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Tuesday, July 16, 2019

Guidelines for making perfect structural design

This civil engineering article focuses on the least standards which should be maintained for the design of various RCC structural elements like the columns, beams, slab and foundation as well as the least safe standards for the reinforcing bars to be applied for making the design of the above mentioned structural elements.
Minimum cross-sectional dimension for a Column should be 9″x 12″ (225 MM x 300 MM). It is the minimum approved size.
It is always recommended to utilize M20 grade concrete for construction as per IS 456:2000. The least steel in a 9″ x 9″ column should be 4 bars of 12 MM with stirrups of 8 MM steel rings at a spacing of 150 MM centre to centre. In a 9″ x 12″ column, more bars (6 bars with 12 mm diameter) should be added to sustain the total efficiently.
Least RCC beam size should not be lower than 9″x 9″ (225MM X 225MM), with an supplementary slab thickness of 125 MM.
Normally, there should be minimum of 4 bars, with 2 bars having 12 MM thickness in the bottom of the beam, and 2 bars having 10 MM at the top of the beam.
A concrete cover of 40 MM should also be provided. It is suggested to utilize M20 grade of concrete (1 part cement : 1.5 parts sand : 3 parts aggregate : 0.5 parts water).
Minimum thickness of RCC slab should be 5″ (125MM) since a slab may comprise of electrical pipes which are implanted into them which could be 0.5″ or more for internal wiring and as a result the depth of slab is decreased at specific places that lead to cracking, weakening and water leakage throughout rains. Therefore, a least thickness of 5″ should be retained.
Minimum size of foundation for a single storey of G+1 building should be 1m x 1m, where safe bearing strength of soil is 30 tonnes per square meter, and the anticipated load on the column does not surpass 30 tonnes.
The depth of footing should be minimum 4′under ground level. It is suggested to get to depths up to had strata.
Minimum Reinforcing bar details:
1. Columns: 4 bars of 12mm steel rods FE 500.
2. Beams: 2 bars of 12 mm in the bottom and 2 bars of 10 mm on the top.
3. Slab
a) One Way Slab: Main Steel 8 MM bars @ 6″ C/C and Distribution Steel of 6 mm bars @ 6″ C/C
b) Two Way Slab: Main Steel 8 MM bars @ 5″ C/C and Distribution Steel of 8 mm bars @ 7″ C/C
4. Foundation: Initially, there should be 6″ of PCC layer. Over it, a tapered or rectangular footing with minimum 12″ thickness should be arranged. Steel mesh of 8 mm bars @ 6″ C/C should be placed. In a 1m X 1m footing, there should be 6 bars of 8 mm on both segments of the steel mesh.
Guidelines for making perfect structural design

Published By
Rajib Dey

Monday, July 15, 2019

Common thumb rules for civil engineering works

Thumb Rules is very important for any civil engineer, Site engineer or civil supervisor to obtain instant decisions on the construction site. By applying thumb, the engineers can get the solution with a simple mathematical formula and take proper decisions wherever required. Before applying these thumb rules, it should be kept in mind that the thumb rule can only provide fairly accurate results never the correct results.

The following types of thumb rules for civil engineers are commonly used in construction work :-

Thumb rule for measuring the Concrete Volume relating to the area:
The volume of concrete necessary = 0.038 m3/square feet area.

As for instance, if Plan Area = 40 x 20 = 800 Sq. m., total necessary volume of concrete will be as follow :-
= 800 x 0.038m3 = 30.4m3

Thumb rule for Steel quantity necessary for Slab, Beams, Footings & Columns:
Essential quantity of steel in residential buildings = 4.5 Kgs – 4.75 Kgs / Sq. Ft.
Essential quantity of steel in commercial buildings = 5.0 Kgs-5.50 Kgs/Sq. Ft.

