From: "Sprague, Harold O." <SpragueHO(--nospam--at)bv.com>
Date: Tue, 2 Jan 2001 08:37:39 -0600
In addition to Neil's comments.
If you are replacing horizontal or diagonal members, you will have to
provide bracing support of the legs while you are replacing the diagonals or
horizontals. This is done with a device called a saddle clamp. The lack of
a saddle clamp or their misuse has caused several tower collapses during
retrofits. Also, many towers (like the Andrew / Grasis towers) are designed
using A449 bolts which do not have installation requirements like A325
bolts. A449 bolts are only used in bearing connections, and should be
tightened to snug tight.
Most telecom towers are hot dip galvanized, this can add some complications
for welding. It does not preclude welding, but it does complicate the
process. As will the distortion caused by the welding process. Distortion
will be more of a problem on the cold formed members of a tower.
If the tower manufacturer is still in business, I would run your retrofit
plan by them.
Harold O. Sprague
> -----Original Message-----
> From: Neil Moore [SMTP:nmoore(--nospam--at)innercite.com]
> Sent: Monday, January 01, 2001 6:26 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: retrofitting of towers
> Bolts: It depends on what kind of bolts you are using. If the bolts are
> high strength and designed as slip-critical, then the standard high
> strength tensioning is required. If they are in shear, then we use a
> "snug-tight" method. If you are worried that the "snug-tight" method
> loosen, then use Anco nuts. Some tower fabricators perform the high
> strength torquing as well as using the Anco nuts.
> Welds: If you are bolting in new members and you are using pipe with end
> tabs, the fillet welds require no special inspection. If there are other
> types of welds, then the shop should be certified with welding procedures
> already established.
> Any inspection should be performed by a certified welding inspector. If
> you want more information on welding inspection, review Section 6 of the
> Structural Welding Code (ANSI/AWS D1.1)
> >we are currently undergoing retrofitting of our telecom towers. we will
> be additiong additional atennae and our consultants have checked the
> and they require strengthening. my questions are:
> >1. additional horizontal and diagonal members will have to be added. is
> there a code requirement regarding the tightness of the bolts? i.e. up to
> what torque should they be tightened to?
> >2. how do you inspect the effectiveness of the welds of the additional
> members? what do you look for in inspecting the welds?
> >thank you very much
> >arman rivera