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Re: Base Isolators

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Lead provides good energy dissipation characteristics (almost 
elastic-perfectly plastic hysteresis), has a relatively low yield
stress (1450 psi), has a decent shear modulus prior to yield, and
and has excellent fatigue properties under cyclic loading to plastic 
regime.  Steel fatigues faster than the lead at plastic loading levels
(I think), but the higher shear strength and stiffness of steel 
definitely reduces the amount of change in structural period 
resulting from bearing yielding.  

Far as I recall, the steel plates are high-strength rather than A36, 
but that is mostly an assumption, so you'd want to check that with 
an expert.  There are a couple of refs on LRB experimental tests that 
came up for a recent class assignment.  If you're interested, email me 
directly & I'll forward them along.  

There are two types of rubbers used in bearings.  One is apparently a 
fairly low-damping, highly elastic, somewhat nonlinear variety.  The 
other type has high-damping characteristics.  That's all I know.
A good reference is:

	Skinner, Robinson, and McVerry.  An Introduction to Seismic 
	Isolation.  John Wiley & Sons.  New York.  1993.

HTH,

Charley



-- 
Charles Hamilton, EIT                   Graduate Student Researcher     
Department of Civil and                 Phone: 949.824.8694
    Environmental Engineering           FAX:   949.824.2117 
University of California, Irvine        Email: chamilto(--nospam--at)eng.uci.edu