of Nonlinear Systems
Nonlinear systems also limit the forces the structure experiences. A structural member or protective device exhibits force- displacement behavior which limits the forces to the ultimate strength of the member or device, as shown below. The forces in an elastic system, on the other hand, are limited only by the earthquake forces.
Since nonlinear systems limit forces, by Newton's 2nd law they must also limit accelerations.
In addition, nonlinear systems allow the designer to control the damage distribution. Except for the base-isolated system, the systems shown below are statically determinate at the near-collapse limit state and thus the forces in all members and the foundation are known. The designer chooses locations where local damage is acceptable, and designs the rest of the structure to be stronger, thus limiting damage to the designated areas.
The major difficulty with designing systems to respond nonlinearly is determining the design displacements. A large part of this course will be devoted to various ways of estimating expected displacements. Several ways of doing this are: