3.9—DESIGN WIND LOADS ON STRUCTURES Figures 3-3 through 3-5 depict application of loads on

various types of structural supports.

3.9.1—Load Application C3.9.1

The wind loads acting horizontally on a structure shall be determined by the areas of the supports, signs, luminaires, signals, and other attachments and shall be applied to the surface area as viewed in normal elevation.

The effective projected area (EPA) is the actual area multiplied by the appropriate drag coefficient. If the EPA is provided for the luminaire or attachment, the design wind pressure (Article 3.8.1) shall be computed without incorporating the drag coefficient Cd.

Confirm with the component supplier literature and so forth regarding the incorporation of Cd in the reported EPA.

3.9.2—Design Loads for Horizontal Supports

Horizontal supports of luminaire support structures and all connecting hardware shall be designed for wind loads, Wl

and Wh, applied at the centers of pressure of the respective areas.

Horizontal supports of sign structures (cantilevered or bridge type) and traffic signal structures shall be designed for wind loads, Wh and Wp, applied normal to the support at the centers of pressure of the respective areas.

Horizontal supports for span-wire pole structures shall be designed for wind loads, Wh and Wp, where Whmay be applied as a series of concentrated loads along the span wire.

3.9.3—Design Loads for Vertical Supports C3.9.3 The vertical supports for luminaire structures, traffic

signal structures (excluding pole top mounted traffic signals and post top luminaire structures), and sign support structures shall be designed for the effects of wind from any direction.

An acceptable method to design for the effects of wind from any direction is by applying the following two load cases of normal and transverse wind loads acting simultaneously. This method is applicable where all signs are approximately in one plane and is not applicable for structures with arms in two or more planes.

The Specifications provide a simplified means to account for the effects of wind from any direction. Other more rigorous methods that appropriately account for the effects of wind from any direction may also be used.

Load Case

Normal Component (nc)

Transverse Component (tc)

1 1.0 (BL) 0.2 (BL)

2 0.6 (BL) 0.3 (BL)

SECTION 3:LOADS 3-21

The basic load (BL) for the structures with rigid horizontal supports shall be the effects from the wind loads, Wv, Wl, Wp, and Wh, applied at the centers of pressure of the respective areas of the structures and normal to the sign faces. Nonsymmetrical single roadside sign supports shall be designed for normal and transverse components (nc, tc).

The transverse components may be distributed in proportion to the relative lateral stiffness and restraint conditions of the supports.

Vertical supports for span-wire pole structures (provided only a single span wire is attached to each support) may be designed for the full wind loads, Wv, Wp, and Wh, applied normal to the span wire, without the application of the transverse components (tc).

The transverse components (tc) may be neglected for the design of typical span-wire structures (provided only a single wire is attached to each support), because the wind direction resulting in the maximum tension in the span wire should be normal to the span.

A possible exception would be if the combined projected areas of the sides of the attachments are significantly greater than their combined projected areas parallel to the span.

3.9.4—Unsymmetrical Wind Loading

To allow for unsymmetrical wind loading, the loading conditions stipulated in Articles 3.9.4.1 through 3.9.4.3 shall be used in conjunction with those of Articles 3.9.2 and 3.9.3 to compute the design torsional load effects. The resulting torsional stresses shall be included with the wind load stresses for the fully loaded structure.

3.9.4.1—Overhead Cantilevered Supports

For vertical supports with balanced double cantilevers (i.e., equal torsional load effects from each arm), the normal wind load shall be applied to one arm only, neglecting the force on the other arm. For unbalanced double cantilevers, the normal wind loads shall be applied only to the arm that results in the largest torsional load effect.

When vertical supports have more than two arms, and the arms are mounted opposite or at diverging angles from one another, the wind load shall be applied to one arm when balanced or only to the arm that results in the largest torsional load effect when unbalanced.

3.9.4.2—Concentrically Mounted Supports C3.9.4.2 For high-level (pole or truss type) lighting structures,

pole top mounted luminaire supports, pole top mounted traffic signals, or roadside signs with single supports, the torsional load effect for concentrically mounted attachments shall be calculated as the wind loads, Wp, Wl, and Wh, multiplied by 0.15 b, where b is the width measured between the out-to-out extremities of the attachments.

For nonconcentrically mounted attachments, the torsional load effect shall be calculated using the net torque.

A minimum 15 percent eccentricity is required for concentrically loaded support structures.

Figure 3-3—Loads on Sign Support Structures

SECTION 3:LOADS 3-23

Figure 3-4—Loads on Luminaire Support Structures

Figure 3-5—Loads on Traffic Signal Support Structures

SECTION 3:LOADS 3-25

3.10—REFERENCES

ANSI. 1982. Minimum Design Loads for Buildings and Other Structures, Report No. ANSI A58.1-1982. American National Standards Institute, New York, NY.

ASCE. 1961. “Wind Forces on Structures,” Transactions 126, American Society of Civil Engineers, New York, NY, Part II, pp. 1124–1198.

ASCE. 1990. Standard Minimum Design Loads for Buildings and Other Structures, Report No. ANSI/ASCE 7-88. American Society of Civil Engineers, New York, NY.

ASCE. 1994. Standard Minimum Design Loads for Buildings and Other Structures, Report No. ANSI/ASCE 7-93. American Society of Civil Engineers, New York, NY.

ASCE. 1996. Standard Minimum Design Loads for Buildings and Other Structures, Report No. ANSI/ASCE 7-95. American Society of Civil Engineers, New York, NY.

ASCE. 2006. Minimum Design Loads for Buildings and Other Structures, Report no. ASCE/SEI 7-05. American Society of Civil Engineers, Reston, VA.

