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Home My WebLink About1118 N.E. FRONTAGE ROAD (HUB PARK - NEXTEL COMMUNICATIONS) - PDP - 33-00 - CORRESPONDENCE - WTE / WTF INFORMATIONhave not had one structure fail due to overloading (even in the extreme cases that wind speeds have exceeded design values). We use the latest standards, wind speed information, and sophisticated analytical tools to ensure that we maintain our unblemished record for quality. I hope this letter helps increase your comfort level relating to communication structure failure. If you have additional questions or comments, I may be reached at (503) 315- 4515. Sincerely, Adrian McJunkin, P.E. Communications Division Pole Engineering Team Leader Page 3 of 3 monopole sections, the wind must exceed all of our estimates for magnitude, duration, as well as overcome the factor of safety determined from the design. For instance, this monopole is designed for an 80 mph Basic Wind Speed. This Basic Wind Speed translates into a sustained, gusted wind speed of 129 mph at the top of the monopole. Considering the remaining factor of safety available in the design, and a survivable wind speed which considers the ultimate yield strength of the steel and the minimum factor of safety available, failure of the monopole would not be expected until wind speeds exceeded 175 mph. Beyond 175 mph we can only make an educated guess as to the failure mechanisms that would take place. The term Failure used above only suggests that "local buckling" has occurred at this point. "Local Buckling" is the result of a relatively small portion of the shaft distorting by "kinking" the steel. Local Buckling does not cause a free falling pole, rather it relieves the stresses from the pole at this location. If wind speeds continue to increase, the pole may continue to buckle and eventually crumple/fold over upon itself. Once this takes place, a significant reduction in wind load will cause the pole not to experience further deformations. In the above scenerio, we are assuming sustained, gusted winds. In reality, a gust would soon dissipate and, after this peak wind is gone, the stress in the pole would be reduced. Poles are flexible, forgiving structures which are not generally susceptible to damage by impact loads such as a wind gust or earthquake shocks. It may take some time for the entire structure to "see" the impact loading. Even after a local buckle, the pole has significant capacity. It is this capacity along with the transitory nature of the loading that prevents a pole from "falling over." It should also be noted that typical antennas are designed to survive 125 mph. With the absence of antenna loading the pole would have additional capacity. Valmont/Microflect's Pole design and full-scale testing have provided the public with a very reliable product. Poles have gone through extensive full scale testing, resulting in a history of being extremely reliable. This public, in my professional opinion, has been well served. Valmont/Microflect has provided structures that have performed well during the earthquakes in California, the hurricanes in the South (including Hugo, Andrew, and Opal), and a number of tornadoes. Valmont/Microflect has never experienced an in service failure of a communication pole due to weather induced overloading, even though, as in the cases of Hurricane Hugo and Hurricane Andrew, the wind speeds may have exceeded the design wind speed. Valmont/Microflect has no direct experience with monopole failures. However, from what evidence we have seen from other vendor's experiences, it can be stated that it is rare for a monopole to fall in a radius larger than, say, half it's height, and that in most cases it will collapse in a small confined area as it comes down upon itself. Valmont/Microflect's communication towers have proven to be very reliable products. In our over 40 years of engineering and fabricating thousands of towers and monopoles, we Page 2 of 3 August 24, 2000 Jim Jenkins City of Springfield 601 Ave. A Springfield, MI 49015 Ph: (616) 96572354 Fx: (616) 965-0114 Subject: Failure Modes for Tapered Monopoles and mounting appurtenances. Nextel Site: MI-2324E — Dickman Rd. Proposed 150' Communications Monopole Structure Dear Mr. Jenkins, We understand that there is some concern on the part of local building officials regarding the potential for failure of