|TO:||All Design Section Staff|
|DATE:||July 29, 1997|
|SUBJECT:||BDM Section 9.2-4 Location of Confinement Zones Extension of Confinement Reinforcing Into Crossbeams and Footings|
Section 9.2-4 of the BDM is amended as follows:
4. Location of Confinement Zones
The locations of confinement zones for circular columns are shown in Figure 9.2.1-2 and
for tapered rectangular columns in Figure 9.2.1-3.
The locations of confinement zones are the same for columns of any shape.
Column ends that are framed into footings, multicolumn crossbeams, or longitudinal frames
must have confinement reinforcing
extending into the column (measured from the bottom of the crossbeam, top of footing, or top of footing pedestal) over the larger of:
a. The lesser of:
- 1/6 the clear column height, or
- The maximum column dimension. For wall type piers where plastic hinging occurs only on the weak axis, use the shortest dimension.
b. 18 inches
The confinement reinforcing shall extend into the crossbeam and footing as follows:
- For straight longitudinal column bares, extend the confinement reinforcing to the end of the longitudinal column bars. Note: To minimize reinforcing congestion, the longitudinal column bars and confinement reinforcing should be detailed to terminate 3" below the longitudinal crossbeam reinforcing in the top of the crossbeam.
- For hooked longitudinal column bars, extend the confinement reinforcing to the beginning of the longitudinal column bar hook curvature.
Longitudinal column bars are typically hooked where they terminate in footings. Therefore, extend
the confinement reinforcing to the beginning of the longitudinal column bar hook curvature.
c. Drilled Shafts
Longitudinal column bars in drilled shafts are typically straight. Therefore, extend the confinement reinforcing to the end of the longitudinal column bars.
Note: The above amendments override the details shown in Figure 9.2.1-2 and Figure 9.2.1-3 with regard to extension of confinement reinforcing into crossbeams, footings, and drilled shafts.
These BDM changes will assure good performance of column load/moment transfer.
cc: M. M. Lwin, 47340
F. Higgins, 47340