Thumb Rules For Civil Engineers recommended by B N Datta for the Steel quantity that will be applied for several members of the building :-

Proportions of Steel in Structural Members:

1) Slab – 1% of the total volume of concrete
2) Beam – 2% of the total volume of concrete
3) Column – 2.5% of total volume of concrete
4) Footings – 0.8% of the total volume of concrete

As for instance, suppose the length, width and depth of the slab are 5m, 4m and 0.15m. Now, the quantity of steel for the slab will be computed as follow :-

Initially, it is required to work out the concrete volume.
The total volume of concrete for the slab = 5x4x0.15 = 3m3

Secondly, work out the quantity of steel with formula as follow :-
Based on the guidelines provided in B. N. Dutta reference book, the quantity of steel in slab is 1% of the total volume of concrete used.
Thumb rule to work out the quantity of steel in above slab = Volume of concrete x density of steel x % of steel member.

The weight of steel necessary for above slab = 3x7850x0.01 = 235 kgs

To make perfect calculation, use bar bending schedule.

To learn how thumb rules are applied to calculate the shuttering area and the quantity of cement, sand, course aggregate in several grades of concrete, click on the following link

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Common thumb rules for civil engineering works

Published By
Rajib Dey

Saturday, July 13, 2019

Inspection & Testing Method of concrete

This civil engineering article focuses on the test method required for evaluating the concrete work.
Concrete construction activities should be done on the basis of the job site specifications, methods and drawings. Concrete inspection and testing should be executed by experienced personnel to ensure that requirements of the specifications, methods and drawings are satisfied.
Tests of concrete is conducted to make sure that the compliance to specifications should be performed by a certified Concrete Field Testing Technician.
If not mentioned anywhere else in the specifications and/or drawings, at least six concrete cubes should be developed and treated as a set. If not mentioned anywhere else, the cubes will be tested in the following ways :-
2 cubes at 7 days
2 at 28 days
2 held in reserve
The results obtained from the test, should be noted on a spreadsheet and in a way conformable to QC procedure: Statistical Techniques.
Unless stated otherwise in plan specifications or drawings, one set of cube should be created for each 150 cubic yards of concrete laid as defined in building codes. Minimum one set of cubes should be formed on each day concrete is laid irrespective of the quantity of concrete.
Application of QC procedures: Process Control as a guide, Contractor should fix a meeting with the subcontractor before pouring the first concrete. This meeting will be conducted so that the subcontractor can narrate his/her plans for the concrete pour along with all the areas scheduled in this section of the procedure.
Batch Plant Inspection: Contractor retains the power to examine any and all concrete batch plants which will deliver concrete to the construction site. A “walk through” inspection should be carried out before the production of concrete is started.
If it is required, examinations can be done throughout concrete production. Given below, the major inspection items for every type of batch plant inspection:
Preliminary Inspection
• Check that aggregates are loaded in exact bins
• Examine that aggregates are not polluted
• Examine that scales and measuring devices contain current calibration stickers and seem to function perfectly
• Examine that the plant contains a current local authority approval certification
• Examine that concrete trucks remain in proper working condition
• Examine that entire operation of the plant seems to be professional, systematic, relatively clean, well maintained, etc.
• Examine that batch plant operators should have adequate knowledge (verify their certificates or certifications)
• Examine that batch tickets provide crucial information (amount of hold back water, list of ingredients, batch times, size of load, indication of mix ordered, etc.)
• Examine that the plant and delivery equipment can form homogeneous concrete as per the requirements of ASTM C-94
• Make sure that the plant and delivery equipment satisfy the capacity requirements of the job
Throughout Concrete Production (if necessary):
• Examine that correct mix has been loaded into the batch plant computer
• Examine that equipment is working properly (admixture dispensers, scales, moisture indicators, etc.)
• Examine that truck counters have been reset to zero once the mixing water has been added to the mix
• Examine that water used to “wash down” the concrete truck prior to leaving the plant area does not enter the concrete mix
• Examine that the amount of hold back water is stated on the batch ticket
• Make sure that the concrete coming out from the plant will satisfy the specifications for temperature, air content and slump (testing at the plant should be conducted if required)
Concrete Mix Design: All proposed concrete mixes should be provided to Consultants via main contractor for verification and approval before application. The projected mixes delivered for use shall comprise of a concrete strength break history as stated in ASTM and shall include suitable test results and/or certificates of conformance on all constituents which will be applied in the certain concrete mixes.
Inspection & Testing Method of concrete

