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Re: Decoupling of anchor bolts

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> From: "Rich Lewis" <seaint04(--nospam--at)lewisengineering.com>

> Harold,

> I have a late quick side question here.  If you do not put shear in anchor
> bolts, how do you specify and detail a connection for a pre-engineered metal
> building?   I've never seen a PEMB supplier install shear lugs.  Is there
> some other detail you would use in this application?

> Rich

Permit me to also add my insights:

Short answer:
If the (foundation) designer is uncomfortable with allowing shear transfer
through the rods, then add a shear key or other means - either by request to
the PEMB manufacturer or in the field - by your design.

(Has anybody seen a PEMB failure due to base/foundation interface issues? I
would be interested in any information available.)

Long answer:
The PEMB market has developed from small, relatively unimportant, truly
pre-engineered, moderately redundant structures to, in various degrees,
large, critical, minimally pre-engineered, low-redundancy structures.

Unfortunately, the industry does not act as a single entity in their
practices or desire to educate the engineers who interface with PEMBs (e.g.
foundations, masonry, tilt-up, etc.). In many cases, the Owner, consultants
and building authorities do not adequately understand the professional,
safety and commercial liability issues at these interfaces.

In this regard, the manufacturers will not (cannot) go beyond identifying
anchor rod size, grade and pattern that would be adequate to meet their
design assumptions AT THE UNDERSIDE SURFACE OF THE BASE PLATE. Another
engineer must be contracted (foundation designer, typically) to ensure that
practical means are provided to ensure that the design reactions can be
transferred from the base plate to the foundation. This may or may not
include shear through the anchor rods but the anchor rod section will be
adequate to handle the forces (caveats exist).

Most PEMB manufacturers will not supply anchor rods because of interface
liability issues - the manufacturer's sales rep may use other words.

It is common for the PEMB manufacturer to provide small base plate holes,
relative to the anchor rod size and the AISC recommended hole diameters.
Therefore, only small movements are likely to occur before adequate bearing
contact. For small, relatively unimportant, moderately redundant structures,
this is not a problem when the foundation is designed to resolve the shear
from the anchors.

However, for newer, large, critical, minimally pre-engineered,
low-redundancy structures the foundation designer, or whoever is responsible
for the design interface from base plate to foundation, may need to take
matters into their own hands. If the designer is uncomfortable with allowing
shear transfer through the rods, then add a shear key or other means -
either by request to the manufacturer or in the field - by your design.

An example of a design check that is _NEVER_ done by the PEMB manufacturer:
Rod lateral bearing on foundation concrete (e.g. shear transfer from rod to
concrete).

Regards
Paul
-- 
Paul Ransom, P.Eng.
ph 905 639-9628
cell 905 802-3707
fax 905 639-3866
ad026(--nospam--at)hwcn.org

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