CEMP-E
TI 809-02
1 September 1999
the steel frame elements attached to the diaphragm. Load transfer to frame elements that act
as chords or collector elements is usually through welds or headed studs.
c. Metal Deck Diaphragms with Nonstructural Concrete Topping. Metal deck diaphragms
with nonstructural concrete fill are typically used on roofs where gravity loads are light. The
concrete fill, such as very lightweight insulating concrete (e.g. vermiculite), does not have
useable structural properties. If the concrete is reinforced, reinforcing steel consists of wire
mesh or small diameter reinforcing steel. To act as a diaphragm load transfer must be the
same as that provided for a metal deck diaphragm without concrete topping.
d. Horizontal Steel Bracing (Steel Truss Diaphragms). Horizontal steel bracing (steel
truss diaphragms) are often used in conjunction with structural metal roofing systems where
the strength and stiffness of the metal roofing is incapable of carrying in-plane loads. Steel
truss diaphragm elements are typically found in conjunction with vertical framing systems that
are of structural steel framing. Steel trusses are more common in long span situations, such
as special roof structures for arenas, exposition halls, auditoriums, industrial buildings, and
aircraft hangars. For steel truss elements with large in-plane loads, diagonal elements may
consist of angles, tubes, or wide flange shapes that can act in both tension and compression.
Diagonals which can act in both tension and compression are preferred, however with
lightweight metal buildings the diagonals are often steel rods which can act only in tension.
Sufficient load path reliability should be provided for diagonals in accordance with the
redundancy recommendations of Chapter 2. Truss element connections are generally
concentric, to provide the maximum lateral stiffness and ensure that the truss members act
under pure axial load.
9-4. BASIS FOR DESIGN.
a. Metal Roofing. The basis for the design of metal roofing is provided in TI 809-29,
"Structural Considerations for Metal Roofing."
b. Metal (Steel) Deck Diaphragms. Steel deck diaphragms will be made from materials
conforming to the requirements of the American Iron and Steel Institute (AISI), Specifications
for the Design of Cold-formed Structural Members," or ANSI/ASCE 8, "Specifications for the
Design of Cold-formed Stainless Structural Steel Members."
(1) In-plane Loads. Nominal in-plane shear strengths will be determined in
accordance with approved analytical procedures. Design strengths will be determined by
multiplying the nominal strength by a resistance factor, φ, equal to 0.60 for mechanically
connected diaphragms, and equal to 0.50 for welded diaphragms. Analytical procedures
contained in the Steel Deck Institute, Inc., "Diaphragm Design Manual #DDM01" are accepted
means for calculating in-plane shear strengths. Limits are placed on diaphragm span and
depth to span ratios to keep diaphragm in-plane displacements small enough to prevent
cracking of walls. The maximum span and span to depth ratio depends on diaphragm stiffness
and wall ductility. These and other additional requirements for diaphragms and their
connections are provided in TI 809-04, "Seismic Design for Buildings."
(2) Out-of-Plane Loads. Design loads and design requirements for out-of-plane loads
for bare metal deck roofing will be in accordance with TI 809-29, "Structural Considerations for
9-2
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