1. Scope
The requirements of this section shall govern only ribbed steel roof deck construction of varying configurations used for the support of roofing materials, design live loads and SDI construction loads shown on page 3.
Commentary: Suspended ceilings, light fixtures, ducts, or other utilities shall not be supported by the steel deck.
2. Materials
2.1 Steel Roof Deck: The steel roof deck units and accessories shall be fabricated from steel conforming to Section A3 of the latest edition, (1996) of the American Iron and Steel Institute, Specifications for the Design of Cold Formed Steel Structural Members. The steel used shall have a minimum yield strength of 33 ksi (230 MPa).
2.2 Tolerances:
Panel Length: Plus or minus 1/2 inch (13 mm).
Thickness: Shall not be less than 95% of the design thickness.
Panel cover width: Minus 3/8 inch (10 mm), plus 3/4 inch (20 mm).
Panel camber and/or sweep: 1/4 inch in 10 foot length (6 mm in 3 meters).
Panel end out of square:
1/8 inch per foot (3 mm in 300 mm) of panel width.
Commentary: The above tolerances reflect the fabrication processes for steel deck products. Variation in cover width tolerances may vary due to trucking, storage, and handling.
The steel roof deck shall be manufactured from steel conforming to ASTM Designation A611-97, Grades C, D or E or from A653/A 653M-97 Structural Quality grade SS33 or higher.
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If the published product literature does not show the uncoated steel thickness in decimal inches (or millimeters) but lists gage or type numbers, then the thickness of steel before coating with paint or metal shall be in conformance with the following table:
| Type No. |
Design Thickness |
Minimum Thickness |
| In. |
mm |
In. |
mm |
| 22 |
.0295 |
0.75 |
.028 |
0.70 |
| 20 |
.0358 |
0.90 |
.034 |
0.85 |
| 18 |
.0474 |
1.20 |
.045 |
1.15 |
| 16 |
.0598 |
1.50 |
.057 |
1.45 |
3.1a Allowable Stress Design (ASD): The maximum working stress shall not exceed 20 ksi (140 MPa). The unit design stress shall in no case exceed the minimum yield strength of the steel divided by 1.65 for specific design uniform loads. The unit design stress shall be increased 33% for temporary concentrated loads provided the deck thus required is no less than that required for the specific design uniform loads.
3.1b Load Resistance Factor Design (LRFD): The load and resistance factors and the load combinations shall be as required by the AISI specification.
Commentary: Either ASD or LRFD design is acceptable to the Steel Deck Institute. If LRFD uniform load tables are desired, the SDI Roof Deck Construction (1999) is a source.
3.2 Section Properties: Structural properties of roof deck sections shall be computed in accordance with the American Iron and Steel Institute (AISI) Specification for the Design of Cold-Formed Steel Structural Members, 1996 edition.
Commentary: Arbitrarily assumed effective compression flange widths shall not be allowed. Testing shall not be used in lieu of the above in determination of vertical load carrying capacity of steel deck.
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3.3 Load Tables: Uniform loads determined for published tables shall be based on equal adjacent two and three span conditions and on single spans. Appropriate combinations of shear and bending shall be made to determine the published loads. Widths of 2” (50 mm) for end bearing and 4” (100 mm) for interior shall be used to check web crippling. Deflection coefficients shall be 0.013 for single spans, .0054 for double spans and .0069 for triple spans.
Commentary: For deck layouts that provide more than three equal spans, the user can apply the loads published for three spans. Published uniform load tables do not apply for adjacent spans that differ in length by more than 10%.
3.4 Maximum Deflections:
Deflection of the deck shall not exceed L/240 or 1 inch (25 mm) whichever is less, under the uniformily distributed design live load. All spans are to be considered center-to-center of supports.
Commentary: The adequacy of deck edge support details should be reviewed. At the building perimeter, or any other deck termination or direction change, occasional concentrated loading of the roof deck could result in temporary differences in deflection between the roof deck and the adjacent stationary building component. Supplemental support such as a perimeter angle may be warranted.
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