Issue 62

Y. Boulmaali-Hacene Chaouche et alii, Frattura ed Integrità Strutturale, 61 (2022) 61-106; DOI: 10.3221/IGF-ESIS.62.07

equal2 according to Eurocode 4 [8].The stress-strain relationship of confined concrete can be deduced from the charteristic parameters of unconfined concrete with confining conditions. The stress-strain curve of confined concrete is shown in the (Fig.3).For concrete confined by circular steel tube sections, the maximum strength cc f and the corresponding strain  cc [17–19].

Figure 3: Stress-strain curves of concrete unconfined and confined by circular hollow sections [17].

In order to simulate the axial compression behavior of tubular steel sections filled with concrete with circular cross sections and according to the studies of Richart et al [20], the calculation formulas are as follows:   1 1 cc ck f f k f (6)

        1 2 1 ck ck k f f

 

(7)

cc

For ich the values of 1 k and 2 k are 4.1 and 20.5 respectively. For circular steel columns filled with concrete, B. Kebaili [11] proposed that the values of l f be determined by the following relationship:       1 2 0.578 y t f f D for   21.7 47 D t (8) where: D = external diameter of the tube section ; t = wall thickness of the steel tube; y f = yield strength of the steel section. The stress-strain curve of confined concrete, as shown in Fig.3 is expressed in three parts. The first part defines the linear property of confined concrete and the proportional limit stress can be assumed to be equal to cc 0.5f . The initial Young's modulus of the confined concrete is calculated from the empirical formulation given by EC4 and calculated from the formula    0.3 cc cc E 22000 f /10 . The Poisson's ratio of the confined concrete has the value (0.2). The second part of the stress-strain curve describes the non-linear part, before the concrete reaches its maximum strength, from the proportional limit stress 0.5 cc f to the maximum strength of the confined concrete cc f . This part is given as follows:

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