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Distribution of Wind Loads to diaphragm in Spreadsheets
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- Subject: Distribution of Wind Loads to diaphragm in Spreadsheets
- From: "Dennis Wish" <dennis.wish(--nospam--at)verizon.net>
- Date: Fri, 18 Apr 2008 21:32:16 -0700
I’m seeking some advice or comments from those of you
who have created tools (spreadsheets or any other type of programming is
applicable). I am struggling with a decision as how best to model a lateral
distribution of loads tributary to the diaphragms in a multistory light-framed
structure that complies with flexible analysis. The most conservative model would calculate the end zones of
the block that I am modeling and simply apply the end zone wind force across
the entire diaphragm width. The logic is that the location of interior
resisting shear elements probably do not align with the location where 2a and
the Interior zone meet which makes the calculation in a spreadsheet where lines
of resistance change a bit difficult to calculate. The second choice is to assume the building is broken into
blocks and that each block is consistent in width and depth at each diaphragm
level. In this choice the total load caused by both end zones (2a*w_{wind})
and interior zones can be calculated for the entire tributary area at the edge
of the diaphragm. Calculating the total diaphragm load due to wind would then be
divided by the tributary area of the entire diaphragm width in the block and
this load (in psf) would be applied to the entire edge of the diaphragm as a
unit load (2a*w_{wind} is combined and proportioned into the unit shear
at the level under consideration). The first choice is very conservative while the second can
store the corner shears (2a*w_{wind}) for use later when designing the
wall cladding and components. The second is less conservative but easier to
deal with when attempting to look at the entire structure in order to compare wind
and seismic in each line of resistance. The second also makes it easier to turn
shear resisting elements on and off and quickly rebalance the distribution of
forces in each interior and exterior grid line where a shear resisting element
occurs. Finally, when designing each line of resistance for the
worst case Wind vs. Seismic force at that grid line or line of resistance, the
actual load becomes conservative by the nature of using the worst case
reaction. Do you: 1.
Apply the corner zone shear across the entire diaphragm
(tributary height adjacent to diaphragm) and compare against seismic OR 2.
Do you calculate the end zone at 2a*w_{wind}
and average this into the Interior zone loads to apply across the diaphragm and
compare against seismic. 3.
Does it matter? TIA Dennis
S. Wish, PE Dennis S. Wish, PE California Professional Engineer Structural Engineering Consultant La Quinta, CA 92253 dennis.wish(--nospam--at)verizon.net http://structuralist.wordpress.com http://www.structuralist.net |
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