Smarf Building Cape Canaveral Air Force Station, Florida

24 • Interface September 2002
PROJECT BACKGROUND AND
INFORMATION
Historical Data
The Solid Motor Assembly and
Readiness Facility (SMARF) Building is a
hangar-type structure constructed in or
about 1990 (Photo 1). The original roof on
the facility was a structural standing seam
metal roof system installed over a single
layer of polyisocyanurate insulation over a
metal deck secured to steel beams. The roof
has an area of about 60,500 ft2 and is
approximately 245 ft. above grade. On
March 13, 1993, this facility was subjected
to moderate wind speeds of about 80 MPH
Photo 1: Exterior view of SMARF Building.
SMARF
BUILDING
CAPE
CANAVERAL
AIR FORCE
STATION,
FLORIDA
At the 1994 RCI Convention in San Antonio, Texas,
Richard Canon presented a paper regarding the investigation
of a roof failure following a wind event on the Solid Motor
Assembly and Readiness Facility (SMARF) located at Cape
Canaveral Air Force Station, Florida. The topic, “High Rise
Roof Investigation Design and Construction,” was of particular
interest because of the techniques Canon had developed to
resist extremely high wind uplift pressures with a peak of up to
300 psf.
This innovative roof has now been in service for seven
years. During that time, it has been exposed to a number of
significant wind events with no reports of damage. This article,
written for a follow-up presentation at the 2002 RCI
Convention in Galveston, Texas, will relate both the history of
the project and the results of an investigation of the roof’s performance
after seven years. The investigation includes: uplift
testing, fastener pullout testing, a review of the flashing systems,
a review of the sheet metal component performance, and
the performance of the roof system design.
The article should be beneficial to those interested in the
design and performance of roof systems on tall buildings with
high exposure to wind events and accompanying high wind
pressures.
BY RICHARD (“DICK”) P. CANON, RRC, PE, FRCI
BLAKE S. JOPLIN, EIT
S. THOMAS WATSON, MSCE, EIT
Seven
Years
Later
September 2002 Interface • 25
during a low-pressure, cyclonic
weather system that moved
through the Cape Canaveral Air
Force Station, Florida, area.
After that event, it was reported
that the roof had been partially
displaced, presumably as a
direct result of negative uplift
pressures.
Canon Consulting was
retained by the Air Force to
investigate the cause of the
SMARF roof displacement.
Canon issued its preliminary
report on March 24, 1993, finding
that the roof system failed
due to a combination of
improper design and improper
construction. The firm recommended
a redesign of the roof
and installation of a retrofit roof
system.
The Air Force then directed
Canon Consulting to design a
new roof assembly, retaining
only the original steel deck and
beams. As part of its design,
Canon subcontracted Clemson
University in Clemson, SC, to conduct a “Wind Pressure Study”
under the direction of Dr. Tim Reinhold, PE, with assistance
from Dr. Scott Shiff, PE, also of Clemson. During the study,
Canon Consulting did the following:
• Conducted a boundary layer wind tunnel study of a 1:200
scaled model of the SMARF Building.
• Designed an innovative and revolutionary negative pressure
suppression wind diverter/spoiler system.
• Simulated the negative pressures to the decking system at
design wind loads.
• Simulated the negative pressures to the roof membrane
system at design wind loads.
• Designed a technique to enhance the existing roof deck
to accommodate the design wind loads.
• Introduced a new roofing assembly that could meet the
design wind loads.
Roof System Installed in 1994
Canon Consulting designed the retrofit roof system to the
then current design wind velocity of 100 mph and negative
(uplift) pressures of 220 psf. Referring to Figure 1, the roof crosssection
was as follows, from top to bottom:
• Granular surfaced Siplast modified bitumen cap sheet,
torch applied (P30HTFRTG).
• Siplast modified bitumen base sheet, torch applied
(P20EGTG).
• 5/8”-thick Georgia Pacific Dens-Deck, primed and
mechanically fastened (1/ft2) to a new retrofit steel deck.
• 1.5” Atlas AC Foam II polyisocyanurate (25 psi), mechanically
fastened concurrent with the Dens-Deck.
• 12 mil polyethylene film air seal with sealed seams.
• New, 20-gauge galvanized wide rib steel deck installed
with ribs offset (ribs bearing on the flanges of the original
steel deck).
• Original, 22-gauge painted wide-rib steel deck with the
attachment and side laps enhanced (original).
