Experimental Research On Square Concrete Columns Strengthened With Carbon Fiber Reinforced Plastics Sheets At Low Temperatures

Experimental investigations were conducted on the failure modes, mechanical behaviors of square concrete columns at low temperatures. Then analytical investigations were carried out based on the experimental results. The major studies and conclusions are as followed:(1) Plain concrete columns strengthened with CFRP sheets were axially tested at low temperatures of 5℃,-5℃ and -10℃, respectively. For separately wrapped square plain concrete columns, the axial compressive strength increased 34.26%, 24.38% and 38.88% at 5℃, -5℃ and -10℃, respectively. For fully wrapped square plain concrete columns, the axial compressive strength increased 53.38%, 40.06% and 47.48% at 5℃, -5℃ and -10℃, respectively.(2) Reinforced concrete columns strengthened with CFRP sheets were axially tested at temperatures of 10℃, 5℃, 0℃, -5℃ and -10℃, respectively. At the same conditions of CFRP kinds, the amount of CFRP and wrapped form, the average axial compressive strength increased 17.83%, 6.63% and 9.09% at 10℃, 0℃ and -10℃, respectively.(3) The experimental results showed that using CFRP sheets could effectively increase the axial compressive strength and deformation capacity. The axial compressive strength was related to the curing temperatures. The improving extent of axial compressive strength decreased with the falling temperature, and when the temperature dropped to a certain value, the improving extent increased with the falling temperature.(4) For square plain concrete columns, after the stress exceeds the peak stress, the stress may ascend slowly with adequate confinement, or it may be almost unchanged with moderate confinement, or it may descend slowly with deficient confinement. The axial strain increases rapidly until the rupture of the CFRP sheets.(5) The experimental stress-strain diagram has three different stages. Firstly, the initial portion of the stress-strain response of confined concrete follows the path of unconfined concrete. Secondly, after exceeding the unconfined strengthen of concrete, the curve starts to form a transition zone. Finally, the CFRP sheets are fully activated and the confining stress provided by the CFRP sheets continues to increase with the applied load...