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COLUMNS

Column :

A column is a vertical member in a structure used to transfer the loads from slabs to the

foundation below. Columns are the primary components in a multi-storeyed building. The

design of the column plays a vital role in structural design, as any lapse leads to total

collapse, unlike other structural components. So the Design Engineer should be well versedwith the computation of forces acting on the column & the proper visualisation on the

behaviour of the columns under such forces.

Column Classification:

Le Pedestal Stub Short Long

Le (Minimum) 0 2.5 b 4 b >12 b

Le (Maximum) 2.5 b 4 b 12 b 60 b

If the slenderness ratio (Le /D ) is less than 3, those vertical members are calledPedestals. If the slenderness ratio is greater than 3 , those vertical members are calledColumns.

1.0 Classification of Columns:A column may be classified based on different criteria such as(a) shape of cross- section(b) slenderness ratio(c) type of loading(d) pattern of lateral reinforcement

(a) Shape of cross-section :

The common shapes of columns in practice are(1) Square columns(2) Rectangular columns(3) Circular columns(4) L-shaped columns(5) T-shaped columns(6) Cruciform (Swastik)(7) Hexagonal columns.


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(b) Based on slenderness ratio:If the slenderness ratio (effective length of column to least lateral dimension ) is less than

12, it is called as short columns. (Clause 25.1.2 of IS: 456-2000)

If the slenderness ratio (effective length of column to least lateral dimension ) is greater

than 12, it is called as long columns or slender columns. However, the maximumslenderness ratio of a column should not exceed 60.

(c) Type of Loading :

Column can be classified as(1) Axial loaded columns(2) Axial load with uniaxial moment(3) Axial load with bi -axial moment

(d) Based on Types of lateral reinforcementColumn can be classified as

(1) Tied column(2) Spiral column(3) Composite column

(1) Tied Columns : The main longitudinal bars are enclosed within closely spaced lateralties.

(2) Columns with helical reinforcement: The main longitudinal reinforcement bars areenclosed within closely spaced and continuously wound spiral reinforcement.


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(3) Composite Columns: The main longitudinal reinforcement of the composite columnsconsists of structural steel sections or pipes with or without longitudinal bars.

Braced & Unbraced columns :

(i) Braced Columns:

Columns can be planned in a structure so that they do not have to resist any horizontal

loads due to wind or earthquake. Thus, for example, when the columns of water-tower are

braced, the wind load is taken by the intersection of column bracings. In tall buildings lateral

supports like shear walls can be provided so that the lateral loads are taken by them. Such

columns are called braced columns.

(ii) Unbraced Columns :Other columns, where the lateral loads have to be resisted in addition to vertical loads by

the strength of the columns themselves, are considered as unbraced columns.Bracing

can be in one direction or in more than one direction, depending on the likelihood of the

direction of the lateral loads.


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If the column is subjected to large bending moment M as compared to axial load P (saye = M > 0.5 ) assume bars to be equally placed on opposite face likeD PDdoubly reinforced section.

If P is large compared to bending moment M (say e = M < 0.5 ) assume.D PD

bars to be uniformly placed all around the periphery.

4.0 IS CODE RECOMMNDATIONS FOR DESIGN OF COLUMNS

1).Unsupported length of column: (Clause 25.1.3 of IS 456-2000)The unsupported length L of a compression member is defined as clear distance between

the end restraints. In the case of column in a framed structure, unsupported length is taken

as follows for the different structures.

(a) Beam-slab floor construction:It is the clear distance between the floor and the framing into the columns in each

direction at the next higher floor level.


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(a) Flat Slab construction:It is the clear distance between the floor and lower extremity of the capital, the drop

panel, or slab whichever is the least.

(c) In columns restrained laterally by struts(as in case of a staging for overhead tanks), it

is the clear distance between the consecutive struts in each vertical plane, provided

two such struts shall meet the columns at approximately the same level and the

internal angle between vertical planes through the struts does not exceed 135 .Such

struts are expected to have sufficient rigidity to restrain the column against lateral

deflection.


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(d)` In columns restrained laterally by struts or beams with brackets used at the junction, it

is taken equal the clear distance between the floor and the lower edge of the bracket

provided that the bracket width equals that of the beam strut and at least half that of

the column.

2) Effective length: (clause 25.2 of IS 456 -2000)

The effective length of a column is a length between points of zero bending moment or

between the points of contra flexure of a column in that plane. It depends upon the end

conditions as regards restraint against rotation and that against transverse displacement.

Effective Length of Compression Members (Table 28 of IS 456 2000)

Degree of End Restraint of Compressive Member TheoreticalValue ofEffectiveLength

Recommended value ofEffective Length

Effectively held in position and restrained againstrotation at both ends (Both ends fixed) 0.5L 0.65LEffectively held in position at both ends, restrainedagainst rotation at one end (One end fixed & oneend hinged )

0.7L 0.80L

Effectively held in position at both ends, but norestrained rotation (Both ends hinged) 1.00L 1.00LEffectively held in position and restrained againstrotation at one end, and at the other restrainedagainst rotation but not held in position 1.00L 1.20L

Effectively held in position and restrained againstrotation at one end, and at the other partially

restrained against rotation but not held in position --- 1.50LEffectively held in position at one end but notrestrained against rotation, and at the other endrestrained against rotation but not held in position 2.00L 2.00L

Effectively held in position and restrainedagainst rotation at one end but not held in positionnor restrained against rotation at the other end(One end fixed one end free) 2.00L 2.00L


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Typical idealized Effective length of Column

Sl.No. Boundary Conditions Effective length1 Simply supported at both the ends L

2 Fixed at both the ends 0.65L3 Fixed at one end and hinged at the other 0.80L4 Fixed at one end and constrained against rotation at the

other end1.20L

5 Fixed at one end and free at the other end 2.0L6 Columns in Portal frames with fixed bases & having lateral

sway1.50L

Sl.No. Boundary Conditions Effective length

7 Columns in Portal frames with hinged bases & having lateralsway

2.0L

8 Interior Columns in Multi storey frames above G.L. 0.80L9 Exterior Columns in Multi storey frames above G.L. 1.20L10 Crane carrying Columns in braced buildings L

Determination of effective length of Column and Type of Column:

When there are longitudinal and cross walls in both directions, the frame is assumed to bea non- sway frame. In such cases, the effective length lies between 0.65L to L, where Lrepresents buildings frame may be taken as follows:

(ii) For any intermediate storeyLeff=L= unsupported Length

= floor to floor height depth of shallower beam(300mm or more dependingon the span)(iii) For Top storey

Leff= 1.20L where L is unsupported Length as defined above.

