ANALYSIS OF BEAMS PRESTRESSED WITH UNBONDED INTERNAL OR EXTERNAL TENDONS

The present study describes a nonlinear analysis model developed for the prediction of the complete moment versus deformation response of concrete beams containing bonded prestressing tendons, unbonded prestressing tendons (metallic or otherwise), and nonprestressed conventional reinforcing bars. The model uses an extensive iterative procedure for calculating the stress in unbonded tendons, f(ps), by performing a nonlinear analysis at various locations along the beam. The analysis is performed several times during any loading stage until the stress f(ps) is calculated within a reasonable tolerance. Two important issues not addressed in previous investigations are considered in modeling the curvature distribution, namely: (1) The effects of member span-to-depth ratio and the level of shear force on the flexural deformations; and (2) the change in eccentricity under load (i.e., second-order effects) for beams containing external tendons. Experimental verification was carried out using beam tests taken from 15 different investigations that occurred between 1962 and 1990. Excellent correlation was observed between predicted results and experimental observations.