ABSTRACT
The effect of specimen size on strength in self similar fiber-reinforced polymer (FRP) confined circular concrete columns where FRP wrap thickness are scaled with column size, is studied. Unlike many previous studies, a deterministic size effect is found to exist in large specimens. The mode of failure is seen to be critical: a size effect occurs whenever a specimen fails due to brittle fracture and shear banding. However ductile failure, induced by plastic dilation of concrete followed by FRP rupture, does not lead to a size effect. It is shown that there is increasing tendency for brittle failure with increase in specimen size; however if the confining pressure is maintained above a threshold value, this can be prevented. A simple analytical model is used to study the observed behavior. A scaling procedure, applicable to sufficiently confined specimen, is proposed.
The procedure uses strength data from laboratory-scale specimens to estimate the strength of large field specimens. A newly obtained expression for the confining pressure, which does not assume that the FRP wrap is a thin shell, is seen to be crucial to the scaling procedure. In addition to the energetic size effect, the effect of randomness in tensile strength distribution is also investigated. Incorporation of random material strength using a non-Gaussian random field is seen to make little difference to the peak strength and size effect. However the correlation length of the random field is seen to have a strong influence on the post-peak response in unconfined specimens. The effect of imperfections in the FRP-concrete interface on the strength and stress-strain response is also studied. An attempt is made to identify critical imperfection geometries and imperfection locations. Finally, the influence of the FRP-concrete bond on the response of FRP confined hollow columns is studied, and the size effect in such columns is investigated.
Key words: Concrete, FRP, Columns, Energetic Size effect, Scaling, Stochastic size effect
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