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Re: Wind damaged residences in Kansas

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I agree with alot of what Harold said...............lack of
enforcement..............insurance companies willing to
pay...............inadequate load paths to the ground............lack of
required holddowns................etc. Engineering of the wood frame for houses
is not required by the local codes so it is typically left up to the contractor.

When we design wood frame commercial buildings, we inevitably get complaints of
overdesign from contractors, owners and architects who all believe "it is just a
big house"and therefore it should be built just like all the other houses.  I
know of many structural engineers who refuse to work on wood frames because of
the hassle that we constantly face when we design it by the codes.
Unfortunately, poor performance of these houses during a moderate wind storm
confirms that something is wrong with what is being allowed, but it seems like
nothing changes. I hate to say it but, until the losses are big enough (like
Homestead, Florida during Hurricane Andrew) nothing will change. There is too
much momentum trying to keep things the same (we are fighting an uphill battle).
Any suggestions? Anyone who wants to take up this cause?

Jim Kestner, P.E.
Green Bay, Wi

Harold Sprague wrote:

> 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
>
>