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This paper gives first a short overview of some basics of blast wave propagation and blast wave reflection. The reflected overpressure-time history, which is the design load, depends on the shape and geometry of the structures where the blast wave is reflected. It presents some shape studies which show the influence of shaping on the explosion design load. These shape studies include horizontal shapes (e.g. cross section of columns), vertical shapes (e.g. facades) and spatial shapes of buildings. The paper further shows that shrub plantings reduce blast loads. It also discusses the use of flexible materials and constructions and the influence of the urban situation on the design.

The development of material laws for concrete subjected to highly dynamic loadings is a topic of current research. Explosive charges or high-velocity impacts produce high pressures in the kilobar region within microseconds. Hydrocode simulations by coupling of Lagrangian with Eulerian grids have been carried out, considering the interaction between explosive loading and the structure. Concrete is a composite material with a variety of inhomogenities. By homogenization of the microstructure, a macroscopic approach in the framework of continuum mechanics has been adopted. Appropriate constitutive laws that enable the nonlinear ratedependent as well as the local damage behaviour to be modelled had to be introduced. A new damage law that describes void compaction as well as the classical theory of plasticity had been taken into account. An equation of state had to be provided to ensure the compliance with conservation laws on which hydrocodes are based. To obtain the necessary material data, experimental investigations were indispensable. Therefore, a series of ®eld tests with specimens which were concrete slabs exposed to explosive contact charges has been conducted.

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The standard approach in protective design is to model blast loads with a triangular pulse shape which is characterized by the peak reflected overpressure and the reflected impulse. The US and European threat levels, GSA and ISO EXV, define pressure-impulse combinations for blast load characterization. However, this approach neglects the underpressure phase. The actual decay of a blast load is nonlinear and can be modeled more accurately with an exponential approach which takes into account the underpressure phase. When considering underpressure effects, however, special attention should be paid to the modeling of the different reflection effects for the over- and underpressure phase. The authors derive a new reflection coefficient for the maximum underpressure. Based on a single degree of freedom system, the authors then determine the influence of the reflected underpressure phase for different systems. Especially for flexible systems subjected to weak blast loads, the underpressure significantly dominates the structural response. In these cases, the standard triangular approach is not on the safe side. This paper presents new demarcation criteria to rapidly assess the influence of the underpressure phase.