Detailing of Beams
- Beam carries transverse external loads that cause bending moment, shear forces and in some cases torsion
- Concrete is strong in compression and very weak in tension.
- Steel reinforcement is used to take up tensile stresses in reinforced concrete beams.
- Mild steel bars or Deformed or High yield strength deformed bars (HYSD) are used.
- HYSD bars have ribs on the surface and this increases the bond strength at least by 40%
Bar Bending Schedule
- Drawings generally include a bar bending schedule
- The bar bending schedule describes the length and number, position and the shape of the bar
- Anchorage in steel bars is normally provided in the form of bends and hooks
- The anchorage value of bend of bar is taken as 4 times the diameter of bar for every 450 bend subjected to maximum of 16 times the diameter of bar.
Standard hooks for detailing:
The beams are classified as:
- According to shape: Rectangular, T, L, Circular etc
- According to supporting conditions: Simply supported, fixed, continuous and cantilever beams
- According to reinforcement: Singly reinforced and doubly reinforced
Reinfrocement Cover in Beam:
- Minimum cover in beams must be 25 mm or shall not be less than the larger diameter of bar for all steel reinforcement including links.
- Nominal cover specified in Table 16 and 16A of IS456-2000 should be used to satisfy the durability criteria.
Types of Reinforcement in Beams:
Generally a beam consists of following steel reinforcements:
- Longitudinal reinforcement at tension and compression face.
- Shear reinforcements in the form of vertical stirrups and or bent up longitudinal bars are provided.
Side face reinforcement in the web of the beam is provided when the depth of the web in a beam exceeds 750 mm. (0.1% of the web area and shall be distributed equally on two faces at a spacing not exceeding 300 mm or web thickness whichever is less)
Specification for the reinforcement in beams is given in clause 8.1 to 8.6 of SP34
- While drawing the details of a beam following convention representation of bars are used
- Mild steel bars : ?; HYSD bars: # or
- Main bars are shown by thick single line.
- Hanger bars are shown by medium thick lines.
Different forms of stirrups used in beams
Typical drawing of a simply supported beam