9. Horizontal Length of the Special Boundary Elements
The special boundary elements must extend horizontally from the extreme compression fiber a distance equal to the following: | |
| ACI 318-19 (18.10.6.4(a)) |
| |
The largest neutral axis depth, c, used in the determination of lbe is calculated from a strain compatibility analysis using the axial force and nominal moment strength from ACI Eq. (5.3.1e) in Table 2.
Figure 7 - Strain and Force Diagrams (ϕPn = Pu = 22,793.1 kip and ϕMn = 467,210.25 ft-kip)
It is evident that the calculated horizontal length of the special boundary element includes the 24 in. thick flange and extends 30.98 – 24.0 = 6.98 in. into the web. According to ACI 318-19 (18.10.6.4(d)), a special boundary element must extend at least 12 in. into the web for flanged sections. Based on the 10.0 in. spacing of the #8 longitudinal bars in the web, use a 24 in. extension into the web. |