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Home My WebLink AboutA11 n INGINMED �i . .. -,WIDEAVORS a,r, 0: EMER.SON �a 1VC:QRPDRATED � .� vr, u ' i4. :7?k'1�m1: AlNa'M ... is The Experienced AoIni of View ACTIVE MEMBER May 7, 2003 Trevor Wood Selective Site Consultants 8500 West 110"' Street Suite 300 Overland Park, KS 66210 Reference: Design and Reliability of a Tapered Tubular Monopole with a Fall_zone, Quality of Steel and Fabrication of a Monopole Structure Various Monopole Sites In response to your inquiry regarding the design and anticipated reliability and fallzone radius of a monopole structure, EEI would like to offer the following comments: 1) The monopole structure is designed to meet the requirements of the ANSI TIA/EIA 222-E&F (June 1996) titled Structural Standards for Steel Antenna Towers and Antenna Supporting Structures. It also meets or exceeds the requirements of The 2000 International Building Code (IBC), BOCA®National Building Code, 2001 California Building Code, 2001 Florida Building Code, 2002 Building Code of New York State and the Manual of Steel Construction ASD Ninth Edition by the American Institute of Steel Construction. Furthermore, the foundation and anchor bolts meet the requirements of the American Concrete Institute's Building Code Requirements for Structural Concrete (ACI 318-98) and 2000 IBC FS=2. The pole itself is also designed to meet the provisions of the American Society of Civil Engineers (A.S.C.E.) Design of Steel Transmission Pole Structures, which was originally published in 1973 and most recently updated in 1990. 2) Based on the location of this structure, the monopole is designed to withstand the TIA/EIA 222-E&F fastest mile wind speed, the 2000 IBC 3-second gust wind speed and any local code requirements as specified by our customer. The wind exceeds the 50-year maximum anticipated wind velocity at 33 ft above ground level. Additional factors are applied to increase the wind loading, e.g., a gust response factor is imposed in order to account for sudden changes in wind speed, a height coefficient to account for increasing wind speed with height, and an exposure coefficient. Based on these conservative coefficients, the structure could in fact survive even greater wind loads than the basic design wind speed without any failures. C Reference: Design and Reliability of a Monopole Quality of Steel and Fabrication of a Monopole Structure 3) The monopole structure design is controlled by wind induced loads, however, earthquake induced loads are also evaluated with all building code requirements being satisfied. Vertical loads (i.e., gravity loads) are minimal on these types of structures, approximately 20% of the maximum capacity. 4) The design and loading assumptions which are used for the analysis of these structures are very conservative in nature when compared to other building codes, as a result, structural failure is highly improbable. 5) Failure of a steel monopole structure is defined as being that point at which the induced stresses exceed the yield strength of the material. At this point,deflections will be induced in the structure, which will no longer be recoverable once the load has been removed. Hence, a permanent deflection in the monopole would exist. 6) The induced loads must be sustained for a long enough period in order that the structure has time to respond to the load without its removal. Monopoles are flexible, forgiving structures, which are not generally susceptible to damage by impact loads such as wind gust or earthquake shocks. 7) As the structure leans over from the induced loads, it presents a markedly reduced exposure area for the development of wind-induced forces. This would result in the lowering of the applied forces and, therefore, the reduction of stresses and a halting of the structural deflection. 8) Hypothetically, let's assume that a pole becomes overloaded. The typical consequence of this overloading is "local buckling" where a relatively small portion of the shaft distorts and "kinks" the steel. Upon the removal of the applied load, the structure will not return to a plumb position. This does not cause a free falling pole. Even though the buckle exists, the cross section of the pole is capable of carrying the entire vertical load. As a result, wind induced loads could not conceivably bring this type of structure to the ground due to the excellent ductile properties, design criteria, and failure mode. In the event of an unlikely failure, the monopole can be designed to collapse within a fall zone radius (approximately 1/3 to 1/2 pole height). 7610 Senther Drive Engineered Endeavors,Inc. Mentor,OH 44060 l Reference: Design and Reliability of a Monopole Quality of Steel and Fabrication of a Monopole Structure 9) Further proof to the integrity of these structure-types are the fact that all EEI monopole structures in the Florida region withstood the direct impact of Hurricane Andrew with absolutely no structural damage reported. Wind loading was reported to be in the range of 100-120 MPH. Most recently, all EEI monopoles in the Wilmington, NC region withstood the force of Hurricanes Bertha and Fran, which had wind speeds of 105 MPH and wind gusts of 115 MPH. 10) Extensive research has been conducted to determine if any monopole tower (steel tapered tubular)has ever failed. All research,which includes database searches as well as interviews with tower designers and city engineers,has concluded that there has not been a single incident in which a monopole has fallen due to natural causes. 11) EEI has never experienced a structural failure due to wdathered induced overloading. EEI personnel have over 25 years combined experience in design and fabrication of these types of structures. In response to your inquiry regarding the quality of steel and fabrication of a monopole structure: 1) The monopole is fabricated from ASTM A572 Grade 65 material with a controlled silicon content of 0.06% maximum to promote a uniform galvanized coating. The base plate material is fabricated from Grade 60 material. All plate material meets a Charpy V-Notch toughness requirement of 15 ft-lbs @-20°Fahrenheit. By meeting the strict toughness requirement, the monopole is best suited to resist the cyclic/fatigue type loading (i.e., wind induced loading) these structures exhibit. Monopoles made of pipe sections or other types of steel do not meet these rigorous requirements. The toughness specification is based on 35 years of taper tubular poles being designed and manufactured for the electrical transmission and communication industries. 2) Anchor bolts are fabricated from A615 Grade 75 material. The bolts are 2 '/4 in diameter, made from#18J bar stock. All threads are rolled. Anchor bolts come complete with two (2) A194 Grade 2H hex nuts. The anchor bolt material must also meet a Charpy V-Notch toughness of 15 ft-Zbs @ -20'Fahrenheit, to resist the cyclic/fatigue type loading (i.e., wind induced loading) these structures exhibit. 7610 Jenther Drive Engineered Endeavors,Ine_ Mentor,OH 44060 •L Reference: Design and Reliability of a Monopole Quality of Steel and Fabrication of a Monopole Structure EEI guarantees the quality of steel used on the entire monopole. Material Certifications (Mill Test Reports) are available on all material at the time of fabrication. The toughness requirement should be taken very seriously, for over the lifetime of the structure not having this toughness requirement, "toe" cracks may occur at the base of the structure and the structure could ultimately fail. Fabrication of the monopole is performed in accordance with the provisions of the AISC Manual of Steel Construction and ASCE's Design of Steel Transmission Pole Structures. All welding and inspection is in accordance with the American Welding Society's Specification D1.1- latest revision. Testing and inspection reports are available upon request at the time of fabrication. EEI's monopole fabricator has two important certifications as a quality fabricator, these include: AISC (American Institute of Steel Construction, Inc.) Conventional Steel Structure Certification and QM1 ISO 9002-1994. In conclusion, due to the aforementioned items,monopole structures do not experience or have ever experienced "free fall" type failure due to wind or seismic induced loads. I hope that these comments address the issues, which you might encounter relative to the anticipated performance of monopole structures and quality of steel and fabrication. However, I will be most happy to answer any specific questions, which you might have. ®F�11,9 Sincerely, r• MICHAEL R. `' •� Engineered Endeavors, Inc. _ MOREL NUMBER E,30291 a `%.,,�T0FES5i -,N%%% 5 Lynn A. Padgett, P.E. Michael R. Morel, P.E. Project Engineer Vice President of Engineering 7610 7enther Drive Engineered Endeavors,Inc. Mentor,OH 44060