Recoverability of FRP composite-RC bridge piers

Based on the nonlinear pushover test results, it is clear that a residual drift ratio of 1% does not correspond to a specific column drift ratio, since many parameters affect the performance of these columns. However, it is interesting to stress that there is a zone of the drift ratio between 2 and 3.5% within which the recoverability limit state could be checked. Hence, the endpoint of the recoverable state can be defined by evaluating the residual inclination value within this zone. Ultimately, Fahmy et al. (2009) recommend three limit states for FRP-RC bridge columns as shown in Fig. 14.8. The first state is the state of pure recoverability whose end corresponds to column drift ratio 2% as shown Fig. 14.8. Here, the residual deformation of all the represented columns is below the recoverability limit. The second state is the state of recoverability limit check which falls between the 2% and 3.5% column drift ratios. The third state is the irrecoverable one, where the residual deformations exceed the recoverability limit. 

In the study of Fahmy et al. (2010a), suitable FRP design assumptions and concepts certifying the reality of post-yield stiffness are defined and summarized as follows  

7 Recoverability limit of FRP-retrofitted RC bridge columns with (a) flexural and lap-splice deficiencies and (b) shear deficiencies. 

The minimum design level of the FRP confinement ratio should be 0.12 for columns with continuous reinforcement, and it should be 0.25 in case column reinforcement is lap-spliced at the plastic hinge zone. 

To avoid shear failure, horizontal FRP wrapping should limit the column dilation in the loading direction up to a dilation strain 0.004. 

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