Batts, M. E., M. R. Cordes, L. R. Russell, J. R. Shaver, and E. Simiu. 1980. Hurricane Wind Speeds in the United States, NBS Building Science Series 124. National Bureau of Standards, Washington, DC.

Brockenbrough, R. L. 1970. “Suggested Structural Design Criteria for Steel Lighting Standards,” US Steel Report 6, Project No. 57–019–450, January 1970.

Davenport, A. G. 1967. “Gust Loading Factors,” ASCE Journal of the Structural Division. American Society of Civil Engineers, New York, NY, Vol. 93, No. ST3, June 1967.

Delany, N. K., and N. E. Sorensen. 1953. Low-Speed Drag of Cylinders of Various Shapes, Report No. NACA-TN-3038.

National Advisory Committee for Aeronautics (now National Aeronautics and Space Administration), Ames Research Center, Moffett Field, CA.

Durst, C. S. 1960. “Wind Speeds over Short Periods of Time,” Meteorology Magazine. Vol. 89, pp. 181–187.

Fouad, F., Initials Author, and Initials Author. 2003. Structural Supports for Highway Signs, Luminaires, and Traffic Signals, NCHRP Report 494. Transportation Research Board, National Research Council, Washington DC.

Georgiou, P. N., A. G. Davenport, and B. J. Vickery. 1983. “Design Wind Speeds in Regions Dominated by Tropical Cyclones,” Journal of Wind Engineering and Industrial Aerodynamics. Elsevier, Amsterdam, The Netherlands, Vol. 13, pp. 139–152.

Jackson, P. S., and J. C. R. Hunt. 1975. “Turbulent Wind Flow over a Low Hill,” Quarterly Journal of the Royal Meteorological Society. Reading, New England, Vol. 101.

James, W. D. 1985. Effects of Reynolds Number and Corner Radius on Two-Dimensional Flow Around Hexdecagonal Cylinders, AIAA-83-1705. In Proc., AIAA Sixth Computational Fluid Dynamics Conference, Danvers, MA, American Institute of Aeronautics and Astronautics, Reston, VA.

James, W. D. 1971, Wind Tunnel Tests of a Two-Dimensional Round-Cornered Dodecagonal Cylinder. Meyer Manufacturing, Red Wing, MN.

James, W. D., and J. M. Vogel. 1996. Variation of Section Drag Coefficient with Variation in Reynolds Number for Square Cylinders with Various Corner Radii. Valmont Industries, Valley, NE.

Krayer, W. R., and R. D. Marshall. 1992. “Gust Factors Applied to Hurricane Winds,” Bulletin of the American Meteorological Society. American Meteorology Society, Washington, DC, Vol. 73, pp. 613–617.

Lemelin, D. R., D. Surry, and A. G. Davenport. 1988. “Simple Approximations for Wind Speed-Up over Hills,” Journal of Wind Engineering and Industrial Aerodynamics. Elsevier, Amsterdam, The Netherlands, Vol. 28.

Liu, H. 1990. Wind Engineering: A Handbook for Structural Engineers. Prentice Hall, Englewood Cliffs, NJ.

Marchman, III, J. 1971. “Wind Loading on Free-Swinging Traffic Signals,” Transportation Engineering Journal. American Society of Civil Engineers, New York, NY, Vol. 97, No., TE2, pp. 237–246. (May 1971)

Marchman III, J. F., and W. P. Harrison, Jr. 1971. Wind Loading on Traffic Signals, Report to Hapco Company, Abingdon, VA. Virginia Polytechnic Institute, Blacksburg, VA.

McDonald, J. R., K. C. Mehta, W. W. Oler, and N. Pulipaka. 1995. Wind Load Effects on Signs, Luminaires, and Traffic Signals Structures, Report No. 1303-F. Wind Engineering Research Center, Texas Tech University, Lubbock, TX.

Minor, R. C. 1972. Wind Tunnel Tests of Elliptical and Round Tubes. Hapco Company, Abingdon, VA.

Peterka, J. A. 1992. “Improved Extreme Wind Prediction for the United States,” Journal of Wind Engineering and Industrial Aerodynamics. Elsevier, Amsterdam, The Netherlands, Vol. 41, pp. 533–541.

Peterka, J. A., and S. Shahid. 1993. “Extreme Gust Wind Speeds in the U.S.,” Proceedings, 7th U.S. National Conference on Wind Engineering 2. University of California, Los Angeles, Los Angeles, CA, pp. 503–512.

Sherlock, R. H. 1947. “Gust Factors in the Design of Buildings,” International Association for Bridge and Structural Engineering. IABSE, Zurich, Switzerland, Vol. 8, pp. 207–236.

Simiu, E. and R. H. Scanlan. 1986. Wind Effects on Structures, Second Edition. John Wiley & Sons, New York, NY.

Simiu, E., M. J. Changery, and J. J. Filliben. 1979. “Extreme Wind Speeds at 129 Stations in the Contiguous United States,”

Building Science Series, Report 118. National Bureau of Standards, Washington, DC.

Texas Transportation Institute. 1967. Wind Loads on Roadside Signs on Highway Sign Support Structures, Vol. 2. Texas A&M University, College Station, TX.

Thom, H. C. S. 1968. “New Distribution of Extreme Winds in the United States,” Proceedings of the American Society of Civil Engineers 94, No. ST7. American Society of Civil Engineers, New York, NY.

Vickery, B. J., and L. A. Twisdale. 1993. “Prediction of Hurricane Wind Speeds in the U.S,” Proceedings, 7th NationaI Conference on Wind Engineering 2. University of California, Los Angeles, Los Angeles, CA.

SECTION 4:ANALYSIS AND DESIGN—GENERAL CONSIDERATIONS

T ABLE OF C ONTENTS