Formacore Curtain Wall Design Criteria
The Formacore panel is a ¼" thick all metal composite exterior curtain wall panel. The panel consists of an aluminum honeycomb core laminated to an aluminum face and liner.
Formacore panels are typically supported along the perimeter by aluminum extrusions, or they are supported at each end with any intermediate supports as required. Panels which are supported along the entire perimeter give improved deflection performance. The edge grip detail and the rout and return are two common details.
Deflections due to wind loads are discussed in the following sections. Use interpolation to determine deflections of spans not shown in Tables 5-1 thru 5-4.
Panels Supported Along Four (4) Edges
Table 5-1 shows deflections for a panel supported along the entire perimeter. The "a" dimension is the smaller of the width and length of the panel. The maximum ratio of "b" to "a" is 3:1 for Table 5-1 to be valid.
Load / deflection values shown were obtained by extensive testing of four-side simple support conditions. Although accurate for the conditions under which the tests were run, the chart may be conservative for continuous or simple spans with edge fixity; therefore the values should be considered as a guide only.
Calculate the maximum deflection for a 4 x 8 Formacore aluminum honeycomb panel supported along its perimeter by aluminum extrusions and subjected to a 30 psf wind load.
From Table 5-1 for a 30 psf wind load and an “a” dimension of 36 inches (and wider) = 0.026 in/ft2. The maximum deflection in the panel is 0.026 (in/ft2) x (4x8) – 0.0832”
Single Span Panel
Table 5-2 shows deflections for panels used as single span
Calculate the maximum deflection for a 2 x 4 Formacore composite panel supported at each end such that the panel spans 48” and is subjected to a 20 psf win load.
From Table 5-2 for a 20 psf load and a 48” span, the deflection is 1.45 inches.
From Table 5-2 for a 20 psf load and a 48” span, the deflection is 1.45 inches. Please not that the width of the panel does not effect the deflection for a single span conditions.
Double Span Panel
Table 5-3 shows deflections for panels used as a double span.
Calculate the deflection for the same panel as in Single Span Panel with a support as midspan.
From Table 5-3 for a 20 psf load and a 24” span, the deflection is 0.040 inches. Please note that the width of the panel does not affect deflection for double span conditions.
Panel with Stiffeners
When calculated deflection or unstiffened panels exceed allowable deflection, stiffeners may be attached to the back of the panel. The resulting panel deflection is then dependent on the moment of inertia and spacing of the stiffeners. Because of the complex interaction between the stiffener and the panel, deflection of panels using stiffeners can best be determined by testing. In lieu of testing, the following procedure may be used to estimate the maximum deflection of the panel.
Table 5-4 shows the deflection for stiffened panels. The deflection values plotted on the graph in Table 5-4 have all been divided by the center-to center stiffeners spacing in inches. These values are all based in a stiffener having a minimum moment of inertia of I = 0.25 in.4
Calculate the maximum deflection for a 3’-0” x 10’-0” Formacore aluminum composite panel supported along all fur sides with stiffeners located 40” center-to-center and subjected to a 35 psf wind load.
From Table 5-4 for a 35 psf wind load and panel dimensions as stated above, the maximum deflection in the panel is estimated to be 0.008 (inch/stiffener spacing in inches) x 40 (stiffener spacing in inches) – 0.032 inches.
Panels without Stiffeners
In substitution of panel stiffeners when calculated deflection or exceed allowable deflection, panel thickness can be increased to provide increase panel rigidity (inches/lb.). By increasing the panel thickness, stiffeners are no longer required to meet deflection requirements. Refer to Chart 5-5.
|Overall Thickness||Face Sheet||Back Sheet||Weight per
|.24” (6.0 mm)||.040” (1.0 mm)||.020” (0.5 mm)||1.0 lb/ft2||6,300 in/lbs|
|.39” (10.0 mm)||.040” (1.0 mm)||.020” (0.5 mm)||1.08 lb/ft2||19,800 in/lbs.|
|.59” (15.0 mm)||.040” (1.0 mm)||.040” (1.0 mm)||1.43 lb/ft2||52,000 in/lbs.|
|.79” (20.0 mm)||.040” (1.0 mm)||.040” (1.0 mm)||1.51 lb/ft2||95,000 in/lbs.|
|.98” (25.0 mm)||.040” (1.0 mm)||.040” (1.0 mm)||1.59 lb/ft2||148,000 in/lbs.|
The deflection of perimeter extrusions shall not exceed 1/175 of the clear span. Project specifications may limit the extrusion deflection to less than 1/175 of the clear span.
The deflection of the panel between the extrusions supports shall not exceed 1/60 of the least clear span between supports. Panel stiffeners are not considered supports. Project specifications may limit the panel deflection to less than 1/60 of the clear span.
Panel section is governed by deflection for the loads and spans shown in Table 5-1. Bending stress may be the governing criteria for panels used as a simple and double spans as shown in Tables 5-2 and 5-3.
Thermal expansion is an important consideration of any Formacore panel system. As the panel temperature increases, the panel will try to expand. If the edges of the panel are restrained, this expansion will appear as panel bow. It is recommended that the thermal expansion of the panel not be restricted. The coefficient of linear expansion for Formacore panels is 0.00128/100ºF.
Sample Calculation – Thermal Expansion
A Formacore panel is exactly 15’ long at 60ºF. Find the length at 90ºF assuming the ends are free to move.
Change of length:
Δ = 0.00128 x 15’ x 30º F/100 = 0.00576 feet
Δ = 0.00576’ x 12” /1’ = 0.069 inches
The length of the panel at 90º F. is approximately 15’ 1/16”.
All of the principal components of the Formacore panel-its aluminum face, core and liner-are inorganic. Because they are, they do not contribute in any way to the ignitability or flame propagation characteristics of the total wall assembly. (A controlled quantity of laminating adhesive is the only organic component of the panel.)
When tested in accordance with ASTM E84 (a test method for testing the surface burning characteristics of building materials), painted Formacore panels were rated at:
|Side||Flame Spread||Smoke Developed|
Proper attachment of the Formacore panel system to the building structure is essential. It is the responsibility of the fabricator to insure that the fastening system is adequate to resist the specified wind load.
Contact PortaFab Corporation if code approvals are required.