Behaviour of Uniaxial Reinforced Concrete Columns Strengthened with Ultra-High Performance Concrete and Fiber Reinforced Polymers

Abstract

This article investigates the behaviour of strengthened concrete columns usingjacketing ultra-high-performance fiber reinforced concrete (UHPFRC) and carbonfiber-reinforced polymer (CFRP) under uniaxial loaded. The jacket was connectedto the column core using shear connectors and (CFRP) fixed as a strip on thetension zone between the column cores and the jacketing. Seven column samplesof square cross-section (120 x120) mm at the midsection with overall length of1250 mm were cast using normal strength concrete (NSC) and having similarlongitudinal and transverse reinforcement. The samples were made and testedunder axial load at eccentricity equal to 120 mm up to failure. Test parameters werethe thickness of jackets (25 and 35) mm and the width of CFRP (0,8, and 12) cm.Column specimens were tested, one of them was reference without anystrengthening, and the other specimens divided into two groups (A, and B), andeach group included three specimens based on the parameters. Group (A) hasUHPFRC jacket thickness 25 mm and CFRP width (0,8, and 12) cm respectively,and group (B) has UHPFRC jacket thickness 35 mm and CFRP width (0,8, and 12)cm respectively. The outcomes of the article show that increasing the thickness ofjacket, and width of CFRP lead to increase in the load carrying capacity about(110.5%,168.4%, and 184.2%) for group A, and (157.9%,226.3%, and 263.2%) forgroup B compared with the reference column due to delay in the appearance ofcracks and their distribution. The mid-height lateral displacement of columns wasdecreased about (66.6%,42.3%, and 35.9%) for group A, and (46.15%,38.46%, and32.3%) for group B, also the axial deformation of specimens decreased about(71.7%,60.86%, and 55.86%) for group A, and (65.5%,60.5%, and 53.4) for groupB compared with the reference column. The ductility of columns that werestrengthened with UHPFRC jacket only was increased about (13.67%,19.66%) forthickness(25,35) mm respectively, because of that UHPFRC jacket was contentedon steel fibers, and the percentage decrease of ductility was about (5.1%,and 12%)for group (A), (1%,and 9.4%) for group (B) when bonded CFRP in the tension zonewith width (8 ,and 12) cm respectively. The results show improvement in the initialand secant stiffness when, increased the thickness of jacket, and width of CFRPbecause of increase in the size of columns and improvement in the modulus ofelasticity. The toughness increase was about (273.97%,301.55%, and 304.5%) forgroup A, and (453.69%,511.93%, and 524.28%) for group B compared with thereference column because of increase in the size of specimens and delay theappearance of cracks.