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RE: wall anchorage to metal deck flexible diaphragm

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97 NEHRP Recommended Provisions 5.2.6.3.3 "In metal deck diaphragms, the
metal deck shall not be used as the continuous ties required by this section
in the direction perpendicular to the deck span."

Scott M Haan P.E.
Plan Review Engineer
Building Safety Division http://www.muni.org/building
Development Services Department
Municipality of Anchorage
phone:907-343-8183  fax:907-249-7399
mailto:haansm(--nospam--at)ci.anchorage.ak.us



-----Original Message-----
From: Gerard Madden [mailto:GMadden(--nospam--at)mplusl.com]
Sent: Wednesday, June 27, 2001 2:01 PM
To: seaint(--nospam--at)seaint.org
Subject: wall anchorage to metal deck flexible diaphragm


Searched the archives on this topic and found some discussion and was
wondering if anyone had more opinions or reference they could site one way
or the other.

When anchoring CMU and Concrete walls to an unfilled metal deck flexible
diaphragm there is some debate as to the effectiveness of the deck and its
connections to behave as intended. 

Here are the issues/conditions

1) When the deck flutes are parallel to the wall being anchored, it is very
weak and would crumple and expand like an accordion. Some mentioned they
design the anchors at the joists or purlins every  4-8ft on center -
avoiding the use of the deck as a subdiaphragm. However, if an angle was
welded to the underside of the deck to stiffen it, I think you could rely on
the deck to behave as a subdiaphragm similar to wood as long as the angle
drags into the building far enough so it develops the diaphragm shear demand
from the wall anchorage. The drag should terminate with a perpendicular
steel member to take the chord out of the sub diaphragm.

2) When the deck flutes are perpendicular to the wall being anchored, it is
much more stiff and is good in resisting wall separation (tension at the
weld). When the wall moves into the diaphragm (compression) the buckling
stiffness of the deck should be investigated and struts should be provided
if necessary.

3) The wall anchorage provisions still apply for metal deck diaphragm even
though the provisions were primarily developed due to cross-grain
bending/tension failures of wood ledgers. My understanding is that equally
valid is the idea that local failures should be avoided to ensure the global
system and its assumptions function properly (i.e. roof support for out of
plane wall design is treated as a roller support in a beam analogy")

4) The puddle welds are adequate to transfer both tension and compression
loads at the ledger.

If anyone can point me to a solid reference or share their thoughts on these
matters, I'd appreciate it. We are involved in a large prison project with
many buildings and would like to be as efficient as possible in regard to
this issue. Most of my wall anchorage experience has been with wood
diaphragms, so I am tending to think that little is different here in terms
of the need for subdiaphragms and load path continuity. Project is in Zone 4
97 UBC - 1 story CMU and Tilt Up.

thanks in advance,
-Gerard
SF, CA



Gerard Madden, P.E.
Civil Engineer

Middlebrook + Louie, Structural Engineers
71 Stevenson Street, Suite 2100
San Francisco, CA 94105
Tel: 415.546.4900
Fax: 415.974.3680
Email: gmadden(--nospam--at)mplusl.com
Web: www.mplusl.com


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