Florida Structural Engineers - Aluminum Association of Florida

Florida Structural Engineers - Aluminum Association of Florida
Florida Structural Engineers
South Florida Chapter
January 8, 2008
Miami Lakes, Florida
Aluminum Association of Florida, Inc.
Joe Belcher ~ David Miller
AAF Code Involvement:
Historical Perspective
• 1998: commits to participate FBC
• 1999: commits to wind tunnel testing
• 2001: submits Table 2002.4 load table and
related code provisions
• 2004: AAF Guide adopted into FBC
• 2005/2006: AAF sponsors and moderates
Consensus Engineering Design Conferences
• 2006/2007: updates/revises prescriptive
guide
(AAF Guide to Aluminum Construction in High
Wind Areas)
Wind Tunnel Testing Program 1999
Consultants:
Timothy Reinhold, Ph.D., P.E.
Charles Everly, P.E.
(ASCE7 Windload Committee)
Phase 1 at Virginia Tech (screen drag force)
Phase 2 at Clemson (scale models)
Boundary Layer Wind Tunnel - Clemson
Test bed & scale model
High Frequency Force Balance
Attached Shed Screen Roof Enclosure
AAF Guide to Aluminum Construction in
High Wind Areas (2003 Edition Current)
• an alternative design methodology for
typical aluminum patio projects of lesser
complexity (not a standard)
• developed beginning in 2001
• adopted into FBC 2004
• implemented October 2005
• Updated 2006/2007
AAF Engineering Consensus Conferences:
(2005/2006)
AREAS OF DISAGREEMENT
•
•
•
•
Magnitude of pressures
Application of pressures
Behavior/Properties of Extrusions
Behavior of the Frame
Engineering Consensus
Conferences 2005-2006:
1. Establishes interpretation on Table
2002.4 and submits code change to
simplify and clarify
2. Establishes simultaneous loading
3. Explores proper use of the ADM in
evaluating extrusion capabilities
Table 2002.4 (post Dec 8th, 2006)
Basic Wind Speed (mph)
100
110
120
Surface
130
140
150
Exposure Category (B or C)
Design Pressure (psf )
B
C
B
C
B
C
B
C
B
C
B
C
Horizontal
Pressure on
Windward
Surfaces
12
17
13
18
15
21
18
25
21
29
24
33
Horizontal
Pressure on
Leeward
Surfaces
10
13
10
14
13
17
14
19
15
23
18
27
Vertical
Pressure on
Screen
Surfaces
3
5
4
5
4
6
5
7
6
8
7
9
Vertical
Pressure on
Solid Surfaces
10
14
11
15
13
18
15
21
17
24
20
28
Table 2002.4 Notes:
• 1. Pressures include importance factors determined in accordance with
Table 1604.5.
• 2. Pressures apply to enclosures with a mean enclosure roof height of
30 ft (10 m) or less. For other heights, multiply the pressures in this
table by the factors in Table 2002.4A.
• 3. Apply horizontal pressures to the area of the enclosure projected on
a vertical plane normal to the assumed wind direction, simultaneously
inward on the windward side and outward on the leeward side.
• 4. Apply vertical pressures upward and downward to the area of the
enclosure projected on a horizontal plane.
• 5. Apply horizontal pressures simultaneously with vertical
pressures.
• 6. Table pressures are MWFRS Loads. The design of solid roof panels
and their attachments shall be based on component and cladding loads
for enclosed or partially enclosed structures as appropriate.
• 7. Table pressures apply for all screen densities up to 20 x 20 x 0.013”
mesh. For greater densities use pressures for enclosed buildings.
• 8. Table pressures may be interpolated using ASCE7 methodology.
