Flexural analysis of posttensioned reinforced concrete beams using external steel bars

A nonlinear analysis based on the incremental deformation method has been presented to predict the flexural response of reinforced concrete (RC) beams strengthened with externally unbonded steelbars instead of tendons. The steel bars (with ultimate strength between 668 and 788 MPa) generally have lower strength than tendons (with ultimate strength between 1400 and 1900 MPa), and can be posttensioned simply by tightening nuts or turnbuckles, unlike a tendon. The load– deflection, load–external bar stress and moment–curvature over the entire loading range are examined to evaluate the flexural response of RC beams with or without external steel bars. To satisfy force equilibrium, iterative processes for obtaining the neutral axis and external bar stress in the cross-section are performed. This iterative procedure with nonlinear analysis is essential because there is an interrelationship between the neutral axis, external bar stress, and beam deflection. The nonlinear analytical results for the deflection and external bar stress show good agreement with experimental values. Additionally, deformed shapes such as varying neutral axis and curvature distribution along the beam span, which were not observed in experimental tests, are also exhibited.