ENGINEERING SPECIFICATIONS

1.0—Design Standard       1997 Uniform Building Code

2.0—Material Properties   6061-T6 Aluminum

Tensile Strength:                        Fu = 38,000 psi

Within 1" of weld:                 Fuw = 24,000 psi

Yield Strength:                           Fy = 35,000 psi

Within 1" of weld:                 Fyw = 20,000 psi

Shear Strength:                         Fsu = 24,000 psi

Shear Yield Strength:                 Fsy = 20,000 psi

Compression Coefficient:            kc = 1.12

Tension Coefficient:                    kt = 1.0

Safety Factor (Ultimate):             nu = 1.95

Safety Factor (Yield):                 ny = 1.65

3.0—Aluminum Tower Section Properties

Section
Size

Leg
Centers1, b

(in.)

Moment
Arm1,
d

(in.)

Leg
Tube
Size

Wind
Area2,
Aw

(ft2 )

Section
Weight

(lbs)

Allowable
Moment,
MR3

(lb-ft)

Allowable Horizontal Shear3, VR
(lbs)

Unstiffened
Bracing

Stiffened
Bracing4
6"5 5.0 4.33 100 2.46 21 2100 480 1160

11"

10.0

8.66

100

1.8

15

4200

390

1130

131

2.2

20

6900

390

1140

14"

13.0

11.26

100

1.9

19

5400

740

1910

131

2.3

23

8900

750

1910

172

2.9

36

17,300

770

1910

18"

16.75

14.51

131

2.5

28

11,400

1210

2880

172

3.0

40

22,100

1230

2880

225

3.7

59

38,500

1270

2880

22"

20.5

17.75

172

3.3

46

26,900

1760

4010

225

4.0

65

47,200

1820

4010

26"

24.5

21.22

172

3.5

54

32,000

2290

5320

225

4.2

73

56,400

2350

5320

30"

28.5

24.68

172

3.7

58

37,200

1930

5440

225

4.4

77

65,600

1990

5480

288

5.2

96

96,300

2050

5520

35"

33.25

28.80

172

4.1

70

43,100

2320

6770

225

4.8

89

76,500

2380

6810

288

5.6

108

112,300

2450

6860

1 See Figure 1.

2 Projected area for wind perpendicular to face, per 8-foot high tower section.

3 Values shown include 1/3 increase in allowable stress as permitted by UBC Sec. 1612.3.2.

4 All five diagonals on each side stiffened.

5These sections only available in 12 foot lengths.

4.0—Aluminum Leg Tube Properties

Leg
Tube Size

Outside
Diameter, OD
(in.)

Inside
Diameter, ID
(in.)

Wall
Thickness, t
(in.)


Area, A
(in2 )

Moment of
Inertia, I
(in4 )

Radius of
Gyration, r
(in.)

100

1.000

0.750

0.125

0.344

0.03366

0.313

131

1.310

1.030

0.140

0.515

0.0893

0.417

172

1.720

1.334

0.193

0.926

0.274

0.544

225

2.250

1.750

0.250

1.571

0.798

0.713

288

2.875

2.323

0.276

2.254

1.924

0.924

5.0—Wind Pressure According to the UBC [From UBC Section 1620]

The design wind pressure for any given height above ground level is determined in accordance with the following formula:

P = Ce Cq qs Iw

where P is the pressure in pounds per square foot, Ce is the combined height, exposure and gust factor, Cq is the pressure coefficient, qs is the wind stagnation pressure, and Iw is the structure importance factor. Values for Ce, Cq and qs are given in the following tables; the value for Iw is normally 1.0.

5.1—Combined Height, Exposure and Gust Factor (Ce) [From UBC Table 16-G]

Height Above Ground (feet)

Exposure D

Exposure C

Exposure B

0-15

1.39

1.06

0.62

20

1.45

1.13

0.67

25

1.50

1.19

0.72

30

1.54

1.23

0.76

40

1.62

1.31

0.84

60

1.73

1.43

0.95

80

1.81

1.53

1.04

100

1.88

1.61

1.13

120

1.93

1.67

1.20

Exposure D represents the most severe exposure in areas with basic wind speeds of 80 mph (129 km/h) or greater and has terrain that is flat and unobstructed facing large bodies of water over 1 mile in width relative to any quadrant of the tower site. Exposure D extends inland from the shoreline ¼ mile (0.40 km) or 10 times the tower height, whichever is greater.

Exposure C has terrain that is flat and generally open, extending ½ mile (0.81 km) or more from the site in any full quadrant.

Exposure B has terrain with buildings, forest or surface irregularities, covering at least 20 percent of the ground level area extending 1 mile (1.61 km) or more from the site.

 

 

5.2—Pressure Coefficients (Cq) [From UBC Table 16-H]

Structure or Part Thereof

Description

Cq Factor

Open-Frame Towers1,2