# 2.12. Standard Wind Speed Conversions¶

Since the wind speed ($$V(600s, 10m, z_0)$$) from the NJcoast SHP Tool is averaged over the time window of 1 hour, a number of standard conversions parse the wind speed to the 3-second and open-terrain PWS (i.e., $$V(3s, 10m, Exposure C)$$):

1. Computing $$\alpha$$ and $$z_g$$ by ASCE 7-16 ([ASCE16]) Equation C26.10-3 and C26.10-4 taking $$c_1 = 5.65, c_2 = 450$$ for units in m):

(2.12.1)\begin{align}\begin{aligned}\alpha_{SHP} = c_1z_0^{-0.133}\\z_{g,SHP} = c2z_0^{0.125}\end{aligned}\end{align}
1. Computing the gradient height $$V(600s, z_g, z_0)$$ using the power law expression:

(2.12.2)$V(600s, z_g, z_0) = V(600s, 10m, z_0) \times (\frac{z_{g,SHP}}{10m})^{1/\alpha_{SHP}}$

3. Computing the Exposure C (open-terrain) wind speed at 10m height $$V(600s, 10m, Exposure C)$$, with $$\alpha_C = 9.5$$ and $$z_{g,C} = 274.32 m$$ ([ASCE16]):

(2.12.3)$V(600s, 10m, Exposure C) = V(600s, z_{g,C}, z_0) \times (\frac{10m}{z_g})^{1/\alpha_C}$
1. Converting the result to 3s-gust wind speed using the ESDU conversion [ESDU02]:

(2.12.4)$V(3s, 10m, Exposure C) = V(600s, 10m, Exposure C) \times \frac{C(3s)}{C(600s)}$

where $$C(3s) = 1.52$$ and $$C(600s) = 1.05$$ are the Gust Factor from the ESDU conversion.

ASCE16

ASCE (2016), Minimum Design Loads for Buildings and Other Structures, ASCE 7-16, American Society of Civil Engineers.

ESDU02

Engineering Sciences Data Unit (ESDU). (2002). “Strong winds in the atmospheric boundary layer—Part 2: Discrete gust speeds.” ESDU International plc, London, U.K.