6.5, 6.6 r-c/
ITEMS 6.5. & 6.6.
(
ftyy of 11
MEMORANDUM
lk •
River TO: Planning Commission
FROM: Scott Harlicker, Assistant Planner IV
DATE: September 24, 1996
SUBJECT: Request for Conditional Use Permit
by AT&T Wireless Services, Public
Hearing Case No. CU 96-23 and Request
for Zone Change, Public Hearing Case
No. ZC 96-17
Request
AT&T Wireless Services is requesting a zone change to rezone certain property
to Antenna Overlay District and a conditional use permit for a wireless
communication antenna pole and equipment building.
• Location
The property being utilized is located east of Highway 10, south of 175th Avenue
alignment and west of the Burlington Northern Railroad tracks, part of parcel
75-002-3303
Zoning/Land Use
C3 (Highway Commercial) / HB (Highway Business)
Attachments
• Location map
• Zoning map
• Site plan
• Elevation drawings of pole and equipment building
• Service area coverage maps
• Letters from AT&T dated August 27,1996 and September 12, 1996
Background
• AT&T Wireless Services is proposing to lease an area approximately 60' by 57' in
order to construct a 199 foot tall pole on which they will mount cellular
13065 Orono Parkway • P.O. Box 490 • Elk River, MN 55330 • (612) 441-7420 • Fax: (612) 441-7425
Memo to Planning Commission
Page 2
September 24, 1996
• telephone antennas. They are also proposing to construct a 12' by 24' building to
shelter equipment.
The area the applicant plans on leasing is located in the northeast corner of a
12.5 acre lot adjacent to the west side of the Burlington Northern Railroad
tracks. The area to be leased is currently undeveloped and contains a stand of 8"
to 12" diameter pines. The adjacent land uses include Riverview Sports and
Marine and undeveloped land, both commercially zoned and residentially zoned.
The site is flat and will require little grading.
The site will be serviced by a 12 foot wide gravel drive with access from the
Highway 10 service road. The gravel drive will be located within a 20 foot wide
access easement over the adjacent properties to the west.
In order to better manage the potential proliferation of antennas in the city
cellular antennas should be capable of being used by other cellular providers.
This pole has been designed so that it can accommodate additional antennas for
use by other cellular companies
Overview
Rezoning
• In order to construct the proposed antenna, a rezoning of the property is needed
to Antenna Tower Overlay district (AT). This special overlay district was set up
to manage the proliferation of antenna towers and to insure their proper
placement regarding the health, safety and welfare of the community. This
overlay district does not change the underlying Highway Commercial (C3)
zoning, all the uses allowed and the dimensional regulations in the C3 zoning
district will continue to be allowed on land zoned into the AT.
In considering a rezoning request of this nature, consideration should be given to
the existing conditions within the area directly and indirectly affected by the
rezoning proposal as well as compatibility with surrounding land uses. The
existing conditions of adjacent properties include undeveloped residential zoned
and commercial zoned property and some older commercial buildings along the
Highway 10 frontage road. The adjacent properties to the north, west and south
is zoned either highway commercial or light industrial. To the west is the
railroad tracks and undeveloped residential zone property. The rezoning of this
lot to AT should not adversely affect the property under consideration or the
adjacent properties and it would not be incompatible with the surrounding land
uses.
The applicant has also provided information identifying changes and advances
• in the cellular telephone industry that make it necessary to construct an
antenna at the proposed location. They have also provided coverage maps of the
Memo to Planning Commission
Page 3
September 24, 1996
area showing the expanded coverage that would result in the placement of the
•
proposed antenna.
Recommendation
It is recommended that the Planning Commission recommend approval of the
rezoning request to Antenna Tower Overlay District based on the following:
1. The rezoning would not adversely affect the property under consideration.
2. The rezoning would be compatible with surrounding land uses.
3. The applicant has shown that the proposed rezoning to AT is necessary in
order to provided effective cellular phone coverage for this area.
Conditional Use Permit
Performance standards
The application was compared to the following performance standards found in
Section 900.12.19 (Antenna Tower Overlay District):
• 1. The applicant has provided a letter from the manufacturer of the pole,
Valmont Industries Inc., which gets into the structural and engineering
details of the pole and why there is no danger of the pole collapsing on to
adjacent property. This letter is included for your review.
2. There is only one tower proposed for this lot and the lot exceeds the one
acre minimum lot size requirement.
