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Determination of BASE PRESSURE for a BOX CULVERT

 
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gauravmaroo
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PostPosted: Sat Jan 10, 2009 5:04 am    Post subject: Determination of BASE PRESSURE for a BOX CULVERT Reply with quote

Dear all
i need to analyze a twin cell box culvert having following dimensions

CARRIAGEWAY WIDTH= 13.5 M
HEIGHT ABOVE GL=6 M
SPAN OF ONE CELL = 5 M EACH
TOTAL SPAN=10 M
DESIGN FOR (DL+SIDL+.5LL+TEMP+EARTH PRESSURE)
SBC OF SOIL=18 T/M2

SO MY QUERY IS HOW CAN I MODEL THE SUPPORT CONDITION FOR SLAB WHICH IS RESTING OVER SOIL UNIFORMLY.

ONE OPTION IS THAT BY TREATING IT AS RIGID FOUNDATION AND HENCE BASE PRESSURE INTENSITY= TOTAL LOAD/AREA OF BOTTOM SLAB
IN THIS CASE I AM GETTING BASE PRESSURE INTENSITY =11 T/M2

SECOND IS DEFINING FOUNDATION AS SEMI RIGID STRUCTURE AND PROVIDING SPRING SUPPORT AT CLOSE SPACING AND GIVING THEM STIFFNESS IN PROPORTION TO SOIL CAPACITY.
IN THIS CASE AT THE OUTER SPRING SUPPORT BASE PRESSURE INTENSITY=22 T/M2
BY DIVIDING SPRING SUPPORT AREA TO VERTICAL REACTION. IN SUPPORT OTHER THAN BELOW THREE WALLS OF TWIN BOX CELL BASE PRESSURE INTENSITY <8 T /M2


LAST OPTION IS TO TREAT FOUNDATION AS FLEXIBLE AND  MODELING A MAT FOUNDATION WHICH GIVES A PRESSURE INTENSITY =13 T/M2. HERE UNIFORM PLAT ELEMENT IS USED WITH 3D MODELLING.

SO WHAT SHOULD BE THE CORRECT APPROACH TO DETERMINE THE DEPTH OF FOUNDATION OR IN OTHER WORDS BASE PRESSURE INTENSITY OF SOIL AS WE NEED TO DESIGN IN CASE OF OPEN FOUNDATIONS.AS THESE ARE UNIFORMLY SUPPORTED ON SOIL.

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Last edited by gauravmaroo on Sat Jan 10, 2009 6:12 am; edited 2 times in total
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PrachiThube
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PostPosted: Sat Jan 10, 2009 6:01 am    Post subject: Determination of SBC of foundation soil for a BOX CULVERT Reply with quote

SBC and Base pressure are two different parameters.
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gauravmaroo
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PostPosted: Sat Jan 10, 2009 6:06 am    Post subject: SBC AND BASE PRESSURE Reply with quote

I THINK BY GETTING BASE PRESSURE VALUES WE WILL CHECK FOR SBC
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Avi
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PostPosted: Wed Jan 14, 2009 6:31 am    Post subject: Re: Determination of SBC of foundation soil for a BOX CULVER Reply with quote

PrachiThube wrote:
SBC and Base pressure are two different parameters.
SBC and Base Pressure are two different parameters correct but Base Pressure cannot exceed SBC value.
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gauravmaroo
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PostPosted: Wed Jan 14, 2009 6:42 am    Post subject: i need solution plz Reply with quote

Dear all i know what is base pressure but my problem is how can i calculate it as there are lots of methods i mentioned..what practice ppl in industry are following.
kindly provide reply with some help..

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PostPosted: Wed Jan 28, 2009 6:46 am    Post subject: SEISMIC CLAUSES APPLICABLE ON BOX CULVERT Reply with quote

AS PER IRC 6 CLAUSES 222

1) CLAUSE -222.7-WE NEED NOT TO TAKE SEISMIC FORCE ON LIVE LOAD WHEN ACTING IN TRAFFIC OR LONGITUDINAL DIRECTION.MEANS WE WILL USE 0.18(DL+SIDL).

2) WE WILL USE 0.18(DL+SIDL)+0.5(0.18*LL) WHEN ACTING IN TRANSVERSE DIRECTION .HENCE 50% OF LIVE LOAD TO BE USED.

3) CLAUSE-222.10 PARTS OF STRUCTURE EMBEDDED IN SOIL SHALL NOT CONSIDERED TO PRODUCE ANY SEISMIC FORCES.


>>>DO THESE CLAUSES MEANT TO ECONOMIES THE DESIGN OR IS THERE ANY TECHNICAL EXPLANATION FOR CONSIDERING THE EFFECT RELATED TO LIVE LOAD.AS WE ALSO INCREASE PERMISSIBLE STRESSES BY 50% ALONG WITH THESE CLAUSES.