Published By
Rajib Dey

Friday, July 12, 2019

Sample quotation for constructing an indoor badminton court

In this civil engineering article, you will get a sample quotation with quantities of construction material to design and develop an indoor badminton court.
• The structure should contain a basement height of 1’0” from Natural ground level.
• Footing pit size 4’x4’x6’-10mm dia @8” c/c main, 8mm dia @8” c/c alternate.
• Column size – 9”x9” (6 nos 16mm dia and stirrups 8mm dia @8” c/c)
• Plinth size – 9”x9” (4nos 12mm dia main reinforcement and stirrups 8mm dia @ 8” c/c)
• Brickwork should be done with superior quality chamber bricks containing cement mortar in 1:6.
• Basement height 2’-0” Basement inside filling with soil. Over the soil PCC is laid with 1:4:8 with 40mm blue metal.
• Plastering with cement mortar 1:4 exterior wall.
• One coat of white cement and two coats of Asian exterior emulsion should be applied.
• Grano flooring with blue metal chips over PCC in the basement.
• CEMENT: Dalmia/Ultratech/Ramco
• BRICKS: Chamber
Total Area of the Building is supposed to be 54’-0” x 54’-0” = 2916.sq.ft.
Subject: Metal Roofing Shed
‘A’ Truss Length x Width: 58’ Feet x 54’ Feet =3132.Sq. Ft
CLADDING WORK (27’x54’) + (27’x54’) + (30’x54’) + (30’x54’) =6156. Sq. ft
Sub: Fabrication and construction of traditional steel structure with Cooler coated Galvalume.
Columns: Delivery and installation of 12 Numers.150×100 Columns (MS I BEAM Height 32’ Feet) Columns Base Plates should have 20 mm thickness 300 mmX300mm & Columns top Plates should have 8 mm thickness.
Base foundation 25 mm 1’5’Feet 48 Numbers
Columns Bracing Support ( X 4 Numbers)
A Type Trusses: Delivery and installation of of 4 Numbers. Trusses 54.0” Feet span formed 50X50mm MS Square Pipe Bottom Rafter as 50X50mm MS pipe with inner cross 30X30 Straight as 30X30 mm pipes medium (ISI 2mm thickness) Lighting Support 1 No Inclusive.
Paint Works: One coat of premier & two coats of enamel paint.
Roof Sheet: Color coated Galvalume CCGL JSW sheet (0.47mm) and its accessories.
Purlin > 60×40 (ISI 2mm thickness) Square Tube purlin.(1000+1300=1Numbers)
To get more details, click on the following link
Sample quotation for constructing an indoor badminton court

Published By
Rajib Dey

Thursday, July 11, 2019

Corrective measure to check pile foundation failure

Pile foundation contains sound bearing strength, good durability and small differential settlement with regards to other foundation types.
Pile foundations are normally provided in the following conditions :-
1. Low bearing strength of soil.
2. Non-existence of perfect bearing stratum at shallow depths.
3. Greater loads from the super structure for which shallow foundation may not become inexpensive or feasible.
But pile foundations become damaged and collapse specifically throughout earthquakes because of the following purposes.
1. Inadequacy of sufficient boring
2. Improper soil grouping
3. Soft strata under tip of pile
4. Insufficient driving formula (wrong data)
5. Imperfect size of hammer leads to deficient penetration, too light or get damaged if too heavy
6. Misapprehension of load
7. Damaged of encased piles
8. Buckling of piles
9. Cracking of piles
10. Vibration that leads to lateral or vertical movement
11. Flowing strata resulting from adjoining excavation or bank sloughing
12. Tension failure of concrete pile for shortage of reinforcement
13. Eccentricity because of bowing or falling out of plumb
14. Deterioration caused by lower ground water level
15. Insect and marine borer attack and erosion
16. Detachment of concrete caused by poor quality of concrete or reactive aggregate
17. Failure of the thin shell of the piles
18. Overweight owning to earthfill.
Corrective measures to get rid of failure of pile foundation:
1. Preliminary repair like encasement or replacement
2. Extraction of partial load
3. Underpinning
Corrective measure to check pile foundation failure

