[en] This paper presents experimental, analytical and numerical study of impact perforation of steel plates with the aim to develop the procedures to assess the perforation of steel against tornado-generated missile impact. In the experiment, flat plates of SS400 steel and SUS304 stainless steel were perforated by a square pipe with cross section 200 x 300. Projectile mass and impact velocity were kept constant, namely, approximately 1300 kg and 17 m/s. Perforation limit thickness of SS400 and SUS304 flat plate was determined to be 9 mm and 6 mm, respectively. BRL formula was used for the analytical study, and equivalent diameter of square pipe for BRL formula was defined based on the experimental data. Numerical simulations of some experiments were also carried out and the effect of thermal softening and stress triaxiality on failure strain have to be taken into account in the material model in order to reproduce the experimental results. (author)