constructionСтроительство и реконструкцияBuilding and Reconstruction2073-7416Орловский государственный университет имени И.С. Тургенева10.33979/2073-7416-2024-111-1-64-77construction-694Research ArticleБЕЗОПАСНОСТЬ ЗДАНИЙ И СООРУЖЕНИЙBUILDING AND STRUCTURE SAFETYДеформативные характеристики нагруженного бетона при нестационарном нагревеStrain parameters of loaded concrete under transient heating conditionsЛевитскийВ. Е.LevitskyV. E.

Левитский Валерий Евгеньевич, кандидат технических наук, доцент, доцент кафедры «Строительные конструкции, здания и сооружения», 

г. Москва.

Levitsky Valery E., Candidate in Technical Sciences, Associated Professor, Associated Professor of the Department of Building Construction, Buildings and Structures,

Moscow.

dobriy_vecher@mail.ruФГАОУ ВО «Российский университет транспорта»Russian University of Transport202421022024016477Copyright © Левитский В.Е., 20242024Левитский В.Е.Levitsky V.E.Данная работа распространяется под лицензией Creative Commons Attribution 4.0.This work is licensed under a Creative Commons Attribution 4.0 License.https://construction.elpub.ru/jour/article/view/694

Теория накопления повреждений в бетоне как неоднородно-хрупком материале применительно к условиям высокотемпературного резкорежимного нагрева дополнена предпосылкой об инвариантности предельных структурных напряжений, позволяющей представить развитие нелинейного компонента деформации и снижение прочности как единый процесс. Характеристикой этого процесса является коэффициент упругости (коэффициент секущего модуля) бетона, приобретающий в рассматриваемой постановке характер энтропийного параметра повреждённости материала. Следствия данной предпосылки сформулированы в виде базовых термомеханических соотношений, благодаря которым появляется возможность представить реакцию бетона на действие температуры и нагрузки как результат действия двух деградационных механизмов: испарения влаги из геля цементного камня и разрушения структурных связей с ростом температуры, которые реализуются соответственно в виде линейного и нелинейного компонентов силовой деформации.

Предложена методика нормализации (представления в относительном к начальному значению виде) кривых развития силовых деформаций бетона, которая позволяет обоснованно разделить эти компоненты при анализе кривых деформирования и найти необходимые для их описания температурные параметры в условиях нагрева в нагруженном состоянии. Выявлено, что при той же нагрузке и температуре повышение деформативности при нагреве бетона в нагруженном состоянии по сравнению с нагружением после нагрева происходит за счёт увеличения линейного компонента при сохранении его доли в составе полной деформации, характеризуемой коэффициентом упругости, постоянной. Показано, что допущения, принятые в существующих моделях деформирования нагруженного бетона при нестационарном нагреве, являются частными решениями и определены условия, при которых их применение становимся возможным.

The theory of damage accumulation in concrete as a heterogeneous-brittle material, as applied to conditions of high-temperature, abrupt heating, is supplemented by the premise of the invariance of ultimate structural stresses, which makes it possible to imagine the development of a nonlinear component of deformation and a decrease in strength as a single process. A characteristic of this process is the elasticity coefficient (secant modulus coefficient) of concrete, which in the formulation under consideration acquires the character of an entropy parameter of material damage. The consequences of this premise are formulated in the form of basic thermomechanical relationships, thanks to which it becomes possible to consider the reaction of concrete to the action of temperature and load as a result of the action of two degradation mechanisms: evaporation of moisture from the gel of cement stone and destruction of structural bonds with increasing temperature, which are realized respectively in the form of linear and nonlinear components of force deformation.

A method of normalization (representation in a form relative to the initial value) of the development curves of force deformations of concrete is proposed, which allows us to reasonably separate these components when analyzing the deformation curves and find the temperature parameters necessary for their description under heating conditions in a loaded state. It was revealed that at the same load and temperature, an increase in deformability when heating concrete in a loaded state compared to loading after heating occurs due to an increase in the linear component while maintaining its share in the total deformation, characterized by the elasticity coefficient, constant. It is shown that the assumptions made in existing models of deformation of loaded concrete during unsteady heating are partial solutions, and the conditions under which their use becomes possible are determined.

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The authors declare that there are no conflicts of interest present.