(iv) For Columns in bottom storeyWhen plinth beams are not providedLeff=L= Distance between bottom of footing to the underside of the shallower

beam at first floor level.When plinth beams are providedLeff=L= Distance between top of plinth beam to the underside of the shallower

beam at first floor level.It may be noted that plinth beams are normally provided just below ground level and not at

the ground floor level, so that peripheral walls can retain the plinth filling.

If there are no walls first floor as in case of apartment buildings in cities where parking space

is provided underneath the entire structure above rests on the columns. In this case, there is

a possibility for way to occur and hence the effective lengths of the columns below are taken

equal to 1.2L to 2L depending on the end conditions. Here L is length of column from the

soffit of shallower beam of first storey to the bottom of footing.


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3) Slenderness Limits:

The Column dimensions should be selected in such a way that it fails by material failureonly and not by buckling. To ensure this criterion, the code recommends that the cleardistance between restraints (unsupported length) should never exceed 60 times the leastlateral dimensions of the column ( Clause 25.3.1 of I.S 456- 2000 ).

(The unsupported length of a column shall not exceed 60 times its least lateral dimensionwhen both of its ends are either fixed or hinged)

For unbraced columns, it is recommended that this value is limited to 30. In cantilever inaddition to the above restriction ( L 60 b), the value of L = (100 b2 / D ), where D is depthof cross section measured in the Plane under consideration and b is the width of crosssection (Clause 25.3.2 of I.S 456 -2000).

(The unsupported length of a column shall not exceed (100 b2 / D) when one of its end freei.e. unrestrained.)

4) Minimum Eccentricity : ( Clause 25.4 of I.S 456 -2000)

Every column to be designed for a minimum eccentricity emini. ( in any plane) equal to the

unsupported length / 500 plus lateral dimension / 30, subject to a minimum of 20 mm. For a

column with a rectangular section, for bending about major axis x x bisecting the depth of

column D

exmini. = l / 500 + D / 3020 mm ( whichever is greater )

Mini. Eccentricity, eminib for bending about major axis y- y bisecting the width of the column

eymini. = l / 500 + b / 3020 mm ( whichever is greater )

For non-rectangular & non-circular cross-sectional shapes, it is recommendedthat, for any given planeemini = le / 300

20 mm (whichever is greater ) where le = effective length of column in the planeconsidered.Note: When mini. Eccentricity requirement control, the bending only about one axis at atime shall be considered and NOT as a case of biaxial bending.

For a given lateral dimension h, the mini. Unsupported length up to which emini. =20mm can be obtained as follows:L/500 + h/30 = 20mm

L = 500 (20- h / 30)Max. unsupported length up to which emini. = 20 mm is given as follows

h inmm

150 200 230 250 300 350 380 400 450

L inmetre

7.50 6.67 6.17 5.83 5.00 4.17 3.67 3.33 2.50


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5) Longitudinal Reinforcement: (Clause 26.5.3.1 of I.S 456 -2000)

(i) Minimum Reinforcement: The Longitudinal bars must, in general, have a cross

sectional area not less than 0.8 % of the gross area of the column section.

In very large sized columns (where the large size is dictated, for instance, by architectural

considerations, and not strength) under axial compression, the limit of 0.8% of gross area

may result in excessive reinforcement. In such cases, the Code allows some concession by

permitting the minimum area of steel to be calculated as 0.8 % of area of concrete

required to resist the direct stress, not the actual (gross) area.

(ii) Maximum Reinforcement: The max. cross-sectional area of longitudinal bars should

not exceed 6 % of gross area of column section. However, a reduced maximum limit of 4 %

is recommended in general in the interest of better placement and compaction of concrete

and, in particular, is lapped splice location.

(iii) Minimum Diameter: Longitudinal bars in columns should not be less than 12 mm in

diameter and should not be spaced more than 300 mm apart (centre - to centre ) along

the periphery of the column.

(iv) Maximum Diameter: 40 mm for Fe 415 & Fe 500.

(v) Common Diameter of bars used: 12,16,20,22,25,28

(vi) Minimum number of bars: 4 in rectangular columns ; 6 in circular columns & one bar

located at each corner or apex in T, L or other cross-sectional shapes.

(vii) Common Numbers used: 4,6,8,10,12

(viii) Maximum spacing of bars: 300 mm when measured along periphery of column.

(ix) Cover to Reinforcement : A minimum clear cover of 40 mm or bar diameter

(whichever is greater), to the column ties is recommended by the code (Clause 26.4.2.1 of

I.S 456 -2000) for columns in general; a reduced clear cover of 25 mm is permitted in small-

sized columns (D 200 mm and whose reinforcing bars do not exceed 12 mm) .

Transeverse Reinforcement : ( Clause 26.5.3.2 of I.S 456- 2000)

(i) General : All longitudinal reinforcement in a compression member must be enclosedwithin transverse reinforcement, comprising either lateral ties( with internal angles notexceeding 135) or spirals.


