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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4.2. Tensile Strength

The tensile strength of concrete is much lower than that of the compressive strength, and hence tensile strength of concrete is often neglected in strength calculations at room and elevated temperatures. Concrete is weak in tension and for NSC, tensile strength is only 10% of its compressive strength and for HSC, tensile strength is further reduced [Kodur (2014)]. However, from fire resistance point of view, it is an important property, because cracking in concrete is generally due to tensile stresses and the structural damage of the member in tension is often generated by progression in micro-cracking [Mindess et al.(2003)]. Under fire conditions, tensile strength of concrete can be even more crucial which may lead to spalling in concrete member [Khaliq and Kodur (2012)].Thus, information on tensile strength of HSC, which varies with temperature, is crucial for predicting the fire induced spalling in HSC members. Table 4presents the variation of splitting tensile strength of NSC as a function of temperature as reported in previous studies[Chang et al.( 2006), Bazantand Chern (1987), Terro (1998)], Eurocode provisions [EN 1992-1-2 2004] and the present study. The ratio of tensile strength at a given temperature, to that at room temperature, is plotted in Figure 3. The plot shows a range of variation in splitting tensile strength as obtained by various researchers for NSC with conventional aggregates as well as the results of the present study. As per the Eurocode [EN 1992-1-2-2004] Clause 3.2.2.2 the tensile strength of concrete should be normally ignored (conservative), but it is necessary to take account of the tensile strength, when using advanced calculation method. The reduction of characteristic tensile strength with temperature predicted by different models and the present study in elaborated Table 4. Table 4: Tensile strength models for concrete at high temperature Literature Models at elevated temperature EN 1992-1-2 -2004 ck t cr crT f f K ,  1 ,  ck t K C T C o o 100 20     500 100 1    T K ck,t C T C o o 600 100   Chang et al. (2006)   T f f cr crT 1.05 0.0025   C T C o o 100 20   cr crT f f 0.80  C T C o o 200 100     T f f cr crT 1.02 0.0011   C T C o o 800 200   Bazant and Chem (1987)   1.01052 0.000526    T f f cr crT C T C o o 400 20     1.8 0.00252    T f f cr crT C T C o o 600 400     0.6 0.0005    T f f cr crT C C T o o 1000 600   Terro (1998) f cT f cr f crT '

  

   

f c '

C T C T

C o

20

400

   

o

Present study

f f

( 0.0009    T f cr ( 0.0014    T f cr

0.9678) 1.1205)

crT

C o

400

800

o

crT

C o 800 

0  crT f T

Fig. 3. Variation of Normalized tensile strengths with temperature from various models.