In case of a projectile impact on a reactor building of a nuclear power plant, stress waves propagate from the impacted wall to the structure’s interior. It is important to assess the effect of dynamic responses generated by the projectile’s impact on internal equipment, because stress waves are likely to excite high-frequency vibrations of internal equipment. The OECD (Organization for Economic Co-operation and Development) / NEA (Nuclear Energy Agency) launched the IRIS (Improving Robustness Assessment Methodologies for Structures Impacted by Projectiles) benchmark project in order to assess the dynamic response of a nuclear facility to projectile impact, and the third phase of IRIS (IRIS 3)  contributes to the investigation of the dynamic responses of reinforced concrete (RC) structures that house internal equipment. We have participated in IRIS 3 and have performed calibration analyses of projectile impact tests on a structure that models a reactor building that houses internal equipment. Specifically, we have developed and validated a numerical approach to investigation of impact responses of an RC structure that houses internal equipment through calibration correction. This paper presents partial simulation results of the dynamic responses of this structure and discusses the effects of support conditions of the internal equipment and stress wave propagation.