• Steel beams bolted to steel girders (original).
The contract for the repairs was awarded to GRI of Orlando,
Inc., Casselberry, FL. Their work started in January of 1994 and
was completed in June of 1994. During the construction, Canon
Consulting provided quality assurance construction observation
services on a daily basis for the Air Force.
PURPOSE OF THE EVALUATION PROGRAM
The roof on the SMARF building, now over seven years old,
has been subjected to several noteworthy wind events since
completion with no reports of wind damage. Due to the unique
design undertaken on this facility to accommodate high negative
wind uplift pressures (± 220 psf), and since the Air Force, Navy,
and others (including the private sector) have utilized the system
it developed, Canon Consulting envisioned conducting an evaluation
of the performance of the roof.
Richard P. Canon, RRC, PE, discussed the concept of such a
study with the Chief of Range/Base Civil Engineering Operation
for Cape Canaveral, who agreed and requested a proposal,
which Canon Consulting provided. On October 4, 2001, Canon
was subsequently authorized to do an evaluation of the performance
of the roof and to provide a written report.
Figure 1: Roof cross-section.
PROJECT STAFFING
The above-listed scope of work was accomplished by, or
under the direction of Richard P. Canon, RRC, PE, a registered
structural engineer in several states who is experienced in roof
surveys, investigations, and roof design. Some of the work was
accomplished by engineering assistants Blake S. Joplin and
S. Tom Watson, who are Engineers-in-Training (EITs) and roof
consultant interns with Canon Engineering.
PROCEDURES
On January 3 and 4, 2002, Canon, Joplin, and Watson were
escorted to the roof of the SMARF Building. Timothy L. Kersey
represented Siplast, the manufacturer and warrantor of the roof
system, on the building. Employees from the roofing repair contractor
were also on site to assist in the testing and to make repairs
to test sites. Because of operation inside the facility at the time of
evaluation, no testing was done on two areas of the roof.
The project procedures are summarized below.
Visual Inspection of Roof Membrane, Flashings, and Sheet
Metal
The authors observed the subject roof area, using general
recommendations of the Roof Consultants Institute and other
accepted industry procedures. Observed roof condition deficiencies
indicating workmanship, material defects, or damages were
noted and are presented below. The roof’s leak history was also
discussed with the building operations manager.
Test Cuts for Analysis
Samples of the membrane were extracted to determine the
physical properties of the in situ membrane. Due to time constraints
with the SMARF building’s ongoing mission, Canon was
limited in its available site time. To conserve time, test cut samples
would be extracted at some of the negative pressure test site
locations where cutting of the roof would already be taking
place. The original proposal had anticipated taking four random
membrane test cuts for laboratory analysis. Test cuts were
extracted from test sites U-1, U-2, U-5, U-6, and one near P-7.
(See Drawing R-2 for location.)
Each sample was carefully separated from the Dens-Deck,
placed in a self-sealing polyethylene bag, and labeled by project
name, location, Canon project number, the name of the sampler,
date of extraction, and physical size. Samples were returned to
Canon Consulting’s office for repackaging and submitted for
analysis.
Laboratory Analysis of Roofing Membrane
Samples of roofing membrane extracted from four of the negative
pressure test sites were subjected to a battery of tests typically
utilized to monitor the performance of their products. All
tests were conducted according to ASTM D 5147-97, “Standard
Test Methods for Sampling and Testing Modified Bituminous
Sheet Materials” and ASTM D 6163-00, “Standard Specifications
for Styrene Butadiene Styrene (SBS) Modified Bituminous Sheet
Materials Using Glass Fiber Reinforcements.”
The following tests were run: tensile strength, elongation at
maximum load, elongation at 5% of maximum load (also known
as ultimate elongation), low temperature flexibility at -4.0°F,
-13°F, and -22°F, and high temperature stability at 230°F and
248°F. Tests were also run on the surface sheet’s granule embedment.
Visual Inspection of Wind Diverter/Spoiler System
To the best of the authors’ knowledge, the wind diverter/
spoiler system shown in Photo 2 is the first such assembly used to
reduce the negative (uplift) pressures on a building in the U.S.
Canon Consulting, therefore, had to develop its own test protocol
to assess its condition. The inspection process the firm developed
consisted of randomly choosing numerous panels and
looking for any indication of loose U-bolts connecting the aluminum
spoiler panels to the handrail assembly. Penetration pockets
(pitch pans) for the handrail legs and for the struts bracing
the handrail at the spoiler panels (Photo 3) were also examined.
