© 2016 Tech Science Press. A simple constitutive model, called semi-implicit model, for cyclic loading is proposed for steel materials used for structures such as building frames in civil engineering. The constitutive model is implemented in the E-Simulator, which is a software package for large-scale seismic response analysis. The constitutive relation is defined in an algorithmic manner based on the piecewise linear combined isotropic-kinematic hardening. Different rules are used for the first and subsequent loading states to incorporate characteristics such as yield plateau and Bauschinger effect of rolled mild steel materials. An optimization method is also presented for parameter identification from the results of cyclic and monotonic loading tests. Therefore, the proposed model is readily applicable to practical elastoplastic analysis of building frames. Accuracy of the model is demonstrated in an example of a cantilever subjected to various types of cyclic loading.