Reinforced Concrete: Calculating Irregular Shapes

[derryck1234]

In my reinforced concrete textbook, we only have formulas and procedures for rectangular, or webbed and flanged beams. What do I do if I have an irregular shaped beam? How do I calculate the reinforcement?

 

[Studiot]

Exactly the same way as with any other rc beam.

1) Establish the horizontal compressive and tensile forces due to bending

2) Locate of the neutral axis. This will be an unknown at the outset, give it a symbol as a distance from the top (compressive) surface.

3) Solve for the position of the neutral axis by equating the compression moment (= conc area x conc stress x compression level arm) to the tensile moment (= steel area x steel stess x tensile lever arm)

4) Distribute the compression force over the concrete in the compression zone, using either a rectangular block.

5) Use the tensile force to determine the required area of steel from max allowed steel stress.

6) Set the steel a distance equal to the cover from the bottom of the beam and choose suitable bars to achieve the area calculated in step 3.

7) If there is insufficient concrete area (ie compressionn is too great) then you will have to repeat, adding in compression reinforcement and using the modular ratio (1:15) apportion the compression between the upper (compression ) reinforcement and the concrete.