FEATURES OF MODELING REINFORCED CONCRETE PROTECTIVE STRUCTURES BY AN EXPLICIT METHOD IN CALCULATIONS FOR TEMPERATURE FORCE LOAD

Mathematical modeling is currently the basis for approximate methods of calculations and determination of the stress-strain state (SSS) of structures under temperature effects. It allows numerical finite element (FE) methods to obtain valid solutions to many complex problems in cases of force and temperature loads acting on statically indeterminate reinforced concrete structures, including taking into account plastic deformations and non-stationary three-dimensional temperature fields. The article describes the main stages of explicit modeling of reinforced concrete protective structures under power loads and thermal problem features, based on the capabilities of the LS-DYNA software package. The algorithms of mathematical modeling with a detailed step-by-step justification of the applied dependencies of the explicit method are described. It is indicated that the correct choice of interaction criteria and substantiated models based on the analysis of the structure allows obtaining adequate results of the numerical experiment, confirmed by other researchers. Dependencies are given that allow calculating the function values at a future time step using already known function values at the current step and its derivatives. The calculation of the FE node speeds using the explicit method of integrating dynamic equations is performed using an expression that is an explicit numerical method for solving the dynamic equations. A basic expression is given for calculating the accelerations of FE nodes when performing approximation of time derivatives using the finite difference method. For a complete set of FE, the fundamental possible displacements of nodes, the generalized equation of conservation of energy of a solid deformable body, which is discretely imposed on the FE mesh, are taken into account. For the case of temperature loads in fire mode, an approach to solving a thermal problem is presented. It is shown that a substantiated methodology using elements of explicit and implicit methods allows one to correctly solve the posed thermal problem, taking into account the nonlinear deformation of the materials of the reinforced concrete protective structure and spatial temperature fields from the external temperature load.