بررسي آزمايشگاهي بهسازي لرزه اي ستون هاي بتني با استفاده از نوارهاي پيش تنيده frp

Experimental study on seismic retrofitting of columns using prestressed FRB belts

The retrofit techniques for the reinforcement concrete columns, which are arguably the most critical component of many structures, are aimed at increasing the confinement for the concrete. Among the existing retrofit techniques, fiber reinforced plastic (FRP) are increasingly being considered for use as wraps, jackets, casings, due to their high strength to weight ratio and corrosion resistance. In this paper, columns with cross section of YAxYA cm and height of A • cm were investigated by lateral cyclic loading test. Three specimens had axial load with the ratio of • and the remaining ones had axial load with the ratio of • ,Y. Ten specimens were wrapped only by lateral confining FRP strips that two of them were retrofitted by Aramid FRP strips and the others were retrofitted by Carbon FRP strips. Furthermore, four specimens were retrofitted by lateral confining AFRP strips as well as longitudinal CFRP fabrics that two of them had also one layer CFRP wrap. In each group of specimens, one sample was as reference column without any retrofitting and two others were retrofitted by unstressed (passive confinement) and prestressed FRP strips (active confinement). The experimental results showed that lateral FRP confinement caused significant increase in ductility and strength of the specimens, but FRP prestressing had no considerable effects on ductility comparing to the unstressed case. The most important effect of FRP prestressing was less propagating cracks and closing the existing cracks of the structure. Lateral FRP confinement of concrete columns (passive and active) causes increase in compressive strength of concrete. This increase can be calculated by using Richarts and Mandrʹs formulations. Furthermore, active and passive confinement can increase the shear capacity of weak cross section and the brittle shear failure mode can be changed to the ductile flexural failure mode which is more desirable. By using Japanese code, a new formulation was developed for calculation of shear capacity of retrofitted concrete cross section by prestressed FRP strips.