Blast and Impact Loading and Response of Structures
Full Session with Abstracts
Safety-related structures in nuclear power plants are designed to sustain the effects of impact loading due to a spectrum of high kinetic energy design-basis tornado-generated missiles without losing the structure safety function. A typical design process for the target structure involves evaluating the global response using a single degree-of-freedom elasto-plastic approach, and evaluating the local missile penetration resistance using empirical formulas developed by regression analysis of test results. The loading functions for evaluating the global response have traditionally been approximated by a triangular, rectangular or sine function depending on the type of missile used. Acceptance criteria for global response is based upon limiting global ductility below a specified threshold. The acceptance criteria for local missile penetration of the target is determined by computing the required panel thickness (based on empirical equations) to preclude penetration, perforation or back side scabbing of the target due the impact of the missiles. This analysis approach often yields a conservative estimate for the required thickness of concrete panels, which is suitable for new construction. However, for existing concrete panels suffering from degradation, using this approach may result in unwarranted conservatism, which can lead to expensive repairs.
This paper examines using an explicit finite element approach for a concrete panel that is being repaired. The response of a degraded concrete panel is evaluated for being struck by a rigid missile at the panel center for the design-basis loading. The impact time history response is determined using a finite element solution obtained using the explicit LS-DYNA solver. LS-DYNA is a nonlinear explicit finite element code for the dynamic analysis of structures which is particularly well-suited for impact and penetration analysis. The effect of the concrete section loss is captured by reducing the section thickness and determining the time history response accordingly.