Page 33 - Civil Engineering Formulas

2
R
Radius of gyration
≈
a 2
a 2
+
24
−
48
12r 2
6R 2
Section modulus
(approx)
180°
n
cos
I
AR
4
R
I
r
=
=
=
c
I
h 3 b 1 2 b 1 2 + 6bb 1 + 6b 2 I h + 2b 1 2 + 12bb 1 12b 2 h 2 = c + 2b 1 ) 12 (3b + b 1 ) 6 (2b
Moment of inertia a 2 ) − (6R 2 a 2 ) + (12r 2 (approx) + 6bb 1 + b 1) + 36 (2b 2b 1 + 3b h b 1 + 2b
= A 24 A = 48 AR 2 = 4 6b 2 I = 1 3
I h c = Geometric properties of sections.
Equilateral polygon A = Area R = Rad circumscribed circle n = No. of sides a = Length of side of octagon c b 1 2 FIGURE 2.1
Section r = Rad inscribed circle Axis as in preceding section b b 1 2
13