Dynamic Behavior of Concrete: Constitutive Models - Dynamic Behavior of Concrete and Seismic Engineering - page 59

The ejection of a block follows bending or shear failure. The order of magnitude
of the ejection speed is closely linked to the speed of the structure element at the
moment of failure, therefore to its transient dynamic response. The formation of
small rubble and dust type fragments is linked to the characteristics of the dynamic
failure of the material. If the failure of the structure is accompanied by a blast wave,
the latter will carry the fragments along. The effect of that blast dragging along is
inversely proportional to the fragment size.
2.1.4. Loading range
2.1.4.1. Pressure level
The main feature of dynamic loading is that it involves very high-pressure levels,
completely out of the typical range of structures under quasi-static loading. The
shock of a motor vehicle against a concrete structure, for example, can generate a
several hundredths of a MPa pressure inside the latter. The consequence on a
material such as concrete is compaction, i.e. an irreversible volume strain. Figure 2.4
shows the behavior of a compacted concrete (the concrete called MB 50 has been
the subject of various studies within the frame of the “GEO” laboratories network
[BAI 99]).
Figure 2.4. Hydrostatic compression tests of MB50 concrete.
Mean stress-volume strain diagrams (from [BUZ 99])