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Thursday, February 21, 2019

Some useful guidelines to work out the total loads on a column & footing

This article is about calculation of loads for column and footings design.
The following types of loads operate on a column :-
1. Self weight of the column x Number of floors
2. Self weight of beams per running meter
3. Load of walls per running meter
4. Total Load of slab (Dead load + Live load + Self weight)
The columns are also susceptible to bending moments which should be included in creating the final design. There are different types of advanced structural design software like ETABS or STAAD Pro which can be applied to design a good structure efficiently. The calculation for structural loading In professional practice is based on some fundamental assumptions.
For Columns: Self weight of Concrete is approximately 2400 kg per cubic meter that is identical to 240 kN. Self weight of Steel is approximately 8000 kg per cubic meter. Suppose a large column having size of 230 mm x 600 mm with 1% steel and 3 meters standard height, the self weight of column is approximately 1000 kg per floor, that is identical to 10 kN. So, here, the self weight of column is taken as among 10 to 15 kN per floor.
For Beams: The calculation is same as above. Suppose, each meter of beam contains dimensions of 230 mm x 450 mm exclusive of slab thickness. So, the self weight is approximately 2.5 kN per running meter.
For Walls: Density of bricks differs among 1500 to 2000 kg per cubic meter. For a 6″ thick wall with 3 meter height and 1 meter length, the load can be measured per running meter equivalent to 0.150 x 1 x 3 x 2000 = 900 kg which is equivalent to 9 kN/meter. The load per running meter can be measured for any brick type by following this method.
For autoclaved, aerated concrete blocks like Aerocon or Siporex, the weight per cubic meter should remain among 550 to 700 kg per cubic meter. If these blocks are utilized for construction, the wall loads per running meter remains as low as 4 kN/meter, that leads to cutback in construction cost.
For Slab: Suppose the thickness of the slab is 125 mm. Now, each square meter of slab contains a self weight of 0.125 x 1 x 2400 = 300 kg that is similar to 3 kN. Suppose, the finishing load is 1 kN per meter and superimposed live load is 2 kN per meter. So, the slab load should remain 6 to 7 kN per square meter.
Factor of Safety: Finally, once the calculation of the entire load on a column is completed, the factor of safety should also be taken into consideration. For IS 456:2000, the factor of safety is 1.5.
Some useful guidelines to work out the total loads on a column & footing

Published By
Rajib Dey

Wednesday, February 20, 2019

Some useful tips to enhance the longevity of concrete piles

If concrete is mixed perfectly and compacted to a solid impervious, the longevity of all the construction materials is significantly increased in a non aggressive atmosphere.

The strength of concrete is influenced by sulphate and sulfuric acid that takes place normally in soils, erosive chemicals existent in industrial waste in fill materials and organic acids and carbon dioxide existent in ground water.

A solid, properly compacted concrete can efficiently safeguard the concrete piles, pile cap and ground beams against the attack by sulphates. The low penetrability of dense concrete resists or significantly controls the ingress of the sulphates into the pore spaces of the concrete.

That's why high strength precast concrete piles are mostly recommended for application. Although these are not acceptable for all the site conditions and bored cast in situ / driven cast in situ piles, so, at the time of application, these should be designed perfectly to attain necessary degree of impenetrability and defiance to aggressive action.

Both high alumina cement and super sulphated cement are not suitable for piling work. As an alternative, reliance is provided on the resistance of solid impervious concrete that is formed with a low water cement ratio. Coating of tar or bitumen on the surface, metal sheeting or glass fibre wrapping filled with bitumen may be chosen.

A layer of heavy gauge polythene sheeting provided on a sand carpet or on blinding concrete is arranged to safeguard pile caps and ground beams on the underside. The vertical sides are safeguarded once the formwork is eliminated with the use of hot bitumen spray coats, bituminous paint, trowelled on mastic asphalt or adhesive plastic sheeting.

Preventative measures against the aggressive action caused by sea water on concrete should only be taken into consideration with regard to precast concrete piles. Cast in situ concrete is utilized only as a centering to steel tubes or cylindrical precast concrete shell pills. The precast concrete piles for marine condition, a minimum ordinary portland cement content of 360 kg/m3 and a maximum water cement ratio of 0.45 by weight should be chosen.

Some useful tips to enhance the longevity of concrete piles

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Rajib Dey

Tuesday, February 19, 2019

How to measure superimposed loads on a column

The objective of a column is to withstand axial and lateral forces and transmit them securely to the footings in the ground.

In this exclusive article, you will learn how to work out the superimposed loads on a column in a structure with some easy-to-follow steps.

Columns provide support to the floors in a structure. Slabs and beams transmit the stresses to the columns. So, it is crucial to make a strong column.

A column stands for a compression member, the effective length of which surpasses three times the minimum lateral dimension. Compression members whose lengths remain under three times the minimum lateral dimension, are constructed with plain concrete.

