Among the ''theories'' applied to model concrete behavior, damage mechanics has proven to be efficient. One of the first models for concrete introduced into such a framework is Mazars' damage model. A new formulation of this model, called the ''l model'' and based on a coupling of elasticity and damage within an isotropic formulation, is proposed herein for the purpose of 3D cyclic and dynamic loadings. Unilateral behavior (i.e., crack opening and closure) is introduced by use of two internal variables. A threshold surface is then associated with each of these variables. The shape of such surfaces has been chosen to model as accurately as possible concrete behavior under various loadings, i.e., tension, compression, shear, biaxial and triaxial, in the aim of simulating a large number of loading types (monotonic, cyclic, seismic, blast, impact, etc.). Applications of this model are presented on plain or reinforced concrete elements subjected to a range of loadings (e.g., multiaxial, cyclic, dynamic). A comparison with experimental results serves to demonstrate the effectiveness of these various selected options.

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A fundamental issue that arises in the framework of probabilistic seismic risk analysis is the choice of ground motion intensity measures (IMs). A new structure-specific IM, namely, relative average spectral acceleration (ASA R ), is being proposed herein, and a comparison with current IMs is performed based on (1) a large data set of recorded earthquake signals;(2) numerical analyses conducted with state-of-the-art finite element (FE) models, representing actual load-bearing walls and frame structures, and validated against experimental test; and (3) systematic statistical analyses of the results. According to a comparative study of the case of nonlinear structural behavior, the ASA R proves to be the most efficient IM with respect to demand parameters, such as maximum interstory drift, frequency drop and maximum ductility demand. Beyond the sufficiency and simplicity of its formulation, which allow for the use of existing ground motion prediction models, the ASA R offers a promising IM for performance-based seismic design and/or assessment.