Abstract
The axial compression strength of concrete columns has been proved to be significantly enhanced by external confinement. In this perspective, the use of Fiber-Reinforced Polymers (FRPs) has been extensively studied. In practical applications, the FRP-confinement is installed on loaded columns, which can already be significantly deformed, while theoretical models neglect this aspect. This paper concerns a new experimental investigation on the possibility that a pre-existing axial load affects the FRP-confinement of concrete. The research program also aimed at the development of a new analysis-oriented-model for the prediction of the compressive strength of FRP-jacketed concrete columns, depending on the level of the axial load, acting before the confinement. For this purpose, series of small-scale concrete cylinders were first loaded, then confined with Carbon FRP, and finally subjected to destructive pure axial compression tests. Four different levels of pre-existing loads were simulated, including the un-loaded condition.
Highlights
In the last years, a large diffusion of Fiber-Reinforced Polymers (FRPs) composites has been experienced in the civil engineering field
According to the aforementioned purposes, the present paper shows the results of an experimental program regarding pure axial compression tests of small-scale concrete cylinders, which were confined by Carbon FRP (CFRP) jackets under different pre-loading conditions
All collected experimental outcomes have been related to the index between the elastic modulus of the fibers (Ef) on the concrete (E0) and the geometrical ratio of reinforcement ((4ntf)/D), where D is the equivalent diameter of the cross section, n is the number for FRP layers, and tf is the thickness of each FRP layer, typically referred to dry fibers
Summary
A large diffusion of FRP composites has been experienced in the civil engineering field. Various important parameters of the FRPconfinement were analyzed in the past decades: cross-sectional type, compression strength of the unconstrained concrete, fiber type, number of FRP-layers and their thickness, presence of internal reinforcement within the concrete sample, confinement technique, presence or absence of preload on the column prior to the execution of the confinement itself, etc. All of these factors affect the results of compression tests more or less significantly, but only a few studies are related to the effect of the pre-load. The conclusions are not always comparable since the ratio between the concrete grade and tensile properties of FRP may be very different, as starting data
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