A beam is a horizontal structural member in a building to resist the lateral loads applied to the beams axis. The structural member which resists the forces laterally or transversely applied to the (beam) axis is called beam.
In beams, loads are acting transversely to the longitudinal axis, which produces the shear forces and bending moment. The lateral load acting on beams are the main cause bending of the beam. The beams are responsible to transfer a load from the slab to the column. The load distribution pattern is,
Slab |> Beam |> Column |> Foundation
That beam which is connected with the column and this connection is called direct support while the beam connected with beam and this connection is called indirect support.
Purpose of beams
The beam is a structural element that is capable of withstanding load primarily by resisting its bending forces. They are made of steel or reinforced concrete (RCC)or steel. The beams are used in structure to
Counter bending moment and shear forces.
Connect the structure together.
Provide a uniform distribution of loads.
In the beam, the different reinforcements were used having different purposes such as
Support bars – These bars are located in the top portion of the beam and just function to hold the stirrups in place.
stirrups – To counter the shear stresses (shear force).
Beams are generally characterized by their profile (shape, cross-section, length, material). This member of RCC structures is placed horizontally to carry the load and counter both bending and shear stresses.
The standard size of the beams,
In a residential building is 9 ʺ × 12 ʺ or 225 mm × 300 mm according to the (IS codes).
The minimum size of the RCC beam should not be less than the 9 ʺ× 9 ʺ or 225mm × 225mm with the addition of slab thickness which is 125mm.
Purpose of stirrups in the beam.
Stirrups are used to counter the shear force. It is also called shear reinforcement in the beam.
Shear force is maximum at the end supports (simply supported beams) and zero at the mid of the span that’s why the spacing of stirrups or rings is closed to each end supports as compared to the mid.
Stirrups are made in a rectangular shape with reinforcement bars and which is wrapped around the top and bottom bars of the beam.
Sometimes, stirrups are placed diagonally and vertically to avoid the shear failure in case of cracks in beams.
Classification of beams:
Generally, beams are classified by the shape of their cross-section, by their length and by their equilibrium conditions.
According to the support conditions:
1: Simply supported beams:
A simply supported beam is supported at both ends. These beams are mostly used in general construction.
Supported freely to rotate at the two ends on walls or columns.
Have no moment resistant at support.
2: Continuous beams:
A beam which has more than two supports this kind of beam is called continuous beams. Two or more than two supports are used between these beams and these beams are similar to the simply supported beams.
Supported on two or more vertical supports.
It is considered as a more economical beam as compared to others.
The beam over which both sides have an overhanging called double overhanging beam.
3: Fixed beams:
A beam which is fixed at both ends it is called a fixed beam. Fixed beams are not allowed the vertical movement or rotation of the beam. In this beam, no bending moment will produce. Fixed beams are only under the shear force and are generally used in the trusses and like other structure.
Both ends of the beam rigidly fixed with supports.
4: cantilever beams:
A beam which is fixed at one end and free on other end is called overhanging beam. These beams carry loads of both shear stress and bending moment. These beams are generally used in the bridge trusses and another structural member.
Its one end is fixed in wall or column and the other side is free.
In cantilever, the tension zone is located at top and compression in bottom
5: Overhanging beam:
A beam which is supported by two points but on the third point is hanging or not support it is called overhanging beam. It is a combination of the cantilever and the silmply supported beam.
Its ends extend beyond the columns or walls.
The overhanging portion in unsupported or may locate both sides of the beam.
Types of loads on beams
1: Point load or concentrated load
The point load is defined as a load applied on a single location of the whole span length of the beam.
It is also called a concentrated load.
Act over a small distance.
The load is denoted by P and the arrow shows the load direction.
2: Distributed Load:
This load is divided into two main loads such as,
Uniformly distributed load (UDL)
The loading magnitude remains the same to the whole span of beam called uniformly distributed load.
It is denoted by q or w.
Uniformly varying load (UVL)
The load whose magnitude is continuously varying throughout the span of the beam.
It is also called a non-uniformly distributed load.
It is also divided into two further types Triangular or Trapezoidal Load.
3: Couple Forces
This force act on the same span haing the same load and opposite forces.
In case of unequal load, the one force make the beam to rotate.
Expresses as kip.m, kg.m, N.m, lb.ft etc.
Reinforcement in RCC Beam
1: Single reinforcement beam
The reinforcement is provided in the tension zone of the beam called a single reinforcement beam.
Responsible to carry ultimate bending moment and tension.
Compression is counter by concrete.
Practically this beam is not applicable.
2: Double reinforcement beam
The reinforcement is provided in both zones (Tension and compression).
Double reinforcement is use when the depth of beam restricted.
This reinforcement beam is use in structures.
Clear the following terms concepts,
The algebraic sum of all forces acting on either side of the section is known as shear force.
Any moment is produced in a beam due to applying load on them, the element causes to bend under this phenomenon is known as bending moment.
Deflection in a beam is produced by loads, temperature, poor construction and settlement and also by the bending moment and axial force.