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Unformatted text preview: inertia of the area of the raft respectively about the
x and y axes through the centroid,
17 IS : 2950 ( Part I ) - 1981
I,, = J xydA for the whole area about x and y axes through the
ee, o,, = eccentricities in the x and y, directions
centroid. of the load from the For a rectangular raft the equation simplifies to: where
LIand b :.=-: dimensions of the raft in the x and y directions
NOTE - If one or more of the values of ( q ) are negative, as calculated
formula, it indicates that the whole area of foundation is not subject to
only a part of the area is in contact with the soil, and the above formula
good, provided appropriate values of L,. I,. I,., e z and ey are used with
area in contact with the soil instead of the whole area. APPENDIX by the above
will still hold
respect to the E ( Clause 5.2.1 )
CONTACT PRESSURE DISTRIBUTION AND MOMENTS
BELOW FLEXIBLE FOUNDATION
E-l. CONTACT PRESSURE DISTRIBUTION E-l.1 The distribution of contact pressure is assumed to be linear with
maximum value attained under the columns and minimum at mid span.
El.2 The contact pressure for the full width of the strip under an interior
column load located at point i (pi ) can be determined as ( see Fig. 3B ):
pi = 7 , 48_Mi
I’ = average length of adjacent span ( m ),
Pi = column load at poiflt i ( t ), and
Md = moment under an interior columns located at i.
18 ___-_ ._._ IS : 2950 ( Part I ) - 1981
E-l.3 The minimum contact pressure for the full width of the strip at the
middle of the adjacent spans p,,,~ and pmr can be determined as
( see Fig. 3A ): P It PmZ = ZPi~--ppt7; pmr = 2Pi -k - pi;
Pmr f pm = +
where I,, 16as shown in Fig. 3A.
El.4 If E-2.3( a) governs the moment under the exterior columns, contact
pressures under the exterior columns and at end of the strip pd and pe can
be determined as ( &see
Fig. 3C ): 6M. - 4P* + & ps = 3M. po = -C-a- - pml1 - PC
2 Ps, pm, M,, II, C as shown in Fig. 3C.
E-l.5 If E-2.3 ( b ) governs the moment under the exterior columns, the
contact pressures ps and pe are determined as ( see Fig. 3C ):
pc = pc = L!!&?$
1 1 E-2. BENDING MOMENT DIAGRAM
E-2.1 The bending moment under an interior
Fig. 3A ) can be determined as:
M<=-g column located at i ( see ( 0.24ti + 016 ) E-2.2 The bending moment at midspan is obtained as ( see Fig. 3B ):
M, = Mo + MI
M,, = moment of simply supported beam where I, pr( I ), pd( r ), jrn are as shown in Fig. 3B.
19 fbL.- _..-..^_. .__. ~-.-._
. IS : 2950 ( Part I ) - 1981 3A Moment and Pressure Distribution 3B Pressure Distribution Over an Interior Span 3C. Moment and Pressure Distribution
FIG. 3 at interior Column at Exterior Column MOMENT
AND PRESSURE DISTRIBUTION COLUMNS
20 IS : 2950 ( Part I ) - 1981
E-2.3 The bending moment M, under exterior columns can be determined
as the least of ( see Fig. 3C ):
a) ..I+ ( 013h6 + 1.06 AC - 0.50 ) b) ( 4 4c_+
_. ~_P* - pr, __ 2 ”
&)C APPENDIX F ( czuuse 5.2.1 .l )
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This note was uploaded on 03/14/2014 for the course CE 684 taught by Professor Prof.deepankarchoudhury during the Spring '13 term at IIT Bombay.
- Spring '13