Time-History Analysis Method

DOE-STD-3014-96

The permissible ductility ratio, , 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 6.3.3.3).

Time-History Analysis Method. A time-history response analysis method

6.3.3.2

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

m[x(t)][v(t)]2

F(t)

Pc[x(t)]

(6-14)

where:

load necessary to crush or buckle the fuselage;

x(t)

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

aircraft;

v(t)

velocity of the uncrushed portion of the aircraft

at time, t;

empirical correlation factor (use a value of 0.9 unless

justified otherwise).