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This paper deals with the numerical impact analysis of tubular thin-walled steel-made elements with induced folding for energy dissipation application. The excellent deceleration of the impacting mass of axial collapsing structures favors their use in energy dissipation applications, such as impact resistance and rockfall protection. Dynamic Finite Element analyses have been carried out to evaluate the performance of vertical assemblies of cold-formed steel cell-shaped elements welded on each other to form collapsible tubular elements. In turn, these have been gathered in groups and restrained by galvanized steel wires to create modules. The axial collapse, which is the most effective energy absorption mechanism, has been triggered by shaping the elements' edge as serpentine. In the analysis, several assembly configurations have been subjected to a freefall rhombicuboctahedron-shaped rigid block impact; Falling height, impact angle, and block mass have been varied to investigate their effect on the performance. The numerical results show a good agreement when compared to those obtained through a real-scale experiment.

The calculation of structures made of the assembly of several walls requires finite element modeling, henceforth, it gives rise to a large number of degrees of freedom. The actual work shows that the number of parameters is reduced by using boundary elements to derive the stiffness matrix of the element. The proposed technique gives origin to a positive definite and symmetrical matrix due to the use of constant boundary elements. Moreover, the resulting matrix can be assembled together with finite element ones in order to obtain the description of complex three-dimensional structures. Sub-structuring and multi-region modeling are possible and continuity relaxation between elements as well as interface and nonlinear constitutive laws can be comprised. Some examples are reported in order to verify the accuracy and feasibility of the procedure for the elastic case.

In this paper an application coupling the Isogeometric Boundary Element Method with the continuum damage mechanics is proposed in three-dimensional geometry. The novelty of the approach stands both in the discretization phase in which independent NURBS functions are used to model geometry plus governing variables and in the computation step where a special mapping procedure is applied to compute the arising volume integrals. The the use of the internal cells is avoided. The implementation is verified on a simple test case.