Networking the World TM 86 Leon Kempner, Jr., P.E. Bonneville Power Administration February 6, 2000 IEEE Three Second Gust Extreme Wind Speed Map, CP2363

Networking the World TM 87 Why Change Rule 250C? Ü Current Extreme Wind Map, Based on Fastest Mile Wind Speed Ü New wind data and engineering wind maps are based on Three (3) Second Gust extreme Wind Speed Ü Fastest Mile wind speed, no longer collected Ü Three Second Gust speed collected at more stations Ü The Three Second Gust Wind Speed was first presented in ASCE 7-95

Networking the World TM 88 Ü The Three Second Gust Wind Speed represents a better database and analysis of available data Ü The NESC should be consistent with other Engineering Loading Standards, Guides and Codes such as, ASCE-7, EIA/TIA-222, ASCE-74, IBC, etc. Ü This change is the right thing to do, Standard/Engineering Creditability Why Change Rule 250C? (Continued)

Networking the World TM 89 Database/Analysis Continental Winds: è 485 weather stations, min. 5 years of data è Data was assembled from a number of stations in state-size areas to reduce sampling errors è Fisher-Tippett Type I extreme value distribution, 50 year return period è Insufficient variation in peak gust wind speeds to justify contours è 33 ft. above ground, Exposure C

Networking the World TM 90 Database/Analysis Hurricane Winds: è Based on Monte-Carlo simulations è The coastline was divided into discrete points spaced at 50 nautical miles. è Hurricane contours over the Atlantic are provided for interpolations and represent values for Exposure C over land. è Importance factors are accounted for in the map wind speeds, >1.0 at the coast to 1.0, 100 miles inland.

Networking the World TM 91 Fastest Mile Vs. 3 Sec. Gust FASTEST MILE SPEED 3 SECOND GUST SPEED

Networking the World TM 92 Gust Response Vs Gust Factors l GRF - Accounts for Dynamic effects of gusts on the response of T-line components - Gusts may not envelop the entire span between T-line Structures - Values can be Greater than or Less than Represents the ratio of peak gust load effect to the selected mean extreme load effect

Networking the World TM 93 Gust Response Vs. Gust Factors l Gust Factor - The Ratio of the gust extreme wind speed at a specified averaging period, e.g. 2 seconds, to the selected mean extreme wind speed, e.g. 10 minute. - Used as a multiplier of the mean extreme wind speed to obtain the gust wind speed. - Values Greater than 1.0 (Typ )

Networking the World TM 94 NESC Extreme Wind Format Equations l Figures l Tables CP2363

Networking the World TM 95 Gust Response Factor, G RF l Davenport Equations, “Gust Response Factors for Transmission Line Loading,” Proceeding, 5 th International Conference on Wind Engineering, 1979 l ASCE 74, “Guidelines for Electrical Transmission Line Structural Loading,”1991 l ASCE 7, “Minimum Design Loads for Buildings and Other Structures,” 1995 l IEC 826, “Loading and Strength of Transmission Lines,” 1991

Networking the World TM 96 3 Second Gust Wind Pressure Where: k Z - Velocity Pressure Exposure Coefficient, C, as defined in Rule 250C.1, Table V - Basic Wind Speed, 3-second gust wind speed, miles per hour, at 33 ft. above ground, an annual probability of 0.02 (50 year return period), Figure s I - Importance Factor, 1.0 for structures, wires, and their support facilities. G RF - Gust Response Factor, as defined in Rule 250C.2. C d - Shape Factor, as defined in Rule 252B. q Z = * k Z * V 2 * I * G RF * C d

Networking the World TM 97 K Z Parameter

Networking the World TM 98 G RF Parameter

Networking the World TM 99 Table Values Represent a Uniform Change 3% 7% 4% 3% 4%

Networking the World TM 100 Tables of Factors 1. Recommend General Equation for height greater than 250 ft. Velocity Pressure Exposure Coefficients Structure/Wire Gust Response Factors 1. Recommend General Equations for tower height, h, greater than 250 ft. and span length, L, greater than 2000 ft.

Networking the World TM 101 General Equations Structure k Z = 2.01*(0.67*h/900) (2/9.5) Wire k Z = 2.01*(h/900) (2/9.5) (for 15 ft.  h  900 ft.) Velocity Pressure Exposure Coefficients Structure G RF = ( *E S (B S ) 0.5 )/k V 2 Wire G RF = ( *E W (B W ) 0.5 )/k V 2 E S = 0.346*(33/(0.67*h)) 1/7 E W = 0.346*(33/h) 1/7 B S = 1/( *h/220) B W = 1/(1+0.8*L/220) Structure/Wire Gust Response Factors E = Exposure Factor B = Dimensionless response term corresponding to the quasi-static background wind load k V = 1.430

Networking the World TM 102 Example q Z = *k Z *V 2 *I*G RF *C d q Z = *V 2 *C d CP2363 C q Z = *k Z *V 2 *G RF *(I*C d ) q Z = *k Z *V 2 *G RF *C q Z = *V 2 *C 70 mph À 12.54C 80 mph À 16.38C 90 mph À 20.74C 9Ì 75Ì 25Ì 7Ì 10Ì Wind in Tower (Height 141 ft.) 141 ft Kz Twr GRF Wind in Wire (1000 Ft. Span) Kz Wire GRF 74 ft ft ft ft Note: No Gust Factor

Networking the World TM 103 Example (Continued) 141 ft. = *1.3*(90mph) 2 *0.859*C = 23.2C psf Wire Wind 74 ft. = *1.2*(90mph) 2 *0.712*C = 17.7C 99 ft. = *1.3*(90mph) 2 *0.698*C = 18.8C 124 ft. = *1.4*(90mph) 2 *0.687*C = 19.9C 141 ft. = *1.4*(90mph) 2 *0.687*C = 19.9C psf Tower Wind Pressure

Networking the World TM 104 Example (Continued) C2 20.7C á CP 23.2C á C2 20.7C á CP 17.7C á CP 18.8C á CP 19.9C á C2 20.7C á C2 psf CP psf

Networking the World TM 105 Review of CP2363 l Presents the 3 second gust extreme wind speed approach l Updates the NESC extreme wind speed map to current wind engineering knowledge l Presents statistically better wind speed data l Technically correct/consistent approach for determining wind loading