Published By
Rajib Dey

Wednesday, July 10, 2019

How to determine the cutting length of chair bar in slab & footings

The chairs in reinforcement are provided for the following reasons.
1. It retains the gap among the two bars as well as upper and lower cage reinforcement.
2. It provides strong supports to the bars.
3. It improves the strength of the structure and retains the tension in RCC.
4. It raises the tension property of concrete.
5. It reduces the scope for collapsing of the building because of the failure of compression and tension zone.
6. While vibrating, it holds the upper cage bar from collapsing.
7. The diameter of the bar should not be lower than 12 mm.
The chair bars should be made of the scraps in the jobsite.
In this civil engineering article, detail information is given for finding out the cutting length of chair bar in slab and footings.
The height is treated as the most crucial part of any chair as when the height is known, it becomes easier to determine the leg and the length of head.
The height of the chair bar will be determined with the following formula :-
Height = Height of footing – (2 x clear cover) – (dia of bottom main bar) – (dia of top main bar + dia of top distribution bar)
The head of the chair bar will be determined with the following formula :-
Head = (2 x spacing of top distribution bar) + 100
The leg of the chair bar will be determined with the following formula :-
Leg = (2 x spacing of bottom main bar) + 50
To learn the detail calculation process, go through the following video tutorial.
How to determine the cutting length of chair bar in slab & footings

Published By
Rajib Dey

Tuesday, July 9, 2019

How to get rid of common errors in concrete floor slab construction

To get rid of common errors in concrete floor slab construction, various steps like perfect base preparation, mix design, placement, finishing, and curing should be taken.

Typical concrete floor slab thickness in residential construction should be 4 inches. In case the concrete has to sustain extreme loads irregularly, the thickness should be five to six inches; as for instance, motor homes or garbage trucks.

To arrange the base, the ground level should be dug according to the perfect depth to provide for the slab thickness. Take out all organic material and large hard objects like stones and tree roots to a depth of minimum 4 inches. If it is required to develop the grade, apply gravel or sandy soil, and compress the final base with a vibratory plate or equivalent device.

The edge is built up with any straight material that can be fixed into position. If case of constant non-availability of straight lumber, plastic or metal forms should be used. Fix a string line with grade stakes or batter boards to provide a square, level reference prior to place the formwork.

For the concrete mix, it should satisfy the compressive strength requirements (normally 3000 pounds per square inch) devoid of measures that lead to extreme shrinkage. The shrinkage and cracking are increased because of the existence of water, a plasticizer should be used to attain required slump.

Also provide fibers to check plastic shrinkage cracking. Greater strength and entrained air are necessary for exterior slabs susceptible to freezing weather or deicing chemicals.

It is suggested not to add water at the jobsite more than 1 to 2 gallons per cubic yard. In case, extra slump is essential, take advice from the mixer truck driver concerning the quantity of water to be included devoid of taking the concrete out of specification.

Spread the concrete accross the slab area as close to its final position as possible, and then rake it into exact location. Hardens low-slump mixes manually with a vibrator or apply a vibratory screed. Complete with the least force and strokes of the float required to attain a smooth surface.

Develop control joints no farther apart than 24 to 30 times the slab thickness and at no time exceeding 15 feet along both the width and length of the slab by pushing a 1-inch deep grooving tool into the surface.

To keep Joint spacing more than 15 feet, different types of load transfer devices should be used which range from dowels or dowel plates. For slabs with long joint spacing or no joints, steel reinforcement will be suitable.

It will raise the chances for random cracking, but will maintain cracks firmly to keep up superior structural performance.

The curing process should be initiated when the finished surface can counter damage. The concrete should not be enabled to freeze or dry out. Arrange a curing compound over the surface, or apply proper moist curing.

In case of freezing, the slab should be wrapped with an insulator, like insulating blankets or a 4-inch-thick layer of straw that is weighted down so that it can’t blow away. Unless the concrete attains a strength of minimum 500 psi, put the insulator in place. It normally happens within a few days.

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How to get rid of common errors in concrete floor slab construction

Published By
Rajib Dey