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Abstract. The paper presents the outcomes of the research aimed at the verification of the computational model simulating a reinforced concrete beam employing spar and 3D finite elements, with account taken of physical nonlinearity. Structural calculations involved in R&D and design effort must factor in non-linear structural behavior both of the material and of structural elements. In particular, this is valid for the analysis of special types of impact (seismic, accidental etc.). However, design models under development may incorporate significantly varying models of nonlinear materials as well as different kinds of finite elements, and both have to be verified. This article considers two models of a hinged (pinned) beam. In the first case, the modeling was based on 3D elements for concrete and on spar elements for reinforcement using Euler-Lagrange coupling of finite elements belonging to concrete and reinforcement (three-dimensional model). The second case the simulation based on spar finite elements (spar model). Both the spar model and 3D model allow for non-linear nature of concrete and reinforcement. In case of concrete the material was set using the Continuous Surface Cap Model, while the reinforcement was modeled involving a bilinear diagram of material behavior. Problem settingDesign calculations of buildings and structures performed to take account of a particular case or type of impact require that the non-linear nature of structures' and materials' behavior be factored in. The present research presents a verification of a reinforced concrete beam. Two models of a hinged (pinned) beam were devised during the research: a three-dimensional model consisting of 3D elements with concrete and reinforcement coupled, and a spar model (Figure 1).

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Abstract. This article considers the issue of taking non-linearity into account when performing design calculations for buildings and structures exposed to intense seismic impact. The existing rule codex 14.13330.2014 «SNIP II-7-81* "Construction in seismic areas" regulates the possible behavior beyond the elastic range with by introducing a damage tolerance factor. However, extensive research conducted by the authors of this article and other experts in the seismic resistance theory reveal that the values of this factor for buildings of various structural layouts must be corrected. The paper investigates the behavior of multi-element systems exposed to seismic impact, the structural layouts of them being as follows: wallsupported slab systems, reinforced concrete rigid frame buildings and buildings with a metal space frame. Calculations were made which describe the behavior of the buildings exposed to an intense earthquake modeled in the form of accelerograms standardized as 8 points on the MSK 64 scale. The calculations were performed using the LS-DYNA software package which makes use of the direct dynamic method and provides means for making all the calculations in the time domain and for taking the physical, geometric and structural non-linearity into account. The results obtained indicate that wall-supported slab buildings and rigid frame RC buildings collapse due to emerging and developing plastic deformations, while metal frame buildings lose their stability before their bearing capability is exhausted. The research carried out by the authors enabled them to pinpoint the reason for the discrepancy between the obtained values of the damage tolerance factor and the values stipulated by the regulation, as well as to draw a conclusion that these values should be refined.