The permissible ductility ratio, µ, is defined as the ratio between
maximum permissible deflection of a structural system and the
deflection at the effective yield for the system (see Section 126.96.36.199).
Time-History Analysis Method. A time-history response analysis method
of evaluating the global response or collapse of the target structure uses
the inertial and stiffness characteristics of both the aircraft and the target
structure (including its foundation flexibility). One of the acceptable
methods that has been extensively used is outlined below.
This method, called the force time-history analysis method, consists of
two major steps. The first step is to determine impact force time-history
based on the aircraft mass distribution, crushing/buckling characteristics,
impact velocity, aircraft length, and other aircraft structural data, and
conservatively assuming that the target structure is rigid. Impact force
time-history is determined using the momentum principle, similar to the
method developed by Riera (Reference 3) and modified by Muto et al.
(Reference 9). Accordingly, the impact force, F(t), acting on the rigid
fixed target at time, t, is expressed as
load necessary to crush or buckle the fuselage;
distance from the nose of the aircraft to the point up to
which crushing has progressed at time, t;
longitudinal mass per unit length of the uncrushed
velocity of the uncrushed portion of the aircraft
at time, t;
empirical correlation factor (use a value of 0.9 unless