What is the difference of the lead core yield strength at creep loads and earthquake loads?
The hysteretic behavior of lead is dependent on the rate of loading. The yield strength is lower at creep velocities than at earthquake velocities. This is beneficial especially in bridges where the isolator moves over a range of velocities. During the high velocity seismic motion, the yeild stress ranges from 10 to 14 MPa. providing significant levels of damping. For thermal movements, the yield stress is in the range of 4 to 6 MPa, which imposes small forces on the structure. Intermediate values of lead stress resist service loads such as wind and braking.
