Civil Engineering Reference
In-Depth Information
real concrete used in the construction has a higher strength than originally planned.
This can be explained by the fact that, with the goal of achieving low stripping
times, often a higher strength concrete is installed and additionally over the course
of years a further increase of the concrete strength can be expected. Extensive
experience with concrete samples from existing structures proves this phenomenon.
In the case of thin walls and low reinforcement grades the probability that a large
commercial aircraft will cause heavy damages on the structures increases. When
appropriate verifications with lower impact speeds, i.e. smaller than 175 m/s, can be
carried out. In some publicly available studies from pertinent conference papers,
e.g. SMiRT, speeds of 150 m/s or even 100 m/s are assumed. At these speeds even
walls with a thickness of 1.50 m may still be sufficiently sound.
15.3 Global Structural Behaviour: Structural Stability
It must be demonstrated that the global structural stability of a building is assured in
the case of a postulated aircraft impact. To be on the safe side, dynamic analyses are
carried out with a global model without taking into account the local effects but
including the mounting in the foundation. The global structural stability of a large
structure such as a reactor building with a very large mass in comparison to the
impacting aircraft does not pose a large problem from a structural engineering
standpoint. For the disadvantageous impact directions and locations the appropriate
verifications of the load-bearing capacity and position stability can be carried out on
a convoy reactor building for a fast flying military aircraft as well as for a large
commercial aircraft. Due to the fact that the outer enclosing walls are designed to
withstand the local effects of a random impact position they are usually sufficiently
reinforced to ensure the global structural stability. Figure
15.7
shows an example of
such a global mathematical model.
Small buildings whose mass is small in comparison to the impacting aircraft
constitute an exception. In these cases it can become necessary to secure the
building against tipping and possibly to reinforce the connection to the foundation.
This could become difficult to achieve with respect to the load due to the impact of a
large commercial aircraft.
15.4
Induced Vibrations
In addition to the evaluation of the resistance of the outer structure the effects of
vibrations due to a crash onto the structure must be considered in the design of the
interior assemblies and components. Although the regulations do not explicitly
cover the case of an airplane crash the analyses and verifications used for the design
case earthquakes can be adapted. In combination with appropriate engineer-like
adaptations, KTA 2201, Parts 3 and 4 ([
9
,
10
]) can be used as a regulatory reference.
