Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: Standard of Care

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Bill,

I don't know about flat strap bracing in metal studs, but we (current engineer, former iron worker, steel detailer, etc.) used to detail angle bracing 1/8" too short with a minimum of 2 bolts at each end.  You assemble the braces at the high end and drive a bull pin in one bolt hole at the down end and place a bolt in the open hole, tighten the bolt, remove the bull pin, and install the other bolt or bolts as required.

>From what I have seen in flat straps, they are sometimes tensioned by a similar process using predrilled holes (and a bothersome engineer) or by the first screws placed at an angle.  Some do and some don't.  Keep in mind that it is the carpenter trade that does metal studs, not the vastly superior iron worker.  (humor intended)

Water tower rod braces are pretensioned using upset rods and turnbuckles.  They adjust the tension in all of the rods by the sound they make when they are struck with a hammer.  Water towers are interesting because the upset rods allow the elongation to occur over a very long length of rod.  This absorbs beau coup energy, and very few water towers fall down in earthquakes or high winds.  Look at the pictures of the water tower surrounded by damage after hurricane Andrew.

The same problem pops up all over.  Read about the ceiling brace problems with the splay wires and compression strut.  By the time tension is in the splay wire, the ceiling has moved enough to cause damage.

The only industry I know that routinely installs braces to a measured tension is in the guyed stack, telecommunications, and electrical T&D industry which uses in line Dillon meters to directly measure cable tension.  They then verify the tension by inducing and measuring cable vibrations.

Although very approximate, a torque on turnbuckles could be used as a method of providing a minimum tension for rod bracing.

The pretensioning forces are accounted for in guyed stack, T&D, and telecommunications structures.  They are seldom accounted for in building structures.  You have to spoon feed the guyed stack industry on the hows and whys, but the T&D and telecommunications industries have a lot of experience in this arena.

I too have seen rod  braces removed from prefab metal and custom build steel buildings.  It's scary out there.

I hope that this is ample sustenance for Bill's curious mind.

Harold Sprague, PE
Krawinkler, Luth & Assoc.


-----Original Message-----
From:	Bill Allen, S.E. [SMTP:bill(--nospam--at)allendesigns.com]
Sent:	Friday, September 11, 1998 12:08 PM
To:	seaint(--nospam--at)seaint.org
Subject:	RE: Standard of Care

And what about the pretensioning of the rods loading the rest of the
structure?

And, how does one pretension flat strap X-Bracing for metal stud walls?

Curious minds want to know.

Regards,
Bill Allen


-----Original Message-----
From: MSSROLLO(--nospam--at)aol.com [mailto:MSSROLLO(--nospam--at)aol.com]
Sent: Friday, September 11, 1998 11:01 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Standard of Care


Using the rods to square the building will preload the rods.  The rods are
rarely designed for the "added load".  Supply a rod for a 3 kip wind and the
contractor applies 5 kips to square the building.  Seems like a mistake
waiting to happen.

Of the metal buildings I have looked at, an alarming number of them have had
the rods removed.  When I ask the Owner why, they usually say they were
loose
and not doing anything anyway.  So they had no fear of remvoing them.

I have seen one building with the rods later removed.  The 2nd  Owner after
that then cut a lot of overhead doors into the building. The 2nd Owner was
curious if it was normal for a building to "shake" when the wind blows
lightly.  Guess I should have told him "no it is not normal, they usually
just
fall over."

<<application/ms-tnef>>