The interaction between loading plates and supporting structures is very much dependent upon the relative rigidity of the system. This paper first illustrates how an indiscriminate application of the relative rigidity concept can lead to erroneous conclusions in such systems. The paper then applies the concept to explain reported observed failure modes in pipe systems under explosive loads. Numerical studies are presented which simulate the behaviour of square pipe systems under static and explosive loads using the concept of relative rigidity in conjunction with the finite element method. The results of the analysis confirm the hypothesis of the relative rigidity concept. Experimental verification of the theoretical predictions and numerical modelling results are obtained by simulating the explosive failure patterns in simple freezing experiments. The analysis presented in this paper demonstrates the importance of the concept of relative rigidity for explaining certain kinds of observed failure and fracture phenomena. Key words: cracks, explosives, geometric distortion, load transmitting plate, pipes, relative rigidity, soil – foundation interaction, stress waves.