Oh no..So Many beams ?

Overview:

No one can  imagine  a building without the presence of beams…different types ,different uses.

This article takes the reader to the interesting world of beams which strengthen and also adore any building.Here we shall only talk about Beams in a RCC structure since the Beams provided in the steel structures justifies  a separate post .

So let us start with the basics first.

What’s a beam ?
Beam is a horizontal element of a structure and spans between one or more supports.

TYPICAL RCC FRAMED STRUCTURE WITH BEAMS & COLUMNS
TYPICAL RCC FRAMED STRUCTURE WITH BEAMS & COLUMNS
Every beam has a purpose:

In general ,if something is to be kept on an opening, we need a beam. However,there could be other situations necessitating a beam
1.Tying columns together.
2. Supporting masonry above
3. Supporting slab above : This is most common function of a beam.
4. Supporting slab below : This you shall see in a porch or in a sunk portion of the toilet.
5. Supporting secondary  beams :
6. Suspending accessories:
6.1 Electrical luminaries
6.2 Electrical cables
6.3 Air handling ducts
6.4 Suspended ceiling
7. Supporting water tank above

OBSERVE THE GRID OF BEAMS IN THE STAGING OF THIS HUGE OVERHEAD WATER TANK.
OBSERVE THE GRID OF BEAMS IN THE STAGING OF THIS HUGE OVERHEAD WATER TANK.
Normal load distribution:

In a RCC framed structure, the load of occupants is taken by a slab which gets transferred to a beam. Beam transfers this load to column

Geometry of a beam:

Most common geometry of a beam is rectangular. The depth of beam shall always be larger than the width. This beam is stronger than if beam width is larger than the depth.

This rule shall be deviated only in the case of a band beam {Hindi:Patli } since width shall be 115 MM but depth is 75mm.
BAND BEAM OR PATLI WITHIN THE AAC BLOCKS PARTITION WALL
BAND BEAM OR PATLI WITHIN THE AAC BLOCKS PARTITION WALL

Criterion of beam design:
Beam depth is derived as follows:

1.It should be such that the stress on the extreme fibres shall not exceed the safe stress limits for that material.
2.The deflection shall not exceed the specified limits.
Higher value of the 1 & 2 shall be normally specified as the beam depth.
Types of beams:

Based on their function beams can be grouped as :
1.Below the plinth( In Substructure)
1.1Tie beam
1.2 Ground beam
1.3 Plinth beams: At plinth level
2.Above the plinth( In Super-structure)
2.1Sill beam: Below the window
2.2Band beam( Marathi: Patli )
2.3Lintel
2.4Roof beams
2.5 Spandrel
2.6 Hidden beam:
This name is given because this beam is not visible after slab is cast. Basically slab is not designed to take direct load of a masonry wall. The hidden beam receives wall load and transfers to main beams.

PLINTH BEAMS IN A RESIDENTIAL BUILDING
PLINTH BEAMS IN A RESIDENTIAL BUILDING
2.7 Inverted beam : When the slab is below the beam , such beam is known as the Inverted beam.
This is usually provided at 3 situations :
1. Sunk slab for the toilet
2.Porch beams
3.Staircase mid landing
PORCH in a 40 years old building. with CANTILEVER  INVERTED BEAMS and SIMPLY SUPPORTED SLAB
PORCH in a 40 years old building.
with CANTILEVER INVERTED BEAMS and SIMPLY SUPPORTED SLAB

2.8 Coping beam ;

This provided at the top of a masonry parapet wall in order to protect the bricks from getting dislodged due to wear and also to provide a bracing to the wall. Quite often , reinforcement is avoided in coping and only concrete is cast in a rectangular shape.

Remember :

Difference between a Band beam ( Marathi  : Patli ) & a Coping is that there is nothing on top of Coping whereas masonry is continued after Band beam.

COPING AT THE TOP OF A BRICK MASONRY PARAPET.
COPING AT THE TOP OF A BRICK MASONRY PARAPET.
3.Based on the supporting pattern, beams can be categorized as below:

3.1 Cantilever beams: Only one support
3.2 Simply supported : Two supports
3.3 Continuous beams: More than two supports
3.4 Overhang beams : Two supports

4.Based on their shape in plan , ( or how do they appear from above) the beams can be divided into:
4.1.Straight horizontal beams:
4.2 Straight  inclined beams:
4.3 Curved beams:

5.Some beams are just unique and need special mention:

5.1 Pergola: 

Set of beams at smaller spacing which don’t have a slab above. This is mainly an architectural feature and usually given at the terrace level.

PERGOLA: LOOK AT THE TOP OF THE WHITE BUILDING. YOU SEE SEVERAL BEAMS WITHOUT A SLAB ? THAT'S PERGOLA.
PERGOLA:
           LOOK AT THE TOP OF THE WHITE BUILDING.
                   DO YOU SEE SEVERAL BEAMS                                       WITHOUT  A SLAB ?
THAT’S PERGOLA.
5.2 Grid beams:

Set of beams in two perpendicular directions and at a closer spacing which together support a slab above.

GRID BEAMS WITH SLAB
GRID BEAMS WITH SLAB
5.3 Portal beam:

Portal is a structure which has integrated beam and two columns .

 5.4 Arch:

The interesting thing about arch is that it is a compression member. Arch cab also be said to be a remote predecessor of the concept of pre-stressed  concrete.( we shall talk about this some other time ).

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