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(ii) Lateral ties :

(a) Diameter of bars : max., or 6 mm whichever is higher.(b) Pitch : Least of the following(i) Least lateral dimension of column b(ii) 16 times diameter of smallest longitudinal bar i.e. 16 mini(iii) 300 mm

Helical reinforcement :

Pitch : mini. of 75 mm (core dia / 6)Not less than 25 mm, 3 h

PLANNING ASPECTS

1. Columns should preferably be located at or near the corner of a building and at the

intersection of walls.

2. The spacing of columns shall be such that the span of the beam is not less than 2.5m

nor greater than 10.0m. Spans of 4 m to 6 m give normal sizes of beams.

Single bay Portal frames may be adopted for spans ranging from 6.0m to 12.0m.

The spacing of frame may vary from 3.50m to 4.0m.

3. The centre to centre distance between columns should be decided based on

limitations on spans of supporting beams.

4. Where architectural or functional requirements demand large open space, number of

columns have to be kept along the periphery giving large spans for the beams.

5. Columns should be avoided inside a big hall as it makes the functional utility and the

appearance and obstructs the clear view and the usable space.


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6. Where providing a column footing on a boundary poses a difficulty, columns may be

taken inside so that the footing is inside the boundary line and floor beams be

cantilevered out beyond the columns to support beam carrying walls along the

boundary. Brackets may be taken out from the column in continuation of cross beams

to support walls along the boundary line. Alternatively, a combined footing or a strip

footing may be provided.

7. Select the position of columns so as to reduce bending moments in beams: Where

the locations of two columns are very near (eg) as it occurs when the corner of a

building and the point of intersection of walls come very close to each other, then one

column should be provided instead of two at such a positions so as to reduce the

beam moment. In buildings small offsets (such as PQ) are provided from architectural

considerations. Now the question arises whether to provide the column at P or Q.

Consider only the point loads(excluding load

transferred by floors) transferred by beams B1 and B2. If only column P is provided

beam B1 will transfer a concentrated load at Q. In such a case beam B3 will have

larger span and subjected to concentrated load at Q thereby there will be

considerably increase in bending moment. Instead of this if the column is located at

Q , the cantilever moment due to the reaction of B2 at P will relieve the B.M. in B3,

thus providing a cheaper alternative. Under certain rare circumstances to satisfy the

functional requirements, it may not be possible to provide upper storey columns

above the columns at the parking level. Then the column at parking level is required

to support the eccentric columns at upper storeys. In such a case the column S at


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parking level is splayed as shown in Fig. or provided with a bracket to support the

columns at the upper storey. However, the column at parking level will be subjected

to heavy concentrated loads transferred from the columns of upper storey.

8. Avoid larger spans of beams: When the centre to centre distance between the

intersection of walls is large or where there are no cross walls, the spacing between

two columns decides the span of the beam. As the spans of supported beams,

because spacing of columns decides the span of the beam. As the span(and the

length) of the beam increases, the required depth of the beam, and hence its self

weight, and the total load on beam increases. Columns are in general, always

cheaper compared to beams on the basis of unit cost. Therefore, large spans of

beams should preferably be avoided for economy reasons.


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In this case, either one column at C can be provided making ACB a two span continuous

beam or two columns can be provided at E and G to form AB a three span continuous beam.

In the first case, spans AC and CB will be larger and the beam has to carry two point loads,

one at E and the other at G, transferred from secondary beams. This will require heavier

section for the beam in the latter case, when two columns are provided one at E and another

at G, the beam becomes a three span beam. Length of beam is reduced and it is required to

carry only one concentrated load and that too on central span which further reduces the

moment in outer spans AE and GB without appreciable increase in design moment in

position EG leading to considerable reduction in the cost of beam.

On the other hand since the cost of column is nearly proportional to the load on it, increase in

cost of columns and footings due to provision of two columns at E and G (carrying half the

load), over the cost of providing single column at C will be comparatively less than the

increase in the cost of beam due to providing single column. Thus, the second alternative is

likely to work out to be cheaper. This is more true in the case of multistory building frames.

8. Projections of columns outside the wall should be avoided as far as possible.

9. The columns should be so oriented that the depth of column should be perpendicular

to the major axis of bending.

D b

b

X X y Y

D

XX - Major axis of bending

YY - Minor axis of bending

D - Perpendicular to axis of bending

b - Parallel to axis of bending

10. When the effective length of column in one plane is greater than that in the

orthogonal plane, the greater dimensions shall be in the plane, having larger

effective length so as to reduce leff /D ratio to increase the load carrying capacity of

the column.

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PRACTICAL ASPECTS

1.Trial Section:Least lateral dimension (b) = width of beam .Normally 230 mm or

Lef /12 whichever is greater.

Area of cross-section of column (Ac)

80 to 100 mm2 per every 1 KN ultimate load carried by the column depending on the

grade of concrete used. Area required for concrete is roughly @10 N / mm2 for all

grades of concrete.

Trial section can be fixed initially using the following guide values.

Grade ofConcrete

M15 M20 M25

Externalcolumns

2500 2000 1500

Internal

columns

1800 1500 1200

D= large dimension of column = Ac /b

Steel strength for Fe 415Dia of rod in mm Ultimate capacity in KN / bar

12 3016 6020 9025 140

2. Recommended Size of columns :

Size of columns to be kept as follows:

For Square columns : multiples of 50 mm up to 500 mm

For Rectangular columns : multiples of 100 mm above 500 mm.

Circular columns are preferable for dia greater than 200 mm.

Practical Sizes of columns adopted in Practise :

Square Column Rectangular column

230 x 230 230 x 300 300x 500 500 x 600

300 x 300 230 x 380 300x 600 500 x 800400 x 400 230 x 450 400x450 600 x 700450 x 450 230 x 600 400x530 600 x 800500 x 500 300 x 400 400x 600600 x 600 300 x 450 450x600


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Circular Column :

300 dia

400 dia

450 dia

500 dia600 dia

3. Approximate of load carrying capacity of column for a known section

(i) CONCRETE STRENGTH:

Concrete area incm2

Load carrying capacity of Concretein Tonnes

M15 M20 M25100 4 5 6

(i) STEEL GRADE Fe 415

Bar Dia.

