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Regarding Design of Plinth Beam
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khaja092
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PostPosted: Sat Feb 20, 2021 7:30 pm    Post subject: Regarding Design of Plinth Beam Reply with quote

It can be designed as normal beam
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Ujjwal
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PostPosted: Sun Feb 21, 2021 2:23 pm    Post subject: Plinth Beam Reply with quote

Ujjwal wrote:
someshwar ganti wrote:
I feel that a Plinth beam cannot be designed as a Normal Continuous beam like that in a Roof beam.

1. the Plinth beam is Normally casted on a CRS masonry, which gives it support through out the length of the BEAM hence our normal BM equations will not really apply,  

   Please note for a roof beam the wall is constructed much later hence normal equations apply.


Besides the Wall load on the plinth beam, most of the sites (especially factory sheds etc) will have tractors, tippers running on the some of the bays of the plinth beams, These beams survive only because there is a CRS wall supporting the beam through out.

hence in my opinion , design it as a normal beam because the construction loads on plinth beams (atleast in some bays ) is much higher than the wall load on the beams, in such a case the CRS support below the beam will prevent the deflection etc hence the failure.
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Dr. N. Subramanian
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PostPosted: Sun Feb 21, 2021 7:39 pm    Post subject: Reply with quote

Even if there are openings are there you can consider composite action- for windows you will have 2.5 feet brick wall and there will not be doors in the outside walls. You can't take 4.5 inch wall to give composite action.
Best wishes
NS


quote="hishamajmalpc"]Sir,
Most of the cases there will be openings in wall (Doors/windows). Can we assume composite action in those cases?[/quote]
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vikram.jeet
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PostPosted: Sun Mar 28, 2021 4:02 am    Post subject: Reply with quote

If soil is expansive , it is better to design plinth beam for masonry load as normal beam. But in other soils plinth beam rest on filled up soil and some relief in moments due to soil beam interaction is permitted .also as  indicated by NS sir the masonry with rcc at bottom act together to form composite action. But still plinth beams need to to be designed for full equake moments and no relief is admissible for seismic moments.

Best tgds
Vikramjeet
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Arunachalam
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PostPosted: Sun Jun 20, 2021 5:10 pm    Post subject: Plinth beams reg Reply with quote

Plinth beams for my experience to be designed much care as there may be some openings below it for cable ducts, openings etc. Also in ground floor level the masonry infill height is much more than the upper floors. in large buildings vechicle unloads the construction mateials inside Gf level during construction periods. Also the soil below the plinth beam though we provide base concrete or brick on egde as in practice may subject to settlements which directly affect the plitn beam. In lager plinth height  compare to the road level gives thrust on sides of plith beam, in this caseit actsm as retaing wall along with brick masonry. under the prevailing site condition while design proper care required as per my opinion than normal floor beams.
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vikram.jeet
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PostPosted: Mon Jun 21, 2021 3:44 am    Post subject: Reply with quote

Plinth Beams

As the name indicate, the beam provided at Plinth Level  are plinth beams. It surves multi functions :

1. It supports the ground storey wall Loads
2.  It reduces the slenderness of column to which it is attached
3. It resist Seismic forces by providing joint restraints to column

Outer peripheral Plinth Beams:
There is always some 300mm to 500mm level difference between Plinth Level and outside Ground Formation Level. Plinth beams are provided at PL. Hence there is need to provide some masonry wall underneath Plinth beams which can go some 0.45 m below Formation GL of outside with some pcc pooting of 375mm to 450mm. The gravity loads are thus shared / fully taken by masonry.
Plinth beam is subjected to some % of gravity moment , but it must be designed for FULL SEISMIC MOMENTS and also shear s

Inner Plinth beams
These are laid on 40 to 50mm PCC directly over Plinth fill soil well compacted. Normally these inner PBeams do not support any wall, but sometimes half brick partition wall. These are also designed with some % of gravity  BM + FULL EQ MOMENTS, And also shears
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es_jayakumar
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PostPosted: Tue Jun 22, 2021 1:56 am    Post subject: Reply with quote

On many occasions we provide Grade Beams at or below the GL. They carry the load of the plinth masonry, in addition.

E S Jayakumar
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vikram.jeet
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PostPosted: Tue Jun 22, 2021 3:49 am    Post subject: Reply with quote

Yes, Grade beams are sometimes required at FGL. Then plinth beam is not provided , and Grade beam serves the role of Plinth beam .
Plinth masonry load is in addition to ground storey load as rightly enlightened by Er ES Jayakumar.



es_jayakumar wrote:
On many occasions we provide Grade Beams at or below the GL. They carry the load of the plinth masonry, in addition.

E S Jayakumar
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