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2021-01-05

[EN] FAQ 004892 | Why do I get such a small amount of reinforcement for the upstand beam? The amount ...

Question:
Why do I get such a small amount of reinforcement for the upstand beam? The amount of reinforcement for the downstand beams is significantly larger.

Answer:
While Member 1 is an upstand beam, Member 2 is a downstand beam. This results in a compression axial force for Member 1, and a tensile force for Member 2.

For the concrete design, a compressed cross-section is more favorable than a tensioned cross-section. For comparison purposes, here are the axial forces of the members:

Now, if you deactivate the axial forces for the design in RF-CONCRETE Members, the result is a required reinforcement that is affine to the moment distribution:

With this setting, you are on the safe side for Member 1, but on the unsafe side for Member 2.