Safe Load carrying capacity in Tonnes

As per Vazirani &Chandola

As per Chandra Handbook

12 2.15 2.03

16 3.82 3.62

20 5.97 5.6525 9.33 8.83

28 11.7 11.08

32 15.28 14.47

36 19.34 ---

40 23.85 ---

3. Longitudinal reinforcement :

(Clause 26.5.3.1 of IS 456-2000)Ast Dia of Bar No. of bars Spacing of bar

Minimum Maximum Mini. Max. Minimum Maximum0.8% ofc.s.areaof column

6%(Preferable4%)

12 mm 50 mm 4 300 mm

4. Other aspects :

1) Normally size of column should not be altered for at least four floors in multi-storied

buildings.

2) A section less than 200 x 200 mm is generally not preferred.


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3) For columns, rich concrete mixes like M25 and M20 in the lower storey of multi-storey

building will lead to economy. Column sizes should be chosen on the higher side and

richer concrete mixes and age factors shall be used in the lower storey. For

durability, the minimum concrete mix in all concrete members shall be M 20.

4) For achieving economy in shuttering, column size can be kept the same throughout

the height of building ( or in steps of a few storey at the least ) varying the

reinforcement and the concrete mix as required in the design.

5) Slender columns should be avoided, if possible , as these consume more steel than

that required for the corresponding short columns.

6) In earthquake prone areas, square columns will prove more economical than

rectangular columns, as these columns will have to be designed for

earthquake effect in each principal direction .

5. Grouping of Columns:

There are number of columns in one building and size of all columns cannot be

different as formwork is uneconomical. Usually not varying by more than 10 to 20%

and which have their effective lengths equal may be grouped together and then the

columns are designed for the loads that they carry. The columns carrying maximum

load may only be designed in that group and the same section be adopted for all the

columns in that group. This saves the computational efforts and save labour during

the execution of work. This is of prime importance in practical design.

6. Estimation of Loads:

The design of column necessitates determination of loads transferred from beam at different

floor levels. Loads are transferred from slabs to beams and then to columns. Hence, slabs

and beams are normally designed prior to the design of columns. This method enables one

to assess the loads on columns more accurately and thereby and design of column becomes

realistic and economical.

However, in practice, many times situation arise which require the design of columns andfootings to be given to the clients prior to the design of slabs and beams. In such situations,

loads on columns and footings are required to the assessed using judgement based on past

experience or using approximate methods. The loads on the columns can be determined

approximately on the basic of floor area shared by each column. These loads are normally

calculated on the higher side so that they are not less than the actual loads transferred from

slabs / beams. In such cases, the design of column is likely to be uneconomical.


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In case of load bearing structure (Masonry building ) the loads may be calculated as follows:

External wall =25 KN/ m / floor

Internal wall =35 KN/ m / floor

In general the load of 20 KN/ m / floor may be taken for calculation of loads on columns.

Framed structure:

S.No. Column Type Residential building Office building1 Corner column 22 KN/ m2 24 KN/ m2

2 End row middlecolumn(Side column)

17 KN/ m2 19 KN/ m2

3 Interior Column 12 KN/ m2 14 KN/ m2

Add 2 KN / m2 for stair case and Toilet area

As per U.H.Varyani:

S.No. Column location Load intensity over Tributary Floor Area at all supporting levels

1 Corner Column 25 KN/ m2

2 Exterior Column (Side Column) 20 KN/ m2

3 Interior Column 15 KN/ m2

When Column loads are calculated on the basis of the tributary area method, 5% extra

increase in column loads is incorporated to account for unforeseen items and also for elasticbeam shear effects.

When Column loads are calculated by the method of beam reactions, 15% reduction in

Column loads should be made to get realistic loads. This is due to the fact that slab loads in

beams are calculated by the formula wlx / 3 or wlx /6 {3- (lx / ly)2 } which otherwise, lead to

excessive column loads.

In both the methods, live load reduction in multi storeyed buildings should be made as per

relevant code and the column loads, as per modified above, shall be used for column and

footing design and also for earthquake analysis.

Reduction on Floor live loads:In assessment of loads on columns, the reduction in total live loads on floor may be made asspecified under.

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Number of floors carried by the column under % of reduction of total live load on all


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consideration floors above the column under consideration

1 0

2 103 20

4 305 to 10 40

10 or more 50

No reduction shall be made in the case of columns in warehouses, garages and other

buildings used for storage purpose and factories and workshops designed for a live load of

5000 N/m2. However for buildings such as factories and workshops designed for a live load

of more than 5000N/ m2 the reduction shown above may be made provided that the loading

assumed for any column, is not less than, it would have if all floors had been designed for a

live load of 5000 N /m2 with no reduction.

Column loads can be cross checked by using 3-D computer (or space frame analysis )

under VL = (DL + LL)

Computation of Floor load on Column :

(A) Exact Method :

This method is used when the beam end shears are known prior to column design.

The load on column at each floor level is given by

Pufloor = V1 +V2 +V3 + V4 +Pa + Pselfwhere V1,V2,V3,V4 are the end shears of

beams meeting at the floor under consideration from all the four directions 1,2,3,4.

Pa = axial load coming from above

Pself=self weight of the column at the floor under consideration.

(B) Approximate Method:

This method may be used when the column design is required to be done prior to

design of slabs and beams. The loads are calculated based on Tributary area

method.

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P = wAN whereP = Total axial loadW= total loading intensity in KN/m2

A = Tributary area in m2

N= No. of storeys.When column loads are calculated on the basis of this method, 5% extra increase

in column loads is incorporated to account for unforeseen items and also for elastic

beam shear effects.


