In the design of a rectangular RC beam, the depth of the equivalent rectangular stress block (a) is related to the neutral axis depth (c) by the factor beta_1. For concrete with f'_c = 5000 psi, what is the value of beta_1?

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Civil Engineering QUESTION #6625

Question 1

In the design of a rectangular RC beam, the depth of the equivalent rectangular stress block ($a$) is related to the neutral axis depth ($c$) by the factor $\beta_1$. For concrete with $f'_c = 5000$ psi, what is the value of $\beta_1$?

0.85
0.8✔️
0.75
0.7

Correct Answer Explanation

For $f'_c$ between 2500 and 4000 psi, $\beta_1$ is 0.85. For $f'_c > 4000$ psi, $\beta_1$ is reduced by 0.05 for every 1000 psi increment. $0.85 - 0.05 \times ((5000-4000)/1000) = 0.80$.

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