3. The height of the tower, 199 feet, does not exceed the 240 foot maximum
height allowed in the zoning code. Because of the proposed height of the
tower does not exceed 200 feet, the applicant is not required to file with
the F.A.A. for authorization. However, the applicant has indicated that
they will supply a report prior to receiving a building permit.
4. No portion of the pole, supports or related equipment extends across any
right-of-way, property line, public street or sidewalk; the pole and the
equipment building comply with the setback requirements.
5. The applicant has indicated that the pole will be designed to exceed the
the wind loading factor prescribed in the Uniform Building Code.
410
Memo to Planning Commission
Page 4
September 24, 1996
• 6. The applicant has indicated that the tower will be grounded against
lighting strikes and will comply with the electrical requirements of the
city.
7. The tower will be constructed to discourage climbing in that the climbing
apparatus will be removed within 12 feet of the ground. Staff is also
suggesting that the facility be fenced.
8. Because of the placement of the pole on a remote section of this 12.5 acre
lot, the design and color of the pole and the existing vegetation, the offsite
impacts will be minimal. The pole will be painted arctic ice blue to blend
in with the sky and will be placed in the rear of the property in a grove of
pine trees. There is no lighting proposed for this pole so lighting will not
be a factor. The limited traffic associated with maintenance of the site
will not have an impact on the transportation system.
The applicant has provided a diagram showing the different frequencies
at which television, radio and cellular broadcast. The applicant has stated
that they have not received any report of television or radio interference
nationwide. The applicant contacted the St. Paul office of the F.A.A. and
their office had not received any complaints of interference caused by
cellular phones.
• Impact on Property
The zoning code states that multiple principle buildings on a single lot require a
conditional use permit. Since this pole is considered a principle structure, any
further development of the property will require a conditional use permit.
Recommendation
It is recommended that the Planning Commission recommend approval of this
conditional use permit to construct a 199 foot tall antenna tower and equipment
building with the following conditions:
1. A six foot high non-climbable fence shall enclose the facility.
2. The tower shall not contain any signage, including logos, except as may be
required by State and Federal regulations.
3. The tower and equipment building shall be removed with 6 months of
cessation of operation unless a time extension is granted by the City
Council. In the case of multiple users of this tower, this condition shall not
1111 become effective until all users of the tower cease operations for 6 months.
Memo to Planning Commission
Page 5
September 24, 1996
• 4. Should Burlington Northern Railroad have any concerns, they shall be
addressed prior to the issuance of a building permit.
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5201 EAST RIVER ROAD, SUITE 308
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PHONE (6 1 2) 571 -2500 FAX (6 1 2) 571 - 1168
AT&T WIRELESS SERVICES
OF MINNESOTA, INC.
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5201 EAST RIVER ROAD, SUITE 308
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•
Cellular Division AT&T Wireless Services
2515 24th Avenue South
Minneapolis, MN 55406
612 721-1660
FAX 612 721-4770
August 27, 1996
Honorable Mayor and City Council Members
Planning Commission
City of Elk River
13065 Orono Parkway
P.O. Box 490
Elk River,MN 55330
RE: Conditional Use Permit Application
Wireless Communication Antenna Site
• Honorable Mayor, Council Members, and Commissioners:
This letter accompanies an application for a Conditional Use Permit to construct a Wireless
Communication antenna site on land owned by Mr. Les Lundquist and Mr. Floyd Kruse. The property
as is sits today is currently undeveloped.
The request is being made in the name of AT&T Wireless Services. The fee owners have consented to
this application and have entered into a lease agreement with the applicant for a portion of their
property. Drawings and site surveys of the property accompany this letter.
The Proposed Use.
The site would be used by AT&T Wireless Services, one of the two companies who were
originally licensed by the Federal Communications Commission (FCC) to provide essential cellular
communications services to the Twin Cities. The proposed project would include a steel monopole with
antennas attached to it and the construction of an equipment building to accommodate cellular radio and
switching equipment.
The proposed location is on the approximate northeasterly portion of the property . This
specific site was chosen based on the following criteria:
• AT&T Wireless Services' engineering and system development needs
. • The need for improved cellular coverage as dictated by our customers
\bocfr Recycled Paper
• •
Wireless Communication Antenna Site
• Elk River, Minnesota
Page 2
The proposed site will be contained within approximately a 30'x 50' area. The general area is
surrounded by several Pine trees, which will give aid in the screening of the proposed development. A
fence, if desired by the staff, will be placed around the entire proposed development to create a safe and
secure environment. A site plan, drawings, and photographs of the proposed project accompany this
application.
