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RE: Wind damaged residences in Kansas

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Dennis,
 
I consulted on many residences (new construction and forensics) in the
Midwest where wind rules.  Every time the wind exceeds 70 mph there is
significant damage to residential structures.  There are many reasons for
this; all of which are because of poor design practices that are used
because it is always done that way, and lax inspection.  They are prone to
tornadoes and micro bursts embedded in thunderstorms.  As long as insurance
covers it, and the inspectors don't push it, the home owners are reluctant
to be proactive.   
 
The fragmentation of code authority is also of no help.  Each small
municipality has its own meager residential inspection department which
accepts anything "because everyone else does it that way" and "if we do it
differently, the developers will go elsewhere".
 
When the houses get more expensive, the load paths get more complicated, and
all structural design is done by the framer.  The more expensive the house
the less safe it is.
 
The reasons for the failures are:
1.  No load path for lateral wind forces and wind uplift.  No hurricane
clips or uplift straps.
2.  Most all roof construction is 2 x 6's @ 24" with cripple walls as
required.  Any wall is fair game as a bearing wall.
3.  No uplift details at the ridge or the cripple walls.
4.  End nailing the sills into the studs (no uplift resistance).
5.  The use of spaced 1 x's for roof sheathing (primarily in the Kansas City
area).  Residences of $150,000 or greater generally require a wood roof by
local covenant.
6.  Poor end wall details.  The rim joist at the walls parallel to the
ceiling and floor joists goes into cross grain bending.  (Why do the walls
squeak when the wind blows?)
7.  Use of continuous headers over several windows.  The continuous header
goes into cross grain bending and torsion.
8.  Poor nailing of the plywood shear walls at the corners.
9.  Platform framing even at the "dramatic" 2 story entrance or vaulted
ceiling.  This creates a hinge at midspan of the studs, which pairs up
nicely with the 2 other hinges at the top and bottom.  (2 hinges - good; 3
hinges bad)
10.  Wall studs stay 2 x 4 @ 16" even spanning 17 feet or so.  The
indiscriminate use of #3 grade substituting for #2 grade.
11.  Notches in structural elements at any place the plumbers, HVAC, or
electricians want.  The HVAC guys use a chain saw and cut openings any where
they want without regard to load path.  They create many hinges in one
structural element.
12.  The dry wall contractor's practice of cutting part way into a stud at
mid span to "straighten it".
13.  The only horizontal diaphragm in the ceiling is the gypsum board.
 
Any deviation from these practices causes most builders great
consternation.  I did not even get into the poor concrete and foundation
practices.  Remember all of the new houses that self destructed as they slid
down a creek bank.  The fill was just dumped in.  I have even seen this in
commercial developments where the owner / developer fired the geotech
because the tests came out bad.  (This resulted in pin piles, grout
injection, plumbing repairs, etc.)
 
Since I moved to Colorado where the soil is expansive, high winds, and
increasing seismicity (per 1997 NEHRP) I don't do much residential.
 
Harold Sprague, P.E
The Neenan Company 
harold.sprague(--nospam--at)neenan.com <mailto:harold.sprague(--nospam--at)neenan.com>  
 

-----Original Message-----
From: Dennis S. Wish PE [mailto:wish(--nospam--at)cwia.com]
Sent: Thursday, November 12, 1998 10:51 PM
To: SEA International List
Cc: REACH List
Subject: Wind damaged residences in Kansas


Our local news reported extensive damage in the Mid-west by heavy wind
gusts. In particular, it showed wood framed residences destroyed by an 80
mph wind in the state of Kansas.
Can anyone provide additional information on the causes and contributions to
this type of damage of residential structures?
The design criteria for 80 and 90 mph winds are not uncommon code
requirements in parts of California. I would assume they are more prevalent
in the Midwest due to high exposure area's. 
Therefore, when a failure such as these described by local news is
disclosed, I am concerned were the mode of failure occurs. 
 
If anyone has any additional information on residential damages in the
recent severe weather across the United States, I would appreciate any
input.
 
Please Cc all posts to the distribution on the top of my email. This will be
sent to the SEA International Listservice and the REACH Listservice where we
can share in the discussions.
 
Sincerely,
Dennis S. Wish PE
La Quinta, California