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[TowerTalk] Building Code Issues

 To: [TowerTalk] Building Code Issues k1vr@juno.com (Fred Hopengarten) Tue, 03 Aug 1999 12:01:58 EDT
 ```From: Fred Hopengarten K1VR 781/259-0088 Six Willarch Road Lincoln, MA 01773-5105 permanent e-mail address: fhopengarten@mba1972.hbs.edu if sending attachments: k1vr@gis.net From: Fred Hopengarten To: All Massachusetts Antenna Support Structure Clients To: Date: August 3, 1999 Subject: The Massachusetts Building Code The Massachusetts Building Code requirements for windload on antenna support structures are found at 780 CMR 1611 et seq. In the Sixth Edition, there are two typos and one thing which is difficult to read. If you are thinking about a situation in another state, which also uses BOCA code figures, read on anyway. The Typos. Page 275, table 1611.4 has a note which references table 1611.1a for empirical wind pressure formulas. The reference should be to 1611.4a. Page 276, table 1611.4a has a note which references table 1611.1 for reference wind pressure requirements. The reference should be to 1611.4. Difficult to Read Table 1611.4a is entitled "Empirical Wind Pressure Formulas", which may be used in lieu of the chart at table 1611.4. It is difficult to read the formulas, however, because it is not on one line. Zone 3, Exposure B should read: p=60(h/800) (to the 0.45 power) Sorry, but in ASCII, there is no neat way to type this. Meaning Why should you care? The answer is that if you have a really close situation, where you need that last square foot and you have a fussy Building Inspector, the formula may give it to you. Here's just one example: If you live in Zone 3 Exposure B, your Reference Wind Pressure is 21 p.s.f. (NOT the 30 psf or 86.6 or 90 mph for which Rohn tower is specified). So you can put up a bigger beam than you first thought you could when you ordered the Rohn 25 or 45 you may now own. However, if you are erecting 75 feet and do the formula, which is permitted by the Building Code, you need only build to a specification of 20.67 p.s.f. This gives you an additional one-third of a pound of wind pressure to spare, which may permit one more element on your Yagi. Rohn 45 Specifications -- Read Smaller, Think Bigger Now that we've discussed why the Building Code permits you to erect a bigger beam than you first thought, refer to the Rohn catalog, Drawing No. C870478, General Notes. Note 4 reads: "Tower designs include three side arms, symmetrically placed, having a total effective projected area equal to 8.0 square feet." Thus, if you've read this far, and you are further willing to read the really small font wording pointed out, you may now think and additional 8.0 s.f. bigger! Here's wishing you good DX! ___________________________________________________________________ Get the Internet just the way you want it. Free software, free e-mail, and free Internet access for a month! Try Juno Web: http://dl.www.juno.com/dynoget/tagj. -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com Search: http://www.contesting.com/km9p/search.htm ```
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