Checking of the robustness of precast structural systems based on the energy balance method

Introduction. The robustness requirements should be fulfilled already at the stage of conceptual design of the structural system, taking into account the use of various strategies for its protection from progressive collapse. Compared to monolithic reinforced concrete structural systems, precast concrete systems are more susceptible to the effects of accidental actions. To ensure the integrity of the damaged system in the original prefabricated structural system, it is necessary to provide (reserve) a sufficient number of horizontal (internal and perimetric) and vertical ties with the required degree of continuity and plastic deformability. Materials and methods. Analytical models of the resistance of horizontal ties based on the equations of the energy balance of the system. Results. On a real example of a prefabricated floor, calculations of the required parameters of horizontal ties were performed according to the proposed dependencies, based on the model of the energy balance of the system and the design models included in the standards of various countries. Comparison of the results obtained showed that the calculation models of the norms in a number of cases can give an unsafe result, underestimating the required cross-sectional area of horizontal ties. This is due to the fact that all dependencies for calculating the tie forces are based on constant values of the ultimate deflection (usually from 1/6 to 1/10 of the span) without checking the limiting deformability of horizontal ties. Conclusions. Deformability of ties is one of the basic parameters that should be monitored when checking the robustness of structural systems made of precast concrete. The proposed method, based on the provisions of the energy balance, makes it possible to take into account the limiting deformability of horizontal ties when determining the membrane (chain) forces and calculate the maximum dynamic response of the damaged structural system.