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When column loads are calculated by the method of beam reactions, 15%reduction in column loads should be made to get realistic loads. This is due to the

fact that slab loads in beams are calculated by the formula wlx or3

wlx { 3- (lx)2 } which otherwise lead to excessive column loads.ly

In both these methods, live load reduction in multistoreyed buildings should be made as per

the relevant code and the column loads as modified above, shall be used for column and

footing design and also for earthquake analysis. Column loads can be cross checked by

using 3-D computer( or space frame) under VL = (DL+LL).

Moments in Columns:

Normally moment on column will be obtained by frame analysis using any standard method.

In case of design for corner column for biaxial bending, moment has to be calculated on

both direction of column. For this the moment on one direction ( major

axis) will be obtained by frame analysis. The moment on other direction (minor axis) will beusually be obtained by approximate method using Table given in IS 456 1964 as givenbelow:

Moments in Columns

Condition Moments for frames of one bay

Moments for frames of two ormore bays

External (and similarlyloaded) columns:

Moment at foot of uppercolumn

Me Ku{ --------------- }Kl + Ku +0.5 Kb

Me Ku{ --------------- }

Kl + Ku + KbMoment at head of lowercolumn

Me Kl{ --------------- }Kl + Ku +0.5 Kb

Me Kl{ --------------- }

Kl + Ku +Kb

Internal Columns:

Moment at foot of uppercolumn

--- Mes Ku{ ---------------------}

Kl + Ku + Kb1+ Kb2

Moment at head of lowercolumn

--- Mes Kl{ ---------------------}

Kl + Ku + Kb1+ Kb2

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Note:1. Notations used in the above table are as follows:

Me = bending moment at the end of the beam framing into the column

assuming fixity at the connection.

Mes = Maximum difference between the moments at the end of two beams

framing into opposite sides of the column, each related on the


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assumption that the ends of the beams are fixed assuming one of the

beams unlocated.

Ku= stiffness of the upper column.Kl= stiffness of the lower column

Kb= stiffness of the beam

Kb1= stiffness of the beam on one side of the column and

Kb2= stiffness of the beam on the other side of the column.

2. For the purpose of this table, stiffness of a member may be obtained

dividing the moment of inertia of a cross-section by the length of the

member provided that the member is of constant cross-section throughout

its length.

3. The equation for the moment at the head of the lower column may

be used for columns in a topmost storey by taking Ku as zero.

TABLE C1

AXIAL LOAD CARRYING CAPACITY RATIO OF COLUMNS

Pu/Ag fck Fck (N/mm

2)

Pt % M15 M20 M25 M30 M35 M400.80 0.545 0.508 0.486 0.471 0.460 0.452

0.90 0.563 0.522 0.496 0.480 0.468 0.459


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1.00 0.581 0.535 0.507 0.489 0.475 0.466

1.10 0.600 0.549 0.518 0.498 0.483 0.472

1.20 0.618 0.562 0.529 0.506 0.491 0.479

1.30 0.636 0.578 0.539 0.515 0.498 0.485

1.40 0.654 0.589 0.550 0.524 0.506 0.492

1.50 0.672 0.603 0.561 0.533 0.513 0.498

1.60 0.690 0.616 0.572 0.542 0.521 0.505

1.70 0.708 0.630 0.582 0.551 0.528 0.5111.80 0.726 0.643 0.593 0.560 0.536 0.518

1.90 0.745 0.657 0.604 0.568 0.543 0.525

2.00 0.763 0.670 0.614 0.577 0.551 0.531

2.10 0.781 0.684 0.625 0.586 0.558 0.538

2.20 0.799 0.697 0.636 0.595 0.566 0.544

2.30 0.817 0.711 0.647 0.604 0.574 0.551

2.40 0.835 0.724 0.657 0.613 0.581 0.557

2.50 0.853 0.738 0.668 0.622 0.589 0.564

2.60 0.872 0.751 0.679 0.631 0.596 0.570

2.70 0.890 0.765 0.689 0.639 0.604 0.5772.80 0.908 0.778 0.700 0.648 0.611 0.583

2.90 0.926 0.792 0.711 0.657 0.619 0.590

3.00 0.944 0.805 0.722 0.666 0.626 0.597

TABLE C1 (Continued)

AXIAL LOAD CARRYING CAPACITY RATIO OF COLUMNS

Pu/Ag fck Fck (N/mm

2)

Pt % M15 M20 M25 M30 M35 M403.20 0.980 0.832 0.743 0.684 0.641 0.610

3.40 1.017 0.859 0.765 0.702 0.657 0.623

3.60 1.053 0.886 0.786 0.719 0.672 0.636

3.80 1.089 0.913 0.807 0.737 0.687 0.649

4.00 1.125 0.940 0.829 0.755 0.702 0.662


23/35

4.20 1.162 0.967 0.850 0.772 0.717 0.675

4.40 1.198 0.994 0.872 0.790 0.732 0.688

4.60 1.234 1.021 0.893 0.808 0.747 0.701

4.80 1.271 1.048 0.915 0.826 0.762 0.714

5.00 1.307 1.075 0.936 0.843 0.777 0.728

5.20 1.343 1.102 0.958 0.861 0.792 0.741

5.40 1.379 1.129 0.979 0.879 0.807 0.754

5.60 1.416 1.156 1.000 0.897 0.823 0.7675.80 1.452 1.183 1.022 0.914 0.838 0.780

6.00 1.488 1.210 1.043 0.932 0.853 0.793

Note:1) The design load of axially loaded short column is calculated when the

minimum Eccentricity does not exceed 0.05 times the lateral dimension ofcolumn using the formula

Pu=0.4 fck As +0.67 fy Asc where Pu is Factored Axial load on thememberAc = Area of concrete

Asc =Area of longitudinal reinforcement

2) Based on the above formula and charts given in Design Aid to IS 456

1978 The value of Pu/Ag fck =0.4 + p/100{ 0.67 fy/ fck 0.4} can befound out and tabulated in the above form.

TABLE C 2

TRANSVERSE REINFORCEMENT FOR COLUMNS

Maximum Pitch of Lareral Ties

Smallest

Dia ofLongitudinal

bar

Dia of Lateral Ties in mm Remarks

6 8 10

12 190 -- -- But > b

16 250 250 -- But > b

20 280 280 -- But > b

25 -- 300 -- But > b


24/35

30 --- 300 -- But > b

32 --- 300 -- But > b

36 -- -- 300 But > b

Note:

1) Minimum Dia. Of lateral ties is greater of the following:i) 6mmii) the dia of largest longitudinal bar.