Finally, the overall assembly was examined for indications of any
corrosion, damage, or fatigue to the spoiler assembly.
Above: Photo 2: Wind diverter/spoiler system.
Chamber in place at U-3.
Right: Photo 3: Typical penetration
pocket at spoiler panel strut
filled with two-part pourable sealer.
26 • Interface September 2002
September 2002 Interface • 27
Visual Inspection of the Gutter/Fascia System
Taking into consideration the excessive height of the SMARF
Building (± 244 feet above grade), inspection of the entire gutter
and rake system from the exterior of the building was not feasible
without costly scaffolding or crane rental. For this reason,
the protocol was to select representative locations along all four
edges and inspect the attachment from the roof as shown in
Photos 4 and 5.
As shown in Photo 5, as part of the firm’s 1994 design, the
gutter is secured with a wraparound cradle, a standoff support
bracket, and a hanger bracket secured to the wall girt with a gasketted,
self-drilling anchor. The inspection procedure was for the
engineer (properly secured in safety harness equipment) to lean
over the edge and physically tug or pull on the gutter assembly
and check for any excessive movement or displacement.
The rake assembly was inspected in a similar fashion, except
the fascia was specifically checked to verify that the metal was
still properly engaged to the continuous cleat.
Negative Pressure Testing
On January 3, Canon Consulting performed uplift tests using
a negative pressure chamber specially designed and constructed
by the firm. All negative pressure uplift tests were performed in
accordance with Factory Mutual (FM) Loss Prevention Data
Sheet 1-52 and ASTM E 907-96. Both tests are performed with a
5’-0” x 5’-0” negative pressure chamber as shown in Photo 6. The
negative pressure is measured with a water manometer (Photo 7)
capable of measuring in excess of 300 psf attached to the cham-
Left: Photo 4: Gutter with wrap-around bracket. Note
back of bracket has an extension that is fastened to the
wall girt for securement to resist rotation of the gutter in
high wind conditions.
Below: Photo 5: View inside gutter.
Several loose bolts noted.
Below: Photo 6: Negative pressure chamber in
place. Control valve is at “A.” Manometer is at
“F.” Vacuum is at “D.”
Above: Photo 7: Manometer (“F”), with timer and thermometer. Control
valves at “A” and “B.”
September 2002 Interface • 29
ber (Photo 8). A rigid metal bar with a foot on each end
is placed beneath the chamber resting on the roof surface
(Photo 9). A digital dial indicator gauge is attached
to the bar at the midpoint (Photo 10). The tip of the
dial gauge is in contact with the roof surface near the
center of the test area. As the negative pressure is
increased, the primary operator observes the manometer
and timer. The assistant monitors the dial gauge for
movement of the membrane. Both observe the roof surface
for deflection of the roof covering within the
chamber through the portals on each face and the top.
The system fails the FM 1-52 if the roof assembly
deflects upward more than 0.25 inch. The ASTM
E 907-96 test fails if the roof assembly deflects upward
more than 1.00 inch. For this project, Canon Consulting
considered deflection in excess of 0.50 inch to be a
failure. This was consistent with original design
assumptions.
The typical procedure protocol for FM and ASTM begins at
15 pounds per square foot (psf) and is held at this negative load
for 60 seconds. If the test passes (less than the specified deflection),
the negative load is increased by 7.5 psf and the negative
load is again held for 60 seconds. This process continues until
the design uplift resistance requirement is met or until maximum
deflection in the roof system occurs. This test also fails if the
membrane lifts or “balloons” at any location under the chamber.
Deflection of the roof assembly was noted at the end of each
incremental pressure increase to the nearest ten-thousandth of an
inch (0.0001). The values were recorded on Field Data sheets.
Notes were made of observed ballooning at the test sites.
Because the target pressure on this project was significantly
higher than usually constructed on buildings, a revised sequence
of applying pressure was established. Testing started at 60 psf
and tested thereafter in 30 psf increments. According to FM
Data Sheet 1-52, “The vertical distance of the water column is
the difference between the elevation of the two water columns,
and not the distance of one column from the original 0 set
point.” Therefore, the total head for a 240 psf test is 46.2 inches.
The roof system was designed to meet a minimum negative
or uplift pressure of 220 psf. For these tests, however, Canon
decided to set the target pressure for all test sites slightly higher,
at 240 psf. Three of the seven tests were carried up through 270
Above: Photo 8: Negative pressure capacity of chamber is in excess
of 300 psf. Test pressures ranged from 150 psf to 270 psf.
