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Friday, April 19, 2019

Detail quality control methods in construction works

This civil engineering article sheds light on the inspection method of various civil works as well as necessary documents to carry out an inspection at construction project.

Civil Inspection: Purpose - It is conducted to verify that the civil construction activities accomplished on the construction projects adhere to relevant codes, standards, specifications and drawings.

Scope: The method will involve general inspection standards in relation to safety, survey control, soils inspection, reinforcing steel inspection, concrete inspection, grouting inspection, structural steel inspection.

Construction activities and consequent inspection standard should be based on job site specifications, methods and drawings. As a replacement for jobsite specifications or where referenced with jobsite specifications, national codes and standards should be employed.

Responsibility: Normally, the Main contractor and subcontractors should take the liability to make sure that construction activities are executed compliant with suitable specifications, procedures, drawings, codes and standards.

The contractor is empowered to execute whatever inspections and tests are assumed necessary to make sure that construction activities are accomplished as per job requirements and/or to involve sub-contractors and/or testing agency personnel to conduct these inspections and tests. Contractor is also empowered to evaluate the qualifications of all subcontractor and/or testing agency personnel doing inspections and/or tests, and substitute that personnel if their qualifications do not deem fit for the inspections and tests being executable.

Reference Documents: Given below, a incomplete list of reference documents which are suitable in applying this procedure.

• International standards
• Local Authority codes & specifications.
• Specifications of the project

Safety: Every employee should take the liability for his or her personal safety as well as for others. Each employee should be well versed with the perfect for his or her work. Employees must abide by the personal responsibility for cooperating and conforming to all HSE policies and methods. Before starting the work, all employees must evaluate and gather knowledge on of all relevant safety methods provided in the Construction HSE Policies and Procedures Manual.

Survey Control: Normally, it should be the liability of the main contractor’s/ subcontractors to provide his own survey crew as well as set up survey control for the persistent construction depending on the previously settled control monuments. The contractor should set up and sustain survey control to the precision necessary to satisfy the industry and job site standards and requirements. The contractor may hire a separate survey company instead of employing in house personnel, but may not employ the same survey crew and/or company presently appointed by others in similar project.

Soils Inspection: Earthwork construction works should done as per job site specifications, methods and drawings. Soils inspection should be done by qualified personnel who will ensure that requirements of the specifications, procedures and drawings are fulfilled.

Reinforcing Steel Inspection: Reinforcing steel should be acquired, preserved and managed compliant with procedures of Receipt, Storage and Handling of Products. As part of the receipt inspection, mill test reports should be examined against the exact ASTM standards and fabricated bars should be arbitrarily verified against the bar lists for compliance. Any nonconforming items shall be treated according to procedures.

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Detail quality control methods in construction works

Published By
Rajib Dey

Thursday, April 18, 2019

Process of tension test on steel

Tension test is conducted on mild steel, tor steel and high tensile steel to find out different characteristics like Young’s modulus, ultimate strength, and the percentage elongation. Under this type of test, a steel rod is susceptible to tension load with the use of a Universal testing machine(UTM).

The following equipments are used for conducting Tension Test on Steel:

1. Universal Testing Machine(UTM)
2. Extensometer
3. Scale Vernier Calipers
4. Punching tools

Method for Tension Test on Steel Rod

1. Arrangement of Specimen: In the beginning, the steel rod specimen is cleaned and gauge length is marked on it. The gauge length is measured with the formula Gauge length formula. A punching tool is used to mark the gauge length on the specimen.

2. Range Calculation: A tensile stress value is presumed, based on which the maximum predictable load strength of the rod is worked out. After obtaining the load strength, the range is measured and this range is placed in the UTM.

Assuming working stress = 140N/mm2
Factor of safety = 3.
i.e Ultimate stress = 140×3 = 420N/mm2.
Ultimate load = 420 x area of c\s.

Out of this ultimate load, applicable range should be determined.

3. Positioning the Specimen: The handle is operated in order that the specimen tightly sets to the top base. The left valve is retained in a fully closed position and the right valve in a normal open position. Open the right valve and close it after the lower table is lifted a little. Correct the load pointer to zero with the zero adjusting knobs. By operating the handle, raise the lower crosshead chuck up and tightly grip the lower part of the specimen. As soon as the specimen is arranged, the jaws are locked.