2) Maximum dia of ties is 16 mm.

3) Maximum spacing of ties is least of the following:i) Least lateral dimension of columns

ii) 16 times the dia of smallest longitudinal bariii) 300 mm.

TABLE C 3

STANDARD DESIGN FOR AXIAL LOADED SHORT SQUARE COLUMNS

STEEL Fe 415 CONCRETE : M15, M20, M25

Column

sizeBXD

(mm)

Main Steel Lateral Ties Safe load carrying capacity of

Column (KN)

No. Dia

(mm)

% Dia

(mm)

Pitch

(mm)

M15 M20 M25

230X230 4 12 0.85 6 190 293 363 433

4 16 1.52 6 230 357 427 496

8 12 1.71 6 190 376 445 5144 20 2.37 6 230 439 508 577

4

4

16

12

2.37 6 190 439 508 577

8 16 3.03 6 230 502 571 639

4 25 3.71 8 230 568 635 703

44

2016

3.89 6 230 585 653 720

300x300 4 16 0.89 6 250 505 624 743

8 12 1.00 6 190 523 642 761


25/35

4 20 1.40 6 300 589 707 825

4

4

16

12

1.40 6 190 589 707 825

8 16 1.79 6 250 652 770 888

4 25 2.18 8 300 716 833 951

44

2016

2.29 6 250 734 851 968

8 20 2.79 6 300 815 932 1049

400x400 8 16 1.00 6 300 930 1141 13534 25 1.23 8 300 997 1208 1418

44

2016

1.29 6 250 1014 1225 1436

12 16 1.51 6 250 1078 1288 1498

8 20 1.57 6 300 1096 1306 1516

16 16 2.01 6 300 1223 1432 1641

4

4

25

20

2.01 8 300 1223 1432 1641

12 20 2.36 6 300 1325 1533 1741

8 25 2.45 8 300 1351 1559 1767

16 20 3.14 6 300 1551 1758 196412 25 3.68 8 300 1708 1913 2119

TABLE C 3 (continued)

STANDARD DESIGN FOR AXIAL LOADED SHORT SQUARE COLUMNS


Columnsize

BXD(mm)

Main Steel Lateral Ties Safe load carrying capacity of Column (KN)

No. Dia(mm)

% Dia(mm)

Pitch(mm)

M15 M20 M25

450x450 4 25 0.97 8 300 1166 1434 1701

12 16 1.19 6 300 1247 1514 1781

4 28 1.21 8 300 1254 1521 1788

8 20 1.24 6 300 1265 1532 1799

4

4

25

20

1.59 8 300 1660 1925

12 20 1.86 6 300 1493 1758 2023

8 25 1.94 8 300 1522 1787 2052

8 28 2.43 8 300 1702 1966 2229

8 32 3.18 8 300 1978 2239 2500

500x500 12 16 0.96 6 300 1435 1765 2096

8 20 1.00 6 300 1453 1783 2113

8 22 1.22 6 300 1553 1882 2212

4

4

25

20

1.29 8 300 1585 1914 2243

16 16 1.29 6 300 1585 1914 2243


26/35

12 20 1.51 6 300 1685 2013 2341

8 25 1.57 8 300 1712 2040 2368

20 16 1.61 6 300 1730 2058 2386

16 20 2.01 6 300 1911 2238 2565

12 25 2.36 8 300 2070 2396 2721

20 20 2.51 6 300 2138 2463 2788

16 25 3.14 8 300 2424 2747 3069

Note : Clear cover assumed : 40 mm for M15 and M2045 mm for M25

Effective cover = clear cover + diameter of ties + half the dia ofthe main bar

The columns are designed for minimum eccentricity of 20 mm

TABLE C 4

STANDARD DESIGN FOR AXIAL LOADED SHORT RECTANGULAR COLUMNS


Column

sizeBXD

(mm)


Column (KN)

No. Dia(mm)

% Dia(mm)

Pitch(mm)

M15 M20 M25

230X300 6 12 0.98 6 190 399 499 581

4 16 1.17 6 230 422 513 604

8 12 1.31 6 190 440 531 622

6 16 1.75 6 230 495 585 676

4 20 1.82 6 230 504 594 684

44

1612

1.82 6 190 504 594 684

8 16 2.33 6 230 568 657 747

6 20 2.73 6 230 618 707 797

4 25 2.84 8 230 631 721 810

4

4

20

16

2.99 6 230 650 739 829

8 20 3.64 6 230 732 820 909

230X350 4 16 1.00 6 230 468 574 681

8 12 1.12 6 190 486 592 698

6 16 1.50 6 230 541 647 752

4 20 1.56 6 230 550 655 761

44

1612

1.56 6 190 550 655 761

44

2016

1.82 6 230 588 693 798


27/35

8 16 2.00 6 230 614 824

6 20 2.34 6 230 664 768 873

4 25 2.44 8 230 678 783 888

8 20 3.12 6 230 778 882 985

6 25 3.67 8 230 858 961 1065




ColumnsizeBXD

(mm)


No. Dia

(mm)

% Dia

(mm)

Pitch

(mm)

