OT Screen cages, was Crawl spaces
 

On Apr 19, 10:01*am, "Don White" wrote:
wrote in message

...
On Apr 19, 9:25 am, Richard Casady
wrote:





On Sun, 19 Apr 2009 05:36:11 -0700 (PDT), wrote:
On Apr 18, 3:08 pm, wrote:
On Sat, 18 Apr 2009 11:53:19 -0700 (PDT), wrote:
On Apr 18, 12:38 pm, wrote:
On Sat, 18 Apr 2009 11:44:05 -0400, "Eisboch"
wrote:

wrote in message
.. .
On Sat, 18 Apr 2009 08:02:46 -0400, "Eisboch"
wrote:

We also had a pool enclosure installed at that house. By that
time the
code
requirements were for 150 mph winds.
It was installed by a reputable and licensed company but "Wilma"
still
pretty much destroyed it with 120 mph gusts.

I was involved in some post mortem inspections of failed screen
cages
after Charley. It appears the first thing to fail is the cable
stay
system, then the screen cage just shakes itself apart. I really
believe these should be designed more like a bi-plane than a
bridge
with more cable stays. The forces are more similar.
One of the mitigation in the subsequent code was more diagonal
bracing
in the roof to give them better dimensional stability.

I don't know if this is true or not, but it was suggested to me
that in
hurricanes, it is best to remove or open any doors on the pool
enclosures.
The screen sections are installed in a manner that is supposed to
allow them
to "blow out", reducing the surface that the wind can capture and
thus
reduces the loads on the aluminum frame and braces. Leaving the
doors open
allows the wind "pressure" to equalize within the structure.

Eisboch

We picked apart 5 failed cages of various vintages and none of them
seemed to "blow out" the screen before the structure failed. The
only
real commonality was in every case there was an apparent failure of
the cables in the section that failed first. Once one part fails,
the
rest comes down fairly fast if the wind keeps blowing.
The "flat spline" patio material will hold screen until the screen
itself fails. Round spline will pull out but that is not used here
except in door and window frames.
It is ironic that the old method of through bolting an eye bolt for
the cable stay seems more robust than the new style angle corner
bracket with 8-10 screws in it. The bracket itself fails. (all of
the
new cage failures)
After this, I did add some additional cable stays to my cage and
used
the eye bolt method. Wilma didn't hurt it.
After Charley we found a 40' mango tree on our cage, the oldest
part.
I was amazed it didn't come crashing down but everything was in
compression and that is not the force that pulls them apart.
I ended up having a crane remove it (handy to have a wife in the
construction biz, his number was in her NexTel)- Hide quoted text -

- Show quoted text -

Usually, the greatest pressures in a wind event are the negative
pressures at the corners. Let's say the wind is blowing on the front
of a house. The back corners act like a wing and accelerate the wind.
Those leeward corners are where the negative pressure is the greatest.
I don't know how many times I've seen mobile homes on the highway
where the siding was being blown off, and always on the rear edges.

I agree, that is why I think they should be using aircraft
engineering, more than bridge engineering.
These things become a huge air foil. The same is somewhat true in all
of the wind code engineering. We have specs for positive and negative
pressure ratings on everything.
I usually hear that you do not want to compromise the envelope by
opening windows and doors because that might end up adding a positive
force to an inside surface that is already having a negative force
being applied from the outside. Roof loads are usually where this
comes up.
I know when I was building in Maryland they never gave uplift a second
thought. Everything was assuming the load was down. They usually
didn't even put nuts on the embedded plate bolts. The opinion was they
were just there for horizontal placement.- Hide quoted text -

- Show quoted text -

I deal in a lot of mono sloped flat roofs for industrial buildings.
Uplift is always considered. Pre-engineered buildings are another
story. They build them so light that most of the time, the mitigating
factor on the size of column footings isn't the axial load on the
ground, but they have to be heavy enough to counteract uplift.
Especially if it's a long narrow building, it tries to tip over!

There is a building in Calif that is twenty foot wide and two miles
long. It has never blown over. They muct have bolted it down.

Casady- Hide quoted text -

- Show quoted text -

I was talking to an engineer once who designed a 29 story building in
Bristol used to test elvators. He sid it went down 29 stories too. I
noted "that's to hold it up", he said, "no, it's to hold it down"...
Engineer thing, but I never forgot it...