4. Placing Extensometer: Set the extensometer on the specimen as well as the reading to zero.

5. Load Application: Revolve the right control valve slowly to open position to obtain the required loading rate. When the specimen is under load, gradually unclamp the locking handle. Record the extension at an agreeable load increment. Extensometer should be eliminated prior to attain the yield point. The proper valve should be utilized to employ the load and the left valve should be utilized to deliver the load on the specimen.

6. Vital Load Points: With the surge in load at some point, the load pointer remains stationary. Based on this, the load points to the yield point. With further surge in load, the pointer goes backward and specimen ruptures. The load prior to this breaking refers to the ultimate load. The load at the breaking of the specimen is known as the breaking load.

Process of tension test on steel

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Rajib Dey

Wednesday, April 17, 2019

Types of rollers and their functionalities

Rollers are mainly utilized for the compaction of soil, gravel, sand, crushed stone layers, etc. The functionality of roller is primarily dependent on vibration, impact loading, kneading as well as direct pressure on the relevant layer. The following types of rollers are mostly recognized:

1. Vibratory Roller 2. Tamping roller/ sheep foot rolle 3. Smooth wheel rollers 4. Pneumatic tired roller

VIBRATORY ROLLER: Vibratory type rollers comprise of two smooth wheels/ drums along with the vibrators. One is set at the front and the other one is on the back side of vibratory roller. Both wheels/drums have equivalent diameter, length and weight. Vibratory roller covers the entire area under wheel.

To improve the functionality of vibratory roller, vibrators are also set with smooth wheel rollers. Vibration of vibrators places the particles by initially distressing even the arranged ones. Conversely, the weight of wheels employs direct pressure on the layer. Vibrators are deactivated throughout the reversed motion of roller meanwhile only static weight directly operates on the soil layer.

Vibration facilitates decreasing the air voids as well as inducing condensation of granular soils. In the vibration process of soil layer, the particles are reorganized for deformation of the granular soil caused by oscillation of the roller in a cycle.

SHEEP FOOT ROLLER/ TAMPING ROLLER: Sheep foot roller also known as tamping roller. Front steel drum of sheep foot roller contains several rectangular shaped boots having same size which are settled in a hexagonal pattern.

Coverage area of sheep foot roller remains less i.e., about 8- 12% due to the boots on drums. Sheep foot roller executes compaction with static weight and kneading of relevant layer. It prepares tamping roller suitable for clay soils. Contact pressure of sheep foot roller differs from 1200- 7000Kpa.

Tamping foot roller comprises of four wheels and on each wheel kneading boots/feet are settled. There are more coverage area for tamping roller i.e., about 40- 50%. Contact pressure of tamping roller differs from 1400 – 8500KPa. It is ideal for fine grained soils.

SMOOTH WHEEL ROLLER: Both smooth wheel roller and vibratory rollers are similar. Both contain similar properties. The variation lies with vibratory equipment. Smooth wheel roller does not include any vibrator secured with the drum. In this way, smooth wheel roller becomes perfect for rolling of weaker aggregates, proof rolling of subgrades and in compacting asphalt pavements. Compaction of clay or sand is not recommended for smooth wheel roller sine there are several empty voids in clay soil and sand, which cannot be reduced without vibrators.

PNEUMATIC TIRED ROLLER: Pneumatic tired roller contains a number of rubber tires at the front and at the rear end. Empty spaces exist among the two tires which produce 80% coverage area under the wheels. Pneumatic roller is capable of employing contact pressure ranges from 500 – 700Kpa. Pneumatic tired roller is effective for highways, construction of dams and for both fine grained and non-cohesive soils. It can also be applied for flattening of finishing bitumen layer on highways, roads, streets etc.

Types of rollers and their functionalities

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Rajib Dey

Tuesday, April 16, 2019

Some vital factors of building foundation system

The foundation stands for a supporting member of the structure. The purpose of the foundation is to deliver all loads from the walls or columns of the building to the Earth. A foundation is the part of the building that touches the ground directly.