The axial load bearing strength of a column is derived from the follwoing formula :-

Reinforced Concrete Columns

Besides, axial loads, the column design is dependent on several other factors. Because of beam spans, wind loads, seismic loads, point loads and various other factors, the bending moments and tortional forces are produced.

A column is categorized on the basis of various factors :-

1. Depending on shape
• Rectangle
• Square
• Circular
• Polygon

2. Depending on slenderness ratio: The ratio of the effective length of a column to the minimum radius of gyration of its cross section is known as the slenderness ratio.

• Short RCC column, =< 10
• Long RCC column, > 10
• Short Steel column, =<50
• Intermediate Steel column >50 & <200
• Long Steel column >200

3. Depending on the type of loading
• Axially loaded column
• A column subjected to axial load and unaxial bending
• A column subjected to axial load and biaxial bending

4. Depending on pattern of lateral reinforcement
• Tied RCC columns
• Spiral RCC columns

Least eccentricity
Emin > l/500 + D/30 >20
Where, l denotes unsupported length of column in ‘mm’
D = lateral dimensions of column

The following types of Reinforcements for columns are found :-

Longitudinal Reinforcement
• Least area of cross-section of longitudinal bars should be minimum 0.8% of gross section area of the column.
• Maximum area of cross-section of longitudinal bars should not be in excess of 6% of the gross cross-section area of the column.
• The bars should not be below 12mm in diameter.
• Least number of longitudinal bars should be 4 in rectangular column and 6 in circular column.
• Distance of longitudinal bars measured along the perimeter of a column should not go above 300mm.

Transverse reinforcement
• It may appear in the form of lateral ties or spirals.
• The diameter of the lateral ties should not remain below 1/4th of the diameter of the greatest longitudinal bar and in no case below 6mm.

The pitch of lateral ties should not go beyond
• Minimum lateral dimension
• 16 x diameter of longitudinal bars (small) • 300mm

Helical Reinforcement
The diameter of helical bars should not remain below 1/4th the diameter of largest longitudinal and not below 6mm.
The pitch should not go above (if helical reinforcement is permitted);
• 75mm
• 1/6th of the core diameter of the column

Pitch should not remain under,
• 25mm
• 3 x diameter of helical bar
Pitch should not surpass (if helical reinforcement is not permitted)

Least lateral dimension
• 16 x diameter of longitudinal bar (smaller)
• 300mm

Reinforced Concrete Columns

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Rajib Dey

Monday, February 18, 2019

Different components of super structure

Superstructure stands for segments of the structure that is situated over the surface of the ground. The superstructure is built with different sections of walls, roof, doors, and windows, flooring. The sections of the structure situated on the grounds and underneath the ground floor level are known as the plinth.

The objective of superstructure is to bear different types of loads operating on the structure which range from dead load, live, load, wind load etc. These loads are then transferred to the underlying soil through the substructure.

Each element of superstructure is applied as a specific purpose, but the prime function is to arrange privacy, safety to the inhabitants. Wall and roof safeguards from the surrounding, doors permit entry and give safety, windows arrange requisite sunlight and fresh air and floor provides a leveled surface to live and protection from beneath.

Building superstructure

Column: A column in structural engineering stands for a vertical structural component that disperses the weight of the structure over to other structural components underneath , through compression.

Floor: A floor normally comprises of a support structure known as a sub-floor on top on which a floor cover is placed to arrange a walking surface.

Roof wall :

Flat – Should contain a slight slope for drainage

Shed – A single slope

Gable – Two slopes intersect at a ridge. Two walls expand up to the ridge.

Hip – Two gables, a pyramid is treated as a hip roof.

Gambrel – Four slopes in one direction, the usual barn roof.

Mansard – A four-sided gambrel-style hip roof formed with two slopes on each of its sides with the lower slope, perforated by dormer windows, at a steeper angle than the upper.

Beam: Beam stands for an inflexible structural member formed to bear and transmit transverse loads across space to supporting components.

Different components of super structure

Published By
Rajib Dey

Saturday, February 16, 2019

Common structural members in a building

In this civil engineering article, you will get detail information on different types of structural members in a building.

Beam: Beam stands for a flexure member of the structure. It is exposed to transverse loading like vertical loads, and gravity loads. With these loads, shear and bending are formed inside the beam. Beams belong to horizontal structural members to bear a load successfully.

Beam is generally applied for withstanding vertical loads, shear forces and bending moments.

Columns: A long vertical member that mostly undergoes compressive loads & buckling loads is known as column. Columns stand for vertical, structural members of a structure. They transmit load from beams to footings. Columns are mostly utilized to support beams or arches on which the upper sections of walls or ceilings rest.

Strut: Strut is a compressive member of a structure. This structural member is driven from opposite ends. The purpose of a strut is to withstand compression.

Ties: A tie stands for a structural member that is extended from opposite ends. A tie mainly deals with tension.

Beam-Column: A structural member that is exposed to compression and flexure is known as beam column.

Grid: A group of beams which overlap each other at right angles and exposed to vertical loads is known as grid.