Above: Photo 9: Chamber placed to the side of the test site to position rigid
metal bar with digital dial indicator attached.
Below: Photo 10: Digital dial indicator in position.
30 • Interface September 2002
psf and into the 300 psf range before failure. (See Table A).
In the FM protocol, tests are run in the “field” of the roof, the
“perimeters,” and the “corners.” Because of the unique design of
the SMARF Building, the entire roof was designed and constructed
for a common pressure coefficient of 220 psf with Dens-Deck
fasteners securing the system at a rate of one per square foot.
Canon Consulting randomly selected seven test locations
throughout the roof area. Four were intentionally located near
the corners. The remaining three were in the central portion of
the roof. Due to the confinement of such a small roof, no tests
were conducted on the penthouse over the elevator for safety
reasons. The test sites were given designations of U-1 through
U-7 on the roof. Test cuts were extracted at Test Sites U-1, U-2,
U-5, and U-6.
FM Global Mechanical Pull Testing
In this procedure, a test panel is adhered to the surface of the
membrane and pulled to failure. This is the test protocol Canon
used in its 1993 design development as a basis of construction.
Those design tests gave a working load of
240 psf in one battery of tests and 255 psf
in another independent test done by Trinity
Engineering, Inc. From these, the roof was
designed with an ultimate load of 220 psf.
Prior to arrival on site, the test panels
were pre-assembled by fastening two 24” x
24” x 23/32” plywood panels together with
screws and through-bolts. An eyebolt
assembly was installed through both plywood
sheets. The plywood test panels were
fully adhered at seven test sites to the P30
surface sheet of the roof system on January
3 using “Insta-Stik,” a single-component,
moisture-cured polyurethane adhesive
(Photos 11 and 12). The adhesive was then
allowed to cure overnight, which, although
relatively cold, was adequate for a good
bond.
Left: Photo 11: Placement of “Insta-Stik” to
secure plywood panels for the FM Global
Mechanical Pull Test. Application rate was
determined to be heavier than needed, resulting
in the panel sliding until material cured.
Below: Photo 12: Plywood panel in final
position for testing. Insta-Stik cured for
approximately 20 hours before testing in
relatively cold weather (±35°F to ±50°F).
Below: Photo 13: Membrane trimmed away from edge of panel down to the
top of the Dens-Deck. Eyebolt is in place and ready to attach pull device.
September 2002 Interface • 31
In this field test, the goal was to test for
the membrane’s adhesion to the Dens-Deck,
not the securement of the Dens-Deck to the
steel deck. To accomplish this, Canon decided
to leave the Dens-Deck intact, as it would be
in service (i.e., the Dens-Deck would not be
cut). On January 4, Canon Consulting cut a 2-
inch wide “channel” in the membrane to the
Dens-Deck facer around the perimeter of each
test panel (Photo 13). They then placed a fourfoot
square plywood “collar” with a 30-inch
square cutout around the test panel (Photo 14).
This was to support the test stand’s four legs
and restrain movement adjacent to the test
panel. A Com-Ten Industries Model 341, hand
operated, digital readout test apparatus was
clamped to the top plate of the “quadrapod”
test stand. A chain was connected between the
eyebolt in the test panel and the test apparatus.
Load was applied by slowly rotating the
pull test apparatus’ handle at a constant rate,
thus measuring the weight of the material and
the uplift resistance of the membrane (Photo
15). The load (lbs.) at which the roofing components
yielded was recorded for each test.
These are summarized in Table A.
Assuming a target uplift pressure of 240 psf
on a 2’-0” x 2’-0” (4 sf.) panel, a pull in excess
of 978 lbs. was established as a load passing
the test. [(4 sf. x 240 psf) + (18 lbs. weight of
a test panel) = 978 lbs.].
As with the negative pressure test, the high
target value of 240 psf prompted Canon to
start testing at an initial higher load. Testing
began at 45 psf for one minute. The loading
was then increased in 30 psf increments until
195 psf was reached. Loading was then
increased in 15 psf increments until the target
value of 240 psf was reached or failure, whichever
occurred first. (Note: All tests met the 240 psf loading. Five of
the seven tests were run to 300 psf.)
