Measures of structural damage for global failure analysis

In building codes, the design of structures is generally based on their virgin state omitting most damage processes and disregarding future physical as well as chemical deterioration. Such concepts of disregard of structural stiffness degradation are in principle incapable of quantifying structural failure and thus of describing important aspects in modern structural engineering. The present paper supposes the modeling of local damage and deterioration phenomena on material point level and its mapping onto structural level. Here, it demonstrates that global damage measures, i.e. measures on structural level, can stringently be deduced from the reduction of the current structural stiffness, up to now an unsettled problem. Damage indicators are thus observable during incremental-iterative solutions of the tangent stiffness equation, where they estimate the distance from the actual structural state to failure varying from 0 to 1. Their applicability is finally demonstrated exemplarily on a reinforced concrete beam and a large shell.