Abstract:

An analytical model is developed to determine the stress-strain behaviour of Fibre Reinforced Plastic (FRP) spirally-confined concrete.  A theoretical model was first proposed by M.D. Kotsovos to address the problems of concrete subjected to constant hydraulic confining pressure.  He used the experimental results to make a sound prediction of the stress-strain characteristics of concrete under various circumferential pressures.  However, by using this model, only actively confined concrete can be studied.  The present approach utilises the same concept, but by incorporating the incremental changes of confining pressure during the course of loading, a modified technique has been developed for passively confined concrete.  This approach allows different kinds of materials to be used as spiral confinement so as to provide the necessary confining pressure.  Having determined the concrete strength, the mechanical properties and the spatial arrangement of the lateral confining reinforcement, a complete stress-strain relation can easily be generated.

In order to illustrate the accuracy of the present model, a series of compression tests on concrete specimens with either single spiral or interlocking spirals were carried out, and good consistency was found.  Besides a subtle relation between the spiral leg spacing, the distance between interlocking spirals, and the strength of concrete is observed.

Further, a novel beam design is proposed, and the newly established formulation is employed to analyse the flexural behaviour.  A significant enhancement of strength and ductility capacity is explored.  A full-scale beam reinforced with aramid ropes and aramid spirals was then cast according to the prediction of the present method and those estimations were compared with experimental results.