ec1.py

# import numpy as np
from math import log

"""
Structural wind loading according to Eurocode EN 1991-1-4:2005. 
Initial proof of concept of an OOP approach using Python. 
By Graham Knapp
"""

rho = 1.25  # density kg/m3 from base Eurocode
_document = 'EN 1991-1-4:2005 +A1:2010'


class Site():
    """
    represents a site with a given terrain roughness and basic wind speed.

    test from https://eurocodes.jrc.ec.europa.eu/doc/WS2008/SX016a-EN-EU.pdf

    >>> round(Site(26, 'II').qp(7.3))
    911
    """
    z0_by_terrain = {'O': 0.003, 'I': 0.01, 'II': 0.05, 'III': 0.3, 'IV': 1.}

    zmin_by_terrain = {'O': 1., 'I': 1., 'II': 2., 'III': 5., 'IV': 10.}

    def __init__(self, vb0, terrain, co=1.0):
        self.vb0 = vb0                              # fundamental value of the basic wind velocity in m/s
        self._terrain = terrain                     # terrain category
        self._z0 = self.z0_by_terrain[terrain]      # roughness length in m
        self._zmin = self.zmin_by_terrain[terrain]  # minimum height in m
        self._co = co                               # orography factor

    def iu(self, z):
        """Calclate turbulence intensity at a given height z
        """
        z = max(z, self._zmin)
        return 1 / (self._co * log(z / self._z0))

    def cr(self, z):
        """Calculate mean wind speed ratio at a given height z
        """
        z = max(z, self._zmin)
        return (0.19 * (self._z0 / 0.05) ** 0.07) * log(z / self._z0)

    def qp(self, z):
        """Calculate peak wind velocity pressure in Pa at a given height
        """
        u = self.cr(z) * self.vb0
        _qp = 0.5 * rho * (u ** 2.) * (1 + 7 * self.iu(z))
        return _qp


if __name__ == '__main__':
    import doctest

    doctest.testmod()