Issue 69

S. D. Raiyani et alii, Frattura ed Integrità Strutturale, 69 (2024) 71-88; DOI: 10.3221/IGF-ESIS.69.06

S0

S30

S60

S90

S120

S150

S180

S210

S300

Figure 10: Failure mode of cylinders.

M ECHANICS OF CONFINEMENT

T

he SSWM wrapping exerts a passive confinement action on the concrete cylinder, which occurs due to the lateral expansion of concrete under axial load. A uniform radial pressure created against the lateral expansion of SSWM confined concrete develops the tensile hoop stress, which leads to an increase in axial stress and a corresponding increase in the lateral strain. Confinement modulus and confinement strength In addition to the inherent material properties of concrete, the performance of concrete is influenced by two key factors: confinement modulus and confinement strength. The confinement modulus, denoted as Cs and expressed in Eqn. 3, is defined as the ratio of the increment of confinement stress   r f  to the radial strain   r   , as illustrated in Fig. 11 [13].



f

r



(3)

C

s

r 



(a) Coordinate systems

(b) Axial compression stress

(c) Stresses in SSWM

(d) Stress Equilibrium

(e) Partial confinement due to SSWM

Figure 11: Confinement mechanism.

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