This paper presents an experimental and analytical investigation of the flexural response of box beams reinforced and prestressed using carbon fiber reinforced polymer (CFRP) tendons. Two one-third scale box beams were prestressed using seven bonded pretensioning tendons and six unbonded post-tensioning tendons. A third beam was prestressed with seven bonded pretensioning tendons and six non-prestressed unbonded posttensioning tendons. Beams were reinforced with carbon fiber composite cable stirrups and tested to failure. A computer program was developed to predict deflection, strain, and post-tensioning forces at various loads. A parametric analysis examined the effects of the level of pretensioning and post-tensioning forces on the overall flexural response. Results showed that the beam prestressed using both pretensioning and unbonded post-tensioning tendons had a 26 percent higher ultimate load capacity and 36 percent lower energy ratio than the beam with non-prestressed unbonded post-tensioning tendons. Levels of initial pretensioning and posttensioning forces significantly affect the flexural response and beam failure mode.