The Monopole.
The proposed monopole will provide the support for the cellular antennas and related cabling
necessary to connect the antennas themselves to the radio equipment shelter. It is constructed of steel, is
completely self-supporting, and will be painted Artic Ice Blue to blend with the skyline.
It will be engineered and manufactured by Valmont Industries, Inc. of Valley, Nebraska. We
will provide detailed engineering data for permitting purposes to your Building Inspections Department
when this request is granted.
AT&T has specifically engineered this monopole to allow for potential future co-location by
other wireless providers.
•
Equipment Building.
The proposed equipment building will house radio, computer, and climate control equipment for
this site. The equipment is powered by 220 volt, single phase, AC electric. It will be connected to
AT&T Wireless Services' central switching offices via traditional telephone lines. As a result, no one
will need to be present at the site on a daily basis. There will only be an occasional visit (average of
once a month) for routine maintenance. The equipment produces no noise, smoke, fumes, glare, or odor.
The building itself is approximately 12' wide, 28' long, and 10' high. It is manufactured of a
fiberglass exterior and is designed to meet your codes. It will be brought to the proposed site by truck,
off-loaded, and set on permanent concrete footings.
Antennas.
The antennas will be attached to the monopole and will transmit and receive the FM radio
signals that carry voice and data between the cellular system users and AT&T Wireless Services' central
switch. The physical size of the antennas depends on the type and manufacturer.
The area in which cellular coverage is needed largely defines the required antenna height.
Naturally, topography and surrounding trees and buildings also play an important role in arriving at the
appropriate height. AT&T Wireless Services' engineers have determined that the height necessary at
• this location is 199 feet.
• •
Wireless Communication Antenna Site
• Elk River, Minnesota
Page 3
The Cellular Phone System.
Users of cellular telephone service include members of the business community as well as the
public sector. Commuters, doctors, salespeople, business owners and executives all benefit by using
cellular phones. Additionally, cellular telephones are used extensively by fire, police, and other public
safety officials and departments. The system allows police and others to conduct discreet
communication in the field, and it enables direct communication with individuals in need of assistance
even when a traditional telephone is unavailable.
Cellular phone users can contact "911" to report accidents, fires, or other emergencies without
first having to search for a telephone. Mr. James R. Beutelspacher, 9-1-1 Project Manager for
Minnesota, wrote that "the unimpeded growth of cellular service is an important adjunct to 9-1-1
emergency reporting." .
Cellular is a low-power system. The amount of energy generated from a single cellular phone
channel is approximately 100 watts. This is less energy than is generated by the typical cordless
telephone which is used in many homes today.
The Question of Interference.
•
The cellular phone system operates on a specific set of channels set aside by the Federal
Communications Commission. The filtering of spurious signals is very tightly controlled. Cellular
telephones operate within a strictly regulated set of allotted frequencies between 825 and 845 megahertz
(MHz) and between 870 and 890 MHz. AT&T Wireless Services is currently licensed to operate in over
100 major markets nationwide with hundreds of antennas. There has not been any instance of television
or radio interference reported.
All AT&T Wireless Services sites must be operated in accordance with our FCC license to
provide cellular service in this area. Mr. Albert S. Jarratt, Jr., Engineer in Charge of the St. Paul Field
Office, Field Operations Bureau of the FCC, confirmed that the FCC has not received any complaints of
interference by cellular phone transmissions with home electronic entertainment equipment in any of the
five states in which Mr. Jarratt's office has jurisdiction.
The Cellular Grid.
Cellular service provides subscribers with highly portable phone service by developing a grid of
radio cells arranged in a geographically hexagonal pattern. Each "cell" is created by an antenna which
serves as the link between the customer and the system while the customer is within that particular cell.
As callers move from one cell to the next, their calls are switched, or "handed off," to the next cell's
antenna site.
1110
• •
Wireless Communication Antenna Site
Elk River, Minnesota
Page 4
Each cell can only handle a finite number of calls at any one time. As the number of customers
increases, the grid must be changed to handle the increasing number of calls. This usually means that
more cells need to be created within the same geographical area, resulting in a new grid pattern of
smaller cells. This need for more cellular calling capacity originally brought this antenna site to this
location. Accompanying this letter is information that more thoroughly explains the cellular system.
While the area in which cellular coverage is needed largely defines the required antenna height,
topography also plays a role in arriving at the appropriate height for the tower. This is true because
cellular telephone signals cannot travel through large structures or through the earth.
