Design and Reliability of a Monopole7610 Jenther Drive Engineered Endeavors, Inc. Mentor, OH 44060 Phone (440) 918-1101 ? Fax (440) 918-1108 March 2, 2007 Reference: Design and Reliability of a Monopole Structure in the
Telecommunication Industry Fall Zone Radius Quality of Steel and Fabrication of a Monopole Structure In response to your inquiry regarding the design and anticipated reliability of a
monopole structure: 1. The monopole structure is designed to meet the requirements of the ANSI TIA/EIA 222F (June, 1996) titled Structural Standards for Steel Antenna Towers and Antenna
Supporting Structures and mostly recently published ANSI/EIA-222-G (August 2005) titled Structural Standard for Antenna Support Structures and Antennas. It also meets or exceeds the
requirements of the International Building Code and the Manual of Steel Construction ASD and LRFD 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 Struct?ural Concrete (ACI 318-05). 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 just recently published (2006) as a design standard. 2. Based on the location
of this structure and the applicable design codes, the basic design wind speed of fastest mile and/or 3 second gust is used to deign the structure. An additional case with ice is also
checked based on past historical data on ice accumulation in the area. The specified wind speeds exceed 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. 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.
Reference: Design and Reliability of Monopole Structure in the Telecommunication Industry Fall Zone Requirement Quality of Steel and Fabrication of a Monopole Structure 2 7610 Jenther
Drive Engineered Endeavors, Inc. Mentor, OH 44060 Phone (440) 918-1101 ? Fax (440) 918-1108 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 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 cable 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, theoretically, the monopole is designed to have a high stress point at an intermediate height. This will keep the monopole structure within a certain
fall radius. 9. This monopoles is theoretically designed to collapse upon itself in the event that a catastrophic circumstance arises, however this type of failure has never occurred
on an EEI tapered tubular monopole structure. The initial failure point or high stress point of the monopole can be specified at certain elevations. The structure was designed so that
the stresses in the upper section of monopole are greater than the stresses in the bottom sections. The upper section fails and collapses onto the bottom section producing significantly
less wind area, hence decreasing the loads applied to the structure. As a result, the structure does not “free fall” to the ground and stays within the compound area. 10. Further proofs
to the integrity of these structure-types are the fact that all EEI monopole
Reference: Design and Reliability of Monopole Structure in the Telecommunication Industry Fall Zone Requirement Quality of Steel and Fabrication of a Monopole Structure 3 7610 Jenther
Drive Engineered Endeavors, Inc. Mentor, OH 44060 Phone (440) 918-1101 ? Fax (440) 918-1108 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. 11. In another incident, an EEI monopole withstood the impact of a run away bulldozer, which rammed the monopole
at the base. The monopole stood firm with only a dent in the shaft. After field repairs, this monopole is still in service and performing to its design capacity. 12. EEI has never experienced
a structural failure due to weathered induced overloading. EEI personnel have over 75 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 A871 Grade 60 material. All plate material meets a Charpy V-Notch toughness requirement
of 15 ft-lbs @-20o 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. 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 ¼ 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-lbs @-20o Fahrenheit, to resist the cyclic/fatigue type loading (i.e., wind induced loading)
these structures exhibit. 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