Alt Des Request and Approval 4-13-07.pdflh C. 1 8'30
April 13, 2007
CITY OF EDMONDS
121 5TH AVENUE NORTH • EDMONDS, WA 98020 • (425) 771-0220 • FAX (425) 771-0221
Website: www dedmondsma.us
DEVELOPMENT SERVICES DEPARTMENT
Planning • Building • Engineering
Mr. Harry Daugherty, P.E.
H.B. Daugherty Consulting Engineers
6776 Providence Box 2854
Whitehouse, Ohio 43571
RE: Request for Alternate Design @ 160 West Dayton Street
Harbor Square Athletic Club Dome Structure
VIA FACSIMILE
Dear Mr. Daugherty,
GARY HAAKENSON
MAYOR
The City is in receipt of your alternate design request on behalf of Harbor Square Athletic Club air -
supported roof structure located at 160 West Dayton Street in Edmonds to reduce the minimum snow
load requirement. Section 1608 of the 2003 International Building Code includes the provision to
determine applicable snow loads for roof structures. The City has issued a Building Official
interpretation effective July 1, 2004 that the total Snow Load for Edmonds is 25p -8f. This decision was
based on the Second Edition of the Structural Engineers Association of Washington (SEAW) Snow
Load Analysis for the State of Washington (revised July 1995) which recommended the Ground Snow
Load for Seattle at 20psf and Rain on Snow surcharge at 5psf.
By your calculations the proposed air supported roof structure cannot sustain a snow load of more than
5psf concentrated at the crowyn.. Inreviewing your request you have provided adequate information
and assurance that roof failure from a snow event would typically take several hours, that such
imminent failure would be obvious to all persons which would lead to a quick and safe evacuation, and
that the building owner will be provided with specific operating and emergency response training and
evacuation instructions from the manufacturer. It is my determination as Building Official for the City
of Edmonds that the request for a reduction of snow load for the air -supported roof structure at Harbor
Square is hereby Approved. As Engineer of Record you shall be required to inform the building owner
of the snow load limitations for the building.
Sincerely,
Jeannine L. Graf
Building Official, C.B.O.
' Incorporated August 11, 1890 •
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April 3, 2007
Jeanine L. Graf
Permit Coordinator
City of Edmonds: Fifth
121 Fifth Ave. N.
Edmonds, WA 98020
Dear Ms. Graf.
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H. B. DA UGHERTY, P.E.
Consulting Engineers
(419) 877-0243 tel. URT
(419) 877-9488 fax NTA 4 Q I V I S k O N
www.hbdaugherty.com
6776 Providence — Box 2854 — Whitehouse, OH 43571
1?EVCej re
APR -4 207
"LL)IN(3
We are hereby asking you to review this formal modification request for a permit to install an air -supported
fabric roof structure at the Harbor Square Athletic Club, located at 160 West Dayton Street, Edmonds, WA
98020. The reason for this request is to address the one basic area of the code with which this structure is unable
to comply. This is the inability of this structure to strictly meet the IBC 2003 prescritive design snow load
requirement.
Several factors are presented here in relationship to this issue:
1. `hese structures, being highly flexible, not only experience large deformations under loads, but also
qualitatively change their characteristic shape. For example, under wind loading alone, they may
experience drag forces that tend to shift them sideways, depending on their original proportions, or
to experience pure lift for shallower proportions.
2. When considering the case of pure snow, calculations indicate that the structure cannot sustain a
snow load of more than about 5 psf concentrated at the crown. At loads greater than this the fabric
"dimples" and begins to trap snow and water. This is when there is no wind blowing. In this
condition, if the snow continues to accumulate or if it melts and water accumulates, the "dimple" can
grew and cause continued lowering of the crown. This can, occasionally, result in a total lowering of
th,- fabric to the ground. Such an incident transpires over a period of several hours. It is a condition
thai sometimes occurs in the nighttime, when no one is in the building, and may be due to the lack of
operational attention to a developing scenario. More rarely, it is possible to occur during the daylight
hours when both operational and public occupants are inside. Again, however, if such a condition
occurs in this setting, the occupants have several hours to exit from the building.
3. If one considers the case of wind and snow, or wind and rain for that matter, there is no realistic
numerical analysis that can model all the possible combinations of deflected shapes that could occur.
Usually, the wind and consequential .lateral movement of the fabric simply spills the snow or water
off the lee side. Occasionally, the lateral deflection of the fabric in the wind does not sweep the
snow or water off, which if left to accumulate in greater amounts can cause the fabric envelope to
very gradually lower to the ground. However, the fact is that even in such an unusual circumstance
in which such a condition might develop it does not result in a sudden collapse as would happen in a
conventional rigid structure where a collapse would occur suddenly and without warning. If such a
circumstance should be left to take its eventual path to a lowering to the ground of the air structure, it
would occur over a very long period of time, hours, in fact, and anyone inside the structure would
readily observe it and be able to casually walk out of the structure, at no risk to themselves.
4. Air -supported structures, in all cases, are extremely lightweight. This particular overhead envelope is
lighter than most, comprised of woven fabric containing no barrel cables and has an even lighter
v'e:ght fabric liner. ,,
5. Th --.s kind of structure has been in widespread worldwide use since the 1960's since the 1960's with
an enviable safety record.
6. 1 have personally worked on dozens of insurance projects where air structures have been caught in
viYlent snow storms and have been deflated. I have never seen an instance where any occupant has
be -.:n injured, nor am I aware of any case where anyone has been. On the other hand I have worked
on numerous legal cases where occupants have been injured or killed in tent collapses.
7. Ar.�;horage of the air structure is fully engineered and comprises no risk to anyone that would be
di ! erent from any conventional structure designed to code.
8. Th' air structure supplier, in this case the Farley group, an experienced air structure supplier, will
i5`� e a set of operating instructions that have been tailored to tutor the Owner how to operate this
structure and how to respond to emergency conditions. The Farley Group's Installation Supervisor
w; review the operating instructions with the Owner and/or his designated staff person once the
new membrane is installed and will provide any training necessary for the proper operation of the air
s. -;Acture.
9. T -to structure is installed with a primary inflation system and a secondary system, all tied to an
electrical power supply with an emergency electrical power generator that will automatically start up
in case of loss of primary electrical power supply. This back-up system must be test -operated every
1-5 days to make sure that it deploys as designed and a permanent log of the test cycle must be signed
:l y1 he responsible Owner's staff person immediately after every test.
10. In �Adition, we would require the Owner to monitor the local weather report, hourly, through the
how of operation, and to evacuate the occupants when any violent weather is predicted or observed.
11. a.:. and all the above items are conditions under which virtually all air -supported structures are
ro-i.minely issued permits throughout this country.
In summary, we are asking for relief from the ordinary code requirement to certify that this structure is capable
of sustaining � snow load/or ponding load of more than 5 psf, locally at the crown of the dome.
We thank yo �-or your consideration of this matter. Upon your approval of this item we will proceed to issue
design draw �,,�s and calculations for the project.
Regards,
Harry Daugi�: `�V�
Copy: Doug I =ezt, P.E.
Mike F? agen, The Farley Group
Jason Schmidt, The Farley Group
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specialists in tensile membrane structures