HomeMy WebLinkAboutSDP200800178 Legacy Document 2009-02-11ENGINEERED
ENDEAVORS
23
INCORPORATED #
w
The Experienced Point of View ACTIVE
MEMBER
To Whom It May Concern:
Reference: Design and Reliability of a 103 ft Monopole
Quality of Steel and Fabrication of a Monopole Structure
EEI Quote Number: 09 -0148
EMERSON
February 9, 2009
In response to your inquiry regarding the design and anticipated reliability of a 103 ft
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 -G titled Structural Standards for Steel Antenna Towers and Antenna Supporting
Structures. It also meets or exceeds the requirements of The 2006 International
Building Code (IBC) and the Manual of Steel Construction LRFD Thirteen's 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). 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.
2) Based on the location of this structure, the maximum basic design wind speed
required is TIA/EIA 222 -G and 2006 IBC 90 mph 3- second gust wind. 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 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.
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) 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 is designed
to collapse within a 50 ft fallzone radius and have the theoretical break point at
51 ft above ground level.
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 the 2004
hurricane season and Hurricane Andrew with absolutely no structural damage
reported. Wind loading was reported to be in the range of 120 -140 MPH 3- second
gust wind. In addition, all EEI monopoles in the Wilmington, NC region withstood
the force of Hurricanes Bertha and Fran, which had wind speeds of 125 MPH and
wind gusts of 135 MPH 3- second gust wind.
10) EEI has never experienced a structural failure due to weathered 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 will be 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 A572 Grade 50 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
7610 Jenther Drive
Engineered Endeavors, Inc. Mentor, OH 44060
Phone (440) 918 -1101 ♦ Fax (440) 918 -1108
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 1 3/4 in
diameter, made from #14J bar stock. All threads are rolled. Anchor bolts come
complete with two (2) Al 94 Grade 2H hex nuts. The anchor bolt material must also
meet a Charpy V -Notch toughness of 15 ft -lbs @ -20° Fahrenheit, to resist the
cyclic /fatigue type loading (i.e., wind induced loading) these structures exhibit.
3) The base plate to base section weld is a complete penetration groove. Weld
procedures, material and welder certifications satisfy all requirements of AWS D1.1
American Welding Society standards. Toughness standards are also as described
above.
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 D 1.1 -
latest revision. Testing and inspection reports are available upon request at the time of fabrication.
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. We hope that
these comments address the issues, which you might encounter relative to the anticipated
performance of monopole structures and quality of steel and fabricate
happy to answer any specific questions, which you might have.
Sincerely,
Engineer deavors, Inc.
*oan elkin
Design Engineer
7610 Jenther Drive
Engineered Endeavors, Inc. Mentor, OH 44060
Phone (440) 918 -1101 ♦ Fax (440) 918 -1108