Rational evaluation method for impact response of tornado protection structure using high strength wire net

A practical design of a tornado missile protection structure is becoming a technical key issue in order to meet the New Regulatory Requirements for a nuclear power plant in Japan. Utilization of a net structure is one of the options as realistic protection measures owing to the less severe wind and seismic loads. In this study, high strength wire net (protection net) was selected through material screening tests, and then three kinds of mechanical tests were carried out to establish an evaluation method for impact response of the net structure caused by tornado missiles with respect to the absorbed energy, maximum deformation, etc. At first, impact tensile tests of a piece of protection net were performed to obtain dynamic material properties to be used in a formula for limit value of energy absorption of the net. Secondly, free drop impact tests were conducted using two types of heavy weights (i.e., one is a circular cylinder; the other is with a nose of hollow square pipe). Thirdly, high speed impact tests using a small diameter missile were conducted. These results have allowed us to confirm not only the validity of the formula for impact response evaluation, but also good impact resistant performance of a protection net structure. Moreover, two evaluation methods (simplified and precise methods) for impact response of the structure were proposed. It was confirmed that these values derived from the evaluation methods were in good agreement with the experimental values, and that these methods were applicable to the evaluation of the impact response of this net structure. (author)