Pergamon Inl Solids Slrucfures Vol pp Copyright Elsevier Science Ltd Printed Great Britain All rights reserved COMPOSITE PLASTICITY CONCRETE MODEL FOR PETER FEENSTRAT and RENE BORSTS Delft Univen ity Technology Faculty Civil Engineering Box Delft The Netherlands Received March revisedform March Abstract composite yield function used describe the behavior plain and reinforced concrete biaxial stress under monotonic loading conditions Rankine yield criterion used monitor the plane tensile stresses and Drucker Prager yield function controls the compressive stresses good agreement with experimental data for biaxial stress conditions concrete can thus obtained The approach particularly powerful for the numerical analysis concrete structures either plain reinforced which are predominantly tension compression biaxial stress states Initiation cracking such areas frequently leads brittle uncontrollable failure splitting cracks which can often not handled existing approaches The proposed Euler backward algorithm basecl the composite yield function and enhanced consistent linearization the integrated stress strain relation for use within Newton Raphson method the structural level extremely robust for this particular class problems INTRODUCTION The proper modeling tension compression biaxial stress states plain and reinforced concrete outstanding issue finite element analysis concrete structures that utmost practical importance and very challenging the same time important.