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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Details about various sections of bridge

All the major elements are arranged within three main bridge areas – Foundation (that retains the shallow or deep base of the bridge and transmits it’s load to the bearing strata, it comprises of foundations underneath the primary span of the bridge and the abutments underneath starting points of the bridge), Substructure (piers, abutments, spandrels, caps, bearings, and other elements that retains the top part of construction) and Superstructure (all the segments of the bridge which are assembled on top of the supporting substructure system, it comprises of various components like decking, girders, slab, and everything arranged over the main deck like posts, steel truss system, bridge girder, cable-stayed system, cable suspended systems and more).

The followings are the major elements of the modern bridges:

Abutment – Endpoints of the bridge. They are reinforced to facilitate withstanding extreme lateral pressures.

Pile (also called as beam, footing, and pier) – It stands for reinforced concrete post that is pushed into the ground to function as the leg or support for the bridge. The extent among piles is worked out to provide support to the rest of the structure that will be placed on top of them.

Cap – Cap is located on top of the pile beam that gives extra support and distributes the load to the piles underneath. The amalgamation of Pile and Cap elements is known as Bent.

Girder or Span – It is one of the major components of the bridge that attaches all the Piles beams. It involves several simple spans, a single continuous span that is supported with numerous beams, cantilever spans and cantilever spans with the suspended span among them. They are normally formed with metal or reinforced concrete as well as in the form of haunches girded be bear more load. Girder sections are usually not formed with a simple block of material but built up with truss network (or Orthotropic beams) that enhance their resistance capacity against load. Girders are also utilized as a part of rigid frame network where they are totally attached with frame legs (that may appear as inclined or in V shape).

Superstructure truss network – Truss network that provides supports to travel surface is built with three basic ways – Deck truss where traffic passes on top of truss network, Pony truss where truss network passes among two parallel walls of trusses, and via truss that includes extra cross-braced truss network over and below the traffic.

Deck beam – Simple continuous decks are created with metal or reinforced concrete. They comprise of sub-components like approach slab (attaches main bridge decking with the ground on both sides of the bridge), expansion joint, drainage scupper, curb, running surface, footpath.

Barriers – These are the sides of the bridge decks normally contain extra barrier components like railings, handrails and ground fixtures.

Arch – Arches on the bridges are differentiated with the number of hinges they contain (normally among zero or three) which ascertain the volume of stress and load they can bear securely, and the type of material they are built up (solid material, truss system). Arches underneath the bridge are known as spandrel-braced (cantilever) or Trussed deck arch.

Spandrel – Spandrels belong to the almost triangular space among the main pillar of the bridge and decking. Stone bridges employ filled “closed” spandrels deck arches, whereas the modern bridges are constructed with metal having open spandrel deck arch configurations.

Truss – Framework is created by attaching triangles and other forms that disperse load and stress forces across its whole structure. They are generally segregated into various categories like simple truss (King and Queen posts), covered bridge truss (multiple kingpost truss, Howe truss, long truss, Burr arch truss, town lattice truss, Haupt, Smith, Partridge and Child truss), Pratt truss (and it’s many variations), Whipple truss, Warren truss variations, Howe truss, Lenticular truss, Fink truss, multiple Cantilever truss variations, and suspension truss arches.



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Published By

Rajib Dey

www.constructioncost.co

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Why Steel Roof Truss Is Better Than Timber Truss?

A truss is formed with an assembly of inflexible & elastic members which are connected as the triangles to perform like a beam. The tensile stress of mild steel is secure for working and it is approx. 20 times as compared to structural timber. Therefore, steel trusses are considered as cost-effective, particularly for largest extents. The angles are treated as the most vital elements for steel roof truss among different shapes of steel sections due to their capability to withstand both compressive and tensile stresses in an effective manner. The supplementary angles are created inexpensively as well as connected without any difficulty.

Benefits of steel roof truss as compared to timber truss are presented below:

1. Steel trusses last long as compared to timber trusses.

2. Steel sections that develop the truss are lightweight and are constructed in any preferred pattern to match the requirement of any architectural work.

3. As it is made with steel, the material is not damaged by white ants or other insects.

4. Steel trusses contain strong fire-resisting capacity as compared to timber trusses.

5. As there are no span limitations with steel trusses, they can be utilized for industrial buildings and various other structures where large areas can be covered devoid of any obstructions which may occur to columns etc.

6. The sections which develop a steel truss can be smoothly transported.

7. The sections are acquired in any preferred form or length to match the requirements and less wastage of the material occurs in cutting etc.

8. Due to their trouble-free erection methods, the advancement of roofing work with steel trusses can be done rapidly.

Article Source : www.dailycivil.com

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Published By

Rajib Dey

www.constructioncost.co

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