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# RE: Wind Load Topographic Effects

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Wind Load Topographic Effects
• From: "Jeff Smith" <jeffsmith7(--nospam--at)comcast.net>
• Date: Thu, 1 Jan 2009 20:51:45 -0800

Jeff

Sent: Thursday, January 01, 2009 8:20 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Wind Load Topographic Effects

Sorry Joe! I'm lost. Which clauses give rise to changing the building dimensions?

My understanding is have (ASCE7):

L = downwind or along wind dimension of building (d for AS1170.2 users)
B = across wind dimension of the building (b for AS1170.2 users)
z = reference height
a = extent of edge zones

The reference height varies:
h = building reference height
z=h=he = height to eaves
z=h=ht = height to top/ridge
z=h=h[avg]= average height

Only really need to refer to qz and define z as appropriate.

L & B being relative to direction of wind, are not locked to any given building dimension.

The load on a surface should be based on the actual area of that surface.  Though ASCE7 permits using 1/3rd of span when selecting C&C pressure coefficients and calculating effective wind area, rather than actual load width of the element. Once pressure coefficient determined however the actual area should be used.

So I don't follow where the increase in length comes from.

Regards