One of the keys to cellular engineering is to take care to design each cell to be the proper size. If
a cell is too large, it will interfere with the operation of neighboring cells, and callers will hear other
conversations or "cross-talk." If a cell is too small, some areas between cells will be left without any
service and callers will not be able to use their phones. If a caller is in a valley or if a hill lies between
the caller and the cell's antenna, the area acts as if there is no antenna at all. When topography comes
into play, cellular telephone service can be both difficult to provide and frustrating to use.
Cellular engineers now employ the use of directional antennas in an effort to accommodate the
topography. By increasing the elevation of the antennas and tilting the antennas downward, the cellular
signal is projected over the top of hills and down into valleys without increasing the cell's overall size.
• Indeed, this technology will be employed at this particular site.
The Conditional Use Permit.
The City of Elk River, in it's Conditional Use Permit Application and zoning ordinances set
forth the following standards by which the City Council shall approve, amend, or deny a conditional use
permit:
1. Will not endanger, injure or detrimentally affect the use and enjoyment of other property
in the immediate vicinity or the public health, safety, morals, comfort, convenience or general welfare of
the neighborhood or the City. The property surrounding the proposed site is zoned C-3 Commercial.
The communications facility that is being proposed is designed to serve this types of use, as well as the
general public. Providing improved cellular telephone capacity and coverage to the surrounding area
will have a positive impact for the present and future businesses in the area.
2. Will be consistent with the comprehensive plan. One of the purposes and intents of the
Zoning Ordinance and the Comprehensive Plan is to provide essential services to the public, including
communication services. For the reasons set forth in greater detail above, cell site in this general
location is necessary to provide adequate cellular telephone service to this area of the City and
surrounding areas. Allowing the cell site to be located here, subject to reasonable conditions, is
• consistent with the purpose and intent of the Zoning Ordinance and Comprehensive Plan. The
• •
Wireless Communication Antenna Site
Elk River, Minnesota
Page 5
Comprehensive Plan designates the site for Commercial uses. The cell site is consistent with and serves
this type of use. The use is therefore consistent with the Comprehensive Plan.
3. Will not impede the normal and orderly development and improvement of surrounding
vacant property. AT&T Wireless Services has installed over 100 cell sites throughout the state. In no
instance has there ever been any evidence that a cell site has caused any depreciation of surrounding
property values. Because of the commercial nature of this proposed site, any improvement or
development of the surrounding vacant properties could be developed with out any problem.
4. Will be served adequately by and will not adversely affect essential public facilities and
services including streets,police and fire protection, drainage, refuse disposal, water and sewer
systems,parks and schools; and will not, in particular, create traffic congestion or interference with
traffic on adjacent and neighboring public thoroughfares. The only public utilities or services that the
proposed use requires is electrical services, which is ample for AT&T Wireless Services needs at this
site. The proposed site has access off the service road and has a permanent easement for access to the
property that the pole and shelter will be constructed on. Because of the computerized operation of this
technology, site visits will be infrequent, approximately one visit per month, which will eliminate any
• traffic congestion or interference with traffic on the surrounding public streets.
5. Will not involve uses, activities,processes, materials, equipment and conditions of operation
that will be detrimental to any persons or property because of excessive traffic, noise, smoke,fumes,
glare or odors, dust or vibrations. The cell site that is being proposed will not cause any hazardous or
detrimental activities to any person at the site or surrounding area. All equipment is self contained
within the building which will not create any noise, smoke, fumes, glare or odors.
6. Will not result in the destruction, loss or damage of natural, scenic or historical feature of
major importance. The use would not create excessive additional costs for public facilities or services.
Because of the nature of the proposed site, minimal construction will take place which will not cause
any damage to the site or surrounding area. The general area is mostly zoned Light Industrial which
does not have any scenic or historic features.
7. Will fully comply with all other requirements of the City's Code of Ordinance,
including any applicable requirements and standards for the issuance of a license or permit to
establish and operate the proposed use in the City of Elk River. As stated earlier, AT&T
Wireless Services intends to fully comply with the City's code requirements and work closely
with City Staff.
The granting of the CUP will alleviate problems for AT&T Wireless Services and it's customers
in this area, including city and county departments of public safety.
•
• •
Wireless Communication Antenna Site
• Elk River, Minnesota
Page 6
Conclusion.
This letter should serve to better explain our application and to answer some of your questions.
