Calculation features for flexural reinforced concrete structures strengthed using normal and lightweight concrete under low-cycle loading conditions

Abstract

Reconstruction of old buildings and structures is relevant in connection with the great physical and moral deterioration of their building structures. The consideration of low-cycle loading is relevant for public and industrial buildings, where the level of load on load-bearing building structures does not remain constant over time. From literary sources it is known that loading with a number of cycles up to 2·10⁶ refers to low-cycle loading.

This article presents new dependences are given for determining the load levels corresponding to the microcracks and macrocracks formation. The proposed formulas can be applied to concretes of various classes in terms of compressive strength, as well as for concrete of various types with their corresponding modification.

The parameter k_crc was introduced into the calculation, which allows us to characterize the ability of concrete to resist the action of static low-cycle loads: the higher the coefficient k_crc, the less the effect of static low-cycle loading on the strength and deformation characteristics of concrete. The proposed calculation procedure is harmonized with the provisions of Eurocode 2.

According to the results of empirical studies the coefficient k_c,ρ for claydite concrete was introduced for the first time. The one establishes the effect of the density of claydite concrete on the crack formation limits values.

A description of the transformed strain diagram under low-cycle loading is proposed. Тhe transformed strain diagram takes into account the effect of low-cycle loads on the strength and deformation properties of concrete.

In the case of calculating the strengthened bending elements the negative effect of low-cycle loading on the compressed zone concrete strength in stage before strengthening can be taken into account.