2.12. Standard Wind Speed Conversions

Since the wind speed ( $V (600 s, 10 m, z_{0})$ ) 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., $V (3 s, 10 m, E x p o s u r e C)$ ):

1. Computing $α$ 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{array}{r} \begin{matrix} α_{S H P} = c_{1} z_{0}^{- 0.133} \\ z_{g, S H P} = c 2 z_{0}^{0.125} \end{matrix} \end{array}

Computing the gradient height $V (600 s, z_{g}, z_{0})$ using the power law expression:

(2.12.2)

V (600 s, z_{g}, z_{0}) = V (600 s, 10 m, z_{0}) \times (\frac{z_{g, S H P}}{10 m})^{1 / α_{S H P}}

3. Computing the Exposure C (open-terrain) wind speed at 10m height $V (600 s, 10 m, E x p o s u r e C)$ , with $α_{C} = 9.5$ and $z_{g, C} = 274.32 m$ ([ASCE16]):

(2.12.3)

V (600 s, 10 m, E x p o s u r e C) = V (600 s, z_{g, C}, z_{0}) \times (\frac{10 m}{z_{g}})^{1 / α_{C}}

Converting the result to 3s-gust wind speed using the ESDU conversion [ESDU02]:

(2.12.4)

V (3 s, 10 m, E x p o s u r e C) = V (600 s, 10 m, E x p o s u r e C) \times \frac{C (3 s)}{C (600 s)}

where $C (3 s) = 1.52$ and $C (600 s) = 1.05$ 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.