P.H. Feenstra

A composite plasticity model for concrete

A composite yield function is used to describe the behavior of plain and reinforced concrete in biaxial stress under monotonic loading conditions. A Rankine yield criterion is used to monitor the in-plane tensile stresses and a Drucker Prager yield function controls the compressive stresses. A good agreement with experimental data for biaxial stress conditions in concrete can thus be obtained. The approach is particularly powerful for the numerical analysis of concrete structures, either plain or reinforced, which are predominantly in tension compression biaxial stress states. Initiation of cracking in such areas frequently leads to brittle, uncontrollable failure (splitting cracks), which can often not be handled by existing approaches. The proposed Euler backward algorithm based on the composite yield function and enhanced by a consistent linearization of the integrated stress strain relation for use within a Newton Raphson method at the structural level, is extremely robust for this particular class of problems.

Modelling of Panel Structures

The terms “panel structures” and “planar structures” are used interchangeably to designate two-dimensional structural elements that are loaded primarily in their own plane. They include walls, deep beams, and to some extent also shell elements that are subjected to only membrane stresses.

Analyses of shear-wall panels with a composite plasticity model

A constitutive model for concrete is presented which is formulated within the framework of incremental plasticity. The major improvement of the model is the stable and accurate algorithm which can be derived for tension, compression as well as tension-compression regimes. The analyses of shear-wall panels show that the composite plasticity model is well capable to describe the behavior of these type of structures.

Damage Processes in Solids and Structures and their Numerical Computation

A concise overview is given of some recent developments, mainly by the Delft group, of numerical modelling of damage processes. Attention is paid to discrete methods, where all damage is lumped into interface elements, and to enhanced continuum theories, where higher-order terms, either in time or in space, are added to preserve well-posedness of the rate boundary value problem after the onset of softening.