M15 M20 M25

230X380 4 16 0.92 6 230 495 611 726

8 12 1.03 6 190 513 628 744

6 16 1.38 6 230 568 798

4 20 1.44 6 230 578 693 80844

1612

1.44 6 190 578 693 808

8 16 1.84 6 230 641 756 870

6 20 2.16 6 230 692 806 920

4 25 2.25 8 230 706 820 934

44

2016

2.36 6 230 724 837 951

8 20 2.87 6 230 805 918 1031

6 25 3.37 8 230 884 996 1109

230X400 4 16 0.87 6 230 513 635 7568 12 0.98 6 190 532 653 774

6 16 1.31 6 230 587 708 829

4 20 1.37 6 230 597 718 839

44

1612

1.37 6 190 597 718 839

8 16 1.75 6 230 660 781 901

6 20 2.05 6 230 710 830 950

4 25 2.13 8 230 723 843 964

44

2016

2.24 6 230 742 862 982


28/35

8 20 2.73 6 230 824 943 1062

6 25 3.2 8 230 902 1021 1139




Columnsize

BXD(mm)


No. Dia(mm)

% Dia(mm)

Pitch(mm)

M15 M20 M25

230X450 8 12 0.87 6 190 577 714 851

10 12 1.09 6 190 619 755 892

6 16 1.17 6 230 834 770 906

44

1612

1.21 6 230 641 777 914

12 12 1.31 6 190 660 796 932

8 16 1.55 6 230 705 841 977

6 20 1.82 6 230 756 891 1027

10 16 1.94 6 230 778 842 1049

4

4

20

16

1.99 6 230 788 923 1058

8 20 2.42 6 230 870 1005 1139

8 25 3.79 8 230 1125 1258 1391

230X500 10 12 0.98 6 190 664 816 968

6 16 1.05 6 230 674 831 982

4

4

16

12

1.09 6 190 687 839 991

12 12 1.18 6 190 706 858 1009

8 16 1.40 6 230 752 903 1054

6 20 1.64 6 230 802 953 1104

10 16 1.75 6 230 825 976 1126

4

4

20

16

1.79 6 230 833 984 1135

12 16 2.10 6 230 898 1048 1198

8 20 2.18 6 230 915 1065 1215

4

4

25

20

2.80 8 230 1044 1194 1342

12 20 3.28 6 230 1144 1292 1441

8 25 3.42 8 230 1173 1321 1469


29/35




ColumnsizeBXD

(mm)


No. Dia(mm)

% Dia(mm)

Pitch(mm)

M15 M20 M25

230X530 10 12 0.93 6 190 693 854 1015

6 16 0.99 6 230 706 867 1028

44

1612

1.03 6 190 715 876 1037

12 12 1.11 6 190 733 894 1054

8 16 1.32 6 230 779 940 1100

6 20 1.55 6 230 830 990 1150

10 16 1.65 6 230 852 1012 1172

44

2016

1.69 6 230 861 1021 1181

12 16 1.98 6 230 925 1085 1244

44

2520

2.64 8 230 1071 1230 1388

8 20 2.06 6 230 943 1102 1261

8 25 3.22 8 230 1199 1357 1514

12 20 3.09 6 230 1171 1328 1486

230X600 10 12 0.82 6 190 757 940 1122

6 16 0.87 6 230 770 952 1135

44

1612

0.91 6 230 780 962 1144

12 12 0.98 6 190 797 979 1162

8 16 1.17 6 230 845 1027 1209

6 20 1.37 6 230 895 1076 1258

10 16 1.46 6 230 917 1099 1280

44

2016

1.49 6 230 925 1106 1287

12 20 2.73 6 230 1235 1414 1593

8 25 2.85 8 230 1265 1444 1623


30/35




ColumnsizeBXD

(mm)


No. Dia

(mm)

% Dia

(mm)

Pitch

(mm)

M15 M20 M25

230X680 4

4

16

12

0.80 6 230 853 1059 1266

12 12 0.87 6 190 872 1079 1286

8 16 1.03 6 230 918 1124 1331

6 20 1.21 6 230 969 1175 1381

10 16 1.29 6 230 992 1197 1403

44 2016 1.32 6 230 1000 1206 1412

8 20 1.61 6 230 1082 1287 1493

8 25 2.38 8 230 1301 1504 1708

12 20 2.41 6 230 1309 1513 1716

230X750 8 16 0.93 6 230 981 1209 1437

10 16 1.17 6 230 1056 1283 1511

44

2016

1.19 6 230 1062 1290 1517

8 20 1.46 6 230 1147 1373 1600

12 20 2.18 6 230 1372 1597 1822

8 25 2.28 8 230 1403 1628 1853300X350 8 12 0.86 6 190 584 723 861

6 16 1.15 6 230 639 777 916

4 20 1.20 6 230 649 787 925

44

1612

1.20 6 190 649 787 925

8 16 1.53 6 230 711 849 987

6 20 1.79 6 230 761 898 1036


31/35




Column

sizeBXD

(mm)


Column (KN)

No. Dia(mm)

% Dia(mm)

Pitch(mm)

M15 M20 M25

4 25 1.87 8 230 776 913 1051

4

4

20

16

1.96 6 230 793 931 1068

8 20 2.39 6 230 875 1012 1148

6 25 2.81 8 230 955 1091 1227

300X380 6 16 1.05 6 230 673 823 974

4

4

16

12

1.10 6 190 683 834 984

8 16 1.41 6 230 748 897 1047

4 25 1.72 8 230 812 961 1110

4

4

20

16

1.80 6 230 828 977 1127

8 20 2.20 6 230 911 1060 1208

6 25 2.58 8 230 989 1138 1286

44

2520

2.82 8 230 1039 1187 1334

8 25 3.44 8 230 1167 1314 1461

300X400 6 16 1.005 6 230 699 857 1016

4

4

16

12

1.047 6 190 708 866 1025

8 16 1.34 6 230 772 929 1087

4 25 1.63 8 230 835 992 1150

4

4

20

16

1.72 6 230 854 1011 1169

8 20 2.09 6 230 935 1092 1248

6 25 2.45 8 230 1013 1169 132544

2520

2.68 8 230 1063 1219 1375

8 25 3.27 8 230 1192 1347 1501

300X450 44

1612

0.93 6 190 768 946 1124


32/35




ColumnsizeBXD

(mm)


