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 :-



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



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Published By
Rajib Dey
www.constructioncost.co
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Ultra-High Performance Concrete (UHPC) is a powerful construction material

Ultra-High Performance Concrete (UHPC) alias reactive powder concrete (RPC), is a high-strength, ductile material that is formed by integrating portland cement, silica fume, quartz flour, fine silica sand, high-range water reducer, water, and steel or organic fibers.

The compressive strengths of this type of concrete is up to 29,000 pounds per square inch (psi) and flexural strengths up to 7,000 psi.

The materials are generally delivered in a three-component premix: powders (portland cement, silica fume, quartz flour, and fine silica sand) pre-blended in bulk-bags; superplasticizers; and organic fibers. The ductile behavior of this material is an elementary feature, with the strength to deform and support flexural and tensile loads, even after initial cracking. The application of this material for construction is streamlined with the removal of reinforcing steel and the capacity of the material to be virtually self placing or dry cast.

The strong durability characteristics is formed because of the combination of fine powders chosen for their grain size (maximum 600 micrometer) and chemical reactivity. The outcome is a greater compactness and a small, disconnected pore structure.

Higher density results in creating fewer voids inside, minimizing the scopes for water to infiltrate and create problems throughout the freeze-thaw process. The dense packing also increases the strength of UHPC significantly.

To minimize the carbon footprint of the material, a byproduct of the steelmaking industry (ground slag) is utilized to substitute a significant part of the cement and simultaneously allows to improve the packing density.

A major component in UHPC is steel fibers which include strain-hardening properties to the concrete and as a result when it yields the concrete will bear extreme load before it fails in due course.

UHPC provides huge benefits which range from reduced global costs like formwork, labor, maintenance and speed of construction. Various usages are found bridge beams and decks, solid and perforated wall panels/facades, urban furniture, louvers, stairs, large-format floor tiles, pipes and marine structures.

1. Plumb Bob (For buildings less than 20m in height)
2. Optical Plummet (A transparent plastic sheet is used as a target for checking verticality of tall buildings)
3. Theodolite

Given below the details of material characteristics for UHPC:

Strength
Compressive: 120 to 150 MPa (17,000 to 22,000 psi)
Flexural:15 to 25 MPa (2200 to 3600 psi) Modulus of Elasticity: 45 to 50 GPa (6500 to 7300 ksi)

Durability
Freeze/thaw (after 300 cycles): 100%

Salt-scaling (loss of residue): < 60 g/m2 (< 0.013 lb/ft3) Abrasion (relative volume loss index): 1.7 Oxygen permeability: <10-20 m2 (< 10-19 ft2) Cl - permeability (total load): < 10 C Carbonation depth: < 0.5 mm (< 0.02 in.)

To get more detail information, go through the following link. precast.org



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Published By
Rajib Dey
www.constructioncost.co
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Some useful tips to develop and pour concrete stairs

The renowned concrete contractor, David Odell, has presented an exclusive construction video tutorial that provides some useful construction tips on how to develop and pour concrete stairs (10 steps of stairs).

These are the basic steps for developing concrete stairways. This video will guide you to build up your own concrete stairs. Steps shown in this video comprise of laying out the size, arranging the sub-base, developing the forms, pouring, finishing and curing the concrete from starting to completion.

A "riser" refers to the vertical surface of the step and a "tread" refers to the horizontal surface of the step. To define the whole size of the concrete stairs, initially, you should work out the total rise and run of the steps you are going to form.

To learn the complete process, watch the following video tutorial.

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Published By
Rajib Dey
www.constructioncost.co

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