Proposed Constitutive Law of Uniaxial Compression for Concrete under Deterioration Effects

Abstract

In order to study the ductile deformation characteristics and failure process of plain concrete under uniaxial compression, this paper proposes a new constitutive model. The new model was used to fit and analyze the constitutive curve of concrete under uniaxial compressive under various degradation forms and was compared with the traditional constitutive models. Finally, the new model was used to quantitatively analyze and predict the stress–strain curve of concrete in different degradation periods of a set of freeze–thaw measured data. The results show that, compared with the traditional constitutive model, the new model is simple in form and has few parameters, and the numerical value of the parameter can reflect the ductile deformation capacity of concrete. The fitting curve of the new model has the highest fitting degree with the measured stress–strain curve of concrete, and the goodness of fit (R2) is also the largest. The new model is suitable for fitting the stress–strain curve of concrete under uniaxial compression under various deteriorating forms, and the degree of fit between the constitutive prediction curve and the measured curve is high. It can be seen from the fitting results of the new model parameters that the ductile deformation capacity of concrete decreases first and then increases slightly, which is inconsistent with the law of gradual deterioration of strength. There is a minimum moment of ductility deformation capacity of concrete (MDC). The MDC of O-C40 concrete is about 114 freeze–thaw cycles, and the MDC of O-C50 concrete is about 116 freeze–thaw cycles; the degree of fit between the constitutive prediction curve and the measured curve is high. We hope that the improvement mentioned offers valid reference to the study of ductile deformation characteristics and failure process of compressed concrete under different deterioration forms.

Analysis of Concrete Failure on the Descending Branch of the Load-Displacement Curve

“…However, effective In this study, the application of the basic concepts of fracture mechanics to the substantiation of the total stress-strain relations for concrete under uniaxial compression is considered. Such relationships have been studied in numerous works, reviews of which can be found in the articles [12][13][14]. However, an analysis of the literature showed that the following questions that determine the purpose of this work remained insufficiently studied: How does one explain that concrete samples under uniaxial compression fail on the descending branch of the stress-strain diagram?…”

“…These deviations are permissible for practical use. In this case, the determination of effective stresses and elastic modulus is easy to implement using formulas (8) and (13). Peak values of stresses and strains are used as the initial data for calculations, which are determined experimentally using standard methods.…”

“…as well as Formula(13), shows that, with an increase in deformation, the effective stresses only increase. This explains the phenomenon of the destruction of concrete on the descending branch of the load-displacement diagram.…”

“…For a sufficiently accurate prediction of the behavior of concrete under various influences, a significant number of studies have been carried out to improve the corresponding models, which, however, remain the subject of discussion. When constructing stress-strain models, methods of analytical mechanics, numerical methods and methods of fracture mechanics can be used [11,12], as well as methods of curve fitting to the experimentally obtained data [13][14][15][16]. A typical load-displacement curve is shown in Figure 1.…”

Experimental Study on Mechanical Properties and Pore Structure Deterioration of Concrete under Freeze–Thaw Cycles

“…In the past few decades, numerous studies have been conducted on the evolution laws of mechanical deterioration [ 9 , 10 ] and damage mechanisms [ 11 , 12 , 13 ] of concrete caused by freeze–thaw cycles. Less attention has been given to the problem of assessing the dynamic mechanical properties after frost damage.…”