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Abstract
The research project concerns RC slender columns strengthened with carbon fiber reinforced polymer materials (CFRP). Two-stage experimental program contained of three types of concrete specimens and two slender columns. In the first stage the concrete specimens of the following types of shapes and cross section dimensions were tested: concrete cyl-inders with 150mm diameter and 300mm height, specimens with 100mm square cross section and 200mm height and specimens with rectangular cross section of 105×200mm and 200mm height. The specimens were strengthened with unidi-rectional CFRP wraps and strips, applied in different configurations. The aim of the research was to evaluate the influence of transverse CFRP reinforcement ratio referring to the cross section shape, influence of external longitudinal composite reinforcement on compressive stress carrying, influence of preloading concrete specimens prior to CFRP application and influence of load eccentricity on strengthening effect.
In the second stage the test on two slender columns of rectangular cross section (140×250mm) and 3000mm height was performed to evaluate the influence of CFRP strengthening. Columns were strengthened in two different configurations of CFRP materials. The first column was strengthened longitudinally with 2 S-type strips, glued on both short sides of the column. The second one was strengthened longitudinally by 3 layers of CFRP sheet on both long sides of the column. Both columns were additionally confined in transverse direction with 2 layers of CFRP sheet. The columns were initially pre-loaded with eccentricity of e = 50mm in a stiffer plane.
The same mode due to concrete crushing at mid-height in both columns occurred. The maximal longitudinal strains in compression zone at failure reached –6,0‰ while in the tension zone it was 3-3,5‰. The maximal transverse strain reached 10,0 ‰.
A high ductility of columns was proved by a distinct increase in the column deflections and longitudinal strain meas-ured under the ultimate load.
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