Memorandum

TO:	All Design Section Staff
FROM:	J. Kapur
DATE:	October 23, 2002
SUBJECT:	BDM Section 9.2-4 Location of Confinement Zones, Extension of Reinforcing Into Crossbeams, Footings and Shafts

Section 9.2-4 and figures 9.2.1-1  9.2.1-2, 9.2.1-3, and 9.2.1-4 of the BDM
regarding the extension of column confinement zone are revised 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 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.   1/6 the clear column height
    b.   The maximum column dimension.  For wall type piers where
          plastic hinging occurs only along the weak axis, use the short dimension.
    c.   18 inches

                         The confinement reinforcing shall extend into the crossbeam, footing, or drilled shaft as follows: 

    a.   Crossbeams
          Column longitudinal bars, straight and hooked, shall be detailed
           to terminate 3” below the top longitudinal crossbeam reinforcement.

           The designer shall ensure that the development length of the column longitudinal
           rebars is at least equal to 1.25 L_d.  This development length may be modified by
           the applicable modification factors from AASHTO LRFD section 5.11.2.

           The confinement reinforcement shall extend to the end of the straight longitudinal
           column bars; it shall extend to the beginning of the longitudinal column bar curvature for hooked bars.

b.   Footings
    Longitudinal column bars are hooked where they terminate in a footing.
    Designer shall ensure that the development length of the column longitudinal
    bar is at least equal to 1.25 L_d.  This development length may be further modified
    by the applicable modification factors from AASHTO LRFD Section 5.11.2.
    Extend the confinement reinforcing over a distance equal to the larger of:
        a)    One-half of the maximum column dimension in the bottom half of the column.
        b)    18 inches
        c)   Beginning of the longitudinal column bar curvature

       c.   Drilled Shafts
     Longitudinal column bars in drilled shafts are typically straight.  For extension of
     column longitudinal bars into shafts see Fig. 9.2.1-2.  Extend the confinement
     reinforcing over a distance equal to the larger of:
       a)    One-half of the maximum column dimension in the bottom half of the column
       b)   The minimum column dimension
       c)   18 inches
       d)   End of longitudinal column bars

 If you have any questions, please contact Bijan Khaleghi at 705-7181.

 JK:dsb

MWA/BK

Attachments

cc:      J. A. Weigel, Bridge and Structures – 47340

         F. Higgins, Bridge and Structures - 47340