Behaviour and modelling of concrete in circular hybrid multitube concrete columns

Abstract

Fibre-reinforced polymer (FRP)-concrete-steel hybrid multitube concrete columns (MTCCs) are a new form of hybrid columns recently proposed by the second author. An MTCC consists of an outer FRP tube, a number of inner steel tubes, with the space inside all tubes filled with concrete. The new column has many advantages over existing column forms, including its ample ductility, excellent durability and cost effectiveness. A number of experimental studies have demonstrated the structural advantages of MTCCs and provided the first insight into their structural behaviour. However, the experimental studies do not allow the complex confinement mechanism on the concrete in MTCCs to be thoroughly examined, due to the difficulty in measuring the nonuniform distributions of axial stresses and confining pressures. Against this background, this paper presents an in-depth study on the behaviour and modelling of the concrete in MTCCs. This study started with the development of three-dimensional (3D) finite element (FE) models to simulate the compressive behaviour of circular MTCCs. The FE models were validated using the test results and then used to examine the confinement mechanism of circular MTCCs due to the complex interaction between the multiple tubes and concrete in MTCCs. Furthermore, mechanism-informed one-dimensional (1D) stress-strain models for the concrete in MTCCs were proposed for design use; the models were found to provide reasonably accurate predictions of the FE and test results.