25 January 2005
3-220.127.116.11 External Column Removal.
As a minimum, remove external columns near the middle of the short side,
near the middle of the long side, and at the corner of the building, as shown in Figure 3-
2. Also remove columns at locations where the plan geometry of the structure changes
significantly, such as abrupt decrease in bay size or re-entrant corners, or, at locations
where adjacent columns are lightly loaded, the bays have different tributary sizes, and
members frame in at different orientations or elevations. Use engineering judgment to
recognize these critical column locations.
For each plan location defined for element removal, perform AP analyses for
each floor, one at a time. For example, if a corner column is specified as the removed
element location, one AP analysis is performed for removal of the ground floor corner
column; another AP analysis is performed for the removal of the first floor corner
column; another AP analysis is performed for the second floor corner column, and so
on. If the designer can show that similar structural response is expected for column
removal on multiple floors (say, floors 4 though 10), the analysis for these floors can be
omitted but the designer must document the justification for not performing these
3-18.104.22.168 Internal Column Removal
For structures with underground parking or other uncontrolled public ground
floor areas, remove internal columns near the middle of the short side, near the middle
of the long side and at the corner of the uncontrolled space, as shown in Figure 3-3.
The removed column extends from the floor of the underground parking area or
uncontrolled public ground floor area to the next floor (i.e., a one story height must be
removed). Internal columns must also be removed at other critical locations within the
uncontrolled public access area, as determined with engineering judgment. For each
plan location, the AP analysis is only performed for the column on the ground floor or
parking area floor and not for all stories in the structure.
For both external and internal column removal, continuity must be retained
across the horizontal elements that connect to the ends of the column; see Figure 3-4.