huangyhg

wind pressure distribution around a cylinder
i'm looking for a mathematical approach for determining the distribution of wind pressures around a large diameter cylindrical structure. i know there are lots of aerodynamic factors, gust factors, and ibc shape factors. i am wondering if there's an equation to go with the figure in gaylord (p.26-3) or the factors in the aci committee 334 report.
thanks.
rd78,
is your structure a stack? if so, it may be governed by asme sts-1.
jjf
not a stack and not steel. just basically a very large tank.
australian standard as 1170.2:2002 structural design actions, part 2: wind actions takes the following approach for a cylinder standing on the ground, or supported by columns of a height not greater that the height of the cylinder, with a height/diamater quotient in the range of 0.25 to 4.0.
variables:
theta: angle from wind direction to a point on the wall, in degress
(0-degress is windward face; 180-degress is leeward face)
c: cylinder height
b: cylinder diameter
external pressure coefficient on walls of bins, silos or tanks of unit aspect ratio (c/b = 1):
cp1 = -0.5 + 0.4*cos(theta) + 0.8*cos(2*theta) + 0.3*cos(3*theta) - 0.1*cos(4*theta) - 0.05*cos(5*theta)
factor for a circular bin:
k = 1.0, for cp1 >= -0.15
= 1 - 0.55*(cp1 + 0.15)*log(c/b), for cp1 < -0.15
external pressure coefficient on walls of bins, silos or tanks:
cp = k*cp1
this is based on wind tunnel tests carried out at high reynolds numbers by sabransky and macdonald, kwok and holmes.
sabransky, i.j., 'wind pressure distribution on cylindrical storage silos', m.eng.sc. thesis, monash university, 1984.
macdonald, p.a., kwok, k.c.s. and holmes, j.d., 'wind loads on storage bins, silos and tanks', journal of wind engineering and industrial aerodynamics, vol. 31, 1988, pp. 165-188.
thanks for that info. i understand austria has something similar and chile also has an approach. i plotted them all and they vary quite a bit. we'll just use the more conservative.
now i have to come up with a way to check buckling with the non-uniform external pressure.
you don't say exactly what your application is. but api-650 and awwa d100 both have provisions to prevent buckling due to wind pressure. the designs seem to be reasonably effective in practice. the approach is based on using the wind pressure as a uniform pressure, with appropriate buckling critera for a cylinder.
i would be a little reluctant to get into too much detail about the variation of the wind pressure around the tank. the design codes are not concerned with the actual pressure distribution, but the maximum pressures that can be generated. actual pressure variation would be 3-dimensional, not 2- dimensional, would be time-dependent, and would depend on the proximity of other structures, topography, etc. steel tanks do flex somewhat, and if they "blow in", it is not necessarily a single motion- that is, the shell could vibrate back and forth a bit before finally going too far, and this would be difficult to model.

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