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Column Bases

Raju Sharma

Assistant ProfessorDeptt. Of Civil Engineering

Chandigarh

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Column Bases

Column bases transmit the column load to the

concrete or masonry foundation blocks. The

column base spreads the load on wider area

so that the intensity of bearing pressure on

the foundation block is within the bearing

strength. There are two types of column bases

commonly used in practice

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Slab Base

GussetedBase

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SLAB BASE

These are used in

columns carrying small

loads. In this type , the

column is directlyconnected to the base

plate through cleat

angles. The load is

transferred to the base

plate through bearing

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Gusseted Base

For Columns carryingheavy loads gussetedbases are used. Ingusseted base, thecolumn is connected tobase plate throughgussets. The load istransferred to the base

partly through bearingand partly throughgussets.

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Design of Slab Base

The design of slab base consists in finding the

size and thickness of slab base. In the

procedure given below it is assumed that the

pressure is distributed uniformly under the

slab base.

Size of Base Plate:

(1) Find bearing strength of concrete = 0.45fck

(2) Area of base plate = (pu/0.45fck), where pu is

factored load.

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(3) Select the size of base plate. For economy, as

far as possible keep the projections a and b

equal.

Thickness of Base Plate:

(1) Intensity of pressure

w = pu/area of base plate

(2) Minimum thickness required is given by

ts

= (2.5w(a -0.36)

mo

/fy)ts= thickness of base plate

tf = thickness of flange

0.5

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Connections

(1) Connect base plate to foundation concrete

using four 20mm diameter and 300 mm long

anchor bolts.(2) If bolted connection is to be used for

connecting column to base plate, use 2 ISA

65x65x6 mm thick angle with 20 mm bolts.(3) If weld is to be used for connecting column

to base check the weld length of filler welds