************************************************** *****

Did it have 58 flights of stairs? That must have been a nightmare for you..- Hide quoted text -

- Show quoted text -

Idiot, no wonder you were a public servant, and now a servant for your
drunken son.

OT Screen cages, was Crawl spaces
 

On Apr 19, 9:35*am, wrote:
On Apr 19, 9:25*am, Richard Casady
wrote:





On Sun, 19 Apr 2009 05:36:11 -0700 (PDT), wrote:
On Apr 18, 3:08*pm, wrote:
On Sat, 18 Apr 2009 11:53:19 -0700 (PDT), wrote:
On Apr 18, 12:38*pm, wrote:
On Sat, 18 Apr 2009 11:44:05 -0400, "Eisboch"
wrote:

wrote in message
.. .
On Sat, 18 Apr 2009 08:02:46 -0400, "Eisboch"
wrote:

We also had a pool enclosure installed at that house. *By that time the
code
requirements were for 150 mph winds.
It was installed by a reputable and licensed company but "Wilma" still
pretty much destroyed it with 120 mph gusts.

I was involved in some post mortem inspections of failed screen cages
after Charley. It appears the first thing to fail is the cable stay
system, then the screen cage just shakes itself apart. I really
believe these should be designed more like a bi-plane than a bridge
with more cable stays. The forces are more similar.
One of the mitigation in the subsequent code was more diagonal bracing
in the roof to give them better dimensional stability.

I don't know if this is true or not, but it was suggested to me that in
hurricanes, it is best to remove or open any doors on the pool enclosures.
The screen sections are installed in a manner that is supposed to allow them
to "blow out", reducing the surface that the wind can capture and thus
reduces the loads on the aluminum frame and braces. *Leaving the doors open
allows the wind "pressure" *to equalize within the structure.

Eisboch

We picked apart 5 failed cages of various vintages and none of them
seemed to "blow out" the screen before the structure failed. The only
real commonality was in every case there was an apparent failure of
the cables in the section that failed first. Once one part fails, the
rest comes down fairly fast if the wind keeps blowing.
The "flat spline" patio material will hold screen until the screen
itself fails. Round spline will pull out but that is not used here
except in door and window frames.
It is ironic that the old method of through bolting an eye bolt for
the cable stay seems more robust than the new style angle corner
bracket with 8-10 screws in it. The bracket itself fails. (all of the
new cage failures)
After this, I did add some additional cable stays to my cage and used
the eye bolt method. Wilma didn't hurt it.
After Charley we found a 40' mango tree on our cage, the oldest part.
I was amazed it didn't come crashing down but everything was in
compression and that is not the force that pulls them apart.
I ended up having a crane remove it (handy to have a wife in the
construction biz, his number was in her NexTel)- Hide quoted text -

- Show quoted text -

Usually, the greatest pressures in a wind event are the negative
pressures at the corners. Let's say the wind is blowing on the front
of a house. The back corners act like a wing and accelerate the wind.
Those leeward corners are where the negative pressure is the greatest.
I don't know how many times I've seen mobile homes on the highway
where the siding was being blown off, and always on the rear edges.

I agree, that is why I think they should be using aircraft
engineering, more than bridge engineering.
These things become a huge air foil. The same is somewhat true in all
of the wind code engineering. We have specs for positive and negative
pressure ratings on everything.
I usually hear that you do not want to compromise the envelope by
opening windows and doors because that might end up adding a positive
force to an inside surface that is already having a negative force
being applied from the outside. Roof loads are usually where this
comes up.
I know when I was building in Maryland they never gave uplift a second
thought. Everything was assuming the load was down. They usually
didn't even put nuts on the embedded plate bolts. The opinion was they
were just there for horizontal placement.- Hide quoted text -

- Show quoted text -

I deal in a lot of mono sloped flat roofs for industrial buildings.
Uplift is always considered. Pre-engineered buildings are another
story. They build them so light that most of the time, the mitigating
factor on the size of column footings isn't the axial load on the
ground, but they have to be heavy enough to counteract uplift.
Especially if it's a long narrow building, it tries to tip over!

There is a building in Calif that is twenty foot wide and two miles
long. It has never blown over. They muct have bolted it down.

Casady- Hide quoted text -

- Show quoted text -

I was talking to an engineer once who designed a 29 story building in
Bristol used to test elvators. He sid it went down 29 stories too. I
noted "that's to hold it up", he said, "no, it's to hold it down"...
Engineer thing, but I never forgot it...- Hide quoted text -

- Show quoted text -

Try designing a foundation for material silos (inverted pendulum) in a
high seismic area. First thing the owners want to know is why the mat
foundation is four feet thick or so.