Fastener Pull Out or Withdrawal Testing
Fasteners used to simultaneously secure the Dens-Deck and
polyisocyanurate insulation to the new steel deck in the construction
were tested for pull out or withdrawal resistance. These
tests were performed in general conformance with the American
National Standards Institute (ANSI)/Single Ply Roofing Institute
(SPRI) joint document, ANSI/SPRI FX-1-1996, Section 4.2,
“Standard Field Test Procedure for Determining the Withdrawal
Resistance of Roofing Fasteners.”
This test is typically conducted by driving a new fastener
into a deck with a screw gun to determine the design withdrawal
resistance in pounds. As the intent was to determine the resistance
of the fasteners in place, Canon pulled the fasteners
installed in 1994. These were No. 14 Olympic Roof Insulation
Fasteners.
The firm had a limited window of opportunity to conduct its
test, due to SMARF missions. Canon Consulting decided, therefore,
to utilize four locations where the membrane had already
been removed at the mechanical pull tests and pull three screws
at each location (Photos 16 and 17). See Drawing R-2 for locations.
With the membrane removed at the locations, Canon Consulting
carefully scored and removed the Dens-Deck, leaving the fastener
and 3”-diameter steel plate exposed. Fastener heads were
grasped with the foot of the Com-Ten Industries Model 341,
hand operated, digital readout test apparatus. In this test, force is
applied continuously with a slow, steady application of pressure
until failure. The target pull out or withdrawal value was 485
pounds force, the published value from Olympic’s testing for the
fastener installed. At each site, the reading at failure was recorded
and shown on Table A.
OBSERVATIONS AND FINDINGS
Visual Inspection of Roof Membrane, Flashings, and Sheet Metal
Roof condition deficiencies were observed. For each, Canon
Consulting recommended a course of action and identified the
party (owner or membrane manufacturer) it believed was proba-
Table A: Summary of test results.
32 • Interface September 2002
bly responsible for the repairs.
“Owner repairs” were those that
would generally be excluded from
a manufacturer’s warranty, such as
cuts and tears, physical abuse after
acceptance, caulking, and sheet
metal. All repairs should be made
by a manufacturer approved applicator/
contractor using Siplast
approved materials to avoid
infringing upon the warranty.
Some crazing of the P30 cap
sheet was observed sporadically
throughout the roof. This was
reviewed on site with Tim Kersey
of Siplast. He said that crazing is
typical for an SBS modified bitumen
cap sheet of this age and that
such would not affect the sheet’s
long-term performance. Thus, no
repairs were necessary, per Mr.
Kersey.
Laboratory Analysis of Roofing
Membrane
The samples of membrane were tested. Quoting from the
laboratory report,
“From the Elongation at 5% Max. Load and Low
Temperature Flexibility data, we can conclude that
these membranes have performed well and will continue
to provide excellent elongation and flexibility.
“The granule embedment test showed that the cap sheet
is allowing more granule loss than when [the product] is
new. This is expected since it is the first layer of protection
that takes the environmental abuse… The base sheet
had better results than the cap sheet in all cases. This test
is not usually done on aged materials. We do not have
enough statistical data for comparison on aged products
from Florida. For example, we took samples…. installed in
1992, and the average granule loss was 2.9g. This shows
that it is normal to have a small increase in granule loss
as the product ages.
“Based on sample observation, field inspection, photos
and these results, we can conclude that this membrane
has performed as expected.”
Visual Inspection of Wind Divert/Spoiler System
Richard Canon personally inspected the spoilers. No deficiencies
of any kind were observed. The U-bolt-to-handrail connections
observed were tight and double-nutted. There was no
vibration of the panels checked when struck with the hand, indicating
securement. The brace struts were tight. No unusual corrosion
was observed. The penetration pockets need some
attention relative to water resistance.
Visual Inspection of the Gutter/Fascia System
Donning a safety harness, Richard Canon inspected several
locations on each face of the building to evaluate the attachment
of the gutter and rake fascia assembly. Generally, the gutter is
well secured with no displacement under heavy pulling on the
hanger/strap assembly. At one point of observation on the west
side, two adjacent lag screws into the edge nailer at the gutter
bracket were not driven snugly. They were, however, tight, indicating
they have not been withdrawn or backed out. It is
believed that they were simply never snugged up. (For long-term
performance, this and all other gutter brackets should be
checked and snugged up if found deficient.)
The fascia metal was typically tight to the wall with good
engagement between the fascia piece and the continuous cleat.
At one location, disengagement from the cleat was observed.