HVHZ Design Pressures ASCE7
provision 6.5.15
(Design Wind Loads on Other Structures)
F = qz • G • Cf • Af
where
(Equation 6-28)
qz derived from Equation 6-15 (Velocity Pressure):
qz = 0.00256 • Kz • Kzt • Kd • V 2 • I
where: I = 0.77 (Category I)
Kz = 0.85 (Exposure C Height 0 – 15 ft)
Kzt = 1 (Topographical Factor)
Kd = 0.85 (Directionality Factor)
V = wind speed (140 or 146)
for
V = 140 qz = 27.9 psf;
where V = 146, qz = 30.4 psf
F = qz • G • Cf • Af
where Gust Factor effect G = 0.85, and
Cf = 1.5 from Figure 6-22 (Force Coefficients
for Open Signs & Lattice Frameworks)
BUT, let’s change F to PScreen
by substituting the ratio of solid area
to gross area
Asolid
PScreen = qz • G • Cf •
Agross
Typical screen mesh for screen enclosures
has a wire or thread diameter (Ø) of 0.013 in.
for 20/20 mesh screen, density is:
45% solid, 55% Open; and for 18/14 mesh
37% solid, 63% Open
PScreen for 140 mph is 16.0 psf, and
PScreen for 146 mph is 17.4 psf
These values must be adjusted for roof and wall factors
according to FBC 1622, 0.7 and 1.3 respectively
Design Pressures (psf) – Screen Surfaces
Exposure C – Mean Roof Height 0 – 15 ft
WIND VELOCITY ZONE
140
146
qz
27.9
30.4
20/20 Mesh
16.0
17.4
Walls
20.8
22.6
Roof
11.2
12.2
COMPARATIVE VALUES FROM TABLE 2002.4
Windward
24.9
27.0
Leeward
19.8
21.8
Vertical
6.9
7.4
Applying Pressures to a Typical
Mansard Frame (in 140 mph HVHZ)
Frame Dimensions:
Mansard Frame Spacing = 6 ft
Wall Height (Eave Height) = 9 ft
Rise: 3 ft (Height Overall = 12 ft)
Beam Span = 24 ft
Beam Stitching: 20 inches O.C.
Assumptions: Simple Supports
Post / Beam Connection pinned
HVHZ Roof Beam Loading
Beam Load: Spacing (6 ft) X Pressure (11.2 psf)
HVHZ Wall Loading
Post Load: Spacing (6 ft) X Pressure (20.8 psf)
Table 2002.4 Windward Pressure
Horizontal Windward Load:
Spacing (6 ft) X Pressure (24.9 psf)
Table 2002.4 Leeward Pressure
Horizontal Leeward Load:
Spacing (6 ft) X Pressure (19.8 psf)
Table 2002.4 Vertical Pressure
Vertical Load:
Spacing (6 ft) X Pressure (6.9 psf)
Beam Moment ~ HVHZ Roof Only
Beam Moment ~ HVHZ Combined
Roof & Wall Pressures
Table 2002.4 Simultaneous
Loading ~ Applied Beam Moment
(Bending / Axial Compression)
Mz
Fx
(kip-in) (kips)
dy (2X9)
Ratio
HVHZ load (roof only)
54.3
0
L/192
HVHZ (combined loading)
71.2
.414
L/137
Table 2002.4 (simultaneous loading)
72.1
1.125
L/137
Interaction Ratios for 2X10 SMB:
HVHZ:
Mz
Applied:
71.2
Allowable:
114.4
Table 2002.4
Applied:
72.1
Allowable:
114.4
+
Fx
.414
8.76
+ 1.125
8.76
=
0.669
=
0.758
Interaction Ratios for 2X9 (0.82” X 0.306”) SMB:
HVHZ:
Mz
Applied:
71.2
Allowable:
82.9
Fx
+
.414
=
0.92
=
1.037
6.72
Table 2002.4
Applied:
72.1
Allowable:
82.9
+
1.125
6.72
6"
5-1/2"
Compact Sections [Lumber / Steel]
SYP #2
2X6
Sx = 7.56
Fb = 1.25 ksi
A36 Mild Steel
W 6X15
Sx = 9.72
Fb = 22 ksi
Minimum Mechanical Properties
for Alloy 6063-T6
Ftu = 30 ksi
Fty = 25 ksi
nu = 1.95
ny = 1.65
ADM 3.4.2 Tension in Extreme Fibers of Beams
For Flat elements In Uniform Tension
is the lesser of:
Ftu
F=
kt • nu
(kt = 1.0)
F = 15.2 ksi
Fty
F=
