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Re: Braced Frame Cladding

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I would suggest that you hire somebody with experience with this system to
help.  The learning curve is not trivial.  I would also recommend that your
Client bring on board somebody with experience in casting and erecting
precast panels.

The real issue is allowing the panels to move without resisting seismic
forces.  To do this you typically want to have a horiz joint at the same
elevation all around the building.  

Corners can cause problems because it is easy for one panel to bang against
another.  This often results in large caulking joints.  Remember that when
a caulked joint sees more than 50% strain in compression it will get
stiffer.

The point at which the caulking joints fail in shear or tension is a
function of the joint size and the caulking configuration and material. 
This is not a safety issue but can be a real cost issue for the building
owner.

You typically want the panels to be supported on the perimeter beams
adjacent to the columns so you do not have to deal with live load
deflection in the beams.

The erectors like the gravity supports to be at the bottom of the panels
but if the push pull connections at the top fail the panel is unstable.  On
the other hand if the gravity support is at the top failure of the push
pull connectors should not result in panels falling.

In the past it was common to design push pull connectors using threaded
rods that were assumed to accommodate the movement by bending.  There have
been reports of the rods failing in bending.  A crack forms at the root of
the thread when there is significant bending.

If you assume a bolted connection that slips, provide for enough movement
to accommodate both erection tolerances and seismic movement.  Make sure
that when erected that there is enough room for movement in either
direction.  Limit how tight the bolts are tightened.  Consider testing a
"slip" connection to see how stiff it is.


Mark Gilligan

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