Cables and Arches: Cables are normally suspended at their ends and are granted to sag. The forces then turn to pure tension and are headed along the axis of the cable. Arches have the similarity with cables apart from they are inverted. They bear compressive loads which are directed along the axis of the arch.

Plates and Slabs: Plates belong to three dimensional flat structural components generally constructed with metal which are frequently utilized in floors and roofs of structures. Slabs are identical to plates apart from that they are normally constructed with concrete.

Common structural members in a building

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Rajib Dey

Friday, February 15, 2019

POLEFDN – A excel based construction program for pole foundation analysis

POLEFDN is a MS-excel based spreadsheet program that can be used for making analysis of a pole foundation on the assumption of the application of a inflexible round pier that is supposed free (unrestrained) at the top and exposed to lateral and vertical loads. The spreadsheet particularly makes calculation for the necessary embedment depth, the maximum moment and shear, the plain concrete stresses, and the soil bearing pressures.

This program stands for a workbook that comprises of the following six (6) worksheets:

• Doc - Documentation sheet
• Pole Fdn (Czerniak) - Pole foundation analysis for free-top round piers with PCA/Czerniak method
• Pole Fdn (UBC-IBC) - Pole foundation analysis for free-top round piers with UBC/IBC method
• Pole Fdn (OAAA) - Pole foundation analysis for free-top round piers with OAAA method

• Granular Soil (Teng) - Pole foundation analysis in granular soil with USS/Teng method
• Cohesive Soil (Teng) - Pole foundation analysis in cohesive soil with USS/Teng method

Given below, some useful features of the program :-

This program can deal with both horizontally and vertically applied loads. The vertical load may contain an associated eccentricity that leads to an additional overturning moment to be always assumed to add directly to the overturning moment formed with the horizontal load.

This program guesses that the top of the pier remains at or over the top of the ground surface level.

This program guesses that the actual resisting surface remains at or under the ground surface level. It takes into account any weak soil or any soil that is detached at the top.

The "Pole Fdn(Czerniak)" worksheet guesses that the inflexible pier rotates about a point situated at a distance, 'a', under resisting the surface. The highest shear in pier is supposed to be at that 'a' distance, whereas the maximum moment in the pier is supposed to be at a distance = 'a/2'.

The "Pole Fdn(Czerniak)" worksheet works out the "plain" (unreinforced) concrete stresses, compression, tension, and shear in the pier. The corresponding permissible stresses are also set on the basis of the strength (f'c) of the concrete. It is performed to check whether the steel reinforcing is actually necessary or not. The permissible tension stress in "plain" concrete is supposed to be equivalent to 10% of the value of the permissible compressive stress.

The "Pole Fdn(Czerniak)" worksheet measures the actual soil bearing pressures along the side of the pier at equivalent distances to 'a/2' and 'L'. The relevant permissible passive pressures at those locations are set for comparison.

As all overturning loads are protected with the passive pressure against the embedment of the pier, this program guesses that the pier functions in direct end bearing to withstand only the vertical loading. The bottom of pier bearing pressure is measured that contains the self-weight of the pier, assumed at 0.150 kcf for the concrete.

To download the program, click on the following link

POLEFDN – A excel based construction program for pole foundation analysis

Published By
Rajib Dey

Thursday, February 14, 2019

Plaster of Paris In Construction – Uses and Benefits

Plaster of Paris (POP) is a elementary building material that is mainly applied for coating walls and ceilings as well as for making architectural designs. It comes as dry powder and gets solidified when used along with water and heat.

The following types of plaster of paris is mainly available :-

a. Plaster of paris (Gypsum)
b. Lime Plaster
c. Cement Plaster

POP is originated by incomplete calcination of gypsum or calcium sulfate at 100 – 190 degree C without any admixture. The setting time is 5 – 20 min.

Benefits of Plaster of Paris:

1. It is light in weight and long lasting.
2. It contains low thermal conductivity.
3. It has strong resistance capacity against fire and it is considered as a very good heat insulating material.

4. It does not shrink at the time of setting and as a result it does not form cracks at the time of heating or setting.
5. It develops a thick surface to withstand normal knocks once drying is completed.
6. It blends easily with water and disperses quickly and level.
7. It contains good adhesion on fibrous materials.
8. It provides a solid surface on which the colours are set.

9. It does not provide any chemical action on paint and does not produce alkali attack.
10. Plaster of Paris provides a elegant interior finish. Due to inclusion of gypsum in POP, there is lot of shine and smoothness.
11. It can be easily changed into any shape.

Drawbacks of Plaster of Paris:

1. Gypsum plaster is not recommended for exterior finish as it is dissolved in water to some extent.
2. It’s cost is high as compared to cement or cement lime plaster.
3. It cannot be applied in moist situations.
4. Skilled labor should be appointed for proper application and consequently huge labour cost is required for using plaster of Paris.

Plaster of Paris In Construction – Uses and Benefits

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Published By
Rajib Dey