Alt Design Req 4-4-07.pdfL S k, -%
LA2&iTVrEr,HT STRu{:T"U ES A.S.4CCiATK3.1
April 3, 2007
Jeanine L. Graf
Permit Coordinator
City of Edmonds: Fifth
121 Fifth Ave. N.
Edmonds, WA 98020
Dear Ms. Graf:
H. B. DAUGHERTY, P.E.
Consulting Engineers
(419) 877-0243 tel. TWT
(419)877-9488faar ReHTAL nxnIsio�
www.hbdaugherty.com
5776 Providence — Box 2854 —)Whitehouse, OH 43571
APR -4 zor
EJUILD NG
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. These 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
grow and cause continued lowering of the crown. This can, occasionally, result in a total lowering of
the fabric to the ground. Such an incident transpires over a period of several hours. It is a condition
that 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
weight fabric liner.
5. Tit; 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
violent snow storms and have been deflated. I have never seen an instance where any occupant has
been 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. Anchorage of the air structure is fully engineered and comprises no risk to anyone that would be
different from any conventional structure designed to code.
S. Tip: air structure supplier, in this case the Parley group, an experienced air structure supplier, will
iS;:iie 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 barley Group's Installation Supervisor
wi � i review the operating instructions with the Owner and/or his designated staff person once the
nc;w membrane is installed and will provide any training necessary for the proper operation of the air
structure.
9. T;he structure is installed with a primary inflation system and a secondary system, all tied to an
elcctrical 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
15 ;says to make sure that it deploys as designed and a permanent log of the test cycle must be signed
b v he responsible Owner's staff person immediately after every test.
10. In iddition, we would require the Owner to monitor the local weather report, hourly, through the
hours 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
rG i -.finely 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 a snow load/or ponding load of more than 5 psf, locally at the crown of the donne.
We thank yo c� or your consideration of this matter. Upon your approval of this item we will proceed to issue
design drawi- s and calculations for the project.
Regards,
Harry Daugbc: -Ly, P. .
Copy: Doug Heit, P.E.
Mike Ragen, The Farley Group
Jason Schmidt, The Farley Group
23201
sslor�ni<�
EXPIRES II— IYa.7O0
specialists in tensile membrane structures