When necessary data for the given aircraft are not available, an
approximate method given in Appendix C may be used to determine F(t),
by scaling available impact force time-histories of other similar aircraft
(see Reference 1).
The second step is to develop a structural model of the impacted
structure and perform a dynamic analysis using the impact force time-
history computed in the first step or the one obtained from Reference 1.
Structural Evaluation Criteria. Deformation responses computed for
various target structural components by either the energy-balance
method or the time-history analysis method are then used to compute the
ductility ratio (the ratio of computed displacement to elastic
displacement). Computed ductility ratios are then compared to the
permissible ductility ratios specified below to determine if the component
would deform excessively or collapse under impact loads.
a. For concrete structural components, the permissible ductility ratios
shall be as specified in ACI Code 349, Appendix C, Section C-3. For
beam columns, walls, and slabs carrying axial compression loads, the
provisions of Paragraph C 3-8 of ACI Code 349, Appendix C, shall be
b. For steel structural components, the permissible ductility ratios shall
be as specified in Section Q1.5.8 of AISC Nuclear Specifications,
ANSI-N690 (Reference 11). For plate structures, the permissible
ductility ratio of 10 is recommended.
Potential loss of SSC safety functions resulting from structural
deformation and degradation due to aircraft impact should also be