proposed 150' tapered monopole Nextel is proposing for the above site. To address this concern we offer the following: Communications monopole structures designed by Valmont/Microflect are typically sized in accordance with the latest revision of the EIA/TIA 222 Standard entitled "Structural Standards for Steel Antenna Towers and Antenna Supporting Structures." This standard has been approved by ANSI, who has generated the standard for "Minimum Design Loads for Buildings and Other Structures". The standard, which is the basis for design loading for practically every building code and standard in the country, has dealt with the design of antenna support structures for over 40 years. The EIA standard, based on provisions of this nationally known specification, has a long history of reliability. At its core philosophy is it's first and foremost priority to safeguard and maintain the health and welfare of the public. The EIA standard dictates minimum wind loading (the predominant loading on a monopole structure) for each county in the United States. It is Valmont/Microflect's policy to use the wind loading listed in the latest EIA standard as a minimum loading unless the customer specifies a larger value. Statistically, the wind speed listed in the EIA standard has been determined to be that wind which has an average reoccurrence of 50 years (i.e. the magnitude has a 2% chance of occurring in any one year). This wind is the "fastest mile" wind at 33 ft. above ground. By definition, the "fastest mile" wind is the average velocity of a mile of wind passing a fixed point. This "fastest mile" wind is customized with height, exposure, and gust factors that apply to a particular installation which, in effect, increases the wind velocity. The loads generated by this wind speed, along with weight of the monopole sections and any ice loading being considered, are used to design the structural system. To fail Page 1 of 3 3575 25th Street SE Salem, OK 97302-1123 1.800.547.2151 X 302 DID 503.589.6651 Fax 503.363.4613 Email sarahg@valmont.com <mailto:sarahg@valmont.com> -----Original Message ----- From: Israel, John [mailto:John.lsrael@Nextel.com] <maiIto: [maiIto: John. Israel@Nextel.com]> <mailto:[mailto:John.lsrael@Nextel.com] <maiIto: [maiIto: John. Israel@Nextel.com]> > Sent: Saturday, September 23, 2000 10:15 AM To: 'Grant, Sarah' Subject: MO11-SG & L697-DB Sarah, Regarding M011-SG, You were going to send me some generic collapse language for monopoles. Myself and the site acquisition person would like to review this to make sure we accomodate Larimer County. L697-DB: Could you tell me when I can expect the engineering package so that I can get this submitted for permit. Give me a call. Thanks, John Israel Nextel Site Developement / Denver (303)994-4870 Israel, John From: Grant, Sarah [SarahG@Valmont.com] Sent: Monday, September 25, 2000 10:47 AM To: John Israel (E-mail) Subject: FW: MO11-SG & L697-DB FaIlLetter—NeMel MI23 24E Dick... Sarah Grant Regional Inside Sales Representative Valmont Communications Division 3575 25th Street SE Salem, OR 97302-1123 1.800.547.2151 X 302 DID 503.589.6651 Fax 503.363.4613 Email sarahg@valmont.com <mailto:sarahg@valmont.com> -----Original Message ----- From: McJunkin, Adrian Sent: Monday, September 25, 2000 9:28 AM To: Grant, Sarah Subject: RE: MO11-SG & L697-DB Sarah, Attached is a typical fall letter. «FaIlLetter Nextel M12324E DickmanRd.doc>> We only offer them on a site -by -site basis. If the pole has to fall within a particular land parcel, then we have to make special provisions in the design, which will affect the cost if the pole wasn't originally designed to accommodate a fall radius. Since this pole is short (only 2 sections), there really is no way we can offer a weak -link in the design to accommodate a fall radius less than the height of the pole. However, with the large factors of safety, this pole would survive an extremely high wind speed. An extreme survival wind speed is really the only thing we can offer for this pole. Let me know if we need to provide a letter, and I can draft one up for this project. Adrian -----Original Message ----- From: Grant, Sarah Sent: Monday, September 25, 2000 8:44 AM To: McJunkin, Adrian Subject: FW: MO11-SG & L697-DB Adrian, What is the generic language for a fall letter? Sarah Grant Regional Inside Sales Representative Valmont Communications Division