β1 - Concrete Property
β1 is a concrete property that is the "ratio of depth of rectangular stress block to the depth to the neutral axis"
| f'c (psi) | β1 |
| <4000 | 0.85 |
| 5000 | 0.80 |
| 6000 | 0.75 |
| 7000 | 0.70 |
| >8000 | 0.65 |
β_1 = {0.85-0.05{\left(f'_c -4000 (psi)\over 1000\right)}} \ge 0.65
Note: The above equation is valid when f'c ≥ 4000 psi.
where:
f'c= the compressive strength of the concrete