CIVIL ENGINEERING FORMULAS

244 CHAPTER NINE

With fixed supports and a uniform load on the vertical member, Fig. 9.16:

(9.130)

(9.131)

(9.132)

ROOF LIVE LOADS*

Some building codes specify that design of flat, curved, or pitched roofs should
take into account the effects of occupancy and rain loads and be designed for
minimum live loads. Other codes require that structural members in flat,
pitched, or curved roofs be designed for a live load Lr(lb per ft^2 of horizontal
projection) computed from

(9.133)

whereR 1 reduction factor for size of tributary area
1 for
1.20.001Atfor 200 < At< 600
0.6 for At 600
Altributary area, or area contributing load to the structural member, ft^2
R 2 reduction factor for slope of roof
1 for F 4
0.6 for F 12
Frate of rise for a pitched roof, in/ft
rise-to-span ratio multiplied by 32 for an arch or dome

At 200

Lr 20 R 1 R 2  12

1

2 H^2 L

2

2

I 2



M 2 L 2

I 2



1

3 M^2 L^3

I 3



1

6 M^1 L^3

I 3

1

6 WL

2

1

I 1



1

2 H^2 L

2

1

I 1



M 1 L 1

I 1



1

3 M^1 L^3

I 3



1

6 M^2 L^3

I 3

1

8 WL

3

1

I 1



1

2 M^1 L

2

1

I 1



1

3 H^2 L

3

1

I 1



1

3 H^2 L

3

2

I 2



1

2 M^2 L

2

2

I 2

3

1 2

W

V 1

V 2

H

H

M 1 M 2

W

3

1

2

V

V

H 2

H 1

M 1 M 2

FIGURE 9.15 Fixed supports,

uniform load on horizontal member.

(Roark–Formulas for Stress and

Strain,McGraw-Hill.)

FIGURE 9.16 Fixed supports, uni-

form load on one vertical member.

(Roark–Formulas for Stress and Strain,

McGraw-Hill.)

*Brokenbrough and Merritt—Structural Steel Designer’s Handbook, McGraw-Hill.