HomeMy WebLinkAboutFall Zone Letter from Vector Engineers rcvd 2/24/2020 . II
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Project Number: U0142-899-191
February 21,2020
STEALTH®Concealment Solutions
3034-A Ashley Phosphate Rd
North Charleston,SC 29418
REFERENCE: Laurel Stone(Stealth#:VZ16-01355W-17R4)
Fall Zone Letter
To Whom It May Concern:
It is our understanding that a 110 ft concealment pole has been proposed for this site. This monopole will consist of a 60 ft tall
18-sided tapered steel base pole with a 50 ft tall RF friendly concealment section on top. Steel mast pipes will support the
concealment section.
The above-mentioned pole has been designed in accordance with the New York State Building Code,2016 Uniform Code
Supplement(2015 IBC)and the ANSI TIA-222-G"Structural Standard for Antenna Supporting Structures and Antennas".
Additionally,all steel members and connections have been designed to meet the requirements of the AISC Steel Construction
Manual.
The pole has been designed for the following criteria:
1. Wind speed(V): 145 mph(3-second gust)
2. Ice:3/4"radial ice(nominal)with concurrent 50 mph wind(3-second gust)
3. Basic wind speed of 60 mph(3-second gust)for the service condition(deflection limitations only)
4. Structure Class III,Exposure C,Topographic Category I
It has been requested that the proposed monopole be designed for a fall zone radius of 50 ft. We have satisfied this requirement
by ensuring that in the unlikely event of failure,the point of maximum stress will occur in the upper 50 ft(or less)of the
structure. The structure supporting the top section has been designed such that the highest stress within the fall zone is 72%of
capacity. Expected stress ratios of all other structural elements below this point,including pipe mast sections below 50 ft from
the top of the top section,all connections below this point,the base pole,anchor rods,etc.,are at least 15%less than the highest
stress ratio within the top 50 ft of the structure. If the structure fails,it will likely do so within 50 ft from the top of the top
section. Therefore,this structure is designed to have a maximum 50 ft fall zone radius.
Please note that"fall zone"is a term not defined in the standards listed above. Our approach to the fall zone design is described
in the preceding paragraph and is our best attempt to meet what we believe to be the intent of the fall zone request. Current code
does not address failure mechanics. It is difficult to impossible to predict the behavior of a failing structure. Physics of a fall
during a wind event,including possible bouncing or rolling,may place all or part of the ruptured pole section outside of the
intended fall zone. Nonstructural components attached to the steel structure are outside of our scope. Nonstructural components
may break free from the structure and fall outside of the fall zone even at loads below code-specified magnitudes if the
components and their attachments are not properly designed and installed.
We hope this meets your needs. If you have any further questions regarding this matter, please call this office at your
convenience.
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Very truly yours, 1, /y
VECTOR STRUCTURAL ENGINEERING,a1. c "
Firm License#:2202 "
Wells Holmes,S.E. y�6
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Principal Engineer
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02/21/2020
651 W. Galena Park Blvd., STE 101 1 Draper, UT 84020 ""f(801)990-1775/1 (801)990-1776 1 www vectorse.corn