No. Dia

(mm)

% Dia

(mm)

Pitch

(mm)

M15 M20 M25

300X450 8 16 1.19 6 230 831 1009 1187

44

2016

1.53 6 230 915 1092 1269

12 16 1.79 6 230 978 1155 1332

8 20 1.86 6 230 995 1172 1349

12 20 2.79 6 230 1223 1398 1573

8 25 2.91 8 230 1252 1427 1602300X500 6 16 0.80 6 250 818 1016 1214

4

4

16

12

0.84 6 250 829 1027 1225

12 12 0.90 6 190 845 1042 1241

8 16 1.07 6 250 891 1089 1287

6 20 1.26 6 250 943 1140 1338

10 16 1.34 6 250 965 1162 1359

4

4

20

16

1.37 6 250 973 1170 1367

12 16 1.61 6 250 1038 1235 1432

8 20 1.67 6 250 1054 1251 144844

2520

2.15 8 300 1185 1381 1576

12 20 2.51 6 300 1283 1478 1673

8 25 2.62 8 300 1313 1508 1702

300X530 8 16 1.01 6 250 927 1137 1347

12 16 1.52 6 250 1074 1283 1492

8 20 1.58 6 250 1092 1300 1509

12 20 2.37 6 250 1319 1526 1733

8 25 2.47 8 300 1348 1555 1762

12 25 3.70 8 300 1703 1907 2111


33/35




Column

sizeBXD

(mm)


Column (KN)

No. Dia(mm)

% Dia(mm)

Pitch(mm)

M15 M20 M25

300X600 8 16 0.89 6 300 1011 1248 1486

12 16 1.34 6 300 1157 1394 1631

8 20 1.40 6 300 1177 1414 1650

12 20 2.09 6 300 1402 1637 1872

12 25 3.27 8 300 1788 2020 2252

300X680 12 16 1.18 6 300 1253 1521 1790

8 20 1.23 6 300 1271 1540 1808

8 25 1.92 8 300 1526 1793 2060

12 25 2.89 8 300 1885 2149 2414

12 28 3.62 8 300 2155 2418 2680

300X700 12 16 1.15 6 250 1278 1555 1832

8 20 1.20 6 300 1221 1574 1850

12 20 1.79 6 300 1522 1797 2072

8 25 1.87 8 300 1552 1827 2102

12 25 2.80 8 300 1906 2179 2451

8 28 2.35 8 300 1735 2008 2382

8 32 3.06 8 300 2005 2277 2548

300X750 12 16 1.07 6 250 1337 1633 1930

8 20 1.12 6 300 1357 1654 1950

16 16 1.43 6 250 1484 1779 2075

12 20 1.68 6 300 1586 1881 2175

16 20 2.23 6 300 1810 2103 2397

12 25 2.62 8 300 1969 2261 2553

16 25 3.49 8 300 2324 2614 2903

300X840 12 16 0.96 6 250 1447 1780 2112

12 20 1.50 6 300 1694 2025 2355

8 28 1.95 8 300 1894 2229 2558

12 25 2.34 8 300 2077 2406 2734

8 32 2.55 8 300 2173 2501 2828


34/35

TABLE C 5

STANDARD DESIGN FOR AXIAL LOADED SHORT CIRCULAR COLUMNS

STEEL: Fe 415 CONCRETE : M15, M20, M25

Columndia

(mm)


No. Dia(mm)

% Dia(mm)

Pitch(mm)

M15 M20 M25

230 6 12 1.63 6 150 289 344 398

8 12 2.18 6 150 330 385 439

6 16 2.9 6 200 385 439 492

8 16 3.87 6 200 458 511 564

300 6 12 0.96 6 200 406 499 593

8 12 1.28 6 200 447 540 633

6 16 1.71 6 200 502 595 687

8 16 2.28 6 200 575 667 759

6 20 2.67 6 200 625 717 809

380 8 12 0.80 6 200 618 768 918

6 16 1.06 6 200 672 821 971

8 16 1.42 6 200 746 895 1044

6 20 1.66 6 200 795 944 1098

8 20 2.22 6 200 910 1058 1206

6 25 2.60 8 250 988 1136 1283

12 20 3.32 6 200 1137 1283 1429

400 8 16 1.28 6 200 794 960 1125

8 20 2.00 6 200 958 1123 1287

8 25 3.13 8 250 1216 1378 1541

8 28 3.92 8 250 1396 1557 1718

450 8 16 1.01 6 200 928 1137 1347

8 20 1.58 6 200 1092 1301 1509

8 25 2.47 8 250 1349 1555 1762

8 28 3.1 8 250 1530 1736 1941


35/35


STANDARD DESIGN FOR AXIAL LOADED SHORT CIRCULAR COLUMNS


Columndia

(mm)


No. Dia(mm)

% Dia(mm)

Pitch(mm)

M15 M20 M25

500 8 20 1.28 6 200 1241 1500 1758

12 20 1.92 6 200 1469 1726 1983

8 25 2.00 8 250 1498 1754 2011

8 28 2.51 8 250 1679 1934 2190

12 25 3.00 8 250 1854 2109 2362

600 8 20 0.89 6 200 1587 1961 2335

12 20 1.33 6 200 1813 2185 2557

8 25 1.39 8 250 1844 2215 2587

8 28 1.74 8 250 2023 2394 2764

12 25 2.08 8 250 2198 2567 2936

Note:Clear cover assumed : 40 mm for M15 and M20

45 mm for M25Effective cover = clear cover + diameter of ties + half the dia of

the main bar

The load arrived above are for circular tiesFor helical ties the above load shall be multiplied by 1.05

columnplan2r

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