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This outcome has been achieved with the financial support of the Ministry of Education, Youth and Sports of the Czech Republic, project No. 1M0579

Update: 20.11. 2006 1.1.3.2-9

Summary

Based on data compiled in this work proposes

new temperature-dependent relationships /

functions for concrete strength (compressive and

tensile), modulus of elasticity, fracture energy and

Poisson ratio. The curves are designed on thebasis of literature published in [1]. A comparison

of the designed functions with their counterparts

found in existing codes, authoritative design

guides and literature is presented. Surprisingly

enough, functions for selected parameters (namely

fracture energy and Poisson ratio) were not found

in any code although they are necessary for

realistic numerical simulations of structural

responses. For the practical reasons, relationships

proposed in this work are designed as continuous

functions whilst data found in codes are presented

as discrete points in tables. It is believed that ananalytical formulation is friendlier for

implementing computational models, e.g. sort of

transient coupled thermal and structural analysis

and others. The temperature dependence of these

parameters is an important ingredient for the safe

design and assessment of structures undergoing

high temperature loading (fire, etc.).

Field of application

The behaviour of concrete structures at extreme

temperatures is presently a subject of researchconcerning the safe operation of various types of

structures (fire safety of tunnels, chemical

factories, industrial and high rise buildings, power

plants, etc.).

The utilization of the presented results is suitable

for a design of bearing and non-bearing concrete

and reinforced concrete structures that are

presumed to be loaded by high temperatures.

Another possible utilization is for an assessment

of the residual state of existing structures that

were already affected by high temperatures. The

presented functional dependencies of themechanical/fracture parameters of concrete on

temperature extend recommendations of existing

design documents and guidelines. Designed

functions may serve as input data for linear and

nonlinear calculations of structures subjected to

high temperature loading.

Methodological and conceptual

approach

The typical parameters of quantifying material

strength are compressive and tensile strength.

Stiffness is typically quantified by modulus of

elasticity. Another elastic constant related to strain

in biaxial stress state is the Poisson ratio.

Only parameters such as strength and stiffness are

unable to describe concrete behaviour in

complexity. They do not describe the material

from the point of view of toughness, brittleness or

ductility.

The typical parameters used to assess the

brittleness/toughness of concrete are fracture

toughness, fracture energy, the brittleness index

and characteristic length. Each of these

characteristics has a different physical/mechanical

meaning. The knowledge, especially, of fracture

energy is necessary for nonlinear simulations of

structures made of quasi-brittle materials.

A lack of input parameters is a frequent problem

in numerical modelling, mainly their dependences

on temperature (temperature history). Whereas forcommonmechanical parameters (compressive

strength, modulus of elasticity) the data are partly

available. In the field of fracture mechanics at

high temperatures the data are still insufficient

(tensile strength, fracture energy).

A large number of experimental data from

scientific publications were collected in the scope

of this work [1-12]. On the basis of these data,

functional dependencies of concrete

mechanical/fracture parameters on temperature

were designed. The functions are formulated as a

dependence of reduction coefficients kforindividual parameters at elevated temperatures. In

1 INTEGRATED DESIGN OF STRUCTURES AND SYSTEMS FOR CONSTRUCTION1.1 Theoretical bases of integrated design1.1.3 Methods of structural design stressing durability and reliability1.1.3.2 Degradation models; assessment of material imperfections and technological effects,definition of

critical values of degradation impacts, application

Author: Ing. Dita Matesov, Ph.D.; Brno University of Technology

EFFECTS OF HIGH TEMPERATURES ON MECHANICAL PARAMETERSOF CONCRETE COMPOSITES

8/11/2019 Efectos Temperatura

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This outcome has been achieved with the financial support of the Ministry of Education, Youth and Sports of the Czech Republic, project No. 1M0579

Update: 20.11. 2006 1.1.3.2-9

all cases the functions k(t) are designed such that

the reduction parameter k= 1 at temperature t=

20C.

An example of k(t) function for fracture energy

vs. temperature together with the weighted

averages of experimental data is given in fig. 1.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 100 200 300 400 500 600 700 800 900 1000

Temperature, t (C)Reductioncoefficientforfractur

energy(-)

averages from exper. data

regression

Fig. 1 Reduction coefficient for fracture energy ofconcrete vs. temperature.

References

[1] Matesov, D. Fracture/mechanical parameters

of quasi brittle materials at high temperatures for

numerical modelling. Dissertation. Brno

University of Technology, Faculty of Civil

Engineering, Institute of Structural Mechanics,

2005, p. 0-118.

[2] Wu, B., Su, X., Li, H., Yuan, J. (2002). Effect

of high temperature on residual mechanicalproperties of confined und unconfined high-

strength concrete, ACI Material Journal 99(4), pp.

399-407.

[3] Janotka, I., Bagel, L. (2002). Pore structures,

permeabilities and compressive strengths of

concrete at temperatures up to 800C. ACI

Material Journal 99(2), pp. 196-200.

[4] Phan, L. T., Carino, N. J. (2002). Effect of test

conditions and mixture proportions on behavior of

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pp. 239-248

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