Influence of Spirals on the Behavior of Short RC Columns Strengthened by External CFRP
AbstractAn experimental study was carried out to investigate the behavior of normal strength reinforced concrete (RC) circular short columns strengthened by carbon fiber reinforced polymer (CFRP) sheets. Three series comprising total of (15) specimens were loaded to failure under axial concentric compression load. Strengthening was varied by changing CFRP strips number, spacing and wrapping methods. The finding of this research can be summarized as follows; for the columns without CFRP, the influence of the spiral pitch was significant: compared with 100 mm spiral pitch, dropping the spacing to 65 mm and 30 mm increased the load carrying capacity by 25% and 43% respectively. The columns with less internal confinement (lesser amount of spirals) were strengthened more significantly by the CFRP than the ones with greater amount of internal spirals. As an example of the varying effectiveness of the fully wrapped CFRP, the column with spiral pitch at 100 mm was strengthened by 74% with the CFRP. In contrast, the ones with 30 mm spiral pitch only increased in strength with CFRP by 51%. Compared with the control specimen (no CFRP), the same amount of CFRP when used as spiral strips led to more strengthening than using CFRP as hoop strip-the former led to nearly 8% more strengthening than the latter in the case of 100 mm internal spiral pitch. In the case of 65 mm the internal spiral pitch, the difference (between the hoops &spiral CFRP strengthening)is close to 10.5%. The difference between the two methods of strengthening in the heavily spiral columns (30 mm spiral pitch) is more significant.
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