1 September 1999
METAL ROOFING AND METAL (STEEL) DECK DIAPHRAGMS
9-1. INTRODUCTION. This Chapter prescribes the criteria and procedures for the design of
metal roofing and steel deck diaphragms for buildings.
9-2. METAL ROOFING. Metal roofing consists of cold-formed, corrugated, fluted or ribbed
metal sheets attached to the exterior of building structures and exposed to weather to serve as
the exterior covering of the structure. Metal roofing may be either structural, or non-structural.
The structural metal roof is designed so the roofing panels support all out of plane loads.
Forces in the plane of the roof due to lateral wind and earthquake forces are typically resisted
by steel deck diaphragms, or in plane X-bracing. The non-structural roof depends on substrate
to carry the applied loads. Metal roofing may have lapped side seams and exposed fasteners,
standing side seams and hidden metal clip fasteners, or hybrid types such as those with snap
seams or battens that fall somewhere in between. There are many types of metal roofing
produced by the metal manufacturing industry and care must be exercised to ensure that the
type specified is compatible with the main structural system or substrate.
9-3. METAL DECK DIAPHRAGMS.
a. Metal Deck Diaphragms without Structural Concrete Topping. Metal deck diaphragms
without structural concrete topping are usually used for roofs of buildings where the gravity
loads are light (live loads are 1000 kg / meter2 (20 psf or less). The metal deck units are often
composed of steel sheets ranging in thickness from 0.75 mm (0.03 inches) to 2 mm (0.08
inches). The sheets are 600 mm (2 feet) to 900 mm (3 feet) wide, and formed in a repeating
pattern with ridges and valleys. Rib depths vary from 40 mm to 100 mm (1-1/2 to 4 inches) in
most cases. Decking units are attached to each other and to the structural steel supports by
welds or mechanical fasteners. Chords and collector elements in these diaphragms are
composed of steel frame elements attached to the diaphragm. Load transfer to frame
elements that act as chords or collectors is thorough shear connectors, puddle welds, screws,
or shot pins.
b. Metal Deck Diaphragms with Structural Concrete Topping. Metal deck diaphragms
with structural concrete topping are frequently used on floor and roofs of buildings where the
loads are moderate to heavy. The metal deck may be either a composite deck, which has
indentations, or a non-composite deck. In both cases the slab and deck act together to resist
diaphragm loads. The concrete fill may be normal weight or lightweight concrete, with
reinforcing composed of wire mesh or small diameter reinforcing steel. Additional reinforcing
may be added in areas of high stress. The metal deck units are composed of gage thickness
steel sheets, 600 mm (2 feet) to 900 mm (3 feet) wide, and are formed in a repeating pattern
with ridges and valleys. Decking units are attached to structural steel supports by welds or
mechanical fasteners. The concrete topping has structural properties that significantly add to
diaphragm stiffness and strength. The topping should be a minimum of 65 mm (2-1/2 inches)
thick. Concrete reinforcing ranges from light mesh reinforcement to a regular grid of small
reinforcing bars. Metal decking is typically composed of corrugated sheet steel from 22 gage
down to 14 gage. Rib depths vary from 40 mm to 75 mm (1-1/2 inches to 3 inches) in most
cases. Chord and collector elements in these diaphragms are considered to be composed of