Other occurrences of this may be present. (For long-term performance,
every linear foot of the rake should be checked. It may
be necessary to supplement the attachment with fasteners simultaneously
run through the fascia and cleat and into the metal
wall panels. This would provide an enhanced securement and
prevent displacement.)
Negative Pressure Testing
The results of each of the seven negative pressure tests are
summarized in Table A. At test sites where the field pressure did
not achieve the target pressure of 240 psf, the plane of failure
was between the P20 base sheet and the facer of the primed
Dens-Deck. This is precisely where it was anticipated the failure
plane would be. At test site U-1 (at test cut U-1B), there was
separation in a small area between the P20 and the P30. This
occurrence is probably an anomaly due to inadequate melt of the
P30 to the P20 during application.
Photo 14: Plywood “collar” under legs of quadrapod test stand to distribute load. Digital readout pull test
apparatus in place on top of stand. (Connecting chain and eyebolt are not in place in this photo.)
September 2002 Interface • 33
FM Global Mechanical Pull Testing
As stated above, this is the test protocol used during the
original design and was the basis of the construction of the
SMARF roof. The results of these tests are summarized on
Table A. All seven of the tests meet or exceed the target pull of
978 lbs., equivalent to 240 psf. Referring to Table A, note that
one of the seven passed the 270 psf test, and five of the seven
passed the 300 psf test.
Fastener Pull Out or Withdrawal Testing
The results of all twelve fastener tests exceeded the target
value of 485 lbs. force as shown on Table A. The higher values of
over 1,000 lbs. are probably because the screw penetrated both
the over-lay deck and the original deck at point “A” on Figure 1.
CONCLUSIONS AND RECOMMENDATIONS
Membrane, Flashings, and Sheet Metal Condition
The roof membrane and flashings have several deficiencies to
be addressed, but the roof membrane and flashings were determined
to be in good condition. The observed deficiencies should
be corrected as soon as practical, but ideally no later than the
onset of the traditional Atlantic hurricane season, which starts on
June 1, 2002. Some crazing observed on the P30 sheet is worthy
of note, but no repairs are needed per Siplast.
Wind Diverter/Spoiler System Condition
The system of spoilers mounted on the handrail is in good
condition. The connections and bracing are sound and functional.
No repairs to the spoiler components are needed, but Canon
Consulting suggested that it would be prudent to have these
inspected annually or at least on the 10th, 15th and 20th
anniversaries of completion (2004, 2009, and 2014).
Gutter and Fascia System Condition
The gutters are believed to be safe as they are, but since a
random inspection identified several lag bolts that were never
snugly driven, all should be checked and driven snug. The pri-
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Photo 15: Test in progress. Test values ranged from 240 psf to 300 psf.
34 • Interface September 2002
mary concern prior to inspection was rotation of
the gutter. It is now believed that securement is
adequate for the original design, and no enhancements
are needed.
The fascia/cleat system does not have any redundancy
as does the gutter (lag screw and bottom clip).
Since some disengagement of the fascia and cleat was discovered,
more of the same could be present. One option would
be to have the entire perimeter checked by a contractor and
Left: Photo 16: Fastener Pull Out or Withdrawal Test conducted
after removing the membrane and Dens-Deck, leaving the fasteners
and 3” plates exposed.
Below: Photo 17: Plywood panels placed on surface to distribute
load during testing. Values ranged from 528 pounds to 1,274
pounds. Fasteners are spaced at approximately 1’-0” on centers.
September 2002 Interface • 35
repair each disengaged location. Another, more positive system
would be to mechanically fasten all of the fascia and cleats to the
edge nailers at 36” o.c., reducing spacing to ±18” o.c. for a distance
of 15’ from the corners. Self-drilling, gasketted, stainless
steel screws with a thread suitable for fastening into wood
should be used. Although this process may result in some distortion
of the fascia, this should not be too visible from the ground.
Uplift Resistance of the Roof
Based on available weather data, the peak gust at 33’ for the
area occurred on October 16, 1999, with a value of 71.9 knots or
82.8 MPH. Although the roof has not experienced a “design
condition,” testing and observations concluded that the SMARF
roof is performing as intended after seven years of service.
There are no recommendations for corrective actions, as
none are needed.
