13.3 Design of The Steel Rigid Frame

13.
3 DESIGN OF
THE STEEL RIGID
FRAME
LATERAL STRENGTH
AND STIFFNESS OF
COLUMS
13.4 DESIGN OF
THE CONCRETE
RIGID FRAME
THE SLAB – AND – BEAM FLOOR
STRUCTURE
AS SHOWN IN THE FIG. THE FLOOR FRAMING

SYSTEM CONSISTS OF SERIES OF PARALLEL
BEAMS AT 10 FT CENTERS THAT SUPPORT A
CONTINOUS, ONE WAY SPANNING SLAB AND
ARE IN TURN SUPPORTED BY COLUMN-LINE
GIRDERS OR DIRECTLY BY COLUMN.
DESIGN OF CONCRETE COLUMN
The general cases for the concrete column follow:
1. The interior column primarily carries only gravity loads due

to the stiffened perimeter bents.
2. The corner column carry the ends of the spandrel beams

and function as the ends of the perimeter bents in both direction.
3. The intermediate columns on the north and south sides

carry the ends of the interior girders and function as member of
the perimeter bents.
4. The intermediate columns on the east and west sides carry

the ends of the column-line beams and function as members of
the perimeter bents.
A general cost-savings factor is the use of relatively low percentage
of steel reinforcement. An economical column is therefore one with a
minimum percentage (usually a threshold of 1% of the gross section)
of reinforcement. However, other factors often effect design choices
for columns, including:
1. Architectural planning of building interiors: large columns often

are difficult to plan around in developing of interior rooms,
corridor, stair openings, and so on. Thus the smallest feasible
column sizes obtained with maximum percentages of steel are
desired.
2. The ultimate load response of lightly reinforced column borders

on the brittle fracture, whereas heavily reinforced columns tend to
have a yield from of ultimate failure.
3. A general rule of practice in rigid-frame design for lateral loadings

(wind or earthquakes) is to prefer a ratio of nature of ultimate
response described as strong column/weak beam failures.
THANK YOU :D
CORO, JOSHUA
RAY S.
For the intermediate exterior columns, there are four
actions to consider:
1. The vertical compression due to gravity

2. Bending moment induced by the interior framing
that intersects the wall; these columns provide
the end-resisting moments shown in Figure 13.15
3. Bending moments in the plane of the wall bent,
induced by unbalanced gravity load conditions
(moveable live loads) on the spandrels
4. Bending moments in the plane of the wall bents
due to lateral loads
Design for Lateral Forces
Perimeter column/beam bents – major lateral force-
resisting systems for this structure.
When lateral deformation occurs, the stiffer
elements will attract the force first. Therefore, glass
tightly held in flexible window frames, stucco on light
wood structural frames, lightweight concrete block
walls, or plastered partitions on light metal frames
might be fractured first in lateral movements (and often
are). For the successful design of this building. The
detailing of the construction should be done carefully to
ensure that these events do not occur, in spite of the
relative stiffness of the perimeter bents.
Determination of the building weight
Because the columns are all deflected the same sideways distance,
the shear force in a single column may be assumed to be
proportional to the relative stiffness of the column. If the columns
all have the same stiffness, the total load at each story for this bent
would simply be divided by 4 to obtain
Even if the columns are all the same size, however, they
may not all have the same resistance to lateral deflection. The
end columns in the bent are slightly less restrained at their
ends (top and bottom) because they are framed on only one
side by a beam. For this approximation, therefore, it is
assumed that the relative stiffness of the end columns is one-
half that of the intermediate columns. Thus, the shear force in
the end columns is one-sixth of the total story shear force and
that in the intermediate column is one-third of the total force.
The column shear forces produce bending moments in the
columns. With the column inflection points (points of zero
moment) at mid-height, the moment produced by a single
shear force is simply the product of the force and half the
column height.
At each column/beam intersection the sum of the column and
beam moments must be balanced. Thus, the total of the beam
moments may be equated to the total of the column moments,
and the beam moments can be determined once the column
moments are known.
For example, at the second-level of the intermediate
column, the sum of the column moments from fig. 13.18
Assuming the two beams framing the column to have equal

stiffness at their ends, the beams will share this moment in
each beam is
Design of the Bent Columns
The bent columns must be designed for the

following loadings:
1. Vertical compression due to gravity

2. Vertical load due to lateral force action
(overturning)
3. Bending due to gravity loads on both column axes
4. Bending due to lateral loads on the column axis
perpendicular to the bent plane
The bent columns can be considered first for gravity loads
alone to obtain some preliminary sizes. Approximate bending
moments due to gravity produce the column moments shown
in Figure 13.19. The moments for this analysis can be taken
from the girder investigations. For some columns, it is
common that the gravity-only design condition will prevail; this
is most likely for the upper-story columns
Bending moments for lateral load may be taken from
figure. These must be combined with the gravity-
induced actions for a complete analysis, using the
required load combination
When vertical compression prevails for the column design,
reinforcement can be placed symmetrically in the columns.
Special detailing, as required by the UBC, for these bents
determines the placement of both columns and girder reinforcement.
The corner column at the end of the bent is especially vulnerable.
Design of the Bent Girders
Considerations related to the uses of
continuous top and bottom reinforcement
1. Miscalculation of lateral effects, giving some reserved

reversal bending capacity to the girders
2. A general capability for torsional resistance throughout
beam length (intersecting beams produce this effect)
3. A device to hold up the continuous stirrups
4. Some reduction of long-term creep deflection with all

section doubly reinforced to help keep load off the
window mullions and glazing
Relative Stiffness of Bent Members
If story heights vary and beam spans vary, some very

complex and unusual behaviors can be involved.
In many cases, the portion of lateral shear in the columns
will be distributed on this basis.
Most bent analyses assume the column stiffness to be
more-or-less equal to the beam stiffness, producing the
classic form of lateral deformation.
The captive Frame
This has been a major source of problems for
concrete frames affected by seismic forces. It is an
issue for the structural designer of the bents, but it
must be considered in cooperation with whoever is
doing the construction detailing for the wall
construction.

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13.

AS SHOWN IN THE FIG. THE FLOOR FRAMING

1. The interior column primarily carries only gravity loads due

2. The corner column carry the ends of the spandrel beams

3. The intermediate columns on the north and south sides

4. The intermediate columns on the east and west sides carry

1. Architectural planning of building interiors: large columns often

2. The ultimate load response of lightly reinforced column borders

3. A general rule of practice in rigid-frame design for lateral loadings

1. The vertical compression due to gravity

Assuming the two beams framing the column to have equal

The bent columns must be designed for the

1. Vertical compression due to gravity

1. Miscalculation of lateral effects, giving some reserved

4. Some reduction of long-term creep deflection with all

If story heights vary and beam spans vary, some very

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