This thesis describes a detailed investigation into the inelastic performance of circular steel tubes filled with rubberised concrete materials. The study considers rubberised concrete infills with relatively high values of up to 60% volumetric rubber replacement of conventional mineral aggregates. The work includes experimental, numerical and design assessments on composite members subjected to various monotonic and cyclic loading scenarios.
The experimental evaluations involved over 90 members and complementary material specimens. Tests were firstly carried out on rubberised concrete-filled circular steel tubular (RuCFST) members under a wide range of axial and bending loading conditions, as well as their combinations, to examine cross-sectional behaviour. In all cases, the rubber content, represented in terms of the volumetric replacement ratio of mineral aggregates, was varied from 0% (i.e. conventional concrete) up to 60%. A detailed account of the test results and observations are reported, including the strength and failure modes, as well as the confinement and ductility characteristics. Particular attention is given to the influence of the rubber content on the cross-sectional capacity and ductility of RuCFST members in comparison with conventional counterparts.
The cyclic behaviour of RuCFST members was also examined experimentally. Rubberised concrete-filled steel tubes were tested under lateral cyclic deformations with and without co-existing axial loading. A detailed account of the cyclic tests on twelve specimens is provided together with complementary material and cross-section tests. The rubber replacement ratio was varied up to a relatively high value of 60%, under axial loads reaching up to 30% of the nominal capacity. After describing the specimen details and testing arrangements, the experimental results are discussed in detail. The results provide significant insights into the main behavioural characteristics, including the moment displacements response, lateral stiffness, moment-axial strength interaction, plastic hinge length, local ductility and energy dissipation. Overall, the test results demonstrate the favourable inelastic cyclic performance of steel tubes infilled with rubberised concrete, and offer valuable experimental data.
Detailed finite element (FE) models were developed and validated against the test results. Suitable inelastic material modelling techniques with different damage definitions were introduced to account for the specific response of RuCFST members under axial-bending loading conditions. Moreover, modified continuum finite element modelling procedures were employed to incorporate high cumulative deformations and damage development of rubberised concrete under cyclic loading. In addition to the full numerical cyclic analyses, idealised monotonic simulations are also proposed and verified to enable computationally efficient representation of the envelope response.
Parametric assessments were then undertaken to examine the influence of key material and geometric parameters, including the rubber content, material strength and cross-section properties, on the inelastic behaviour. The results of the parametric studies are used to quantify the main response parameters, with a focus on the moment-axial strength interaction, member stiffness, local buckling criteria and other ductility measures. Based on the findings, modifications are proposed to current design procedures in order to provide a reliable prediction of the inelastic response characteristics of rubberised concrete-filled steel tubes. Apart from providing experimentally validated numerical approaches that can be used in future studies, the proposed design procedures are suitable for implementation in practical assessment and design applications.