PROBABLE SAFETY FACTOR OF SMARF
BUILDING ROOF
Canon Consulting suggested that its scope be augmented to
determine the most probable factor of safety of the roof on the
SMARF Building, as this was never determined during the design
phase due to time constraints. The suggestion was granted. The
firm proposes to do the following:
1. Assemble pressure data from wind tunnel testing conducted
as part of Canon’s 1993 design of the roof system.
2. Superimpose on the roof plan the pressure zones relative
to the field of the roof, the perimeters, and the corners,
based upon the installation of the wind spoiler/diverter
system.
3. Analyze the test results from Canon’s field testing (the
original scope of services under this contract) and the
pressure zones (Item 2 above) and determine the safety
factor for the roof assembly.
Drawing R-2: Negative pressure zones.
To accomplish this, Canon Consulting returned to the data
gathered by Dr. Reinhold in the wind tunnel study he performed
with the firm in 1993. From that data, Canon Consulting developed
a composite load contour plot of the SMARF roof. This is
shown on Drawing R-2.
Note on Drawing R-2 that from the wind tunnel study, the
field of the roof and the long axis perimeters along the east and
west sides have a maximum uplift value of 120 psf. The corner
pressures range from 140 psf up to 220 psf with the 220 psf
value applicable at only at a very small segment on the beveled
corner of the building corners as shown on the drawing.
An added objective in this study was to gather sufficient data
to conclude what the most probable safety factor is for the roof,
as constructed. To do this, Canon Consulting superimposed the
uplift contours on the roof plan to determine what the design
uplift pressure was for each test site. Based upon the results of
the test, the safety factor was calculated at each test site as
shown in column “E” of Table A. This information provides data
from which conclusions may be drawn regarding the overall
safety factor of the roof and to better predict the risks for the
building at or near design wind speeds.
To determine the most appropriate safety factor for each test
method, the values of the results of each test method were averaged,
as shown in column “F” of Table A.
• For the Negative Pressure Test, the average Safety Factor
is 1.64.
• For the FM Pull Test (the basis of Canon Engineering’s
original design), the average Safety Factor is 2.30.
• For the Fastener Pull Out Test, the average Safety Factor
is 1.64.
The authors believe that the Negative Pressure Test and the
FM Pull Test are more representative of a test of the roof’s failure
mode under uplift. This is because if a single fastener is overloaded,
its load will be redistributed to the four adjacent fasteners
and thus resist the uplift. In summation, the probable safety factor
on the SMARF roof is derived from the average of the Negative
Pressure Tests and the FM Pull Tests. This value is 1.97.
SUGGESTION FOR ADDITIONAL STUDY
As a closing comment, it would most likely be of value to the
Air Force and others with similar designs if some form of wind
recording device were to be installed on the SMARF Building. A
recording anemometer could be mounted either at the ridge or
on the penthouse. Such equipment may be available at no cost
to the government through the Roof Consultant Institute’s
Foundation. The data gathered and retained over the next 10 to
15 years could add to the assessment and performance of this
unique design. 
Richard “Dick” Canon, RRC,
PE, graduated with an engineering
degree from Auburn University and
worked for the U.S. Army Corps of
Engineers for a few years before
working with Milliken & Co.,
Lockwood Greene Engineers Inc.,
and Law Engineering Testing Co. In
1983, he formed Canon Consulting
& Engineering Co., headquartered
in Spartanburg, SC. He is a Past
President and founding member of
RCI, a member of the RCI Jury of
Fellows, and the 1996 recipient of the Herbert W. Busching
Memorial Award for his contributions to roof consulting. Dick
is a member of the National Society of Professional Engineers,
the American Society of Civil Engineers, and the Southern
Building Code Congress International.
Blake S. Joplin, EIT, graduated
with a Bachelor of Science degree in
Civil Engineering from Clemson
University. He has worked for
Canon Consulting & Engineering
Co., Inc., for approximately four
years. Blake was active in wind tunnel
research while attending Clemson
University and is a member of RCI.
S. Tom Watson, EIT, has a
Bachelor of Science degree in Civil
Engineering from the University of
South Carolina, and a Masters of
Science in Civil Engineering from
Clemson University. He worked
with QORE Property Sciences, Inc.
for three years before joining
Canon Consulting & Engineering
Co., Inc., in early 2001. Tom is a
member of the Construction
Specification Institute and the
American Society of Civil
Engineers.
ABOUT THE AUTHORS
RICHARD “DICK”
CANON, RRC, PE
36 • Interface September 2002
BLAKE S. JOPLIN, EIT
S. THOMAS WATSON,
MSCE, EIT
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