the loads are vertical or inclined.
To facilitate the column or superstructure to stay on a consistent and solid core foundation rather than staying directly on ground.

To learn the detail pile cap construction process for a bridge, go through the following video tutorial.

Video Source: Construction Methodology

Bridge pile cap construction details

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Arka Roy

Pundit Lab – Ultrasonic Pulse Velocity Tester

To check the quality and strength of in-situ concrete in structural members, ultrasonic pulse velocity test is most recommended.

It is applied for the following purposes :-

The uniformity of a material

The existence of voids, cracks or other inner flaws or defects.

Changes in the concrete in due course because of the cement hydration, damage from fire, frost or chemical attach.

The durability or modulus of a material.

The quality of the concrete with regard to specified standard requirements.

It comprises of a pair of transducers (probes) with various frequencies, electrical pulse generator, electrical timing devices and cables.

It is supported with the through-transmission method. It comes with size 180 x 110 x 160 mm. It’s weight is 3 Kg.

Digital display with precision +_0.1 microseconds.

The following testing method is used with the machine :-

Direct transmission

Pulse velocity is estimated in concrete with the arrangement of transducers across the member perfectly opposite to each other.

This method is considered as most perfect & authentic to determine the quality & strength of concrete. If there does not exist any other method, then this method will be suitable.

Semi Direct Transmission

Pulse velocity is estimated in concrete with the arrangement of transducers in planes perpendicular to each other.

This method is not so authentic to determine the quality/strength of concrete.

Process for estimation of pulse velocity :-

Velocity = (Distance travelled/path length)/Time taken

Pulse velocity in concrete will be demonstrated with Km/sec.

Proper correction factors should be used on the basis of site condition & factors which impact the velocity of pulse.

Pundit Lab - Ultrasonic Pulse Velocity Tester

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Arka Roy

How beams are categorized on the basis of different factors

In structural engineering, various structural members are titled on the basis of their behavior under applied load. If the primary mode of delivering the load occurs due to bending then the structural member is known as beam. It can be also said that a beam belongs to a structural component that has the ability to resist load initially by making resistance against bending.

Beams usually bear vertical gravitational forces but can also be applied for bearing horizontal loads (e.g., loads originate because of an earthquake or wind). The loads which beam bear are transmitted to columns, walls, or girders and which then transfer the force to the adjoining structural members and lastly to the ground.

Categorization of Beam: Beams are distinguished with their support condition, profile (shape of cross-section),geometry, equilibrium condition, and their material.

Categorization on the basis of supports: Categorization of beams on the basis of support condition is essential since the bending moment functioning on the beam is directly influenced by the support condition. The difference can be seen in the bending moment diagrams given below. For the equivalent length and loading the bending moment diagram fluctuates significantly with change in support condition.

Simply supported – Beams are supported on the ends which can rotate easily without any moment resistance.

Fixed – Beams are supported on both ends and constrained from rotation.

Over hanging – Simple beams which are expanded beyond its support on one end.

Double overhanging – Simple beams with both ends extending beyond its supports on both ends.

Continuous – Beams are expanded over in excess of two supports.

Cantilever – A projecting beam that is fixed only at one end.

Trussed – A beam is reinforced with the inclusion of a cable or rod to develop a truss.

Categorization on the basis of profile: The type and magnitude of internal stress created in the beam is directly reliant on the shape of the cross-section, thus categorization is necessary on the basis of profile.

Rectangular Beams: I-Beams, T-Beams, C-Beams, Other Cross-sections

Categorization on the basis of geometry: The type and magnitude of internal stress created in the beam is also directly reliant on the geometry of the beam, thus categorization is necessary on the basis of geometry.

Straight Beams, Curved Beams, Tapered Beams

Categorization based on indeterminacy: The design of beam is mainly created for bending moment and shear force. Assessment of these bending moments and shear force is called analysis. A beam is classified into following two categories on the basis of the type of analysis necessary to work out the reaction:

Statically determinate beams: equilibrium conditions tolerable to compute reactions.e.g. simply supported beams, cantilever beams, single and double overhanging beams etc.

Statically indeterminate beams: Deflections (Compatibility conditions) together with equilibrium equations should have been applied to determine the reactions.e.g. propped cantilever, continuous beams, fixed beams.

Categorization on the basis of the material: Various materials contain different advantages and drawbacks for being utilized as a building material for erecting the beams concerning cost and usage, as a result beams are also classified on the basis of the material used for their construction.

Concrete Beams, Steel Beams, Timber Beams

How beams are categorized on the basis of different factors

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Arka Roy

Fundamentals of Post-Tensioning Construction

Construction of post-tensioned slabs on grade is equivalent to applying reinforcing steel, with the exception of the tensioning step.

The placing of cables is done according to the suggestions provided by the engineer and managed to run through the center of the slab. For residential construction, tendons at 48 inches on center are mostly found.

There are huge amount of steel for commercial foundations. Tendons are routed around obstructions without difficulty.

A residential post-tensioned concrete slab will generally be available as 8 inches thick and made of 3000 psi concrete. Once the concrete has attained strength to 2000 psi, normally within the 3 to 10 days suggested by PTI, the tendons are stressed.

Tendons belong to seven high-strength steel wires which are cut jointly and arranged inside a plastic duct. At each end a PT anchor is situated and these are positioned in pockets which are implanted into the slab edge. If the strands are stressed, the wires will also stretch—about 4 inches for a 50 foot strand—to employ 33,000 pounds of load.

Stressing should only be performed with skilled workers. Once the stressing is completed, the tendon is cut off and the pocket in which the anchors are positioned is filled with grout to get rid of corrosion.

Larger structural concrete members are also post-tensioned, particularly in bridges and floors and beams in parking structures. The method is very user-friendly as compared to that utilized for slabs, apart from a bigger scale. The tendons will be “draped” frequently in order that they are low at the center of a beam and high at the supports—this settles the steel at the point of highest tension to retain the concrete kept together firmly.

By applying structural members the duct is frequently grouted entirely following stressing to tie the strand to the concrete along its complete length—these are known as bonded tendons. Unbonded tendons are mainly found in residential slabs and can freely move inside the duct and are safeguarded against corrosion with grease.

PT tendon placement and stressing is generally performed by companies with certified workers who have good skills in this work.

The benefits of PT that there is no cracking (or minimum very narrow cracks) and it has capacity to span additionally. PT slabs on ground can be arranged and stamped similar to any other concrete slab. Surfaces are stained or coated. It should be kept in mind that no cutting or drilling should be done to post-tensioned concrete slabs, because once a tendon is cut, it becomes complicated to repair. Many post-tensioned slabs are stamped to notify the owner and any renovation contractors to make sure that the slab is post tensioned.


Fundamentals of Post-Tensioning Construction

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Arka Roy