Civil Engineering Reference
In-Depth Information
Fig. 15.3
Local transverse force measurements in the impact area according to DIN 25449 [
4
]
A punching cone is assumed which starts at the edge of the impacted area and has a
determined punching angle which was derived from dynamic punching tests. The
stirrup reinforcement within the area of influence of the cone must be able to take
the maximum impact load of the impact load-time function. Requirements for the
plastic straining are not explicitly stated.
More complex models take into account the masses, stiffnesses and plastic
deformation characteristics of the structures which are directly affected. Figure
15.4
shows in principal the functionality of such a model. To determine the loads on the
concrete and rebars in the impact zone the adequate vibration characteristics and the
beneficial effects of inertia are taken into consideration.
The author has derived a simplified design model in [
5
]. The characteristic
curves of the resistance in the punching zone are shown in Fig.
15.5
. In this
model of a double mass oscillator the inertia, the resistance of the concrete and
the contribution of the shear reinforcement as well as the flexural reinforcement
including energy dissipation due to elastoplastic material behaviour is taken into
account. The model was published amongst others in [
6
]. This model was used by
one of the teams participating in the IRIS project (cf. [
7
,
8
]) in Finland as a
pre-calculation method for ballistic tests and correlated fairly well with the results
of the experiments, even in comparison to other complex numerical models.
In addition to the simplified models the use of complex FE models is possible.
To determine the local loads it is often sufficient to use a rotationally symmetric
model with appropriate boundary conditions. For a convoy reactor building a
section from a sphere or rather from a hemisphere can be used as a model as
shown in Fig.
15.6
. An average radius of 32.50 m and a thickness of the steel
reinforced concrete of 1.80 m were chosen for the sectional model shown. The
reinforcements are also considered in detail in the model. When realistic material
