1 September 1999
Metal Roofing." The design for out-of-plane loads for metal deck with structural concrete
topping (composite steel floor deck) will be in accordance with the Steel Deck Institute, Inc.,
"Design Manual for Composite Decks, Form Decks, and Roof Decks."
9-5. METAL DECK DIAPHRAGMS - STIFFNESS FOR ANALYSIS (FEMA 273). Diaphragms
can be considered to be flexible, or rigid. For flexible diaphragms, the lateral forces are
distributed from the metal deck diaphragm to the vertical lateral force resisting elements by
assuming the diaphragm acts as a simple beam spanning between vertical lateral-force
resisting elements. For rigid diaphragms, the lateral forces are distributed to the vertical
lateral-force resisting elements based on the relative stiffnesses of the vertical lateral-force
resisting elements. Flexibility factors, provided in manufacturers' catalogs as well as in the
Diaphragm Design Manual of the Steel Deck Institute, can be used to determine whether the
diaphragm should be considered as flexible or rigid. For bare metal deck diaphragms the
stiffness is a function of metal thickness, rib geometry, fastener type, and fastener spacing.
Procedures for calculating diaphragm flexibility are also provided in TI 809-04, "Seismic Design
9-6. SPECIAL INSPECTIONS.
Periodic special inspection is required for all welding of all steel deck and steel truss
elements of the seismic force resisting system.
Periodic special inspections are required for screw attachment, bolting, anchoring, and
other fastening components within the seismic force resisting system including
diaphragms, drag struts, collector elements, and truss elements.