Behavior Of Concrete Members Strengthened With Carbon Fiber Reinforced Plastic Sheets

Some of the existing reinforced concrete structures with different damage degrees in China need to be retrofitted. The strengthening of RC structures with Carbon Fiber Reinforced Plastic(CFRP) materials has been widely applied, and numerous corresponding studies in this field are carried out. This paper focuses on the behavior of RC columns confined with CFRP sheets under sustained loading and RC beams strengthened with externally bonded CFRP sheets. On the basis of the above tests the practical equations have been proposed for design calculating. The paper includes four parts listed as follows:1 .The performance of eccentrically loaded RC columns confined with CFRP sheets under sustained loading has been evaluated. The test results show that under sustained loading the RC columns confined with CFRP sheets experience a significant increase in strength and deformation, and the levels of sustained loading have the influence on the ultimate loads of the confined columns with small eccentricities. The higher level of sustained loading brings the lower ultimate load.2.According to the confining mechanism for the externally bonded FRP materials and transverse reinforcements, taking into account the effect of sustained load, the effective lateral confining stress on the axially loaded RC columns from the CFRP materials and transverse reinforcements is analyzed respectively. The equations for calculating axial load capacity of strengthened columns under sustained concentric loading are proposed in the form the current design code introduces.3.The experimental research has been carried out on three intact RC beams and four damaged RC beams strengthened with CFRP sheets, respectively. The load capacity,deformation,failure modes and cracks development of strengthened beams are studied. It indicates that the application of CFRP sheets can improve load capacity of strengthened beams considerably. The precracked beams approximately have the same ultimate load as the intact RC beams after the strengthening with externally bonded CFRP sheets. All the strengthened beams possess good ductilities,and obvious signs can be observed before failure. The crack widths of strengthened beams decrease distinctly due to the crack-restricting effect of bonded CFRP sheets.4.Within the conditions and limits of the study, considering CFRP sheets as steel reinforcements, equations for calculating cracks width and spacing of strengthened beamshave been proposed by revising the parameters in the design code. The equations are suitable for practical engineering use.