Architectural Presentation-RAFT FOUNDATION

FOUNDATION
MAIN FUNCTION IS TO CARRY THE LOAD OF THE SUPERSTRUCRURE TO THE SUBSOIL .
SELECTION OF FOUNDATION
THE TYPE OF THE FOUNDATION IS MAINLY DEPEND UPON THE FOLLOWING THINGS :-

TYPE OF CONSTRUCTION.
LOAD BEARING CAPACITY OF OF SOIL.
WHEN STRUCTURE HAS ONLY LIGHT LOADING SUCH AS DOMESTIC DWELLING HOUSE,THE RAFT OR MASS CONCRETE STRIP FOUNDATION IS SUFFICIENT.
THE PLAN SIZE OF A FOUNDATION IS DERIVED FROM
LOAD/
BEARING CAPACITY OF SOIL
TYPES OF THE FOUNDATIONS
STRIP FOUNDATIONS.
ISOLATED OR PAD FOUNDATIONS.
RAFT FOUNDATIONS.
COMBINATION OF ABOVE FOUNDATIONS.
PILED FOUNDATION.

STRIP FOUNDATIONS
REINFORCED CONCRETE STRIP FOUNDATIONS ARE USED TO SUPPORT AND TRANSMIT THE LOADS OF HEAVY WALLS.

ISOLATED OR PAD FOUNDATIONS
THIS TYPE OF FOUNDATION IS USED TO SUPPORT AND TRANSMIT THE LOADS FROM PIERS AND COLUMN.

RAFT FOUNDATION
THE PRINCIPAL OF ANY RAFT FOUNDATION IS
TO SPREAD THE LOAD OF THE ENTIRE AREA OF THE SITE.
A RAFT FOUNDATION NORMALLY CONSISTS OF A
CONCRETE SLAB WHICH EXTENDS OVER THE
ENTIRE AREA. IT MAY BE STIFFENED BY RIBS OR
BEAMS INCORPORATED INTO THE FOUNDATION.
THEY ARE MADE UP OF CONCRETE AND HEAVILY REINFORCED WITH STEEL,SO ENTIRE FOUNDATION WILL ACT AS A UNIT
THE RAFT FOUNDATIONS HAVE THE ADVANTAGE OF REDUCING DIFFERENTIAL SETTLEMENTS AS THE CONCRETE SLAB RESISTS DIFFERENTIAL MOVEMENTS BETWEEN LOADING POSITIONS.

WHERE RAFT FOUNDATIONS ARE USE ?
THE RAFT FOUNDATIONAS ARE USED WHERE THE COLUMN LOAD ARE HEAVY AND THUS REQUIRING LARGE BASES.
WHERE THE BEARING CAPACITY OF SOIL IS LOW, RESULTING IN THE NEED OF LARGE BASE.
THEY ARE USED ON SOFT COMPRESSIBLE SUBSOIL SUCH AS SOFT CLAY OR PIT.
TYPES OF RAFT FOUNDATION
RAFT FOUNDATIONS CAN BE CONSIDER IN THREE TYPES

SOLID SLAB RAFTS.
BEAM AND SLAB RAFTS.
CELLULAR RAFTS.
SOLID SLAB RAFT FOUNDATION
THESE ARE CONSTRUCTED OF UNIFORM THICKNESS OVER THE WHOLE RAFT AREA.

THE EFFECT OF THE LOAD FROM COLUMN AND THE GROUND PRESSURE IS TO CREATE AREAS OF TENTION UNDER THE COLUMN AND THE AREAS OF TENTION IN THE UPPER PART OF THE RAFT BETWEEN THE COLUMN.

OFTEN THE NOMINAL MESH OF REINFORCEMENT IS PROVIDED IN THE FACES WHERE TENTION DOES NOT OCCUR TO CONTROL SHRINKAGE CRACKING OF THE CONCRETE.

BEAM AND SLAB RAFT FOUNDATION
BEAM AND SLAB RAFTS ARE ALTERNATIVES TO THE SOLID SLAB RAFT AND ARE USED WHERE POOR SOILS ARE UNCOUNTERED.
THE BEAMS ARE USED TO DISTRIBUTE THE COLUMN LOAD OVER THE AREA OF THE RAFT, THAT RESULTS IN THE REDUCTION OF THE SLAB THICKNESS.
THE BEAMS CAN BE UPSTAND OR DOWNSTAND DEPENDING UPON THE BEARING CAPACITY OF SOIL NEAR THE SURFACE.
DOWNSTAND BEAMS WILL GIVE A SAVING ON EXCAVATION COSTS WHEREAS UPSTAND BEAMS CREATE A USABLE VOID BELOW THE GROUNG FLOOR IF A SUSPENDED SLAB IS USED.

CELLULAR RAFT FOUNDATION

THESE TYPE OF FOUNDATIONS ARE USED ON SOFT COMPRESSIBLE SUBSOIL SUCH AS SOFT CLAY OR PIT.

SO DURING CURING PROCESS THE REINFORCEMENT AT THE BOTTOM SHOULD BE PROVIDED TRUE LEVEL SURFACE FROM WHICH THE REINFORCEMENT CAN BE POSITIONED.

A BLINDING LAYER OF 50 TO 75mm THICK OF WEAK CONCRETE OR COURSE SAND SHOULD BE PLACED UNDER REINFORSED CONCRETE (RAFT) FOUNDATION.

THE FUNCTION OF THIS LAYER IS TO FILL IN ANY WEAK POCKETS ENCOUNTERED DURING EXCAVATION.
REINFORCEMENT DETAIL OF RAFT FOUNDATION

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