>>>EMBEDDED IN EARTH CASE THAN WHAT WILL BE APPLICABLE IN CASE OF BOX CULVERT , INTEGRAL BRIDGES ETC.

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ibarua
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PostPosted: Wed Jan 28, 2009 10:09 am    Post subject: Determination of BASE PRESSURE for a BOX CULVERT Reply with quote

28 Jan 2009

1. As the LL, i.e.,the vehicle is free to move in the direction of the traffic (longitudinal direction), it will move with the eq. and not have any effect on the structure.

2.  In the transverse direction, seimsic forces arising out of the weight of the vehicle will be transferred to the bridge deck by friction between the tyre of the vehicle and the deck surface.

3.  50% of the LL is to be taken because it is statistically improbable that max. LL and the design eq. will act the same time.

4.  The quake will probably not occur at the same time as the HFL.

5.  Structures below ground or embedded therein will move along with the ground during an eq. -- no out of phase movement -- hence no effect.

Hope this answers your queries.

Indrajit Barua.  

On Wed, 28 Jan 2009 gauravmaroo wrote :
Quote:
AS PER IRC 6 CLAUSES 222

1) CLAUSE -222.7-WE NEED NOT TO TAKE SEISMIC FORCE ON
LIVE LOAD WHEN ACTING IN TRAFFIC OR LONGITUDINAL
DIRECTION.MEANS WE WILL USE 0.18(DL+SIDL).

2) WE WILL USE 0.18(DL+SIDL)+0.5(0.18*LL) WHEN ACTING
IN TRANSVERSE DIRECTION .HENCE 50% OF LIVE LOAD TO BE
USED.

3) CLAUSE-222.10 PARTS OF STRUCTURE EMBEDDED IN SOIL
SHALL NOT CONSIDERED TO PRODUCE ANY SEISMIC FORCES.


Quote:
Quote:
Quote:
DO THESE CLAUSES MEANT TO ECONOMIES THE DESIGN OR IS
THERE ANY TECHNICAL EXPLANATION FOR CONSIDERING THE
EFFECT RELATED TO LIVE LOAD.AS WE ALSO INCREASE
PERMISSIBLE STRESSES BY 50% ALONG WITH THESE CLAUSES.

Quote:
Quote:
Quote:
EMBEDDED IN EARTH CASE THAN WHAT WILL BE APPLICABLE
IN CASE OF BOX CULVERT , INTEGRAL BRIDGES ETC.

------------------------
Gaurav Maroo
MTech(IITR),BE(MBMECJ)
+91-9958538375








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gauravmaroo
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PostPosted: Wed Jan 28, 2009 11:42 am    Post subject: box culvert Reply with quote

i think in case of a box culvert ...the box is empty in middle and not having any soil filled...so how we can take it in category of structures buried under soil.
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prof.arc
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PostPosted: Thu Jan 29, 2009 12:01 am    Post subject: Determination of BASE PRESSURE for a BOX CULVERT Reply with quote

The difference between two directions is due to the friction of the mounted live load.
In the direction of traffic the dynamic friction is considered negligible.
You are debating IRC clauses in your query.
While the codes were formulated for IS:1893, it was felt that culverts need not be included It was thought that they are far too many culverts and it is better to accept the risk of their damage than design all culverts !!
ARC

On Wed, Jan 28, 2009 at 12:16 PM, gauravmaroo <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           AS PER IRC 6 CLAUSES 222

1) CLAUSE -222.7-WE NEED NOT TO TAKE SEISMIC FORCE ON LIVE LOAD WHEN ACTING IN TRAFFIC OR LONGITUDINAL DIRECTION.MEANS WE WILL USE 0.18(DL+SIDL).

2) WE WILL USE 0.18(DL+SIDL)+0.5(0.18*LL) WHEN ACTING IN TRANSVERSE DIRECTION .HENCE 50% OF LIVE LOAD TO BE USED.

3) CLAUSE-222.10 PARTS OF STRUCTURE EMBEDDED IN SOIL SHALL NOT CONSIDERED TO PRODUCE ANY SEISMIC FORCES.


Quote:
Quote:
Quote:
DO THESE CLAUSES MEANT TO ECONOMIES THE DESIGN OR IS THERE ANY TECHNICAL EXPLANATION FOR CONSIDERING THE EFFECT RELATED TO LIVE LOAD.AS WE ALSO INCREASE PERMISSIBLE STRESSES BY 50% ALONG WITH THESE CLAUSES.

Quote:
Quote:
Quote:
EMBEDDED IN EARTH CASE THAN WHAT WILL BE APPLICABLE IN CASE OF BOX CULVERT , INTEGRAL BRIDGES ETC.



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