Design of a column - Reinforced Concrete with FRP Bars: Mechanics and Design - page 331

The results of the column design are summarized next to facilitate the
understanding of the five sequential steps devoted to calculations.

9.2 DESIGN SUMMARY

The slab thickness is 8 in., the dimensions of the beams supported by col-
umn B3 are 14 by 28 in., and the column dimensions are 20 by 20 in. The
following loads are considered:

Slab self-weight 96.7 psf

Superimposed dead load 2.5 psf

MRI dead load 815 psf

Live load 100 psf

Roof uplift 35 psf

Wind lateral force at the roof 100 kip

To analyze the structure and calculate the lateral deflections, the stiffness
of each member type is modified as

I beam = [0.075 + 0.275(E f /E s )] I g = 0.139 I g

I slab = [0.10 + 0.15(E f /E s )] I g = 0.135 I g

I column = [0.40 + 0.30(E f /E s )] I g = 0.469 I g

The structural analysis is conducted for the frame displayed in Figure 9.2
using the modified member stiffnesses. Table 9.1 presents the results of this
analysis for column B3 when individual unfactored loads are applied.
It is assumed that the column is subject to monoaxial bending around
the B axis line. Negative values of the axial load signify tension. The dif-
ference in the moment sign at the top and bottom of the column indicates
double curvature (Figure 9.3). The forces and moments of Table 9.1 can be
combined according to ACI 318-11 to obtain the ultimate factored loads
that are used for design. The ultimate factored loads are listed in Table 9.2.

Table 9.1 Analysis results for unfactored single load cases (column B3)

Bending moment: M (ft-kip)

Load case Axial load: P (kip) To p Bottom Shear: V (kip)

Dead (D) 186.9 52.1 -36.1 6.6

Live (L) 121.9 0.0 0.0 0.0

Wind (W + ) -34.7 -32.0 98.2 9.6

Wind (W - ) -34.7 32.0 98.2 9.7