The steel in the reinforcement concrete structures is used frequently as the natural down conductor in Lightning Protection Systems (LPS). The lightning current distribution and the associated magnetic field are interesting topics for the LPS design and devices protection. The aim of this paper is to show the model developed and the software implementation which computes the current distribution considering the concrete surrounding the steel reinforcement. The model used was the Hybrid Electromagnetic Model - HEM. The grounding system and the soil resistivity were considered into the HEM and an approach did for the HEM expressions in order to compute the coupling between to media are shown. Finally a comparison with experimental results was done and some results are presented in this paper.