The foundation mainly retains the structure up in order that it never goes down in the supporting ground. Foundation retains the structure so it is not swept away with strong winds like tornadoes. The foundation selection is based on the structural system and the nature of the structure.

The foundation of the structure should be secured from the following factors :

a. Sliding
b. Overturning
c. Sinking or settlement
d. Differential settlement

The foundation systems should satisfy the following vital requirements:-

1. The primary requirement for any structure concerning its load resisting strength is that the structure should be built up in such a manner that the combined dead loads, live loads, horizontal loads like earthquake and wind load are defended, passed and transferred to the ground securely in spite of providing any any structural damage, deflection and distortion.

2. Foundation should be pushed deep into the ground in order that the structure is not influenced with ground movement like swelling, shrinking, freezing. The landslide also should not impact the strength of the building. The structure should be secured from any damage and distress.

3. Foundation base should be inflexible with the purpose of reducing the differential settlement, specifically in a situation when superimposed loads are not consistently dispersed over the foundation.

4. Foundation should be situated in such a manner that its performance remains unchanged because of any unanticipated future forces like earthquake and overloading.

5. The design of the foundations is created to withstand the ultimate loading cases combination against overturning and sliding.

6. Foundation should protect from chemical attack in soil. Groundwater and soil may include several types of chemicals injurious to the foundation concrete, the most aggressive one is sulphates. Sulphate attack can normally be alleviated with sulphate resisting cement. Still proper precaution should be at the time of placing the concrete, by vibrating and curing.

7. Foundation should be taken deep enough to withstand the overturning, despite the fact that the bearing strength of the soil is good at adequate depth. Due to adequate depth, swelling can’t occur.

Some vital factors of building foundation system

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Published By
Rajib Dey

Saturday, April 13, 2019

Different grades of Ordinary Portland cement

Ordinary Portland Cement(OPC) is extensively utilized in the construction sectors as primary component for developing concrete, mortar, stucco, and non-specialty grouts. Ordinary Portland Cement is graded on the basis of its strength. The grade specifies the compressive strength of the mortar cube that will be achieved once 28 days of setting is completed.

Grades of Ordinary Portland Cement - The following grades of OPC are available:

1. OPC 33 Grade Cement: This grade of cement is suited for general construction under normal ecological condition.

Compressive Strength of OPC 33 – The average compressive strength of minimum three mortar cubes with a face area of 50 is considered at the time of verifying the compressive strength. These mortar cubes comprise of one part of cement and three parts of standard sand.

Compressive Strength of OPC 33:

a) 72 +/- 1 hour = Not under 16 N/mm2
b) 168 +/- 2 hours = Not under 22 N/mm2
c) 672 +/- 4 hours = Not under 33 N/mm2
IS Code – IS 269 : 1989 for Ordinary Portland Cement, 33 Grade.
2. OPC 43 Grade Cement: Now-a-days, this grade of cement is gaining popularity in the construction sectors. OPC 43 is suitable for general RCC construction where the grade of concrete is up to M30. It can also be applied for the construction of various precast items like blocks, tiles, asbestos products like sheets and pipes, and for non-structural works like plastering, flooring etc.
Compressive Strength of OPC 43:
a) 72 +/- 1 hour = Not under 23 N/mm2
b) 168 +/- 2 hours = Not under 33 N/mm2
c) 672 +/- 4 hours = Not under 43 N/mm2
IS Code – IS 8112: 1989 for 43 Grade Ordinary Portland Cement.
3. OPC 53 Grade Cement: OPC 53 is useful while requiring concrete with greater strength at very reasonable cement content. OPC 53 facilitates 8 to 10% saving of cement in concrete mix design, for concrete M20 and over.
This cement grade is very effective for specialized works like pre-stressed concrete components, several precast items like paving blocks, building blocks etc, runways, concrete roads, bridges, and other RCC works where the grade of concrete remains M25 and over.
Compressive Strength of OPC 53:
a) 72 +/- 1 hour = Not under 27 N/mm2
b) 168 +/- 2 hours = Not under 37 N/mm2
c) 672 +/- 4 hours = Not under 53 N/mm2
IS Code – IS 12269 : 1987 for Specification for 53 grade ordinary portland cement.
Different grades of Ordinary Portland cement

