Seismic analyses of damageable concrete structures

Modem seismic design approaches produce concrete structures which will be damaged at extreme demands, known as "maximum credible earthquakes (MCE)", and often during the design basic expected (DBE) ones. According to the current approach the structure elements (beams, columns, walls, slabs, etc) are sized at reduced level of the demand calculated assuming that the structure behaves linearly elastic. Thus, when the structure elements are challenged by the earthquake farces, yielding develops along with inelastic deforrations which lead to damage by permanent residual displacements, deterioration of strength, and sometime instability. Current elastic analysis methods may miss the effects of local and global damage which may become uncontrollable. Recent developments of analytical tools and engineering software allow tracking the nonlinear-elastic and inelastic behaviour, in order to determine structures' adequacy to performance thresholds. The paper shows the need for nonlinear analysis, along with the customary elastic, showing the principles of step-by-step formulations of stiffness, strength and deterioration used in incremental-static and dynamic approaches.