DUCTILITY OF CONCRETE BEAMS PRESTRESSED WITH CFRP TENDONS

One of the main concerns in the design of concrete beams reinforced and/or prestressed with fiber-reinforced polymer(FRP)materials is the lack of ductility due to the linear elastic behavior of such materials up to failure. The deformation of partially bonded, partially prestressed concrete beams with hybrid FRP tendons and stainless steel reinforcements has been studied by means of an analytical method. It is assumed that a section of the beam has a tri-linear type of moment-curvature relationship for its loading portion and a linear type for its unloading portion. The unloading part of moment-curvature relationship is necessary to determine the residual deflection of the beam from which the ductility index of the beam can be calculated using an energy concept. Predictions from the model are compared with the limited available test data, and reasonable agreement is obtained. A parametric study of the ductility of the prestressed concrete beams with hybrid FRP and stainless steel reinforcements has been conducted. It is observed from the parametric study that increasing the ultimate compressive strain of concrete and unbonded length of tendon can enhance the deformability more efficiently than the ductility of the beam, since only a limited effect on the ductility can be achieved. Moreover, it is seen that generally the influences of the parameters on ductility and deformability of the beam are dependent on the failure mode which may be tendon rupture or concrete crushing.