The minimum reinforcement in beam depends upon the section or zone whether it is tension or compression zone. Beam is a load-bearing structure, so it should be designed very carefully. A small weakness in the beam may cause a collapse of whose slab on it and so the whole buildings.
The beam is the horizontal structural member which transfers a load of the slab to the column. The beam may be subject to both compression and tension force.
Tension force is applied at the top of the beam while compression is applied at the bottom of the beam. So, steel rods are provided at the tension zone i.e at the top of the beam.
More steel rods in the beam may make the beam over-reinforced which may be dangerous in terms of safety. and lesser steel rods in the beam make the beam weak in tension. Here are some most important points which guide proper reinforcement in the beam.
The maximum tension reinforcement of the beam should not be greater than 0.04bD where “b” is the width of the beam and “D” is the Depth of the beam. But, minimum tension reinforcement should not be less than 0.3% and 0.2% of cross-sectional dimensional for plain bars and HYSD bar respectively.
Let us see some more important points to consider while designing reinforcement in the beam. They are given below,
Design Considerations of reinforcement Beam
1) The maximum compressive reinforcement of the beam should not be greater than 0.04bD. Where “b” is the width of the beam and “D” is the depth of the beam.
2) The minimum area of tension reinforcement of beam should not be less than that given by As = 0.85 bd/fy (Where “As” is area of steel cross-section and “fy” is strength of steel)
3) Side face reinforcement is provided if depth of the beam exceed 750 mm. The total area of side face reinforcement should not be greater than 0.1% of the web are and equally distributed on both face subjected to S > 300 mm or web thickness whichever is lesser.
4) At least 1/4th of the tension steel should be carried straight into the supports so as to provide anchorage.
5) In the case of a cantilever beam or slab, the tension is maximum on the top than the bottom. So, the main reinforcement is provided at the top face of the beam or slab.
6) For economical purposes, the stirrups used in the beam should be lesser near support but more in numbers at the mid-span.
7) The maximum distance between stirrups used in the beam should not be greater than 0.75d for vertical and d for inclined stirrups at 45 degrees. Where “d” is the depth of the beam.
8) If the depth of the beam exceeded more than 750mm, then Side face reinforcement should be provided.
I hope this article on “minimum reinforcement in beam” remains helpful for you.
Happy Learning – Civil Concept
Civil Engineer – Ranjeet Sahani