ny
Aluminum Self-Mating Beam Sections
2X8 SMB
8"
2X5 SMB
Wall Thicknesses:
2X5 SMB: Web: 0.050” X Flange: 0.116”
2X8 SMB: Web: 0.072” X Flange: 0.224”
2X9 SMB: Web: 0.082” X Flange: 0.306”
2X10 SMB: Web: 0.092” X Flange: 0.374”
ADM Requirements for Major Axis
Bending Thin-walled Self-Mating Sections
•
•
Tension (3.4.2)
Compression
1. Member buckling (3.4.14)
2. Member halves buckling between stitch
screws (3.4.11)
3. Local component buckling (may take weighted average )
– Web (3.4.18)
– Flange (3.4.15)
ADM Requirements / Axial Compression
Axial compressive strength is the least of:
– Member buckling strength Fcm (tube on full
length) [3.4.7]
– Member buckling strength between stitch
screws Fch [ 3.4.7 for beam halves]
– Local buckling strength (web Fcw [3.4.9] and
flange Fcf, [3.4.8.1], or weighted average Fca)
[4.7.2]
– Reduced member buckling strength due to
interaction between member and local
buckling Frc [4.7.4]
Allowable Bending Stresses for Standard
Industry Profiles
Profile
2X4 SMB
2X5 SMB
2X6 SMB
2X7 SMB
2X8 SMB
2X9 SMB
2X10 SMB
Sx
0.935
1.380
1.920
2.375
4.080
5.910
8.456
Fb
6.3
6.9
6.9
6.9
11.5
13.5
13.5
M
5.9
9.5
13.2
16.4
47.1
80.1
114.4
2X2 Hollow Tube
2X3 Hollow Tube
2X4 Hollow Tube
0.245
0.416
0.649
12.9
13.0
13.4
3.2
5.4
8.7
Flow Thru vs. Non-Flow Thru
SCREEN ENCLOSURE
NON-Flow Thru Condition
Flow Thru Condition
Flow Thru Condition
host structure (S.F.D.)
(U
N
ST
R
E
SS
E
D
)
"Projection"
host structure (S.F.D.)
T
(S
RE
E
SS
D)
"Longitudinal Dimension" of Screen Enclosure
Roof Diagonal Bracing Plan / Mansard Pool Enclosure
Typical Mansard Screen Enclosure
Simultaneous Loading Left > Right + Up
(Table 2002.4 Loading)
2,800 lbs (tension in corner hip)
-3,728 lbs (uplift at corner)
Alternate Bracing Arrangement
-2,167 lbs
2,216 lbs
-1,972 lbs
-2,266 lbs (uplift)
AAF Guide to Aluminum Construction in
High Wind Areas (2007 Edition)
• an alternative design methodology for
typical aluminum patio projects of lesser
complexity (not a standard)
• development beginning in 2006
• adopted into FBC 2007
• to be implemented October 2008
AAF Guide to Aluminum Construction in
High Wind Areas (2007 Edition) FEATURES
• developed by a statewide consensus committee of
engineers, contractors and suppliers
• incorporates loads mandated by the updated Table
2002.4
• incorporates new details and advances in technology and
lessons learned from failures of 2004 / 2005 storms
• more restrictive in scope (size and geometry of projects)
• for pool enclosures, upgrades eave rails, corner posts &
diagonal bracing
• DRAFT COPY DOWNLOADABLE FOR FREE AT THE AAF
WEBSITE (aaof.org)
Expectations
• depends upon market conditions
• new technologies: alloys, profiles
• enforcement:
– Design (Building Department)
– FBPE/FEMC
Resources
•
•
AAF Website: aaof.org
Aluminum Association: aluminum.org
– Aluminum Design Manual
– Screen Enclosure Design (Kissell)
– Aluminum Structures (Kissell)
Email David Miller: aaftechnical@bellsouth.net
OR: dwm@specialtystructure.com
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