Abstract: In spite of the plastic behavior of structure is not often allowed under continuous operating conditions it is quite fit for design when the structure is under loading that only occur a few times during its life. The object of this study is to investigate the response of elasto-plastic SDOF structures subjected to blast loading with different TNT quantities and standoff distances. Numerical analysis by SAP2000 Ver.18 based on bilinear structural resistance function was used in this research. Different structural resistance function values were investigated as a ratio of elastic response resistance function to obtain the degree of economy that satisfied from each case. The result of analysis show, although the maximum displacement of the elasto-plastic system is greater than that of the purely elastic structure, the difference in term of structure capacity is significant. It is concluded that elasto-plastic analysis become entirely feasible, quite appropriate and effective for design of structures subjected to blast load.