ENFD 375 – BASIC STRENGTH OF MATERIALS
QUIZ 5
When checking a reinforced concrete beam for cracking, it is common to use the “gross section”;
that is, the section ignoring the reinforcing bar.
Shown is a “gross section” for a reinforced
concrete beam.
Assume that the concrete has a strength of 5000 psi in compression and 500 psi
in tension (that is correct, concrete has a tensile strength which is 10% of the compressive
strength).
If the section is subjected to a NEGATIVE moment, what is the maximum it can
take?
The beam can fail in 2 possible modes:
1)
Tension at the top
2)
Compression at the bottom
Once you hit the smallest of these 2, the beam fails and you’re done!
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 Spring '08
 Miller
 Tensile strength, Compressive strength, Physical compression, gross section

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