2.12. Standard Wind Speed Conversions

Since the wind speed (\(V(600s, 10m, z_0)\)) from the NJcoast SHP Tool is averaged over a 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. Compute \(\alpha\) 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)\[ \begin{align}\begin{aligned}\alpha_{SHP} = c_1z_0^{-0.133}\\z_{g,SHP} = c_2z_0^{0.125}\end{aligned}\end{align} \]

  1. Compute 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. Compute 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. Convert 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 Factors from the ESDU conversion.

ASCE16(1,2)

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.