DETERMINING DESIGN COMPRESSIVE
STRENGTH OF COMPOSITE COLUMNS
Determine the design compressive strength of a W8 x 40 (A36 steel) encased in a 16 x 16
in (40.6 x 40.6 cm) (fcr = 3.5 ksi) (24.1 MPa) normal-weight concrete column in Fig. 46.
Reinforcement is four No. 7 (Grade 60) bars longitudinally, and No. 3 ties at 10 in (25.4
cm) horizontally;
Calculation Procedure:
- Check the minimum requirements for the column
Checking minimum requirements
(a) For a W8 x 40, A 89 = 11.7 in
2
, total area = 16 in x 16 in = 256 in
2
(1652 cm
2
)
—: = 4.6% > 4% minimum o.k.
256 in
2(b) Lateral tie spacing = 10 in (25.4 cm)
<^2 /3 x 16 in outer dimension = 10.7 in (27.2 cm) o.k.Minimum clear cover = 1.5 in (3.8 cm) o.k.
Horizontal No.3 bars: Ar = 0.ll in
2
per bar> 0.007 in
2
x 10 in spacing = 0.07 in
2
(0.45 cm
2
) o.k.Vertical No.7 bars: Ar =0.60 in
2
per bar> 0.007 in^2 x 11.4 in spacing = 0.08 in^2 (0.52 cm^2 ) o.k.(c) 3.0 ksi < (fcf =3.5 ksi) < 8.0 ksi for normal weight concrete o.k.
(d) Use Fy,. = 55 ksi (378.9 MPa) for reinforcement in calculations, even though actual
Fyr = 60 ksi (413.4 MPa) for Grade 60 bars.