en Research Paper Research Paper In this research a new approach is proposed for elasto-plastic analysis of structures with truss elements. This method covers both perfectly plastic and hardening properties. The Proposed technique uses substituting virtual loads instead of modifying the stiffness matrix. To solve this kind of problems, complementary programming is utilized. Numerical examples demonstrate that elastoplastic analysis by this approach has very good convergence, rapidity, and accuracy. elasto-plastic, truss, hardening, complementary programming, virtual loads 224 235 http://ijce.iust.ac.ir/browse.php?a_code=A-10-569-2&slc_lang=en&sid=1 M. Rezaiee-Pajand 180031947532846005974 180031947532846005974 Yes M. Riyazi-Mazloomi 180031947532846005975 180031947532846005975 No