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Re: pal system

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IMHO and as far as I know, it is a system which works based on dissipating
energy through friction. This type of passive energy dissipating system has
important advantages over other systems; these are, 1)hystretic curves are
very stable 2)no significant strength reduction and stiffness over a good
range of displacement 3) Distinct plateau; i.,e. no significant hardening

The tricky part is you have to find the needed slip-critical froce at every
story level through an iteration process. You need to run non-linear dynamic
time history analyses for a couple of eartquakes, and change values of slip
force until the desired dynamic response is achieved; i.e. displacement and
drift requirements are met.

Of course,then strength of other structural members in a frame have to be
checked, and be somewhat greater than the froces caused by slip forces
applied at every level. In other words, if the strength of members assumed
for the analysis is lower than needed, size of the sections have to be
modified and another round of analyses is needed to acount for change in
stiffness of the modified sections.

This particular type of friction dampers were used in a number of structures
(e.g. library building of Concordia university in Montreal). I think Mr.
Pall has a number of conference papers on this application. There is at
least two papers, as far as I know. One in the proceedings of 5th Canadian
Conference On earthquake engineering, and the other one must be in 11 world
conference on earthquake engineering.

I think Pal friction dampers are pattented. There are other types of
friction dampers with different froce-displacement charactristics which
differ to some extent from one another in the way that friction mechanism is
produced and employed. also add to it special material which is needed and
can be different from type to type. 

I hope this helps,

Majid Sarraf

>Has anyone used and/or heard of a system of steel cross bracing referred to
as PAL bracing. It is some kind of system utilizing damping.
>We are in zone 2 and have not had to use anything too unique for EQ loads.
This type of thing (damping) is likely used more in the zones 3 and 4 for
larger structures.
>If one uses damping for a structure does it require that a dynamic analysis
be done?  I am used to calculating a V and M from statics, codes, etc. I
have taken a structural dynamics masters course but have not used much of
it. (Good for background knowledge though). Are these damping systems
proprietary or do engineers reinvent the wheel often?
>Just wondering....
>David Handy, P.Eng

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                   \               Majid Sarraf             /
                    \             Ph.D Candidate           /
                     \   Department of Civil Engineering  /
                      |        University of Ottawa      |
                      |           Ottawa, Ontario        |
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