Effects Of Biaxial Loading On The High Temperature Behaviour Of Concrete

Abstract

Biaxial compression tests with ordinary concrete have been carried out under steady state and transient temperature conditions. The test results show that even small load levels in a second axis alter the mechanical properties of concrete significantly. The stress-strain relationships show a significant dependence on the temperature level and the stress ratio. The strength under biaxial compressive stress is higher than the strength under uniaxial compression. The volumetric strains increase with increasing stress ratios and increasing temperatures. The failure temperature of specimens being biaxially loaded is higher than the one of specimens that are uniaxially loaded. The modes of failure indicate that the tensile deformation is vital for the failure mechanism of concrete.

A confinement-dependent load-induced thermal strain constitutive model for concrete subjected to temperatures up to 500 °C

“…This assumption is in contrast with the results of the only two sets of experiments involving transient thermal conditions applied under multiaxial compression known by the authors [8,16]. An analysis of these results shows that the experimentally measured LITS state under multiaxial conditions exceeds that predicted by merely superimposing uniaxial LITS states [19].…”

“…In the present paper, the 3D extension method proposed by the authors in [17] is adopted for formulating a LITS model able to capture the behaviour of multiaxially confined concrete subjected to transient temperatures up to 500°C, temperatures representative of nuclear PCPVs subjected to complete fault of their water cooling system. The approach is validated and discussed in the light of the experimental studies by Kordina et al [16].…”

“…The LITS model described in Sections 2 and 3 has been calibrated and verified by modelling transient tests performed by Kordina et al [16] on concrete specimens subjected to uniaxial and biaxial stress states. The objective of these studies was to compare the strain predictions obtained by the traditional method of calculating LITS based on superposition, and the herein implemented confinement-dependent method for temperatures up to 500°C.…”

“…The reference tests consisted of rectangular parallelepiped-shaped concrete specimens subjected to thermal transients under constant uniaxial or biaxial loading conditions [16]. The mechanical loads were applied through four hydraulic cylinders, each with a maximum force of 1000 kN, placed at the inner surface of a high stiffness loading frame.…”

“…However, the few multiaxial tests that are available in the literature show that the situation is more complex and LITS depends on the confinement of the stress state [8,16]. For this reason, a novel approach for modelling LITS as a stress-confinement strain component has been presented by the authors in [17].…”