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RE: AISC 341-05 Section 7.1 bolt shear strength a ductile limit state?

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To Australian codes at least, I always figured bolt failure was a fracture
limit state, the formula for bolt resistance being based on ultimate tensile
strength, not the yield strength. With shear strengths obtained using von
mises stress theory 57% of tensile, rather than maximum shear stress theory
50% of tensile.

But then our codes don't have any mandates over what can and cannot be
considered a simple, rigid, or semi-rigid connection, such is left purely to
the designer.

It is preferable to use bolts in tension not shear, and from that
perspective the extension of the bolt would control, with the limits on
extension most likely being more critical than the strength.

When the bolts are in shear then the controlling factor most likely
deformation of the parent materials, for example difficult to develop the
full shear capacity of a high strength bolt in sheet steel. Bearing and
tear-out determine the limiting capacity of the bolt joint. Similar to the
problems of fasteners in timber, where once again high strength bolts have
limited value.

I believe part of the objective is to control where a plastic hinge may form
in a rigid structure: generally better in the beam than the column, the beam
can go into catenary like a cable. If the bolts in shear are not providing
moment of resistance, through polar inertia of the bolt group, then the
connection is already assumed pinned/hinged. A typical simple connection is
not a true pin, and some yield of the connection plates likely to occur
before say a plastic hinge develops at mid-span causing collapse mechanism.
What don't want to happen is one or both shear connections to failure
without some indicative visually warning.

>From a practical viewpoint need to look at the AISC publications to see what
it says about shear connections. Or take a look at:

Akbar R  Tamboli (1999), "Handbook of Structural Steel Connection Design and
Details", McGraw Hill



Regards
Conrad Harrison
B.Tech (mfg & mech), MIIE, gradTIEAust
mailto:sch.tectonic(--nospam--at)bigpond.com
Adelaide
South Australia


-----Original Message-----
From: Haan, Scott M POA [mailto:Scott.M.Haan(--nospam--at)usace.army.mil] 
Sent: Tuesday, 4 March 2008 12:57
To: seaint(--nospam--at)seaint.org
Subject: AISC 341-05 Section 7.1 bolt shear strength a ductile limit state?

AISC 341-05 Section 7.1 says the design of connections shall be configured
such that a ductile limit state in either the connection or the member
controls the design.

AISC 341-02 7.2 said the same thing for bolted joints.

Silly question: is bolt shear strength for high strength bolts a ductile
yield state or fracture limit state?

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