If we can be of further assistance, please feel free to contact me at 612-844-6741. I will, as well as other
representatives of AT&T Wireless Services will be in attendance at the Planning Commission and City
Council meetings to address any additional questions that you may have. AT&T Wireless Services
appreciates the assistance that we have already received from the City's staff, and we look forward to
working with you to better serve the area.
Thank you for your consideration.
Sincerely,
• Ronald L. Mielke
Real Estate Acquisition Manager
AT&T Wireless Services
Enclosures
•
ATM'
Cellular Division AT&T Wireless Services
September 12, 1996 2515 24th Avenue South
p Minneapolis, MN 55406
612 721-1660
FAX 612 721-4770
Mr. Scott Harlicker
Planning Department
City of Elk River
13065 Orono Parkway
P.O. Box 490
Elk River, MN 55330
Re: Additional information for Antenna Tower Overlay Zone
Dear Scott:
As per our telephone conversation and the Fax that you sent to me, I am sending
you some additional information that you requested. As pertaining to:
1. Elevations: I am enclosing an elevation drawing prepared by Ulteig Engineers,
Inc., depicting the pole, antenna placement and the equipment shelter. The height of the
• pole is 197 feet with the tip of the antenna placed at 199 feet. The equipment shelter
measures 12'x24' in size.
2. Proof of need: I am enclosing colored copies of frequency coverage. One of
the diagrams shows the existing conditions and coverage and the other diagram shows the
improved conditions and coverage. The red area show the acceptable coverage and the
green shows the unacceptable coverage.
3. Proof of non-interference: I am enclosing a diagram showing the different
frequencies that are used by cellular, radio and television stations. Because of the
difference in frequencies, there is no interference caused by the cellular(wireless)
equipment.
4. Revised site plan: The revised site plan shows the access to the site, plus some
of the trees and vegetation that must be removed for the construction of the site. If
required AT&T Wireless Services will replace some of the vegetation with new
landscaping.
5. F.A.A. or Minnesota Department of Transportation regulation: Any tower
that exceeds 200 feet in height, an application must be submitted to the F.A.A. for their
review. Because of the proposed height of the pole and antenna's, AT&T is not required
to file for F.A.A authorization, but AT&T usually files for all locations and has
•
Y_1< Recycled Paper
Page 2
• Elk River,Minnesota
for this particular site. A letter or report will be given to the City of Elk River prior to
receiving a building permit.
6. Antenna Towers shall be designated to withstand a uniform wind loading as
prescribed in the Uniform Building Code: According to Uniform Building Code,towers
shall withstand wind loads to 80 mph. AT&T has the poles engineered to withstand winds
up to 90 mpg with 0.5 inches of radial ice. See attached letter from Valmont Industries,
Inc.
7. Antenna Towers shall be grounded for protection against a direct strike by
lighting and shall comply as to electrical wiring and connections with all applicable
codes and regulations: At the time that AT&T applies for all building permits, drawings
with all specifications will be supplied to the city. AT&T meets and usually exceeds the
requirements set forth by the city.
8. Every Antenna Tower shall be protected to discourage climbing of the
Structure by unauthorized persons. To prevent unauthorized climbing, Antenna Towers
shall comply with one of the following requirements: To prevent unauthorized climbing,
• AT&T removes climbing apparatus within twelve feet of the ground and at times places a
protective fence around the structure.
9. The petitioners for an Antenna Tower must demonstrate, based on the
topography of the site, surrounding structures and vegetation and the design of the tower,
that off-site impacts from items such as lighting, electrical interference, and visual
impacts as well as safety issues will be minimal: The placement of the proposed structure
is placed in an area that minimal population and traffic. AT&T is not proposing to have
any lighting on the structure, thus not causing any interference. The electrical to the site
will be that of existing power that is in the area. The visual impact will be minimal
because of the design that is used by AT&T. The pole is a steel self-supporting monopole.
The color of the pole will be painted a pale blue to blend in with horizon. The safety
issues are addressed in the letter from Valmont Industries, Inc.
Scott, I hope that this addresses all the issues,but if you should if you should have
any other additional questions, please feel free to contact me.
