New stress-strain model for concrete at high temperatures

Abstract

Original scientific paper Concrete is one of the most widely used materials in civil engineering structures. Extremely high temperatures can seriously damage the concrete structure, leading to degradation of its mechanical properties. Considering high temperatures in civil engineering applications is strongly connected with the fire scenarios in which temperatures in concrete can reach 1000 °C. For using computer software for analysis of the reinforced concrete structures, it is essential to formulate constitutive stress-strain models of steel and concrete, which can be done using fundamental approach or by fitting curves to experimental data. In this paper, new stress-strain model was proposed using the two-parameter equation for fitting curves to experimental data. Verification of the model is done using experimental results available in the literature for temperatures up to 800 °C. Comparison with the models available in the literature was provided. The new model showed better agreement with experimental results, especially for the temperatures higher than 500 °C. Keywords: concrete; high temperature; stress-strain curve Novi model za opisivanje krivulje naprezanje-deformacija betona pri povišenim temperaturamaIzvorni znanstveni članak Beton je jedan od najrasprostranjenijih materijala koji se koriste za izradu građevinskih objekata. Djelovanje visokih temperatura može ozbiljno oštetiti strukturu betona, što dovodi do degradacije njegovih mehaničkih karakteristika. Razmatranje glavnih karakteristika ponašanja građevinskih konstrukcija pri visokim temperaturama je povezano s djelovanjem požara, pri kojima se javljaju temperature u betonu i do 1000 °C. Za uporabu računarskih softvera za analizu armirano betonskih elemenata izloženih požarima neophodno je formulirati konstitutivne σ-ε modele kako čelika tako i betona, što se može postići fundamentalnim pristupom, ali i prilagodba krivulja prema eksperimentalno dobivenim podacima. U ovom radu predložen je novi dvoparametarski model za opisivanje krivulje naprezanje-deformacija. Novi model je potvrđen na eksperimentalnim podacima dostupnim u literaturi za temperature do 800 °C. Dana je njegova usporedba s drugim modelima dostupnim u literaturi. Rezultati pokazuju bolje poklapanje s eksperimentalnim podacima, posebice pri temperaturama većim od 500 °C.

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

“…In this work, an analytical model is theoretically substantiated, which coincides with the experimentally substantiated Furamura model [17] known from the literature (an analysis of the Furamura model is also available in [14,18]). In addition to the data known from the literature, the model was analyzed using definitions known in fracture mechanics, such as damage function, effective area, effective stresses, and effective elastic modulus.…”

“…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?…”

“…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.…”

A Damage Model to Trabecular Bone and Similar Materials: Residual Resource, Effective Elasticity Modulus, and Effective Stress under Uniaxial Compression

“…It can be assumed that the model ( 1)-( 18) is too simple to analyze such a complex object as a trabecular tissue, for which some transformation of the structure is possible [40,41] and changes in the interaction of structural elements during tension. The use of models with parameters [35,42] may be promising both for improving the results of the analysis and for expanding the scope of such models [43]. As can be seen, the model (16a) adequately reflects the trends of growth crease of apparent stresses at the stages before and after the point of the stress ex (Figure 10).…”

“…It can be assumed that the model ( 1)-(1 simple to analyze such a complex object as a trabecular tissue, for which some t mation of the structure is possible [40,41] and changes in the interaction of structu ments during tension. The use of models with parameters [35,42] may be promisi for improving the results of the analysis and for expanding the scope of such mode Nevertheless, for compression, quite adequate results were obtained us model ( 1)-(18) (Figures 3, 4, and 6-12). In addition, using the energy criterion in t (3) and the ideas of fracture mechanics [23,24], the following are justified: the resource function (6) and the damage function (7); the formulas for determining fective elastic modulus using experimental data (8), (10), (11), and the apparent m of elasticity (14); the functions of load-displacement (15a) and of apparent stres (16a); and the hypothesis about the consolidation of the particles of the destroyed at the final stage of compression tests (Section 3.4).…”