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 .
What’s a beam ?
Beam is a horizontal element of a structure and spans between one or more supports.
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
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
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.
Criterion of beam design:
Beam depth is derived as follows:
Based on their function beams can be grouped as :
1.Below the plinth( In Substructure)
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 )
2.6 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.
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.
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.
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:
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.
Set of beams in two perpendicular directions and at a closer spacing which together support a slab above.
Portal is a structure which has integrated beam and two columns .
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 ).