Best re ards,
Ronald L. Mielke
• Real Estate Acquisition Manager
VALMONT
• Valmont Industries, Inc. •West Highway 275• P.O. Box 358
Valley, Nebraska 68064-0358 U.S.A. • (402) 359-2201
9/11/96
City of Elk River Planning Department
City Hall
13065 Orono Road
Elk River, MN 55330
ATTENTION: Mr. Scott Harlicker
SUBJECT: Failure Modes for Poles and a Description of the Design Criteria
A T and T Wireless Elk River, MN Pole Valmont Order 12867-96
Dear Mr. Harlicker:
I have been asked to write to you about the mode of failure for pole type structures used to support
cellular antennas and equipment, and give some information to allow you to judge how remote the chances
of that failure occurring would be. I think it would be appropriate to start off by a brief description of the
design criteria that is typically used.
•The poles Valmont supplies are designed in accordance with the E.I.A. / T.I.A. 222 Revision F Standard
entitled "Structural Standards for Steel Antenna Towers and Antenna Supporting Structures." This is an
approved A.N.S.I. standard that has dealt with the design of lattice type structures for a number of years.
Revision E was the first version that went into extensive detail about the design of pole type structures.
The provisions of the standard have, as their foundation, provisions of other nationally known
specifications and standards that have a long history of reliability. This history should be of interest to
you considering the hundreds of thousands of sites throughout the United States which have structures
designed with concepts spelled out in publications like "The Design of Steel Transmission Pole Structures"
(published by A.S.C.E.), and "Standard Specifications for Structural Supports for Highway Signs,
Luminaries and Traffic Signals" (published by A.A.S.H.T.O.). Many of the concepts used to design
poles in these two publications are included in the E.I.A./ T.I.A. 222 Revision F Standard.
The E.I.A. / T.I.A. 222 Revision F requirements would dictate in Hennepin County Minnesota a basic
design wind speed of 80 mph and / or 69 mph with 0.5 inches of radial ice. The wind speed to be used
depends on the location of the site within the state. Valmont's policy is to use the wind loading listed in
E.I.A. / T.I.A. 222 as a minimum loading. A T and T gave us a wind speed of 90 mph with 0.5 inches
of radial ice for this project. This represents and increase in loading of at least 27% more than the E.I.A.
Standard would dictate. Statistically, the wind speed listed in E.I.A. / T.I.A. 222 has been determined to
be that wind which has an average reoccurrence of 50 years. This wind is also a "fastest mile" wind
which means that it is the average velocity of a mile of wind passing a point. For example, a 70 mph
average fastest mile wind would take 51 seconds to pass a point. This standard "fastest mile" wind is
customized with factors that apply to the particular installation. There is a 1.69 gust response factor
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 to account (to some degree) the terrain
effects.
The loads generated by this wind and the weight of the members (along with any ice considered) are then
used to size members of the pole. There is at least a 25% factor of safety required under these conditions.
•This assumes that the wind is blowing from the worst possible direction. Some directions are worse than
others, depending on the equipment attached to the pole, the arrangement, and the orientation. The wind
must exceed all our estimates for magnitude, duration, be at the worst orientation and overcome the factor
of safety.
Let us 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. This does not cause
a free falling pole. After the buckle, the cross section of the pole is capable of carrying the entire vertical
(weight) load and a substantial portion of the load that caused buckling. The pole is likely, however, to be
out of plumb. This may be somewhat dramatic and the buckled section should be replaced.
There are 3 mechanisms which prevent the pole from a free fall type failure. First, as the pole distorts this
distortion may relieve the load from the pole either by orienting the pole more favorably in the wind or, if
buckling has occurred, by reducing the moment arm of the wind force. The second mechanism involves a
redistribution of the stress in the pole after buckling toward the remaining portion of the cross section that
has unused capacity. The third phenomenon and most important, is the nature of the force being applied.
We expect the wind to produce this force. A wind that would cause a buckle would be larger than the
basic wind speed, the gust factor, and the factor of safety combined. 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 takes some time for the entire structure to "see" the impact loading. Even after a
local bckle, the pole has significant capacity. It is this capacity along with the transitory nature of the
"'loading that prevents a pole from "falling over."
Pole design and 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. The public I think, has been
well served. Valmont has provided structures that have performed well during the earthquakes in
California, the hurricanes in the South including Hugo, Andrew and Opal, (we have no word yet on
Fran) and a number of tornadoes. To my knowledge, Valmont 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.
I hope this has helped. Please feel free to call with any comments you may have. I can be reached at 1-
800-345-6825- ext. 3739 and will be glad to discuss any concerns you may have.
Sincerely,
Anthony J. Hansen PE
Manager of Communication Structure Engineering
Valmont Industries Inc.
•