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recognised fact that the stiffness, strength and energy dissipation capacity of structures deteriorate when subjected to cyclic loading. This deterioration is associated with the damage cumulating process in the material which already has micro-defects resulting from the construction and service period. The damage accumulated will inevitably affect the remaining strength or life of structures. Structural failure occurs when the damage has accumulated to a critical level. However, due to the complexity of the problem, there is no generally-accepted practical method in the structural analysis of steel structures that takes into account the damage cumulation effect. A reliable and practical damage cumulation model is thus required in the seismic analysis of new structures and residual-strength/life prediction for the maintenance or repair of present structures.Fracture mechanics has been successfully applied in predicting the failures of many engineering structures with existing macrocracks. However, the deterioration of stiffness and strength of metals occurs well before the initiation of a macrocrack due to the initiation of microcracks, intergranular debonding or decohesion between inclusions and the matrix [1]. This deterioration should be taken into account in a complete and reliable structural analysis. Continuum damage mechanics provides an efficient tool for the analysis of damage cumulation and has been successfully applied in pressure vessels and aeronautics engineering for creep, fatigue and ductile damage problems. Considerable efforts have been made for the application of damage mechanics in civil engineering structures, especially under seismic loading, which is a type of low-cycle fatigue loading.The deterioration of Young's modulus, yield strength and hardening coefficient in the hysteretic model of a material subjected to cyclic loading can be considered to have a relation with the damage variable (or damage index), a basic concept in damage mechanics. To quantify the damage in a material, an appropriate damage variable, which is able to describe the microstructural damaged state in terms of measurable mechanical parameters, is first to be defined. Theoretically, the value of the damage index should fall in the range of 0-1, where 0 corresponds to the undamaged state of the material and 1 the completely damaged state when failure Abstract The research on the development of a reliable analytical model for seismic analysis of steel structures is presented. The non-linear damage cumulation hysteretic model incorporating the deterioration of stiffness, strength and strain hardening for structural steel is proposed and validated. The complete loading history, energy dissipation and the effect of the maximum plastic strain are taken into account in the model. The constants in the model are determined from regression analysis of experimental results of simple standard tensile and cyclic tests. Finite element formulations for beam and structural solid element considering the damage cumulation are derived. A...

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