OT Screen cages, was Crawl spaces
 

wrote in message
...
On Apr 19, 9:25 am, Richard Casady
wrote:
On Sun, 19 Apr 2009 05:36:11 -0700 (PDT), wrote:
On Apr 18, 3:08 pm, wrote:
On Sat, 18 Apr 2009 11:53:19 -0700 (PDT), wrote:
On Apr 18, 12:38 pm, wrote:
On Sat, 18 Apr 2009 11:44:05 -0400, "Eisboch"
wrote:

wrote in message
.. .
On Sat, 18 Apr 2009 08:02:46 -0400, "Eisboch"
wrote:

We also had a pool enclosure installed at that house. By that
time the
code
requirements were for 150 mph winds.
It was installed by a reputable and licensed company but "Wilma"
still
pretty much destroyed it with 120 mph gusts.

I was involved in some post mortem inspections of failed screen
cages
after Charley. It appears the first thing to fail is the cable
stay
system, then the screen cage just shakes itself apart. I really
believe these should be designed more like a bi-plane than a
bridge
with more cable stays. The forces are more similar.
One of the mitigation in the subsequent code was more diagonal
bracing
in the roof to give them better dimensional stability.

I don't know if this is true or not, but it was suggested to me
that in
hurricanes, it is best to remove or open any doors on the pool
enclosures.
The screen sections are installed in a manner that is supposed to
allow them
to "blow out", reducing the surface that the wind can capture and
thus
reduces the loads on the aluminum frame and braces. Leaving the
doors open
allows the wind "pressure" to equalize within the structure.

Eisboch

We picked apart 5 failed cages of various vintages and none of them
seemed to "blow out" the screen before the structure failed. The
only
real commonality was in every case there was an apparent failure of
the cables in the section that failed first. Once one part fails,
the
rest comes down fairly fast if the wind keeps blowing.
The "flat spline" patio material will hold screen until the screen
itself fails. Round spline will pull out but that is not used here
except in door and window frames.
It is ironic that the old method of through bolting an eye bolt for
the cable stay seems more robust than the new style angle corner
bracket with 8-10 screws in it. The bracket itself fails. (all of
the
new cage failures)
After this, I did add some additional cable stays to my cage and
used
the eye bolt method. Wilma didn't hurt it.
After Charley we found a 40' mango tree on our cage, the oldest
part.
I was amazed it didn't come crashing down but everything was in
compression and that is not the force that pulls them apart.
I ended up having a crane remove it (handy to have a wife in the
construction biz, his number was in her NexTel)- Hide quoted text -

- Show quoted text -

Usually, the greatest pressures in a wind event are the negative
pressures at the corners. Let's say the wind is blowing on the front
of a house. The back corners act like a wing and accelerate the wind.
Those leeward corners are where the negative pressure is the greatest.
I don't know how many times I've seen mobile homes on the highway
where the siding was being blown off, and always on the rear edges.

I agree, that is why I think they should be using aircraft
engineering, more than bridge engineering.
These things become a huge air foil. The same is somewhat true in all
of the wind code engineering. We have specs for positive and negative
pressure ratings on everything.
I usually hear that you do not want to compromise the envelope by
opening windows and doors because that might end up adding a positive
force to an inside surface that is already having a negative force
being applied from the outside. Roof loads are usually where this
comes up.
I know when I was building in Maryland they never gave uplift a second
thought. Everything was assuming the load was down. They usually
didn't even put nuts on the embedded plate bolts. The opinion was they
were just there for horizontal placement.- Hide quoted text -

- Show quoted text -

I deal in a lot of mono sloped flat roofs for industrial buildings.
Uplift is always considered. Pre-engineered buildings are another
story. They build them so light that most of the time, the mitigating
factor on the size of column footings isn't the axial load on the
ground, but they have to be heavy enough to counteract uplift.
Especially if it's a long narrow building, it tries to tip over!

There is a building in Calif that is twenty foot wide and two miles
long. It has never blown over. They muct have bolted it down.

Casady- Hide quoted text -

- Show quoted text -

I didn't say they blow over. I said they TRY to tip over. Besides, in
CA it's usually seismic conditions that determines design.


The building is mostly below grade. And it ties both sides of the San
Andreas fault together. Keeps part of Calif from falling in to the sea.
:)