[TowerTalk] 90 MPH Windload and PE Stamp

[Jim Lux]

At 12:47 PM 9/13/2006, kr7x at comcast.net wrote:
>List: 2 iitems in one post
>
>90mph Wind Load:
>
>Is this fastest mile? or 3-sec gust?
>
>But I digress, National Building Codes have been around since the 
>early 50's if not before. There were 3 that were adopted by 
>jurisdictions in the US, the UBC, the SBC and BOCA. Actually there 
>were a few more that were locally developed but in general these 
>were the codes. In the late 90's it was deemed a good idea to put 
>together these three and have one code for the US. It is called the 
>IBC (international building code, go figure) and it was first 
>published in 2000 and has been revised in 2003 and most recently 
>2006. These codes are administratively adopted by individual 
>jurisdictions, state, county, city as the "life-safety" building 
>code governing the design and construction of structures in that 
>jurisdiction. This has been the fact for over 60 years.
>
>How does one get to the finding that it is a recent strategy by 
>local jurisdictions to regulate any specific users?


By whether a given jurisdiction decides to apply what part of the 
code to what kinds of structures.

Say one constructs a garden shed to store tools.  One could probably 
find places in the code which address the construction practices for 
the shed, but one has probably to decide what kind of structure it 
is: is it an accessory use? is it a farm outbuilding? etc.  That will 
determine what building standards are applicable for that use.

In my city, a lot of the code applicability has to do with what sort 
of planning zone it's in (R-1, RPD, M-1, etc.) and a lot of the local 
codes only have relevance in the "planning process" for a tract 
(especially for things that are RPD (residential planned development) 
or CPD.. there are lots of municipal code requirements that are 
"tract design" oriented: size of streets, overall density, slope 
requirements, etc., and aren't particularly applicable for subsequent 
modifications)

There's also differences in things done for and by a business 
(commercial activities) and homeowners.  Homeowners typically have 
had a lot more regulatory latitude than businesses (e.g. you can pour 
all manner of things down the drain at home that would get you a 
chance to contribute to the Superfund if you did them at work), but 
this is changing, and towers are merely one manifestation.

So, back in the good old days, nobody much cared about the safety 
aspects of ham or communications towers, at least from a city 
regulation standpoint.  The owner was responsible, and if something 
bad happened, they were liable.  Sure, there were design standards, 
and if you were a commercial operation, your liability insurance 
carrier would probably require you to follow them.  And, in general, 
it wasn't a problem.  There's relatively few towers in the first 
place. They didn't look much different than big TV antenna setups, 
etc., and failures are rare to boot.

Then comes two parallel trends: no external TV antennas and the 
desire of many businesses to erect large communications structures 
(i.e. cell towers).  Initial attempts to regulate on the basis of 
aesthetic grounds fails, so they start looking for other ways to 
regulate, and look, we can start imposing safety standards (which 
have actually existed all along, but were unevenly applied).


>This being said; I don't see any indication of some subversive 
>activity by the building officials. They are just asking that the 
>structure be design based on latest information utilizing the best 
>available knowledge and techniques.

And, I think there is a trend towards the local authority taking more 
interest in such things, rather than just letting them ride. It's not 
that the standards, per se, have changed all that much, it's that the 
city doesn't want the possible liability exposure from substandard 
installations.


>PE Stamp:
>I have a vested interest in this.
>
>I am a licensed civil engineer and licensed structural engineer in 
>several States and Canadian Provences. In every case the licensure 
>laws have a stipulation concerning stamping of work not done under 
>the licensee's responsible charge. This is wet stamping of drawings 
>and calculations not actually done under your direct supervision or 
>hand. In order to stamp this type of work the licensee must analyze 
>the structure to sufficent detail to assess that the design under 
>question does indeed meet the required code conditions. This is to 
>be an independent proceedure from the original work. The penalty for 
>not following this prescription is forefiture of license.
>Since my licenses are necessary for my livelyhood I would not place 
>them in danger.

And I would expect that any other reputable Engineer would do the 
same. This doesn't mean that it doesn't happen (as the sporadically 
published enforcement bulletin from the CA Board of PE and LS shows..).

But, considering the concept of "photocopied drawings from the mfr 
with a out-of-state PE's stamp on them"...

If you're standing at the counter trying to get planning permission 
for your tower.. The local code may not say much about what is or 
isn't required, or even if a permit (and inspection) is needed. I'm 
going through this now with a barbeque counter in a back yard.. the 
code doesn't say that it's permitted in the desired location but 
neither does it say it's prohibited. And, it doesn't say whether an 
inspection is needed for the barbeque.  It's made of concrete blocks 
about 3 ft high.  Or, maybe it's a miscellaneous masonry structure, 
in which case it has to be at least 5 ft from the property line and 
requires a masonry permit,but I want it on the line, as it happens. 
Hmm, maybe it fits in the garden wall over 30" high category, for 
which a permit is also required, but it can be on the property line. 
Or, maybe it doesn't need a permit at all, in which case the whole 
issue is moot. .. A building permit is definitely needed for the 
electrical service to the convenience outlet for the rotisserie, though.


  In a lot of jurisdictions it may be that actual wet-stamped 
drawings and analysis aren't needed. BUT, there's a big psychological 
sales difference between showing up with some scribbled numbers on a 
napkin and a stack of drawings from the manufacturer with a seal on 
the front that says that some PE, somewhere, at sometime, at least 
took a look at it.  Furthermore, that package of data will be in a 
"familiar form" to that planner at the counter (because many of them 
have some amount of engineering training and experience, even if they 
aren't licensed).  This is a far cry from some plans printed off the 
web or torn out of a magazine.  The counter person is MUCH more 
likely to give you the permit with the decent drawings.. Their 
on-the-spot assessment of "if I sign, is this going to bite me in the 
nether regions later" risk is very different. Likewise, when the 
inspector comes out to look at the footings.

If there are professionally done drawings to compare to, the 
inspector is going to probably take the design as being fundamentally 
sound, and just worry about whether you've built to the drawing 
properly.  If, instead, he's just looking at a hole in the ground 
with a bunch of rebar, he's probably going to wonder if it's big 
enough or the right shape, etc.  Again, it's the "will this bite me 
in the a** later in the unlikely event that something goes wrong" issue.


As far as pricing goes.. A few hundred bucks or even $1000 is a real 
deal.  The going hourly rate for this kind of thing would be in the 
$100-200/hr range (ahem.. this is not the cash in the Engineer's 
pocket, by the way), and most firms wouldn't even bother for less 
than a day's work.   Hank, and other ham P.E.s, essentially do this 
kind of thing as a labor of love or as a civic responsibility; kind 
of like attorneys doing pro-bono work.

I can see a manufacturer of LOTS of antenna systems (e.g. a Rohn or a 
Heights) finding it worth their while to hire enough P.E.s to cover 
all the states needed, because they could spread the substantial cost 
across many units. And, in this situation, the engineer is not 
wet-stamping a particular installation, but a particular analysis 
with a given set of boundary conditions, with the analysis conforming 
to each state's requirements.   Heck, the original design of the 
system probably took several work months: tens of thousands of 
dollars in engineering services.