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This document provides guidelines for determining the dimensions of an annular circular raft foundation with a ring beam to satisfy conditions of maximum and minimum soil pressure. It states that the maximum pressure under the foundation should not exceed the safe bearing pressure of the soil, and the minimum pressure shall be zero or compressive. It provides two equations to calculate the area (A) of the raft and the eccentricity (b) of the vertical load to meet these conditions, using variables such as the total structure weight, load eccentricity, raft radii, soil bearing capacity, overburden pressure, and desired net pressure.

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Balaji Prasath
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35 views1 page

Is. - 0 13

This document provides guidelines for determining the dimensions of an annular circular raft foundation with a ring beam to satisfy conditions of maximum and minimum soil pressure. It states that the maximum pressure under the foundation should not exceed the safe bearing pressure of the soil, and the minimum pressure shall be zero or compressive. It provides two equations to calculate the area (A) of the raft and the eccentricity (b) of the vertical load to meet these conditions, using variables such as the total structure weight, load eccentricity, raft radii, soil bearing capacity, overburden pressure, and desired net pressure.

Uploaded by

Balaji Prasath
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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IS : 11089- 1984

10

s 09

:: 04
cn
w 0.7
3
A
>Q 0.6

o.soI 0.1 0.2 0.3 04 0.5 0.6 0.7 0.8 0.9


VALUES OF b/a

FIG. 1C POSITION OF RING BEAM FOR MINIMUM VALVE OF


THE MAXIMUM MOMENTS
5.2 In case the annular circular raft with a ring beam, two conditions
are ,gcnerally to be satisfied. The maximum pressure under foundation
should not exceed the safe allowable bearing pressure of the soil. The
minimum pressure shall be zero or of a compressive nature. To satisfy
these, the clirnensions of rafts shall be determined as follows:

where

A = ~_____
gall - ( PO - PI )
where
w ~- total weight of the structure above ground
b= eccentricity of the vertical load on base due to over-
turning moment of lateral loads of wind or earthquake
n= outer radius of annular raft or radius of solid raft
b = inner radius of annular raft
.t area of raft
x ( & - 62 )
gall = net safe bearing capacity of soil at base
PO Q overburden pressure due to depth of foundation
PI = net pressure clesired at base.
9

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