The dynamic effects of an airplane crash give rise to load over time functions which depend on the type of aircraft involved (weight, geometry, impact area) and how fast it is travelling when it hits the building (impact velocity). The load over time function must show in each case that the building affected can withstand the loads, both locally (punch-through) and globally (stability, load bearing to foundations) and that the shock induced by the impact does not damage structural members or components inside the building.

We can derive the load over time function by using the RIERA model [47,48]. This assumes a ‘soft impact’, that is a rigid wall and the impacting body then deforming. This assumption can be justified by the fact that the buildings concerned are made of solid reinforced concrete with very thick walls (generally > 1.50 m) and the aircraft body may be taken to be very yielding compared with the building. On a soft impact basis, the reaction force as the ordinate of the load over time function consists of two components: a bursting load component and a component as the product of the aircraft weight and the square of its velocity. The quadratic component shows how important the velocity assumption is.

Figure 5.7 shows the load over time function obtained using the RIERA model for a Phantom F-4 hitting at 215 m/s as mentioned above. The tests conducted on this in Sandia confirmed this theoretical function: it matches the function specified in the RSK guidelines [5], and is often used as a design principle when building new nuclear power plants in Europe.

The RIERA model can also be used to derive load over time functions for commercial aircraft impacts. Compared with a military aircraft impact, the load over time functions obtained for larger commercial aircraft flying at 100-150 m/s give rise to much higher maximum loads and greater pulses accordingly. As a commercial aircraft would have a much larger impact area, on the other hand, the local surface area loads are much less than those of a military aircraft, so that where a military aircraft hits would be much more decisive than a commercial aircraft when conducting the punch-through proof required. It has also been found that the much larger pulse of commercial aircraft in general induces much greater induced vibrations in a building than a military aircraft.