PSI - Issue 14

D. Anupama Krishna et al. / Procedia Structural Integrity 14 (2019) 384–394 A. Krishna et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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4.3. Stress-Strain Response

The behaviour of concrete is characterized by the material property degradation with increased temperature. The mechanical response of concrete is usually expressed in the form of stress-strain relations, which are often used as input data in mathematical models for evaluating the fire resistance of concrete structural members. The compressive stress-strain relationships of concrete under compression at elevated temperature as proposed by different researchers and that from the present study are given in Table 5.

Table 5: Compressive stress- strain relationships of concrete at elevated temperatures Literature Models at elevated temperature EN 1992-1-2 -2004 ) )] / (2 ( ' / [3 3 max max      cT c c T cT Tf   Anderberg and Thelandersson( 1976)   cT 2 

      

   

  

E





cT

crT cT

2 ' 

cT



 2









' 1 30( cT       cT f 

f

) / 130

'

 cT

max  





Kodur et al.( 2004)

c

max

 / : crT cT





1 (1/1 ) / ' n

E n   

2.0

cT 



n

Terro (1998)

cT

c T

2

max,  

  

T

Present study

' 1       ct f



c



T

max,

Figure 4 illustrates stress-strain response of the experimental model at various temperatures till 800 O C.At all temperatures the model exhibits a linear response followed by a parabolic response till peak stress, and then a quick descending portion prior to failure. The rise in temperature and the rate of increase has a significant effect on the stress-strain response of concrete. The strain corresponding to peak stress starts to increase, especially above 500 ∘ C.This increase is significant and the strain at peak stress can reach four times the strain at room temperature.

Fig. 4. Stress- strain response of the concrete from the present study with temperature.

4.4. Modulus of elasticity

Modulus of elasticity of concrete, a measure of its stiffness or resistance to deformation, is used extensively in the analysis of reinforced concrete structures to determine the stresses developed in simple elements and the stresses, moments, and deflections in more complicated structures. Since stress-strain curve of concrete is nonlinear, the modulus of elasticity is determined either by the initial tangent modulus, secant modulus, or tangent modulus method. The principal variables affecting the modulus include (1) richness of the mix (richer the mix, the greater the modulus increase with age); (2) water/cement ratio (higher values reduce modulus); (3) age (modulus increases rapidly during first few months and shows continual increase up to ~3 years); (4) kind and gradation of aggregate