Published By
Rajib Dey

Friday, April 12, 2019

Definition of shear reinforcement and it’s type

Shear Reinforcement means reinforcement that is designed to withstand shear or diagonal tension stresses. Shear reinforcement is generally arranged in the form of stirrups to retain the longitudinal reinforcement as well as capture the shear to which the structure is exposed to.
TYPES OF SHEAR REINFORCEMENT - Described below, common types of shear reinforcement:
1. Vertical stirrups.
2. Bent up bars along with stirrups.
3. Inclined stirrups.
Vertical Stirrups: These belong to the steel bars arranged vertically around the tensile reinforcement at proper distance along the length of the beam. Their diameter differs from 6 mm to 16 mm.
The free ends of the stirrups are fastened in the compression zone of the beam to the anchor bars (hanger bar) or the compressive reinforcement. Based on the magnitude of the shear force to be defended the vertical stirrups may come as one legged, two legged, four legged and so on.
It is recommended to utilize narrowly spanned stirrups to get rid of the diagonal cracks in a better manner. The distance of stirrups adjacent to the supports is less relating to the distance close to the mid-span as shear force remains extreme at the supports.
Bent up Bars along with Vertical Stirrups: Some of the longitudinal bars in a beam are bent up adjacent to the supports where it is unnecessary to use them for withstanding bending moment as bending moment remains very less adjacent to the supports. These bent up bars defend against diagonal tension. Equal numbers of bars should be bent on both sides to maintain consistency. The bars are bent up at more than one point evenly along the length of the beam.
These bars are normally bent at 45º.
This system is very effective for higher shear forces. The total shear resistance of the beam is measured with the inclusion of the bent up bars and vertical stirrups.
The provision of bent up bars should not be in excess of half of the total shear reinforcement.
Inclined Stirrups: Normally, inclined stirrups are arranged at 45º for countering diagonal tension. They are arranged all through the length of the beam.
Definition of shear reinforcement and it’s type

Published By
Rajib Dey

Thursday, April 11, 2019

Some vital guidelines to build up a raft foundation

A raft foundation alias mat foundation refers to a continuous slab that stands on the soil that expands over the whole footprint of the building, thus provides strong support to the building as well as transmits its weight to the ground.
A raft foundation is mostly suitable when the soil becomes weak, since it allows to allocate the weight of the building over the whole area of the building, and not over shorter zones (like individual footings) or at individual points (like pile foundations). It minimizes the stress on the soil.
Stress is merely the weight divided with area. As for instance, when a building measures 5 x 5 weighs 50 tons, and contains a raft foundation, then the stress on the soil is weight / area = 50/25 = 2 tons per square meter.
When the similar building is supported by 4 individual footings with dimension 1 x 1m each, then the entire area of the foundation should be 4 m2, and the stress on the soil should be 50/16, that is around 12.5 tons per square meter. Therefore, if the entire area of the foundation is raised, the stress on the soil is significantly reduced, that means the weight per square meter.
A raft foundation is also effective for basements. Foundations are built up with excavation of soil with the purpose of retaining strong, compact, undisturbed natural soil that remains a few feet underneath ground level.
This soil contains more strength as compared to the loose soil at the surface. When a raft foundation is built up 10 feet under ground, and the concrete walls remain around the boundary to form a sound basement.
Initially, excavate the ground to consistent, flat level to build up a raft foundation.
After that, place a waterproof plastic sheet over the earth, and pour a thin 3" layer of plain cement concrete (PCC) to form a rightly flat and level base for the foundation.
Then, a waterproofing layer is set up, and then reinforcement steel for the raft slab is secured in place. Once all the steel are arranged in exact location, concrete is poured to the required thickness that normally remains in the range of 200mm (8") to 300mm (12") thick for small buildings. The thickness will be increased when it is required to combat heavy loads.
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Some vital guidelines to build up a raft foundation

Published By
Rajib Dey